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Compression

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  • Arthur Thompson
    I had a 4 stroke fail a leakdown test on one of two cylinders that had a rebuilt head assembly. It appeared to be both sets of valves had not been reground. So
    Message 1 of 16 , Mar 4, 2009
      I had a 4 stroke fail a leakdown test on one of two cylinders that had a
      rebuilt head assembly. It appeared to be both sets of valves had not been
      reground. So I had a valve job done and lapped the valves just to give them
      a bit extra polish. Now the engine is back together and the SOB generates a
      grand total of 30psi compression. Since this is the first engine I have had
      to do a valve job on, what should I be looking for to find out why the
      bugger won't compress correctly?

      Art


      [Non-text portions of this message have been removed]
    • darrell
      1: lapping compound under valve / not clean crud under valve. 2: valve lash to tight. 3: Did you remove rings? / Ring upside down / or broken 4: valve timing
      Message 2 of 16 , Mar 4, 2009
        1: lapping compound under valve / not clean crud under valve.

        2: valve lash to tight.

        3: Did you remove rings? / Ring upside down / or broken

        4: valve timing incorrect.

        5: bent valve / sticking
        Darrell
        -------Original Message-------

        From: Arthur Thompson
        Date: 3/4/2009 8:29:32 PM
        To: Small4-strokeEngines@yahoogroups.com
        Subject: [Small4-strokeEngines] Compression

        I had a 4 stroke fail a leakdown test on one of two cylinders that had a
        rebuilt head assembly. It appeared to be both sets of valves had not been
        reground. So I had a valve job done and lapped the valves just to give them
        a bit extra polish. Now the engine is back together and the SOB generates a
        grand total of 30psi compression. Since this is the first engine I have had
        to do a valve job on, what should I be looking for to find out why the
        bugger won't compress correctly?

        Art

        [Non-text portions of this message have been removed]





        [Non-text portions of this message have been removed]
      • Andrew Ekstrom
        Art, Put some bar and chain lube in the cylinder, and see if the compression comes up. If it does then its the rings. If it doesnt you can try putting a little
        Message 3 of 16 , Mar 4, 2009
          Art,

          Put some bar and chain lube in the cylinder, and see if the compression comes up. If it does then its the rings. If it doesnt you can try putting a little vasiline on one valve at a time to try and find out which one is bad. Verify that the valves are closing all the way, remove the rocker arms and test again.

          Later
          Andy

          remember, one change, one test




          ________________________________
          From: Arthur Thompson <boss@...>
          To: Small4-strokeEngines@yahoogroups.com
          Sent: Wednesday, March 4, 2009 9:29:13 PM
          Subject: [Small4-strokeEngines] Compression


          I had a 4 stroke fail a leakdown test on one of two cylinders that had a
          rebuilt head assembly. It appeared to be both sets of valves had not been
          reground. So I had a valve job done and lapped the valves just to give them
          a bit extra polish. Now the engine is back together and the SOB generates a
          grand total of 30psi compression. Since this is the first engine I have had
          to do a valve job on, what should I be looking for to find out why the
          bugger won't compress correctly?

          Art

          [Non-text portions of this message have been removed]




          [Non-text portions of this message have been removed]
        • mike_main@juno.com
          Are you using a differential gage? 80 pounds in, only XX remains? Did you listen at the exhaust for escaping air past the E valve? Hold throttle wide
          Message 4 of 16 , Mar 4, 2009
            Are you using a differential gage? 80 pounds in, only XX remains? Did you listen at the exhaust for escaping air past the E valve? Hold throttle wide open...listen for air escaping past the I valve? Open oil fill...listen for air escaping past the rings? Then lube the cylinder and do it all again. Also, borrow a gage from a friend and verify that you're not being fooled by a bad gage. Then dig a little deeper inside to verify valve lash & cam timing. Become Sherlock Holmes with a wrench. Good luck.
            mike...in Los Angeles...Showers...68F...sweet fresh air. God I love winter!
            ____________________________________________________________
            Digital Photography - Click Now.
            http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTDvmP4oCyPUDqi5m1f0jMZp0XyVstuyOJDj5IFU3tNm8scgZeysZS/

            [Non-text portions of this message have been removed]
          • Arthur Thompson
            Could be lapping compound although I did clean everything with a good degreaser. Rings were not removed, valves and guides were in very good condition except
            Message 5 of 16 , Mar 4, 2009
              Could be lapping compound although I did clean everything with a good
              degreaser. Rings were not removed, valves and guides were in very good
              condition except for the seating area and I double checked the valve timing.
              I am thinking my next trick should be to inject some oil into the cylinder
              to see if it makes the rings improve the seal temporarily. Total compression
              before the head was removed was over 100psi but I don't remember the exact
              number and of course it decayed rather quickly.

              Thanks for the help,

              Art
              From: Small4-strokeEngines@yahoogroups.com
              [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of darrell
              Sent: Wednesday, March 04, 2009 6:37 PM
              To: Small4-strokeEngines@yahoogroups.com
              Subject: Re: [Small4-strokeEngines] Compression

              1: lapping compound under valve / not clean crud under valve.

              2: valve lash to tight.

              3: Did you remove rings? / Ring upside down / or broken

              4: valve timing incorrect.

              5: bent valve / sticking
              Darrell
              -------Original Message-------

              From: Arthur Thompson
              Date: 3/4/2009 8:29:32 PM
              To: Small4-strokeEngines@yahoogroups.com
              <mailto:Small4-strokeEngines%40yahoogroups.com>
              Subject: [Small4-strokeEngines] Compression

              I had a 4 stroke fail a leakdown test on one of two cylinders that had a
              rebuilt head assembly. It appeared to be both sets of valves had not been
              reground. So I had a valve job done and lapped the valves just to give them
              a bit extra polish. Now the engine is back together and the SOB generates a
              grand total of 30psi compression. Since this is the first engine I have had
              to do a valve job on, what should I be looking for to find out why the
              bugger won't compress correctly?

              Art

              [Non-text portions of this message have been removed]





              [Non-text portions of this message have been removed]



              [Non-text portions of this message have been removed]
            • Arthur Thompson
              That s on my list. Thanks. Art From: Small4-strokeEngines@yahoogroups.com [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of Andrew Ekstrom Sent:
              Message 6 of 16 , Mar 4, 2009
                That's on my list. Thanks.

                Art
                From: Small4-strokeEngines@yahoogroups.com
                [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of Andrew Ekstrom
                Sent: Wednesday, March 04, 2009 6:38 PM
                To: Small4-strokeEngines@yahoogroups.com
                Subject: Re: [Small4-strokeEngines] Compression

                Art,

                Put some bar and chain lube in the cylinder, and see if the compression
                comes up. If it does then its the rings. If it doesnt you can try putting a
                little vasiline on one valve at a time to try and find out which one is bad.
                Verify that the valves are closing all the way, remove the rocker arms and
                test again.

                Later
                Andy

                remember, one change, one test

                ________________________________
                From: Arthur Thompson <boss@... <mailto:boss%40flydiver.com> >
                To: Small4-strokeEngines@yahoogroups.com
                <mailto:Small4-strokeEngines%40yahoogroups.com>
                Sent: Wednesday, March 4, 2009 9:29:13 PM
                Subject: [Small4-strokeEngines] Compression

                I had a 4 stroke fail a leakdown test on one of two cylinders that had a
                rebuilt head assembly. It appeared to be both sets of valves had not been
                reground. So I had a valve job done and lapped the valves just to give them
                a bit extra polish. Now the engine is back together and the SOB generates a
                grand total of 30psi compression. Since this is the first engine I have had
                to do a valve job on, what should I be looking for to find out why the
                bugger won't compress correctly?

                Art

                [Non-text portions of this message have been removed]

                [Non-text portions of this message have been removed]



                [Non-text portions of this message have been removed]
              • Arthur Thompson
                Are you using a differential gage? 80 pounds in, only XX remains? [[Art Said:]] Yes and compared to second cylinder to be certain about gauge. Did you listen
                Message 7 of 16 , Mar 4, 2009
                  Are you using a differential gage? 80 pounds in, only XX remains?
                  [[Art Said:]] Yes and compared to second cylinder to be certain about gauge.
                  Did you listen at the exhaust for escaping air past the E valve?
                  [[Art Said:]] Yes and it was. Same for intake.
                  Hold throttle wide open...listen for air escaping past the I valve? Open oil
                  fill...listen for air escaping past the rings?
                  [[Art Said:]] Did not hear much more than a gurgle here.
                  Then lube the cylinder and do it all again.
                  [[Art Said:]] Next on the list of things to do
                  Also, borrow a gage from a friend and verify that you're not being fooled by
                  a bad gage. Then dig a little deeper inside to verify valve lash & cam
                  timing.
                  [[Art Said:]] Rechecked all that but it is very easy to screw upJ
                  Become Sherlock Holmes with a wrench. Good luck.
                  mike...in Los Angeles...Showers...68F...sweet fresh air. God I love winter!
                  [[Art Said:]] Rain, cold and windy in Western WA. Damn I hate winter.

                  __________________________________________________________
                  Digital Photography - Click Now.
                  http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTDvmP4oCyPUDqi5m1f0jMZp0Xy
                  VstuyOJDj5IFU3tNm8scgZeysZS/

                  [Non-text portions of this message have been removed]



                  [Non-text portions of this message have been removed]
                • mike_main@juno.com
                  Art---Off Topic here...I used to live in Friday Harbor. Sort of remember the winters as being a cross between a fire hose and a freezer...almost too cold to
                  Message 8 of 16 , Mar 4, 2009
                    Art---Off Topic here...I used to live in Friday Harbor. Sort of remember the winters as being a cross between a fire hose and a freezer...almost too cold to work on anything metal for fear of sticking to it, but life does go on. I was 'the kid' at a local boat yard and was always the 'outside man'. Rank has its' privileges.
                    Back on topic...yes, clean everything and maybe Dykem up the valves and seats and then use a very soft lapping compound, but do not fully rotate the valves...just a little back and forth motion. If the valves or seats were ground off center, the Dykem will not be evenly removed all the way around on either the seat or the valve.
                    Again, good luck!
                    mike...in Los Angeles...
                    P.S. I'm sending you some empty clouds back north to be refilled. Send them back when you're ready.
                    ____________________________________________________________
                    Click here to find the perfect picture with our powerful photo search features.
                    http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTEuJE9yRbjf6BzK7ylnmcQJqa7cczJm1HYDAjNPicN9EcSAWhu4iE/

                    [Non-text portions of this message have been removed]
                  • Arthur Thompson
                    Thanks Mike, appreciate the offer. Friday Harbor is a sun belt compared to the Olympic Peninsula where we live. Since 2000 it seems like we are getting a lot
                    Message 9 of 16 , Mar 4, 2009
                      Thanks Mike, appreciate the offer. Friday Harbor is a sun belt compared to
                      the Olympic Peninsula where we live. Since 2000 it seems like we are getting
                      a lot more snow than I remember. Actually, the Honolulu Express started
                      running this week so instead of 20-30 degrees every morning it is now more
                      like 35-40 and getting into the 50s in the afternoon. That usually means
                      winter is over and spring on the way. No shortage of rain or low clouds yet.

                      Arthur Thompson
                      FlyDiver, llc
                      360.490.6268
                      <http://www.FlyDiver.com> www.FlyDiver.com
                      Verner Engine Sales & Service
                      From: Small4-strokeEngines@yahoogroups.com
                      [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of
                      mike_main@...
                      Sent: Wednesday, March 04, 2009 8:10 PM
                      To: Small4-strokeEngines@yahoogroups.com
                      Subject: RE: [Small4-strokeEngines] Compression

                      Art---Off Topic here...I used to live in Friday Harbor. Sort of remember the
                      winters as being a cross between a fire hose and a freezer...almost too cold
                      to work on anything metal for fear of sticking to it, but life does go on. I
                      was 'the kid' at a local boat yard and was always the 'outside man'. Rank
                      has its' privileges.
                      Back on topic...yes, clean everything and maybe Dykem up the valves and
                      seats and then use a very soft lapping compound, but do not fully rotate the
                      valves...just a little back and forth motion. If the valves or seats were
                      ground off center, the Dykem will not be evenly removed all the way around
                      on either the seat or the valve.
                      Again, good luck!
                      mike...in Los Angeles...
                      P.S. I'm sending you some empty clouds back north to be refilled. Send them
                      back when you're ready.
                      __________________________________________________________
                      Click here to find the perfect picture with our powerful photo search
                      features.
                      http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTEuJE9yRbjf6BzK7ylnmcQJqa7
                      cczJm1HYDAjNPicN9EcSAWhu4iE/

                      [Non-text portions of this message have been removed]



                      [Non-text portions of this message have been removed]
                    • r-m-ohler@triton.net
                      Hi, Are you certain that the valve lash is adjusted properly? Have you checked the compression with a bit of oil in the cylinder? Ron
                      Message 10 of 16 , Mar 5, 2009
                        Hi,
                        Are you certain that the valve lash is adjusted properly? Have you checked
                        the compression with a bit of oil in the cylinder?
                        Ron


                        > I had a 4 stroke fail a leakdown test on one of two cylinders that had a
                        > rebuilt head assembly. It appeared to be both sets of valves had not been
                        > reground. So I had a valve job done and lapped the valves just to give
                        > them
                        > a bit extra polish. Now the engine is back together and the SOB generates
                        > a
                        > grand total of 30psi compression. Since this is the first engine I have
                        > had
                        > to do a valve job on, what should I be looking for to find out why the
                        > bugger won't compress correctly?
                        >
                        > Art
                        >
                        >
                        > [Non-text portions of this message have been removed]
                        >
                        >
                      • xlch58@swbell.net
                        ... My guess is that the valve lash is off. Very common on small four strokes. When the valves seats are done the distance between the cam and the valve seat
                        Message 11 of 16 , Mar 5, 2009
                          Arthur Thompson wrote:
                          > Are you using a differential gage? 80 pounds in, only XX remains?
                          > [[Art Said:]] Yes and compared to second cylinder to be certain about gauge.
                          > Did you listen at the exhaust for escaping air past the E valve?
                          > [[Art Said:]] Yes and it was. Same for intake.
                          > Hold throttle wide open...listen for air escaping past the I valve? Open oil
                          > fill...listen for air escaping past the rings?
                          > [[Art Said:]] Did not hear much more than a gurgle here.
                          > Then lube the cylinder and do it all again.
                          > [[Art Said:]] Next on the list of things to do
                          > Also, borrow a gage from a friend and verify that you're not being fooled by
                          > a bad gage. Then dig a little deeper inside to verify valve lash & cam
                          > timing.
                          > [[Art Said:]] Rechecked all that but it is very easy to screw upJ
                          > Become Sherlock Holmes with a wrench. Good luck.
                          > mike...in Los Angeles...Showers...68F...sweet fresh air. God I love winter!
                          > [[Art Said:]] Rain, cold and windy in Western WA. Damn I hate winter.
                          >
                          > _
                          My guess is that the valve lash is off. Very common on small four
                          strokes. When the valves seats are done the distance between the cam
                          and the valve seat is reduced. Same if the valve face is done (since
                          both operate by removing material) Even just dropping a new valve in
                          can cause this, as the new valve will have the maximum stem length and
                          the engine may have had the seats ground before, or the seats may have
                          recessed just from use.

                          Charles
                        • Arthur Thompson
                          I reset the lash on both cylinders with the piston at TDC and the valves fully closed. It is a boxer so had to rotate 180 degrees to do the second cylinder. I
                          Message 12 of 16 , Mar 5, 2009
                            I reset the lash on both cylinders with the piston at TDC and the valves
                            fully closed. It is a boxer so had to rotate 180 degrees to do the second
                            cylinder. I am confident that part is done correctly. It's too easy for
                            valve timing to be wrong but I checked that twice and will check it again.
                            Will inject oil this morning to see what change that makes and also do an
                            air injection with each set of valves opening and closing to see if crud
                            will just blow out.

                            Art
                            From: Small4-strokeEngines@yahoogroups.com
                            [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of xlch58@...
                            Sent: Thursday, March 05, 2009 5:11 AM
                            To: Small4-strokeEngines@yahoogroups.com
                            Subject: Re: [Small4-strokeEngines] Compression

                            Arthur Thompson wrote:
                            > Are you using a differential gage? 80 pounds in, only XX remains?
                            > [[Art Said:]] Yes and compared to second cylinder to be certain about
                            gauge.
                            > Did you listen at the exhaust for escaping air past the E valve?
                            > [[Art Said:]] Yes and it was. Same for intake.
                            > Hold throttle wide open...listen for air escaping past the I valve? Open
                            oil
                            > fill...listen for air escaping past the rings?
                            > [[Art Said:]] Did not hear much more than a gurgle here.
                            > Then lube the cylinder and do it all again.
                            > [[Art Said:]] Next on the list of things to do
                            > Also, borrow a gage from a friend and verify that you're not being fooled
                            by
                            > a bad gage. Then dig a little deeper inside to verify valve lash & cam
                            > timing.
                            > [[Art Said:]] Rechecked all that but it is very easy to screw upJ
                            > Become Sherlock Holmes with a wrench. Good luck.
                            > mike...in Los Angeles...Showers...68F...sweet fresh air. God I love
                            winter!
                            > [[Art Said:]] Rain, cold and windy in Western WA. Damn I hate winter.
                            >
                            > _
                            My guess is that the valve lash is off. Very common on small four
                            strokes. When the valves seats are done the distance between the cam
                            and the valve seat is reduced. Same if the valve face is done (since
                            both operate by removing material) Even just dropping a new valve in
                            can cause this, as the new valve will have the maximum stem length and
                            the engine may have had the seats ground before, or the seats may have
                            recessed just from use.

                            Charles



                            [Non-text portions of this message have been removed]
                          • Noel Loveys
                            Do a differential compression test. Those testers that require you spin the engine are the lyingest things ever developed. Noel From:
                            Message 13 of 16 , Mar 5, 2009
                              Do a differential compression test. Those testers that require you spin the
                              engine are the lyingest things ever developed.



                              Noel



                              From: Small4-strokeEngines@yahoogroups.com
                              [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of Arthur Thompson
                              Sent: Wednesday, March 04, 2009 10:59 PM
                              To: Small4-strokeEngines@yahoogroups.com
                              Subject: [Small4-strokeEngines] Compression



                              I had a 4 stroke fail a leakdown test on one of two cylinders that had a
                              rebuilt head assembly. It appeared to be both sets of valves had not been
                              reground. So I had a valve job done and lapped the valves just to give them
                              a bit extra polish. Now the engine is back together and the SOB generates a
                              grand total of 30psi compression. Since this is the first engine I have had
                              to do a valve job on, what should I be looking for to find out why the
                              bugger won't compress correctly?

                              Art

                              [Non-text portions of this message have been removed]





                              [Non-text portions of this message have been removed]
                            • Arthur Thompson
                              Absolutely correct Noel. Sadly the results were confirmed in my case. 80psi in, 50psi out. I removed the intake manifold and can easily feel the air coming
                              Message 14 of 16 , Mar 5, 2009
                                Absolutely correct Noel. Sadly the results were confirmed in my case. 80psi
                                in, 50psi out. I removed the intake manifold and can easily feel the air
                                coming out. And hear it in the exhaust also . Ran a bunch of cleaner through
                                it, tapped the valve stems with a rubber mallet to pop them open and got a
                                few more psi but it still won't fire. Gonna have to check the valve timing
                                one more time. I did notice that the static advance was 5mm more than it
                                needed to be so will move it back to make start a bit easier. I think I just
                                must have done a crummy job cleaning up the lapping compound. Will get the
                                parts washer out along with the scrubber brush this time.

                                Thanks for the help,

                                Art
                                From: Small4-strokeEngines@yahoogroups.com
                                [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of Noel Loveys
                                Sent: Thursday, March 05, 2009 4:43 PM
                                To: Small4-strokeEngines@yahoogroups.com
                                Subject: RE: [Small4-strokeEngines] Compression

                                Do a differential compression test. Those testers that require you spin the
                                engine are the lyingest things ever developed.

                                Noel

                                From: Small4-strokeEngines@yahoogroups.com
                                <mailto:Small4-strokeEngines%40yahoogroups.com>
                                [mailto:Small4-strokeEngines@yahoogroups.com
                                <mailto:Small4-strokeEngines%40yahoogroups.com> ] On Behalf Of Arthur
                                Thompson
                                Sent: Wednesday, March 04, 2009 10:59 PM
                                To: Small4-strokeEngines@yahoogroups.com
                                <mailto:Small4-strokeEngines%40yahoogroups.com>
                                Subject: [Small4-strokeEngines] Compression

                                I had a 4 stroke fail a leakdown test on one of two cylinders that had a
                                rebuilt head assembly. It appeared to be both sets of valves had not been
                                reground. So I had a valve job done and lapped the valves just to give them
                                a bit extra polish. Now the engine is back together and the SOB generates a
                                grand total of 30psi compression. Since this is the first engine I have had
                                to do a valve job on, what should I be looking for to find out why the
                                bugger won't compress correctly?

                                Art

                                [Non-text portions of this message have been removed]

                                [Non-text portions of this message have been removed]



                                [Non-text portions of this message have been removed]
                              • Noel Loveys
                                Not sure if you have a marker for TDC... if not you have to be real careful not to poke a hole in the top of the piston. I never liked using a locator If all
                                Message 15 of 16 , Mar 6, 2009
                                  Not sure if you have a marker for TDC... if not you have to be real careful
                                  not to poke a hole in the top of the piston. I never liked using a locator



                                  If all else fails and you have to pull the heads I guess you'll have to
                                  replace those gaskets too. Also do a correction calibration on your torque
                                  wrench. Heads should be torque but I don't know what the acceptable error
                                  for head torque is.



                                  Noel







                                  From: Small4-strokeEngines@yahoogroups.com
                                  [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of Arthur Thompson
                                  Sent: Thursday, March 05, 2009 10:51 PM
                                  To: Small4-strokeEngines@yahoogroups.com
                                  Subject: RE: [Small4-strokeEngines] Compression



                                  Absolutely correct Noel. Sadly the results were confirmed in my case. 80psi
                                  in, 50psi out. I removed the intake manifold and can easily feel the air
                                  coming out. And hear it in the exhaust also . Ran a bunch of cleaner through
                                  it, tapped the valve stems with a rubber mallet to pop them open and got a
                                  few more psi but it still won't fire. Gonna have to check the valve timing
                                  one more time. I did notice that the static advance was 5mm more than it
                                  needed to be so will move it back to make start a bit easier. I think I just
                                  must have done a crummy job cleaning up the lapping compound. Will get the
                                  parts washer out along with the scrubber brush this time.

                                  Thanks for the help,

                                  Art
                                  From: Small4-strokeEngines@yahoogroups.com
                                  <mailto:Small4-strokeEngines%40yahoogroups.com>
                                  [mailto:Small4-strokeEngines@yahoogroups.com
                                  <mailto:Small4-strokeEngines%40yahoogroups.com> ] On Behalf Of Noel Loveys
                                  Sent: Thursday, March 05, 2009 4:43 PM
                                  To: Small4-strokeEngines@yahoogroups.com
                                  <mailto:Small4-strokeEngines%40yahoogroups.com>
                                  Subject: RE: [Small4-strokeEngines] Compression

                                  Do a differential compression test. Those testers that require you spin the
                                  engine are the lyingest things ever developed.

                                  Noel

                                  From: Small4-strokeEngines@yahoogroups.com
                                  <mailto:Small4-strokeEngines%40yahoogroups.com>
                                  <mailto:Small4-strokeEngines%40yahoogroups.com>
                                  [mailto:Small4-strokeEngines@yahoogroups.com
                                  <mailto:Small4-strokeEngines%40yahoogroups.com>
                                  <mailto:Small4-strokeEngines%40yahoogroups.com> ] On Behalf Of Arthur
                                  Thompson
                                  Sent: Wednesday, March 04, 2009 10:59 PM
                                  To: Small4-strokeEngines@yahoogroups.com
                                  <mailto:Small4-strokeEngines%40yahoogroups.com>
                                  <mailto:Small4-strokeEngines%40yahoogroups.com>
                                  Subject: [Small4-strokeEngines] Compression

                                  I had a 4 stroke fail a leakdown test on one of two cylinders that had a
                                  rebuilt head assembly. It appeared to be both sets of valves had not been
                                  reground. So I had a valve job done and lapped the valves just to give them
                                  a bit extra polish. Now the engine is back together and the SOB generates a
                                  grand total of 30psi compression. Since this is the first engine I have had
                                  to do a valve job on, what should I be looking for to find out why the
                                  bugger won't compress correctly?

                                  Art

                                  [Non-text portions of this message have been removed]

                                  [Non-text portions of this message have been removed]

                                  [Non-text portions of this message have been removed]





                                  [Non-text portions of this message have been removed]
                                • Arthur Thompson
                                  I do have a TDC marker and also valve timing markers but I always confirm TDC at least once with a dial indicator that I doubt could even scratch the surface
                                  Message 16 of 16 , Mar 6, 2009
                                    I do have a TDC marker and also valve timing markers but I always confirm
                                    TDC at least once with a dial indicator that I doubt could even scratch the
                                    surface of the piston. Factory says a head gasket can be reused if it has
                                    not delaminated but I keep spares in stock so that won't be an issue. Have
                                    the best Snapon torque wrench I could find. So far it has been spot on but I
                                    do check the calibration periodically. The head and cylinder castings are
                                    magnesium alloy and the tolerances are pretty tight. One lousy drop of oil
                                    in a head bolt hole and the damn bolt will NOT stay torqued. When I learned
                                    how to do that as a youngster (on a 1948 Chevy with a cast iron head and
                                    maybe block as well) the rule was put a light coating of oil on the head
                                    bolt before installing it. Blew a head gasket at 75 hours learning not to do
                                    that on the alloy stuff. Company in for the weekend so will probably not get
                                    back to it until Monday.

                                    Thanks again,

                                    Art
                                    From: Small4-strokeEngines@yahoogroups.com
                                    [mailto:Small4-strokeEngines@yahoogroups.com] On Behalf Of Noel Loveys
                                    Sent: Friday, March 06, 2009 6:24 AM
                                    To: Small4-strokeEngines@yahoogroups.com
                                    Subject: RE: [Small4-strokeEngines] Compression

                                    Not sure if you have a marker for TDC... if not you have to be real careful
                                    not to poke a hole in the top of the piston. I never liked using a locator

                                    If all else fails and you have to pull the heads I guess you'll have to
                                    replace those gaskets too. Also do a correction calibration on your torque
                                    wrench. Heads should be torque but I don't know what the acceptable error
                                    for head torque is.

                                    Noel

                                    From: Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    [mailto:Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com> ] On Behalf Of Arthur
                                    Thompson
                                    Sent: Thursday, March 05, 2009 10:51 PM
                                    To: Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    Subject: RE: [Small4-strokeEngines] Compression

                                    Absolutely correct Noel. Sadly the results were confirmed in my case. 80psi
                                    in, 50psi out. I removed the intake manifold and can easily feel the air
                                    coming out. And hear it in the exhaust also . Ran a bunch of cleaner through
                                    it, tapped the valve stems with a rubber mallet to pop them open and got a
                                    few more psi but it still won't fire. Gonna have to check the valve timing
                                    one more time. I did notice that the static advance was 5mm more than it
                                    needed to be so will move it back to make start a bit easier. I think I just
                                    must have done a crummy job cleaning up the lapping compound. Will get the
                                    parts washer out along with the scrubber brush this time.

                                    Thanks for the help,

                                    Art
                                    From: Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    [mailto:Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com> ] On Behalf Of Noel Loveys
                                    Sent: Thursday, March 05, 2009 4:43 PM
                                    To: Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    Subject: RE: [Small4-strokeEngines] Compression

                                    Do a differential compression test. Those testers that require you spin the
                                    engine are the lyingest things ever developed.

                                    Noel

                                    From: Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    [mailto:Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com> ] On Behalf Of Arthur
                                    Thompson
                                    Sent: Wednesday, March 04, 2009 10:59 PM
                                    To: Small4-strokeEngines@yahoogroups.com
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    <mailto:Small4-strokeEngines%40yahoogroups.com>
                                    Subject: [Small4-strokeEngines] Compression

                                    I had a 4 stroke fail a leakdown test on one of two cylinders that had a
                                    rebuilt head assembly. It appeared to be both sets of valves had not been
                                    reground. So I had a valve job done and lapped the valves just to give them
                                    a bit extra polish. Now the engine is back together and the SOB generates a
                                    grand total of 30psi compression. Since this is the first engine I have had
                                    to do a valve job on, what should I be looking for to find out why the
                                    bugger won't compress correctly?

                                    Art

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