130203'47 Chief drive shaft length issue - LONG POST
- Dec 1, 2013
Beware - very long detailed post.
I am working on a1947 Indian Chief motor. I converted it to 80", using Kiwi/Truett and Osborn flywheels. The crankpin came out of the engine, and is going back in. I have a new pinion shaft (Greer), and a new drive shaft (Eastern).
When assembling the engine for the first time, using .063" thrust washers between the flywheels and cases, I got .014" end play before the drive gear and thrust washer was added, and the rods were well centered in the case. Manual calls for .015" - .030" I was pretty happy with that.
The first sign of a problem came when I saw that I would need a .195" thick thrust washer between the left case and the drive sprocket, to get the .005" - .010" specified end play with the gear installed. The thickest thrust washer readily available is .172". By the way, the thrust washer that came out originally was .142".
I thought I might be able to use a combination of two external thrust washers whose combined thickness was .195". That gave me the correct end play on the crank. I found out however that I was really just "kicking the can down the road", so to speak, in terms of alignment problems. Unfortunately I didn't totally comprehend this until I had the engine almost completely together!
The next problem surfaced when I tried to align the drive sprocket and clutch sprocket to within .010", per the manual. Using the .005" shims specified for this purpose, I found that I would need about twelve (!) shims to achieve the specified alignment (.065 total).
This in turn causes excessive end play at the transmission main shaft, and would require a non-standard, thicker thrust washer on the main shaft to get end play within specs.
At this point I reluctantly decided that I really needed to identify and correct the excess drive shaft length problem, so I disassembled the engine completely. After measuring everything as carefully as I could, the only real problem I could identify is that the taper on the flywheel end of the drive shaft is too large a diameter.
The smaller end of this drive shaft taper measures .758" in diameter or so, the old one measures 0.752". All other dimensions between the old and new drive shafts were essentially equal.
The dimensions of the female taper in the flywheel matches exactly between old and new flywheels. If my math is right, the taper appears to be 10 to 1, so a difference of +.006 in taper diameter on the pin (.003" in radius) would shift the pin out by .030".
Very long lead-in to the question. Is this as simple as buying another drive shaft that is more accurately ground? Can a skilled machinist safely grind another .003" or .004" off the drive shaft to get the length I need outside the case, or is the drive shaft case hardened so that this is not adviseable?
Now, some lessons learned learned for the newbie engine builders like me:
1) Read and understand the assembly instructions before disassembling the engine for rebuild. Then make as many measurements (e.g. crank end play) as you can at teardown. If you run into problems later, knowing where you started could be very valuable.
2) Measure every critical dimension of each new part before installing it. I didn't actually install the new drive shaft the first time; it was installed as part of the balancing, which I hired out.
3) Because the clearances and alignment on the Chief are much like a row of dominoes, I recommend that the alignment of the primary sprockets is checked as soon as the bottom end is together, but before progressing to valve train, pistons or cylinders... A lot less work to backtrack if it's required.
Thanks in advance to the "gray beards" out there for all the help. I am starting to learn how one earns the gray beard...
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