1947 John Deere GM Knocking after rebuild

Le9102011

Member
Hello, kinda new to the forums but after scratching my head and staring for a while im gonna ask for assistance. I recently purchased a DuPont Restoration, and the guy I purchased the tractor from said it had a knock in the clutch, and was having trouble keeping the clutch adjusted. I ended up pulling the clutch completely out of the tractor and replaced all of the toggles dogs, t bolts facings springs pressure plate and driver to no avail on fixing the knock. I then got into the crank case, took the rod caps off and wiggled the connecting rods, flywheel side had no movement back and fourth, but the clutch side had about a half of inch of play in the wrist pin. Ended up tearing the tractor down, and the piston wrings feel apart as I took the pistons out, and could tell that there was a lot of taper in the block in addition to seeing a lot of block sealer in the engine. Took the block and had it bored .090 over, to new aluminum pistons with .012 skirt to wall clearance to allow for expansion, took the head down and found cracks in the exhaust valve seats the ran all the way to edge of the cyclone part of the head, so I purchased a crack free head, and put new valves guides and springs, in addition to having it milled to flat. Put the whole thing back together and fired it and was pleased it didn't take much to here her come to life, but the knock was still there, no where near as bad, and when the engine gets to operating temperature the knock seems to go away completely. Checked the flywheel clearance and everything is ok there other than the splines on the fly wheel are shot and the guy I purchased it from put jb weld in the splines to keep it from moving (will be getting a new flywheel here soon) and I also took a slow motion video of it to see if it really was rocking in and out which it wasnt. Sorry this is so long but from what I read everyone usually puts a back story to there, and just curious if this is normal for a cold engine that has been bored out or if I am missing something. Thanks for all of your help...
 
Flywheel and crankshaft splines have to be next to perfect and very tightly assembled to avoid knock and further damage. My guess would be this is the area of concern that deserves correction at this stage. JB weld hands down will never do here, most will call for a taperlock modification for a fix and they are not cheap nor easy to come by. Nothing wrong with your dedication though, amazing story. Best of luck getting this sorted out.
 
Thanks for the input, I was thinking that was the case. I called a guy out in Tennessee that does the taper locks, and he isn't too expensive, and can usually get it done while I wait, but he said that the taper locks he installs may not hold up to a bored G, but I am willing to give it a try since its not too far out of the way when I move from Arizona to Wisconsin, and having a spare flywheel may come in handy since parts for The G's are getting really hard to come by, not to mention getting really expensive..
 
I'm no expert with GM Diesels but .012" PTCW clearance sounds excessive. Is that what they actually recommend?

The fact that the noise goes away when the engine is warmed up sure points towards the cylinder region much like when you have a collapsed piston.......

(quoted from post at 10:18:39 07/05/18) Took the block and had it bored .090 over, to new aluminum pistons with .012 skirt to wall clearance to allow for expansion, took the head down and found cracks in the exhaust valve seats the ran all the way to edge of the cyclone part of the head, so I purchased a crack free head, and put new valves guides and springs, in addition to having it milled to flat. Put the whole thing back together and fired it and was pleased it didn't take much to here her come to life, but the knock was still there, no where near as bad, and when the engine gets to operating temperature the knock seems to go away completely.
 
That is not a GM diesel. It is a model G with gas/all fuel engine tractor but John Deere had to call them a model GM something about being able to raise the price from the war ?
 
I thought so as well, but when I called RTP, they recommend with Aluminum Pistons .002 Clearance for every 1 inch in bore and the machine shop agreed since the pistons will expand a lot more than with cast iron pistons. Stock bore size on a G is 6.125 its almost like throwing basketballs back and fourth, and the neighbors think its cool when its at idle the front end bounces.
 
Umm, yeah........GM model tractor, not a screamin' Jimmy. Not sure what I was thinking? LOL

Even at a 6" bore with aluminum pistons, .012" is a lot. Seems it might be more appropriate for an air cooled application.

Guess it's better than too tight. Just have to live with the piston slap at start up....

(quoted from post at 12:14:11 07/05/18) I thought so as well, but when I called RTP, they recommend with Aluminum Pistons .002 Clearance for every 1 inch in bore and the machine shop agreed since the pistons will expand a lot more than with cast iron pistons. Stock bore size on a G is 6.125 its almost like throwing basketballs back and fourth, and the neighbors think its cool when its at idle the front end bounces.
 
I know by experience that a .090 bore G with aluminum pistons needs over .009 piston to bore clearance,as mine stuck at that..012 should be about right!
 
The shop gave my G .012 clearance too. It did not knock.

Could be the flywheel splines.
 
I wouldn't worry a bit about the taperlok not holding up since it's been bored out. .090 over isn't enough to make a noticeable difference. The bigger gain came from the compression increase the new style pistons have over stock style.

That's definitely the route I'd try next.
 
Thanks for all of the input. The most people are pointing to the flywheel so I bought a flywheel wrench today and gonna take it off and have the taperlock put in it, and hopefully that clears up the problem. My daughter is getting excited to,drive it around with her dad in the next parade here too bad my son doesn?t listen to the old advice of leave the red in the shed so the next project is a little farmall super a.
 
My 630 has knocked cold ever since I had it bored .090 40 years ago and it’s seen a ton of hours since then. After it warms up the knock goes away. I have always suspected the machine shop bored it a little too loose
 
I?ve had a couple of people tell me that as well, the flywheel needs to be addressed since the last thing I want it to do is come loose and off at a
show or parade since the splines are shot and,who knows,how long that jb weld,will,last. If the flywheel fix doesn?t cure the issue then i will just
assume it?s piston slap until the engine warms up. I just want to be sure that it?s done right so this will be around for a long time and my kids can
enjoy them as they get older.

I do have a video of it when it?s cold and after it?s at operating temp. I just don?t know how to post it on here.
 

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