I have a D 2 (5U 16538) whose starting engine does not currently run, but which is close to the top of my project list. The crankshaft has close to 1/8" lateral end play. Is this something that should be fixed immediately? What are the consequences if this is not fixed?
Thanks in advance,
Dogger

"Dogger" wrote:

I have a D 2 (5U 16538) whose starting engine does not currently run, but which is close to the top of my project list. The crankshaft has close to 1/8" lateral end play. Is this something that should be fixed immediately? What are the consequences if this is not fixed?
Thanks in advance,
Dogger

It would contribute to the likelihood of a thrown rod, resulting in a broken bore skirt and a cracked block at the base ( coolant on the other side). Just for starters. On the other hand, it might run like that for a long time, are you lucky?

Maximum crankshaft end clearance is 0.025"
Left unattended the most common result initially is the pounding out of the dowel pin that anchors the thrust bearing (gear end). Events can go downhill from there quite rapidly.

That's the exact situation the running pony I just bought the other day had. Turned out the gear-end main bearing was moving in the case, & the dowel was rocking back & forth when it moved...When I got it apart, that main was totally hammered, the crank had been built back up to standard before, & the flame-spray or whatever they put on it was flaked off... Not good...
I took the crank to my machinist, & he said it looks like it will grind to .020, so total disaster was avoided.
Point being, that much end play needs to be looked at...

I'm still looking at the thrust washer solution posted by OM the other day...PM'ed Uncle Rich about it, but no answer yet.

Should add, & this relates to the other thread about mag shaft breakage, the excessive wobble in the gear-end main was starting to cause some ugly wear patterns on the cam gear. All the more reason to look at it sooner rather than later...

I think this is an inherent design flaw with this starter engine. I wish I would have documented my procedures for modifying the design better, but my focus at the time was getting it running. It was odd to me how the side load is applied to the main bearing protruding out both ends of the crankcase where it is inserted. The forward crank thrust is stopped by the crank pushing on the bearing outward. The rearward thrust is stopped by the tin washer which also acts as the front main seal inner rotating diameter pushing on the same bearing inward. The only thing keeping bearing in place, other than its own press fit is the dowel pin. The total mass of the crank and flywheel pounding back and forth on that main bearing causes the pin to fail and the bearing to rotate closing off lubrication. The bearing fails allowing the crank to jump around tearing up the aluminum camshaft and magneto gear, and eventually rod breakage or crankshaft failure.
There is no question that when the bearings are tight, and everything in order they probably last for awhile, but it's a long term type failure and these machines are 60 years old.
My solution was to machine the new bearings I made shorter than normal so the crank never touches them. I put bronze thrust washers on both sides of the crank but had to machine the crankcase and rear cover to gain extra room for the crank with washers and provide a smooth running surface for the thrust washers should they rotate. Effectively the float between the crank wheels and cases, but the crank is not allowed to pound on the sides of the bearings. The locating dowels only need to keep them from spinning, but I also inserted the bearings with red locktite (bearing mount) to help keep them in place.
2 years later it is still working but I probably have less than ten actual hours of the starter motor running. I think you can click on the address below to find pictures if you have not seen them yet in the post from 2012.

www.acmoc.org/bb/showthread.php?17425-D2...haft-thrust-bearings

Uncle Rich,
How thick are the thrust washers? I'd guess about 1/8" or so.

Inherent design flaw?- no argument there...I told an old Cat guy yesterday about how much end play my pony had-he said "Hell, most of them little SOB's had about that much! so yeah, not an uncommon problem.
But still, they did their job for many years...tough little motors for the conditions they had to operate in.

"Old wrote:

Uncle Rich,
How thick are the thrust washers? I'd guess about 1/8" or so.

I believe they were .090 inch. I found the invoice for them, but no dimensions. I found them at a bearing house called Motion Industies. They were described as TT 2601 Thrust Bearing. I think I had to carve a little out of the inside diameter if I remember correctly or at least bevel them slightly to match the fillet on the crank shaft to wheel. Probably about an 1/8 radius. Everything is good so far. The only thing that remains is to take it apart and inspect it, but that is unlikely. Lol. The only thing on that motor yet is that chuck out of the flywheel you picked up on. Every time I look at that I think about your concerns. Someday I'm going to take that thing off and try to balance it.