I'm trying to revive an old Lawn Boy 2-cycle mower. It runs, but has a ticking sound in the engine. Investigating, I find that the crankshaft has a lot (1/8"+) of (vertical) end play.
I opened the case on a 2nd Lawn Boy engine. (It has other problems.) All I find to limit the crank movement is a shim, between the crank arm and the lower bearing. That seems to limit how far the crank can move down, but I see nothing to keep it from moving up, other than whatever constraint the connecting rod creates.
Question: is this much end play normal for an engine like this? And, if not, how is the movement supposed to be constrained. It seems a lot; but, maybe it doesn't matter, as long as the engine is oriented vertically?
If I understand your description, you have both endplay and worn bearings.
Shims are used to limit crankshaft endplay.
But if you have looseness in the piston and connecting rod, about the only thing I can think of that will give you that is bearing wear, both or either wristpin wear and main bearing wear.
Update: it turns out that the 'shims' (in the 2nd engine) are actually a thrust bearing, with cute little needle bearings in the thrust face. And, that bearing is completely missing in the engine with the large end play. I have no clue how that could be. I know enough of that mower's history to be pretty sure that it wasn't removed. But, I don't find any debris in the case.
Sure could. Thrust bearing is the proper word. Sometimes they are shim like, other times they can be of the needle bearing types. (Speaking in general, for a lot of IC engines}
Once, I rebuilt a 2.5 l L4 Pontiac engine, and when putting it back together, crankshaft endplay was out of spec (loose). I called the machine shop that did the work, and asked them what would be the consequence and how to fix it...No consequence, they said, so I put it back together as was. Worked fine.
If you have slack in the wrist pin or crankshaft bearing, I think you need to deal with it.
Once upon a time I had a '67 Dodge Dart, with the vaunted 225 slant six engine. The car was a horrific heap which I paid less for than I likely have in my pocket now, but the reason that I popped for it was that the body was mostly rust-free, requiring only one minor repair around one of the torsion bar sockets, being from either NC or SC (I forget which - and when I say only one minor repair, I'm not counting dents!) and the owner proudly told me that it had a recently installed remanufactured engine. It did run well once I finally got it started. I proceeded to change all the fluids, fix the wiring and the carburetor that kept it from starting well, replaced the LF fender from when the PO had run it into a parked car (possibly because the brakes were so shot that the rear wheel cylinder pistons were loose in the drums!) completely rebuilt the brakes and had new tires installed. The flexplate broke shortly after :( I unloaded the car on an acquaintance for even less money after the second transmission died due to a busted hose, thanks to the mechanic that I paid to replace it not informing me that the cooler line had been patched with fuel line down under the car where I couldn't see it.
The new owner of the car informed me that after she tore it down, she found that the "recently remanufactured" engine had about 1/4" of crank endplay. Hmm, ya think that might have been why the flexplate busted?
So anyway my assertion is that at least based on my personal experience, keeping the endplay at least close to spec is important to having a reliable vehicle. The sad thing is that had the PO not got boned by the reman engine, I would have likely had good, cheap, durable (if unsightly) transportation for as long as I felt like keeping the thing...
On further inspection, I think the engine that didn't have a thrust bearing never had one, that it was designed that way. The space between the (top and bottom) thrust surfaces in that crankcase was a little less in that engine than in the engine with the bearing.
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