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toakley

Confirming A Suspicion

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toakley
I need to confirm a situation I had with a 5 HP B&S engine on our garden tiler. I had to do a ring job, since the engine had low compression and tended to smoke a bit. I honed the cylinder, purchased std rings and reassembled. The engine fire up and ran smooth for about 20 minutes. It then quit and wouldn't turn over as if it was seized. I pulled it apart and noticed that the cylinder wall was gouged. I had to emery cloth off a burr of metal on the cylinder wall in order to remove the piston. I assumed that I had broken a ring, but no. What might have caused this situation to happen? I'm assuming I can probably re-hone the cylinder wall and try re-installing the piston with the same rings again (which were installed with the correct orientation on the piston, etc). I hadn't checked the ring end gap, but since I used standard not oversize I thought I was home free. Any thoughts?

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toakley
Goatfarmer, I just checked the piston and the wrist pin (not sure if correct spelling) or piston pin as you referred is still in place with both internal rings secure. Any other thoughts?

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land44
check the direction of the piston there should be a little arrow on it that should face the exuhast side of the head. and make sure the rings for the oil and compression are on oppisite sides from each other. also check for piston slap -(causing cylinder scores) after honing the cylinder you might have to large of a gap and will need to get an oversize piston. and rings.

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toakley
Based on replies to my post, I've checked a few of the obvious: Land44: Piston was installed w/ the correct arrow orientation and all rings gaps were off set from one another. In reference to checking for piston slap, that wasn't done at time of reassembly. I did notice some slight vertical scoring along the walls of the cylinder. The main gouge that I mentioned is at a mid-way point in the cylinder. Roy: Upon re-honing / reassembly, I'll replace ring set. Dark: Spark plug is OK, nothing broken or missing. Question: How should I measure for piston slap, what's acceptable / non-acceptable based on rocking the piston from side to side? Secondly, ring end gap measurement, do I fit the rings in the bore at various points and then compare the gap measurements? Anything else I should be doing or checking?

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Dark
Crank the engine over until you feel the resistance of the piston coming up on compression. Crank against compression until the piston is about half way up the cylinder. Now, rock the crankshaft back and forth and listen for a metallic knocking sound. If you hear a knock, you have piston slap and the only way out is to rebuild the engine. The noise called piston slap is caused by one or more pistons having too much clearance between its side skirt and the cylinder walls. In effect, the pistons become too small and wobble in the cylinder bores. It can be cause by an engine simply wearing out a piston seizing because of a lack of lubrication (it runs out of oil) or it's put together wrong. This is easy to check and usually it doesn't happen to all the pistons. But there could be other causes, debris when assembled and such. In effect you put round (circle) rings in an oval piston sleeve. remove the head press/set the piston half in the cylinder then push to one side take a feeler gauge set and start measuring the gap between the piston and the cylinder wall anything close to 10 or over its time for a machine shop. also I don't know what the rings may have hit at TDC as far as ridge I can only hope you used a ridge reamer to remove this before honing.

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almb212
Did you mic(measure) the cylinder bore before honeing to ensure that it was within specs? when you hone you remove even more material,perhaps to much clearance between the piston and the cylinder wall caused the problem. Al

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D-17_Dave
If you had the piston out then you had the rod end and oil slinger removed. Did you replace the oil slinger as it was originally? As for the cylinder, your rework of the cyl. could have left the cyl. rough or out of spec. as far as diameter or out of round. Either can cause the piston to bind in the cyl. Also check the wrist pin and rod for free travel from one side skirt to the other. The wrist pin being tight can bind the piston duplicating the piston slap condition. This condition squeezes the oil out between the piston and cyl. causing the lack of lubrication and the friction which transferred the metal.

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JJ MARSHALL
You didn't use any kind of compound like valve lapping compound when you were honing it did you? i know it's sound crazy but i know a guy that try this on a 10 hp B&S it didn't turn out to good. mess up the walls on his motor. JJ

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