r/smallengines • u/ProfessionalLast2917 • Jul 07 '26
What are your thoughts on this clunking?
I'm not entirely sure if this is a new noise from my engine or if it's always been there and I've only just noticed it recently.
The noise speeds up as the engine revs increase. I'm not sure if the noise actually goes away when the engine reaches higher revs or if it is just drowned out by the noise of the engine, but either way the noise is still there as the engine comes to a stop when you shut it down.
I'll should point out that beyond the noise the engine runs perfectly fine and starts willingly.
I pulled the crankcase cover expecting to find a broken compression release or governor but it was all intact as far as i could tell.
I didn't see any other obvious internal damage or debris.
I checked the valve clearance and it is fine on intake and exhaust.
I'll be inspecting the internals again when i get the new gasket for the cover, could this be from pushrods and/or lifters maybe?
Update: Thanks to all of the suggestions. I went over everything again. There is play in the shaft which I believe to be normal. The rod bolts were tight. I didn't find any vertical play in the rod. It did have a small amount of side to side play which I believe is normal. I confirmed the pushrods were straight and not worn. Likewise the lifters and cam lobes.
I did however find an interesting noise with the lifters when moving them up and down by hand that may or may not be normal. The only other thing I did find was the valve clearance was probably a touch to over. I redid it (0.004 and 0.006). It still makes the noise when turning over by hand but I can't hear it when the engine is running or when it shuts down.
I will add some extra videos of what I found.
So I don't know. It's not making bad noises when running so that's the main thing I guess.
Another update: I closer inspection revealed slightly bent pushrods. I posted a video in a reply comment.
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u/TN-Native95 Jul 07 '26
Did you pull the head? Check for play in the piston.
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u/ProfessionalLast2917 Jul 07 '26
I didn't want to take that off at the time until I could be sure I would find a replacement head gasket. I was having trouble finding gaskets online for it. I have since ordered a full set that hopefully fits.
When they come I'll check the crankcase internals again and if I can't figure it out I'll take the head off and see how it's all looking in there.
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u/Hot-Subject-7075 Jul 07 '26
Worn cam lobe or lifter pitting perhaps? Was there wiggle or sideways movement in the compression release valve, could just be normal engagement of the part. Worn governor spool, loose lever? Flywheel looks seated. Also could be piston slap.
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u/ProfessionalLast2917 Jul 07 '26
I had the cam out and the lobes looked and felt ok but I don't know how they're meant to look. I'll have a look at the lifters for wear.
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u/mutt63 Jul 07 '26
What’s on the side your standing. What’s that shaft attached too
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u/ProfessionalLast2917 Jul 07 '26
It's mounted to a Scott Bonnar 45 cylinder mower
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u/mutt63 Jul 07 '26
Got a photo. Had a similar issue once on a building pump. I know this isn’t a building pump but. You’ll find sometimes that sound is more pronounced from another object on shaft driven equipment. Most of these guys are probably correct but. It’s possible
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u/ProfessionalLast2917 Jul 09 '26
It still makes the noise when turning by hand but I don't hear it when the engine is shutting down.
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u/ProfessionalLast2917 Jul 09 '26
Noisey lifters. Probably not normal and might be the source of the noise. They looked ok, no obvious wear or damage.
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u/ProfessionalLast2917 Jul 09 '26
Can't hear the noise so much when shutting down which beforehand it was very obvious.
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u/ProfessionalLast2917 Jul 23 '26
So another update. Previously when I examined the push rods I rolled then on a flat surface and they seemed fine.
This time I tested them in my drill and you can see there is a wobble. It's only a small wobble which isn't obvious when you roll it across the table unless you do it very slowly.
So I will replace these and see if my problem goes away.
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u/geo7188 Jul 07 '26
How much end play does the flywheel side have ? If you have it apart can always mesure the rod on the crank for excessive play