How to Check for a Spun Bearing?

[fritz1255]

I have a Snapper mower with a 190cc single cylinder engine. It makes a clanging sound while running, and has sheared the flywheel key and actually broken the bushing that holds the blade. My suspicion is a spun connecting rod bearing. Is there any way to check this without tearing down the engine? Would there be noticable play while rotating the crank shaft?

 

[Scrubcadet10]

99.9999% of small engines don't use rod bearings, just aluminum rod and steel crank, but when they wear you do get a clanging noise.
Generally you can remove the cylinder head and see if you can push the piston down and feel for play... I've only heard of that being done, never done it my self.

 

[MowLife]

To check the connecting rod correctly you have to at least remove the sump to check both ends of it for play.

 

[bertsmobile1]

The cheap & nasty test is to turn the engine just past tdc then try & push the piston down.
If it moves at all then the rod it toast.
Hold the crank with one hand and use the thickest thing that you can poke down the plug hole.
Do it several times with your eyes closed so you can concentrate on the feel.
If the rod is gone enough to make an audiable klunk then you should be able to feel rod move a couple of thou.

 

[MowLife]

The reason I suggest pulling apart is I’ve run into wrist pin and piston wear that act like a loose rod or knock.

 

[bertsmobile1]

To be honest you are correct & if it was in my shop it would get the sump pulled if and only if some one was paying for my time to do it.
However the stick in the plug hole method allows me to tell the customer I think they have a terminal failure & any further investigation will cost them money.
Even better, most can actually feel it so they know I am not taking them for a ride.
Most won't bother as I have shelves full of reasonable used walk behind engines for about the same price as doing the quote on a potentially deceased one.
parts prices are a lot cheaper in the USA but down here it is uneconomic to open the sump on a walk behind.
A flogged out big end, loose bin end bolt , loose piston pin or even cracked piston, all of them are fairly well terminal cost wise.
particulaly when I regularly see superceeded / surplus walk behind engines selling in the $ 50 to $ 100 price range.