Cub with knock is home now

Tom in Mo. · Jul 31, 2010

It runs very well and strong except for the knock. I dropped the oil pan and looked around but all looked good. Put fresh oil in and drove it around mowing with the flail mower. Still runs good and still knocks. I will pull the engine this winter and look inside.

Dave_Id · Jul 31, 2010

Maybe it's as simple as adjusting the valves. I had a Minnie Moe where one tappet was out nearly .100 of an inch slop. It didn't run very well though, unlike your Cub.

Tom Fleming · Jul 31, 2010

is the sound truly a knock, or is it closer to a loud tick? If the sound is closer to a tick, check the valve lash.

Also, did you check the connecting rods while you had the pan off? quickest way to check the connecting rods with the pan off is to turn the crank back and forth just a bit with your hand on each rod at the cap. if you feel slop when you "rock" the crank, you have a bad rod bearing. BTW, there is a difference between "slop" and "clearance". You could also check the mains, but that is best done by dropping the caps. You'll need a torque wrench to put them back on.

If those are all good, you might have a bad wrist pin in one of the pistons.

Brownie 450 · Jul 31, 2010

Sure that a sound from the flywheel/ clutch area isn't getting telegraphed up front? Loose flywheel bolts/ worn clutch splines can make noise. Does the sound vary with RPM or engaging/ disengaging the clutch? How about a tooth out of the timing gears?

State of Jefferson · Jul 31, 2010

I haven't experienced it on my Cub, but had a significant knock from the front of my SMTA. Turned out to be some chipped teeth on the cam gear. Could be a possibility...

Ben

Tom in Mo. · Jul 31, 2010

The knock is steady with the RPM. Clutch in or out doesn't make a difference. One thing interesting is it does not knock for the first minute or so after starting, then it knocks until it is shut off and cooled. When I get into it this fall, I will start looking at things on my way into the engine. It absolutely does not smoke a bit, super clear exhaust under any load. This will be a fun project.

Rusty wheel · Jul 31, 2010

While it's still running, get an engine stethescope and try to locate the source of the noise. Might save you some time,work,and money.

Anonymous-0 · Jul 31, 2010

check fan bushings. mine were worn to the point that the fan was catching the shroud and the internal oil slinger was cherping. good luck, d.coleman

Vito · Jul 31, 2010

Could be a bad wrist pin.

Vito

Tom Fleming · Jul 31, 2010

One las question I forgot, and didn't notice if you had posted it. How is the oil presure?

Tom in Mo. · Aug 1, 2010

Oil pressure is lower than I would like it to be according to the gauge on the filter housing.

Joe Dowling · Aug 1, 2010

A few years ago (10) a man I knew asked me to stop by his house to check out his cub that had a knock. When he started it up it had 30 lbs oil pressure and made no noise until he gave it a little gas. He had spun a rod bearing that would slide around and the knock would go away. When the bearing moved around the piston would slap against the head. Had to have the crank reground and a reconditioned rod, new bearings, etc. Runs great now. Good luck.

Cub with knock is home now

Tom in Mo.

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Dave_Id

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Tom Fleming

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Brownie 450

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State of Jefferson

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Tom in Mo.

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Rusty wheel

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Anonymous-0

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Vito

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Tom Fleming

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Tom in Mo.

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Joe Dowling

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