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MM UB Gas, Knock in the Engine?

C

Clodbuster

Member
I bought this about a year ago and it seemed to run fine sitting in a shed, but then it sat around outside not running since. Exhaust is covered but it has a small 1/4" crack in the manifold under the hood area.

I cleaned the gas tank, put in new points, plugs, cap, and rotor, and it runs sweet but has a loud knock. When I ride the brake it goes away and sounds fine and normal.

If it was carbon loose on a piston, would the sound go away under load? I hope it is not a rod bearing, but what else could it be? The tractor was aways taken care of and the oil is clean.

I spun the engine without the plugs in and nothing came out yet. Compression is an even 60 to 70 lbs on all 4 holes so I don't think it is a stuck valve.
 
Is the intake manifold cracked? If so you get an overly lean mixture and it could cause a miss and cause the exhaust valves to burn.
 
I don't think so. I am going to try to suck carbon off of the pistons with the shop vac and then try the water spray trick too.
 
Funny, the O/T things get so much more response.

I have misted water into the carb while running, ran without #4 spark plug and now put it back in and ran a quart of auto trans fluid through the carb. Letting it rest a while.

I think the knock has gotten much quieter but is still there. Getting ready to put a loader on it and hate to have to take it back off to tear the engine apart!
 
(quoted from post at 09:05:23 04/14/09) Funny, the O/T things get so much more response.
Click to expand...

Great observation. Rather than fight it though, go with it. I suggest you move this request for information about your MM U over to the MM tractor forum. There are very few off-topics on the specific tractor forums and they actually care about your questions.

Good luck,

Dean
 
Their is an adjustment on the front of the motor that takes the end play out of the cam. They will knock if the adjustment gets worn. You might try to adjust reset it.
 
might be worthwhile to drop the pan(abig job) and check the rods for looseness at crankshaft and pistons,rather than have to take loader off to do it .
 
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