Need some help and advice - rocker arm problem

davegordon

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I ran over a piece of uneven lawn and my riding mower (17 HP) stopped. I was able to restart it and mow for about 5 more minutes.

But, then the mower died and wouldn't start. It was misfiring and popping.

Then, I took off the OHV plate and noticed that the intake push rod and rocker arm was popped out (but not bent). I was able to take off the cradle and put back the rocker arm and briefly restart the mower.

But, it died again and I haven't been able to get it to turn over since.

Now, there is a rapid knocking sound when I try to turn over (crank) the engine. Please help.

How do I move forward ? Do I need to take apart the entire engine block or just make an adjustment to the valve gaps ?


Thanks,

Dave

(6 Year Old Craftsman riding mower)
 
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dfbroxy

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Please look on the engine for the make and model number and post it. This will help the experts on this site to give you better info. Im only a backyard mechanic, but I would remove the cover and check the flywheel key before I started tearing down the engine. Cross your fingers! Check the rocker arm stud to see if it broke or became loose. Finally, remove sparkplug and rotate engine by hand with the flywheel. Feel and listen for a bump or knock. If there is one the engine may need to be torn down to find the source. Before teardown give the experts a chance to chime in as I may have missed something. Ahh.. Just remembered. How did you reassemble rocker arm and push rod. In other words are you sure you were on TDC when you set your valve gap?
 

davegordon

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Thanks for your help.

The engine is a single cylinder MTD. Not sure about the model number.

The funny thing is, I can only turn the crankshaft 360 degrees, even though this should be 4 stroke engine. I believe the end of the turn, either right or left, is TDC as the piston comes all the way up into the spark plug hole.

Should I be able to go a full 720 degrees by hand ? Not sure.

Here are 2 pics for some perspective:

thumbnail_IMG_0761.jpg
thumbnail_IMG_0760.jpg
 

cpurvis

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Take the valve cover off again and survey the situation.

Yes, you should be able to rotate the crank for as long as you want. Nothing should prevent that.

FYI, it takes 720 degrees of crank rotation to complete one '4-stroke' cycle.
 

davegordon

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I can't rotate the crank more than 360 degrees. It stops and won't move (by hand).

Does this indicate something hitting or broken in the engine ?
 

dfbroxy

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One last thing. Take off rockers and rods on both valves and try rotating engine by hand again. This is done with plug out. It should turn freely. If not then I think its time to check the internals. Also check the outside of block for holes or cracks. You
wouldnt want to rebuild an engine with a cracked block.
 

davegordon

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Ok, here's where I'm at:

Took out the rockers and push rods. Now, I can turn the crank as much as I want, but there is a sticky spot every 360 degrees which requires a little more force than the rest of the turn.

Also, as I turn the crank, lots of oil comes splattering out of the holes (left by the push rods).

Finally, if I try to start it with the key (no gas in the tank), I still hear the rapid knocking.

If this is normal, let me know and I will re-assemble and try to get the valve timing right. But, I don't want to damage the engine further if something is wrong internally.


Thanks,

Dave
 

bertsmobile1

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Without the cam pushing the rockers against the valve springs the engine should turn over freely and easily and smoothly.
Yours does not so there is something wrong and the engine needs to come out & be inspected.
Idf you have a mechanical decompressor on the crank then it could be broken.
Right now it is a simple replacement
 
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