Engine noise

A while back I acquired a 1955 TO35 that had not been running for some time. Now that I have it running the engine makes a rapping sound at idle. Can't hear it at any other engine speed. As you gradually slow it down you don't hear anything until it gets right at idle. With hood and gas tank on it seemed to be coming from the left side of the engine about by #2 cylinder. Found a bent pushrod and replaced it. Still had the noise. Pulled the head and found one bad valve and the need for new guides. Had the head planed and installed new valves and guides. Still have the noise. This time we ran it without the hood or gas tank and determined that the noise is coming from the front by the governor. Then I remembered that last summer when I first got it running the governor seemed unresponsive. Could the governor be making this rapping sound?
I figured if anybody could help, you guys could. Thanks in advance.

I guess it's possible the governor could be making a noise. There is a cage that holds the balls, it is known to break and drop pieces of metal into the pan. The pieces are harmless once they make it to the pan, but on the way down they can get run through the timing gears, which can break or damage a tooth. If the governor is not working, and it's not a linkage problem, it needs to be addressed, good time to inspect the gears.

Another diagnostic trick is to set the RPM to the worst knock, pull one plug wire at a time, see if the noise changes. If it does change, good chance it's a loose piston, wrist pin, or rod bearing. If no change, could be valve noise, timing gear, or ?

Another source of front engine noise, loose crank pulley bolt. Try removing the belt, feel for loosness in the pulley. Start it up with the belt off, listen for difference, could be water pump or generator.

While the gas tank is off, pull the valve cover, recheck the valve lash. Try putting the feeler gauge in with it running, could be a bad rocker arm, cam going flat, worn rocker shaft. But be careful not to mistake creating a miss with the feeler gauge with killing a cylinder as in the plug wire test above.

Info from MF SERVICE MANUAL:

Get yourself a stethoscope:

Bob..

Hi Steve@Advance. Thanks for the advice. I had the oil pan off, no pieces of metal in there. I just thought I remembered reading somewhere that the governor going bad could make a racket. Although this noise never changes, just a steady rapping. I will try the other things you suggested. Thank you.

Hey John Deere D, thanks a lot for the great pictures, they will be a big help. I think I know where I can get my hands on a stethoscope. Will try that soon. I can't get time to work on it every day so it takes me a while to get things done. Joe

I had a similar noise in the front part of the motor of my 1957 TO35.

I looked everywhere and used the scope,

finally had an old farmer friend of mine come over and listen to the noise.

he ran his hand over the motor, finally ask me if the large bolt that holds the crankshaft pulley on to the crankshaft was suppose to be that far out.

problem solved: the bolt had back out and the noise was coming from the crankshaft pulley.

he helped me tighten up the large bolt and all motor noise was solved.

might at least be worth a look see and be sure you crank pulley bolt is tight.

You can use a long screwdriver or something similar as a stethoscope. Place screwdriver to noise and place thumb on end screwdriver and put your ear next to thumb. Move screwdriver around until you find exact location of noise. Be careful around moving parts. I always do this to find noise such as bearings. The old poor farmer fix but it works. LOL

Something else-it could be water pump bearing. Take fan belt off and run engine. If no noise then you have eliminate it. I've had pumps that made noise but didn't leak.

Thank you to all who replied. You have given me some good ideas on how to track down this noise. When I find the answer I will post it on this forum.

I had a similar noise in my TO-20 and only when idling. It turned out to be excessive clearance in the camshaft front bearing. Actually the there is no bearing in the TO-20 as the camshaft runs right in the block surface. I found it by pressing down on the valve spring side of the rocker arm as it was moving up and down while idling. When helping overcome some of the pressure of the valve spring the noise went away.

Hi Crem, thanks for the info. What did you do to eliminate the play. Once I get my carburetor rebuilt I will fire it up and see if this could be my problem. Thanks again. Joe

I just ran it that way. The engine had a lot of use over the years and was finally wore out. I replaced it with a rebuilt engine because of the cost and time of redoing the old one which also had some cracks showing between the cylinders. I believe that a shop can bore out the cam holes and install bearings I am but not sure about that.