Rod knock?

2

2speed

Senior Member
I have a knock that happens at all RPMS, idle on up. Seems to get less when spark is retarded. Shorted the cylinders and it seems to go away on #3. If I short #4 it gets worse....
 
Knocks come from a variety of sources, but your knock sounds like it could be the cam timing gear. Take the side cover off and look at the gear. Turn the engine over by hand to look at all of the gear. The difference when #3 and #4 plugs are shorted could be the location on the gear where it is damaged.
 
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I would take a quick look at the timing gear. Easy place to start.

50/50 chance that could be your problem. If gear is OK? Now you have to make a decision on dropping the pan and looking at a more major repair.

Good luck with your investigation.
 
Finally had some time, and adjust the valves to quiet it down to hear it better. Still a metallic knock, it gets worse as it warms up, quieter when cold. Seems to quiet down when lugging a hill. Definitely gets worse when I ground out number 4.


New crank gear, new aluminum timing gear. Insert bearing engine, so can't really do a check and adjust on the center main. When I put the timing gear on, used a dial indicator and barely get 3 thou for backlash, which means the timing gear could be tight, but there isn't much to adjust on that....
 
Loose flywheel? Retarded timing will quiet a loose flywheel. Noises can often be tough to diagnose without digging into the motor.
 
With inserts you should go in there and at least look at them,not much bearing material before steel on steel and crankshaft damage resulting.
 
Rod knocks quiet down when lugging. If it knocks all the time, the rod bearing on #4 cylinder must be really bad. Check all the bearings.
 
So how old/miles is this engine?

Can you get an assistant in the cab to take the rpms up and down a LITTLE while you stand out there to try and pinpoint the sound?

What do those #3, and #4 plugs look like?
 
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