Motor Knock

[Mad Max (TX)]

I recently inherited a 50 TO 20 in reasonably good condition. Before I got it the tractor has not run in 6 or 7 years. I replaced all wiring, points and rebuilt carb. Changed all oils. The tractor starts easy and runs well and smokes very little. However the motor knocks at low RPMs. Whenever you rev it up the knocking stops. When you bring it back down the knocking starts back up. I have adjusted the tappets. I don't think this motor has ever been rebuilt but I do not know that. This sounds like a rebuild to me. Is there something else that I should try before I condem the engine? Thanks for any advice.

 

[jon corbett]

sounds like your timing (distributer)is off

 

[maxwell99]

if its not a timing issue.
its worth a try to add 1 qt of lucas oil stabilizer to your oil.

this is great stuff and will help old tired engines.
what weight oil did you put in the tractor.

30 weight i would guess.

cost you about $10 bucks to try this,

just drain out 1 qt of your oil and add the lucas.

many of my friends that drive big over the road trucks would never let you change oil in them without adding 1 gal of lucas.

I changed to shell rotella 15w40 in my to-35 and it sure holds much better oil pressure.

i did use lucas when i used 30 weight.

 

[2tractors]

It's probably nothing more than the govenor mechinism,or the upper and lower gears on the cam and crank which come in different sizes to remedy,take a stick and put to ear and listen.If it's bearings then oil pressure will be low and if compression is low then rebuild.My 20 was also noisy.

 

[Tony in Mass.]

I'm with 2. The weights inside the distributor housing can rattle when there is no torgue to pull them outward. When everything else is quiet, you notice the noise. Anything besides that is expensive. So blame it on the weights....

 

[John (UK)]

What is the oil pressure when it is knocking, has it got decent oil pressure. Usually an engine will knock more the faster it runs. Check the Camshaft isn't sliding backwards and forwards in the Cylinder Block. There is a large nut on the front end of the Camshaft that comes slack and it will cause this noise, it will also damage the drive on the bottom of the distributor as well if you keep running it.Listen carefully at the bottom of the distributor for the noise, if it seems to come from there then take off the timing cover. If you need more info about this, email me and I will send [email protected]