K301 knocks
 

Hi Guys. I have this K301 (in another 125 I just acquired) and it has a knock at low idle, but when I give it full throttle the knock goes away, until it starts starts to pull like up a hill or pulling a load. I tore it down because I'm going to rebuild it. When I took it apart, the rear bearing, the one in the bearing plate, came off the crank just by pulling on it by hand (slid right off). The bearing also came out of the bearing plate fairly easy. It had .010 clearance between the bearing race and crank (should be in spec.). Question is, could the crank be slapping back and forth, creating the knocking? It's loudest on the PTO end of the engine. I had the crank miced and it is ok. Before I put money into it, I'd like to know what you guys think.

Thanks for any suggestions.

I'd check the cam end play and for wear in the bore or on the piston causing piston slap. use plasti gauge to check the crank to rod clearance . its pretty cheap and available at most any auto parts store. make sure you torque the rod to spec to get an accurate reading. are you sure the PTO isn't rattling causing the knock or the starter pulley/basket clutch basket key?

I forgot to say that I checked the cam end play (was in spec. .008). The piston don't show excessive wear and the cylinder was miced good. There is no PTO on it and the basket key was tight. So, the one thing that I didn't do was the plastic gauge thing to check rod clearance. I'll get some tomorrow, we have a NAPA, Advance Auto Parts, Autozone and Carquest within 5 miles. Guess I got it covered. :biggrin2:
Thanks a lot for your help.

Does the engine have balance gears in it? If so that could be your knock.

There's no balance gears.
Thanks for the reply.

Could also be the flywheel screen if it doesn't have all four bolts holding it on, or the drive coupler to the driveshaft if it's worn.

If you don't see anything, I'd imagine it was piston slap.

Have you checked the Crankshaft end play? .010-.020" I do believe. I'd also look into Plastigauging the end cap.

Are you saying you have .010 between the bearing ID and the crank where it goes?
I would like to see a light tap/press fit there, not .010.

Flywheel screen has all four bolts and is tight. Drive coupler to the drive shaft also looks good with no slop. As far as piston slap, possible because there is slight movement in the piston side to side.


Checked crankshaft end play, I have .010, manual calls for .003 - .020. Plasti gauging the rod cap is the next thing.

Yes, I have .010 there and the manual says .003 -.020. Seems like a large tolerance, don't it. :biggrin2:

Soooo, to narrow it all down, it seems like piston slap or rod cap.
The fix for that............. Have it bored .010 over and grind the crank .010 under. New piston, rings and rod.

Thanks to all, who have given suggestion to the problem. This was extremely helpful.

darryl, you are not following George I don' thing. He is talking about the rear housing. He wants to know if the bearing has a .010" gap between it and the aluminum rear housing. Like around the circumference of the bearing. It doesn't sound like that is the case..... I believe you keep stating the crank end play.


If your going to grind the crank, no need to plastiguage anything.