motor tech question

[mike stover]

I probably know the answer to this question, but how much play should the be in the conrod bushing on the crankshaft??

I just put new bearings in and have noticed a "click" when rocked back and forth. If you watch the conrod on the crank you can see that there is some slop there. Am i correct in assuming that the conrod should be replaced, or is there normally some slop there?

Thanks, Mike

 

[Kez]

When I got my first K&B 3.5 in the 70's I noticed the conrod big end has a lot of slop. That was a new engine. I wrote K&B about the conrod play and got a reply telling me that it was normal to have 0.002" play in the big end. I also learned that they tried a tighter clearance and the bush would seize in the crank pin and spin.

Over the years I have had many K&B in 3 different sizes and all noticed the play in the conrod. This is more noticeable in a new engine with tight piston fit and when you tried to turn it over without the plug.

Based on the information I received from K&B, I used the conrod until the slop became much worse..like 0.004"

Hope this helps.

kez

 

[Hydro Junkie]

Okay, are you talking between rod bushing and crank pin or between rod and crank discs themselves? This will make a big difference in the answers you get

 

[mike stover]

Okay, are you talking between rod bushing and crank pin or between rod and crank discs themselves? This will make a big difference in the answers you get

Yes between the conrod bushing and the crank pin

 

[Hydro Junkie]

Okay then, now that I know what you're looking at, years ago I was told that the bushing needed to be openned up around .005" larger than the crankpin to prevent conrod and crankpin damage. That works out to around .0025" of slop, making it almost identical to what Kez was told