YM336D - Started knocking loud while tilling

[tcartwri]

I did the plastigauge:

#1 .002"
#2 .002"
#3 .0005" (it pretty well smoshed it.. it was slightly wider than the .001" indicator)

.002 is fine. .0005 is not. However, from what you describe, I can't see how it has become so tight, unless the rod is out of round, and you happened to pick the tight spot.

The bearings look ok to me. The coating on top of the copper layer is only about 0.0001, so just pointing to that as a problem, is a problem in itself.

 

[Barry 1]

Put an old bearing back on it,check the clearance,if it's good,use it. You might have a bad new bearing,First time for everything!
Or switch one of the other new bearings to that rod and check the clearance.
Did you pry the crank back and forth,to see how much end play it has?

 

[Neat 1500]

maybe while its apart try that, swap bearing from 2 to 3 and see if 2 tightens up. if it doesnt your rod #3 is either out of round or bent or if it does the bearing is the wrong size.

 

[tcartwri]

.002 is fine. .0005 is not. However, from what you describe, I can't see how it has become so tight, unless the rod is out of round, and you happened to pick the tight spot.

The bearings look ok to me. The coating on top of the copper layer is only about 0.0001, so just pointing to that as a problem, is a problem in itself.

sorry. didn't realise those were the new bearings. disregard my post.

 

[Car Doc]

so just pointing to that as a problem, is a problem in itself.

The wear is off to one side as in 2 bent rods. I fail to see how you can say the wear is ok?

 

[Domush]

sorry. didn't realise those were the new bearings. disregard my post.

The measurements are with the new bearings installed. The pictures are of the old bearings.

 

[tcartwri]

The wear is off to one side as in 2 bent rods. I fail to see how you can say the wear is ok?

It's just not that unusual in a motor with a lot of hours. The wear in the pictures is really minimal.

 

[Domush]

maybe while its apart try that, swap bearing from 2 to 3 and see if 2 tightens up. if it doesnt your rod #3 is either out of round or bent or if it does the bearing is the wrong size.

I think this is my next step. swapping bearings with the pistons in will be interesting. I worry pulling the head a second time is in my future.

 

[Car Doc]

It's just not that unusual in a motor with a lot of hours. The wear in the pictures is really minimal.

Do you realize rods run parallel to the crank? As simple as that is to say the wear should be apparent it is not normal.

Yes the hours explains the lack of babbit that is normal that it leaves over time and in itself isn't the problem and I have never said it was.

I am saying there are 2 bent rods.

 

[tcartwri]

The measurements are with the new bearings installed. The pictures are of the old bearings.

Ok thanks.

Well then, as others have suggested, the shells can be swapped around to see if you can get the clearance you need. Shoot for 0.0015" to 0.002". Do not shim the caps on the rods. Snap the bearings in dry, and then lube the faces with oil. There is no radial clearance (slop) on 3 because of the tight fitment.

Make sure the caps are on correctly. There is usually a chamfer on one side of the rod big end bore to clear the radius on the crank fillet. Put the cap on backwards, and you can wipe the crank in an instant.