Piston Pin Bearing and Spacer Issues -- Jonsereds 110

[bulletpruf]

Fellas - I'm trying to finish up a Jonsereds 110, a 110cc saw from the early 1970's. I'm hung up on finding a piston pin bearing and spacer issues.

I have an NOS piston, but I only have one of the two spacers (these fit on the piston pin/wrist pin on the outside of the pin bearing). The dimensions are 21 mm OD, 14 mm ID, and 1.36 mm width. I know I can't go to a hardware store and find this in a bin, but does anyone have any ideas on where to find one besides getting one custom made on a lathe?

On the piston pin bearing, I'll obviously need something that's got 14 mm ID to fit on the 14 mm pin. As for the OD, the ID of the small end of the rod is 18 mm, so I'll need a bearing that's about 18 mm in OD. The width is what I'm not sure about. The width of the small end of the rod is 15 mm. Is that it? Or does the bearing need to cover the entire pin from spacer to spacer? If so, that would be 15.5 mm.

Thanks in advance for any info.

Scott

 

[ericm979]

On modern two strokes the rod is usually located by the crank pin and there can be significant play of the piston on the small end when the piston is not in the cylinder. It doesn't matter when it's in the cylinder. Often there are thrust washers on either side of the rod at the big end which lets you know that's how the rod is located.

I'd get the spacer duplicated by a machine shop. It's not hard to make and shoudn't cost much.

The small end bearing looks pretty typical of a japanese motorcycle of the 70s-90s. A YZ85 bearing (also used on a ton of other dirt bikes that size) is 14mm/18mm with a length of 16.2mm. Might be a little long. Perhaps the spacers could be modified or there's a similar bearing that's a little shorter.

 

[bulletpruf]

On modern two strokes the rod is usually located by the crank pin and there can be significant play of the piston on the small end when the piston is not in the cylinder. It doesn't matter when it's in the cylinder. Often there are thrust washers on either side of the rod at the big end which lets you know that's how the rod is located.

I'd get the spacer duplicated by a machine shop. It's not hard to make and shoudn't cost much.

The small end bearing looks pretty typical of a japanese motorcycle of the 70s-90s. A YZ85 bearing (also used on a ton of other dirt bikes that size) is 14mm/18mm with a length of 16.2mm. Might be a little long. Perhaps the spacers could be modified or there's a similar bearing that's a little shorter.

Thanks for the input

 

[Cantdog]

On modern two strokes the rod is usually located by the crank pin and there can be significant play of the piston on the small end when the piston is not in the cylinder. It doesn't matter when it's in the cylinder. Often there are thrust washers on either side of the rod at the big end which lets you know that's how the rod is located.

I'd get the spacer duplicated by a machine shop. It's not hard to make and shoudn't cost much.

The small end bearing looks pretty typical of a japanese motorcycle of the 70s-90s. A YZ85 bearing (also used on a ton of other dirt bikes that size) is 14mm/18mm with a length of 16.2mm. Might be a little long. Perhaps the spacers could be modified or there's a similar bearing that's a little shorter.

Just the opposite on the pro Jonsereds saws. The con rod position on the crankpin is determined by the piston to the upper con rod clearance. On some saws this is determined by a close fit of the con rod between the wristpin bosses....on other models like the one discussed here the piston bosses are machined to allow for the thrust washers with a running clearance of 0.012-0.015" to keep the conrod centered.

 

[Mad Professor]

Just the opposite on the pro Jonsereds saws. The con rod position on the crankpin is determined by the piston to the upper con rod clearance. On some saws this is determined by a close fit of the con rod between the wristpin bosses....on other models like the one discussed here the piston bosses are machined to allow for the thrust washers with a running clearance of 0.012-0.015" to keep the conrod centered.

You might have saved an ugly situation for OP with that post.

 

[ray benson]

Somebody here must have some spark plug indexing washers? Or the auto store for a drain plug washer.

 

[Mad Professor]

Somebody here must have some spark plug indexing washers? Or the auto store for a drain plug washer.

Those are not going to be hardened shim steel. Will crumple and then.........

 

[Cantdog]

Those are not going to be hardened shim steel. Will crumple and then.........

Yes they certainly need to be hardened and the other thing is that the upper con rod bearing and is wider than con rod itself so the place milled into the inner faces of the thrush washers accepts the protruding bearing on both sides.

 

[Cantdog]

It appears I misspoke.......it looks like the thrust washers on the 110 are just flat and not like most of the smaller Jonsereds that used the stepped thrust washers...sorry

 

[Mad Professor]

It appears I misspoke.......it looks like the thrust washers on the 110 are just flat and not like most of the smaller Jonsereds that used the stepped thrust washers...sorry

Well those would be right much fancy washers with a step down. I packrat stuff like those and store well. Lots of junk but if ya need one.....

 

[Cantdog]

Yep pretty fancy.....they facilitate a couple things. One, they set the side play between the wrist pin bosses and the upper con rod centering the lower conrod bearing between the counter weights of the crankshaft. Second they allow the upper conrod bearing rollers to bear fully across the entire width of the upper conrod bearing race. The step in the thrust washer allows the the roller cage to be outside the race...

These are from a 70E but are similar as found in the 52/52E, 621 etc.

 

[Cantdog]

This shows how the thrust washers/shims work centering the lower conrod on the crankpin.