Big End Connecting Rod Bearing Replacement

[sean donato]

a) the interference fit of the pin to the crank wheel may not be the same as it was the first time. Enter the discussion about welding. There was a thread on here years ago about porting a twin cylinder I think echo and where to start and end the weld. That was for strength though.
b) who is offering rod and pin kits for these?

In vintage motorcycles earlier roller cranks were made up from a bunch of different sized rollers to choose from. Later on manufacturing tolerances were better and that was no longer done. A true Harley fanatic probably knows this date. For BMW they stopped the roller crank and went to pressurized oiling in 1970 but if I recall correctly an assortment of roller diameters were available. Some outfit must do this for vintage restorations, Bley who I had their literature has stopped. They made a slightly larger pin and heat treated it. I believe centerless grinding can be used to make the rollers.

Just v blocks is what I have seen in manuals not the bearing thing you created. That key way cut out makes it just about impossible to put the indicator where it should be.

It was a echo 610evl they were welding on, and the way he did it was to limit the possibility of his weld cracking.
They did or used to do quite a few motor cycle/ dirt bike big end bearings at the machine shop I worked for. I never once saw them reuse a cross pin or bearing. Normally the guy would use the lathe,well crank grinder, but basically the same thing. but some times he would set up smaller ones on vee blocks. The roller idea is pretty good, I'd question the tolerances on the bearings and the printed parts vs a good set of vee blocks. But close enough for what your messing with.

 

[Vintage Engine Repairs]

Ironically I’m reading these posts at 1110pm east coast u.s. time, so likely 1110am now for you.

Yep!!

 

[j-jock]

Back in the 80s, one of my buddies was a faller/contractor, and as a result, I ended up with some low time cranks from several Husky 2100s.
I have always been interested in doing the crank swap, because I have at least 2 low time cranks, where the damage on the 1st, is such that I would be able to make one good unit out of the two. (One has a broken crank end, and one of the others, has a broken rod end).
The problem with repairing those saws back then, wasn't finding the crankshaft, it was to find the right hand side of the case. Now, a guy could probably just buy the complete case from a Husky clone, and use the OEM crank in the Chinese case.
I have the press, the lathe, and the measuring equipment, and have been thinking of doing this for quite some time. I was thinking of using dry ice to cool the pin on re-assembly, to make truing up the assembly an easier job.
One day, back around the same time in the 80s, my long time, now retired friend, owned a Husky dealership, and worked on tons of saws (including being a master of magnesium TIG welding). He frequently went on seminars put on by Husqvarna, and I still remember him telling me that he had just returned from a weekend, where they had actually split and assembled cranks. I also remember him saying, that he would never do it because he would have to buy the equipment needed to true up the assembly, and he would never recover the investment.
I also agree with PioneerGuy600, that it wouldn't be a reasonable risk to send a saw with that repair, back into the woods, without having all new parts. Have you seen what some of those fallers do to those saws? Back then, before advent of the harvesting equipment, the woods were crawling with fallers, and there were a lot of cowboys who did bad things to saws.
A very interesting conversation. I should find the time to measure some of the OEM cranks, to see how true they are from the factory. (well, almost from the factory).

 

[Vintage Engine Repairs]

I’d never do this for a commercial user even if I could get new parts - I’d throw in a new crank. This is for me, a casual user of power tools. Mostly for fun, but also to see if it’s possible and then learn now on cheap equipment so that if it becomes something I need to do in the future I can, with more confidence.

It’s important and worthy to seperate this from a fix for commercial guys. Firstly they’d pay a new crank off in a few hours of the job they do that day and secondly their highest priority is reliability. Go new, go oem.

For the 98% of those who are on this forum as hobbyists who like to tinker, repair their gear and enjoy doing it, it’s certainly a viable thing to consider.

 

[Vintage Engine Repairs]

Regarding oem cranks, I just measured one for you, it’s 0.01mm runout. I found in a Yamaha dirt bike manual it says 0.03mm is new, with a limit of 0.05mm.

 

[ericm979]

It’s something I asked a mechanical engineer who worked at the ministry of defence in the Uk. If you take it apart multiple times I’m sure you would go beyond the allowable tolerance. Once, I wouldn’t think so. It took considerable effort on my 6 ton press to seperate it.

View attachment 1071356

If the pin isn’t damaged reuse it, bearings can be brought from a local bearing supplier.

Crankshafts are often rebuilt (though you’d normally use a new pin) on bikes.

Allen Millyard would know! He's well known in vintage motorcycle circles for his crazy home built multi cylinder engines. 5 and 6 cylinders based on Kawasaki triples at first, then he branched out into four strokes. He's pressed a lot of cranks.

Back when I was racing RZ350s it was common to weld the crank pins on race engines. It wasn't done to make up for poor press fits, it was done to keep the pins from moving on cranks that were turning faster than the manufacturer intended and being subject to more force as a result. Stock redline was 9500 but depending on the pipes race engines would be pushed to 12500 or more.

 

[Vintage Engine Repairs]

Allen Millyard would know! He's well known in vintage motorcycle circles for his crazy home built multi cylinder engines. 5 and 6 cylinders based on Kawasaki triples at first, then he branched out into four strokes. He's pressed a lot of cranks.

I agree, he is beyond gifted.

 

[j-jock]

Allen Millyard would know! He's well known in vintage motorcycle circles for his crazy home built multi cylinder engines. 5 and 6 cylinders based on Kawasaki triples at first, then he branched out into four strokes. He's pressed a lot of cranks.

Back when I was racing RZ350s it was common to weld the crank pins on race engines. It wasn't done to make up for poor press fits, it was done to keep the pins from moving on cranks that were turning faster than the manufacturer intended and being subject to more force as a result. Stock redline was 9500 but depending on the pipes race engines would be pushed to 12500 or more.

A friend of mine was into doing stroker and race engines for scooters and smaller dirt bikes, and it was the same thing, the stroker cranks were all welded.