ABC’s

[Adirondackstihl]

Been a long slow process, but I’m putting together a saw. OEM cylinder is labeled “A” and Meteor piston labeled “B”.....or vice versa....can’t remember.
What’s the deal....run it or not?

 

[Chainsaw Jim]

Not unless the cylinder is worn enough to need a larger piston. B should be larger than A. Have you measured what the clearance is?

 

[Adirondackstihl]

I have not measured clearance.
If B is larger than A......I would think there would be clearance issues? No?

I’ll measure tonight if I think of it

 

[Chainsaw Jim]

What are you working on?

 

[Adirondackstihl]

What are you working on?

660

 

[Chainsaw Jim]

Run it.
It would matter if it were a husqvarna.

 

[Chainsaw Jim]

Maybe it's a big bore piston. The only B mentioned in 660 piston part numbers is in reference to the 56mm.

 

[Jon1212]

What are you working on?

A chainsaw....

 

[Adirondackstihl]

Nah....standard bore....stock build.

 

[RYNOSAWR]

It does bring up a good point....

What is the ideal piston to cylinder clearance for these 2 strokes?

Assuming that the cylinder rigidity and cooling fins are different on each model saw casting, as well as the power output might determine piston to cylinder clearance requirements as well because more HP=more heat....


What say the experts??

Is there a basic formula for piston to cylinder clearance as well as ring end-gap?

I have put together some A pistons in some B or AB oem cylinders and they were a hair looser than a matched set, but still ran fine with no piston slap...

B piston in an A cylinder would make me worry if too tight, run a little lean, and not run with good mix oil....

 

[Duane(Pa)]

Awesome thread kids!

 

[sawmikaze]

I thought I was gonna finally learn the alphabet.

 

[RI Chevy]

A B Cs of saw engine rebuilding. Lol

 

[Adirondackstihl]

I thought I was gonna finally learn the alphabet.

Sorry Ryan.....next time....promise

 

[Chainsaw Jim]

Here's a screen grab of the 2100 service manual.

 

[dustinwilt68]

I have used A&B mismatched many times, never had any issues, just check squish, rings account for some differences I think.

 

[huskyboy]

I have used A&B mismatched many times, never had any issues, just check squish, rings account for some differences I think.

Same, no issues here either.

 

[drf256]

If it didn’t matter, there wouldn’t be an A, B or C there.

You’re likely fine and the jug wear will take up the slack.

I always get “AB” slugs because my OCD won’t allow me to put the wrong size piston in a bore.

That being said, I’ve never heard of any issue from a mismatch.

 

[XP_Slinger]

Didn’t know this existed. Something to watch for now, good thread.

 

[Lee H]

Mcculloch did this too with some of there 10 series saws. Seen it with
the PM 850's and seen a few toasted pistons in them as well.