Piston/Cylinder sizes?

[motosierra]

I am a little uncertain about the present configuration for pistons and hope someone can clear this up for me. It used to be that an “A” piston was used in a new “A” cylinder. …. And that a “B” piston was used in a new “B” cylinder or a used “A” cylinder… etc…

Now we have “AB” pistons. I assume that an “AB” piston can be used in a used “A’ or a new “B” cylinder? So what happens if you have a new “A” cylinder…..? What do you use in it? A new “A” piston ..right!... but can you use a new “AB” piston with favorable results?.....thanks

 

[Lakeside53]

If you're talking Stihl, A and B are only available as factory matches to Cylinders. If you just buy the piston, you'll get AB which is suitable for both A and B cylinders. I believe there is only about 2/10,000 inch difference... I've NEVER had a problem using an AB piston in anything.

 

[motosierra]

If you're talking Stihl, A and B are only available as factory matches to Cylinders. If you just buy the piston, you'll get AB which is suitable for both A and B cylinders. I believe there is only about 2/10,000 inch difference... I've NEVER had a problem using an AB piston in anything.

Have you used an "AB" piston in a used B piston? are you sure the differnce is 2/10,000 and not 2/1000?... thanks

 

[motosierra]

Have you used an "AB" piston in a used B piston? are you sure the differnce is 2/10,000 and not 2/1000?... thanks

Correction...Have you used an "AB" piston in a used B cylinder? ...not... "Have you used an "AB" piston in a used B piston? "

 

[Lakeside53]

Correction...Have you used an "AB" piston in a used B cylinder? ...not... "Have you used an "AB" piston in a used B piston? "

yes, and yes, it's not 2/1000... That's a REALLY big gap.

 

[motosierra]

yes, and yes, it's not 2/1000... That's a REALLY big gap.

Wow!..2/10,000... its no wonder that pistons seize due to heat created by lean mixtures...thank you for helps comprehend these tiny measurements..

This question is off the thread but do you know what kind of tolerances are nessary for parts that are press fitted?..thanks

 

[Lakeside53]

Wow!..2/10,000... its no wonder that pistons seize due to heat created by lean mixtures...thank you for helps comprehend these tiny measurements..

This question is off the thread but do you know what kind of tolerances are nessary for parts that are press fitted?..thanks

That's not what I meant.. I was talking about the difference between and A and B, not the Piston<>Cylinder clearance. The A, B and AB are just the result of manufacturing tolerances as tooling wears. Stihl will not sell you just the cylinder - If you order a cylinder, you get a "best match piston of either A, B or AB. if you order just a piston, you'll get an AB (slightly smaller than A, but slightly bigger than B).


Other on AS know more about the issue of press fit, and i'm sure one will answer.