"B" piston in an "A" cylinder?

[Kennygee]

I know there is a difference in an "A" and "B" piston and cylinder but can a used one be used in the other without any harm?I have an A c&p and some one gave me a used "B" piston. Will it work without tearing anything up? This is in an older 266XP that I will be using maybe 15 to 20 hours a year. I know they don't cost that much, but the wife got laid off Friday .I now have to watch my spending a little closer This is the first saw I have ever tried this on as I am a complete newbie at this. I did do a pressure and vacuum test and that all came out good. but I did that without the piston in it.:newbie:I hope I am not being a nuisance by asking all these dumb:newbie: questions. I appreciate all the help in the past !! Thanks

 

[yo2001]

I have done A cylinder with B piston on Stihl before and did work but measure everything for clearance.

 

[Brian VT]

On my motorcycle a B piston is a bit larger than an A.
Normally by the time you need a piston the cylinder plating has worn enough that the B piston is perfect in a used A cylinder.

 

[A.E. Metal Werx]

On my motorcycle a B piston is a bit larger than an A.
Normally by the time you need a piston the cylinder plating has worn enough that the B piston is perfect in a used A cylinder.

did that exact thing on my old 94 kx125.. but that was in 2004... boy did she have some power

 

[Brian VT]

... boy did she have some power

You don't feel it going away over time...but you feel it when it's all back.

 

[motosierra]

I know there is a difference in an "A" and "B" piston and cylinder but can a used one be used in the other without any harm?I have an A c&p and some one gave me a used "B" piston. Will it work without tearing anything up? This is in an older 266XP that I will be using maybe 15 to 20 hours a year. I know they don't cost that much, but the wife got laid off Friday .I now have to watch my spending a little closer This is the first saw I have ever tried this on as I am a complete newbie at this. I did do a pressure and vacuum test and that all came out good. but I did that without the piston in it.:newbie:I hope I am not being a nuisance by asking all these dumb:newbie: questions. I appreciate all the help in the past !! Thanks

It should work just fine...they are both used. If you were tring to use a new B piston in a new A cylinder...that would not be a good idea, but being as the A cylinder is worn and the B piston is worn....it should work out just fine.

 

[A.E. Metal Werx]

You don't feel it going away over time...but you feel it when it's all back.

that is 100% true. for the most part

 

[Kennygee]

B and A piston

I guess then it can't really tear any thing up ,so I might as well try it. This was a "parts" saw and I haven't got in to the carb yet. Oh well ,nothing ventured ,nothing gained.. I did slide it all the way to the top of cylinder and end gap looked O.K. I will find onw of those small wire gauge set and check it . Thanks for the input . I owe so off to work I go. Man working on Sunday's is a bummer!!

 

[outdoortype]

I have done A cylinder with B piston on Stihl before and did work but measure everything for clearance.

What exactly should you measure? I know this is a dumb question but I'm considering putting a slightly used aftermarket piston in a used O.E.M. cylinder.

 

[Brian VT]

-You could measure the bore with a 3-prong instrument and compare that to the diameter of the piston.
-You could put the piston and ring(s) in the bore and measure the gap between the ends of the ring.
The specs./tolerances relating to one of these should be in your shop manual.

 

[yo2001]

I usually measure the piston skirt and crown (top and bottom of the piston) the bore of the cylinder, and ring gaps in various locations for the starter. I'm not an expert but .003" clearance between skirt and bore seems to work okay for me and not too much taper on the piston crown.

 

[PES+]

Between whole letter sizes there is a .01 MM increase per letter.

That is .000394"

More important.....is your used B piston a thin ring piston.

If so you measure the ring end gap a little differently.

 

[SawTroll]

On my motorcycle a B piston is a bit larger than an A.
Normally by the time you need a piston the cylinder plating has worn enough that the B piston is perfect in a used A cylinder.

I believe that was one of the points with the system.

 

[Lakeside53]

It's not practical for most to measure the bore... as PES points out.. the differences are in 10ths... and a worn piston and worn bore will make that meaningless.


The right tool looks like this, but this one is over $400, has a very limted range, and only accurate to 2 10th... There are other tools, but without spending the big $, it's very hard to measure what is requred.

Just put it in.

 

[PES+]

Did you mean

Hundredths?

I shifted a decimal point recently as well.......

 

[litefoot]

that is 100% true. for the most part

:monkey:

MX,
I think we all know what you meant. It's just an odd way of saying it.

 

[Kennygee]

A&B piston

The reason I was asking the one P&C I was going to use Looked worse than the cylinder I have. I t was from a Jonsered 670 Super supposedly. It was an exact match on the intake and exhaust. The casting # were almost the same , one ending with a "W" the other ending with a "Z" I am sending it back. I told my neighbor and he stopped by a friends and told him my dilemma and he had a bunch of old parts and gave him this one and said "see if this will work". I put it in and just checked end-gap and the intake and exhaust and it looked perfect, just a ----Hair gap. I did not think about checking around the end of piston. I will pull it back apart tomorrow at work , if time permits. Thanks for all the input. I will try to post pics some time tomorrow Hopefully I can get it running soon.

 

[Lakeside53]

Hundredths?

I shifted a decimal point recently as well.......

You must have stepped over the CA border again I'm talking "inches". or more to the point, 10th's of thousandths..

A "10th" is 0.0001 inches, at least it is around here.