Cylinders, pistons and the letters on their tops??

I'm rebuilding a saw and got a new piston from the guy from Greece on ebay... that wont let you ask him a question concerning his meteor and episan pistons...or any item for that matter. Any how It has a letter B marked with a letter C more boldly punched into the top of my piston on top of the letter B(like it was remarked)...kinda weird but it seems like a nice episan piston. My cylinder is marked D from the factory...my question is....whats that letter stuff all about and is it that important. It does seem like its small....piston slap will most certainly occur...I think I just answered my own question but thought Id bring the subject up to discuss and learn in more detail about piston and cylinder letter grade/markings?

You are in the right mind set, the letter stands for small differences in the bore diameter. A piston marked with a C would be slightly larger than a piston marked with a A, chances are the C piston would not even fit in a A cylinder. I know I have read on this site somehwere about the proper piston to cylinder clearance and I believe it was 4 thousandths inch, but you will want to check that info.

slipknot said:

I'm rebuilding a saw and got a new piston from the guy from Greece on ebay... that wont let you ask him a question concerning his meteor and episan pistons...or any item for that matter. Any how It has a letter B marked with a letter C more boldly punched into the top of my piston on top of the letter B(like it was remarked)...kinda weird but it seems like a nice episan piston. My cylinder is marked D from the factory...my question is....whats that letter stuff all about and is it that important. It does seem like its small....piston slap will most certainly occur...I think I just answered my own question but thought Id bring the subject up to discuss and learn in more detail about piston and cylinder letter grade/markings?

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Gee I've always gotten my questions answered very quickly from Leo, as many as four different questions conserning one piston.. Questions like dimensions between wristpin bosses and wristpin centerline measurements to the top edge of the crown etc. Usually I'm trying to use a piston in something different than for what he has it listed for so need this type of info and I've found him quite willing to answer all the questions I've asked.

Roanoker has answered the question fairly well as to size codes..the only thing I might ad is the codes differences are usually measured in 0.0000" rather than 0.000" these are very small differences and though perhaps not optimum I would think your "C" piston would run fine in your "D" cyl. Though had it been the other way around it might well be to tight. A lot of replacement pistons will be marked "AB" or "BC" etc. denoting that they can be used in either application.

thanks for a good explanation....the thing i didnt know was the average amount of difference between the 4 codes....I kinda knew how it all worked but thought it would be cool to discuss it....opcorn:

You can do a quick check with feeler gauges, piston skirt to cylinder. A 0.004" should be too tight and a 0.002" should slip right in.

Most saws are about 0.0025-0.003" new.

That is unless you are using a forged hot-rod piston that requires more clearance.

What Kind of saw are you working on? The stihls I've seen have only been marked A, A/B, or B

Mad Professor said:

You can do a quick check with feeler gauges, piston skirt to cylinder. A 0.004" should be too tight and a 0.002" should slip right in.

Most saws are about 0.0025-0.003" new.

That is unless you are using a forged hot-rod piston that requires more clearance.

What Kind of saw are you working on? The stihls I've seen have only been marked A, A/B, or B

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Im porting/building up another cub cadet/efco 152...It has a gilardoni head and im using an episan piston for a oleo-mac 952...its the same saw as the efco 152...a mid grade 51.7cc saw thats damn near a copy of the husky 350 I just got from another member in pieces........both have 45mm pistons..So im going to see if i can use a 350 piston in a efco 152..i'll let it be known here if I find anything....the 350 has an appointment to see the work bench after the efco...so it may get turned into a poor man's 346 with the after market 346 jug.

Oh and the guy from greece...ive bought from him many times and now i wanna ask him if he has anymore oleo-mac 152 episan pistons...ive found they are better quality than the oem efco pistons from vertex...An ebay says the member cannot answer your question at this time....never a problem and now its like im blocked from him.

On the letter grades on efco gilardoni heads...i have 5 and I have every code except 'A'...ive got 2 'B' and 2 'D' and one 'C' cylinders...I may be splittin frog hairs but the one efco with a D cylinder seems like it has more snap to it...a lil more torque...I keep all my saws pretty fresh...so none are low on compression. All are 140+ compression

slipknot said:

both have 45mm pistons..So im going to see if i can use a 350 piston in a efco 152..i'll let it be known here if I find anything.....

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yes please let it be known. i'm contemplating trying to do something similar with an Oly 264f

jerrycmorrow said:

yes please let it be known. i'm contemplating trying to do something similar with an Oly 264f

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Nope nothing works..totally different combustion setup....maybe a fly wheel might work....they seem the same...

The lettering oversize is very common on dirt bike engines, It allows you to get by just replacing a piston in a worn cylinder a few more times, Without it you usually get by replacing the the rings on the first rebuild and the piston on the second, after that you are usually boring and replating and going to a .010-.030 piston for the first overbore. The A,B,C,D pistons let you replace the piston at least twice as long as the plating isnt worn through, Also lets the factory mix and match to make up for manufacturing tolerances

I emailed him directly outside of ebay when I realized the piston was shipping from Greece (I failed to notice that at the time I bought it) and he got back to me the next morning. Seemed like a good guy.

He is a good guy - fast delivery to the UK as well and has always answered my questions:confused2:

Lettering on piston crown does not always specify "size-grade."
Some mfgs stamp letter to indicate how piston should be oriented on assembly. Ex.: Poulan 5500/6000, Stihl 015/020/040, etc. Seems a stamped "A" on a Stihl piston indicates where the exhaust (Ausgang?) port should be relative to piston.

Just saying that general rules-of-thumb aren't absolute. Gotta check repair manual IMHO. :msp_unsure:

I will give rep to the 1st person to get a hold of the greece guy and ask him why he doesnt have any oleo-mac/efco/cub cadet/john deere 45mm pistons for the oleo mac 952. He may not have anymore and I would like to know when/if he will get more....I think it was stihl crazy that went crazy and bought all he had if I remember him saying so. I for some frikin reason cant ask him...ebay wont let me. I remember i gave him all the info for compatible saws as he only had the pistons listed under oleo mac.....and we all know oleo mac is the same saw but different color as efco 152, cub cadet cs5220 and 5018, john deere cs52, and few others, but those are sold in europe..he was unaware of the american market until I informed him through ebay...I sent him about a dozen emails with all the pertinent info and then all of a sudden im blocked or whatever....he has me to thank for increased piston sales...I dont want a discount...i just want more pistons..lol