A, B, and AB cylinders

[trooney]

What will happen if you put an "A" piston in a "B" cylinder... Would it give you less than ideal compression? I remember one time I couldn't get a 262 to rev over 12k for the blowby, put a new piston in it and it revs at 13500 with plenty to spare. Attributed that to a worn piston but could the wrong "size" piston have contributed to that? Just asking.

 

[trooney]

Oops, sorry @Landmark , I reread your post. But I'm still curious if it might have contributed to the loss of power.

 

[Landmark]

Oops, sorry @Landmark , I reread your post. But I'm still curious if it might have contributed to the loss of power.

No problem. I had quoted another post on another forum.

 

[CR888]

This is nothing new or fancy its just how they have been producing cylinders for many decades. My Contra lightning is a 'B' cylinder for example. When they change castings to upgrade the cylinder and do a new production run they have a piston to match. You can break the rules to some extent but a good tuner will match the right piston to cylinder.

 

[Brewz]

In the Meteor catalogue it shows you all the variants and their diameter.
Stihl 026:



I would say an A piston in a B cylinder would be too loose and a B Piston in an A cylinder would be too tight

 

[bikemike]

The Mac 82cc saws have A, B & C variants as well ...

McCulloch is just pain weird anyways

 

[Brewz]

I have just bought a Meteor 288 piston to fit to my 066 soon.
I purchased from HLS as I have had nothing but great service from them thus far.

This thread has woken me up to the A, AB and B pistons and what they are and I went to look at what the Meteors I have purchased were.

The Meteor piston I purchased a while back for my 026 was an AB and looking at the OEM piston it replaces, it was an AB as well so I got lucky.

Now back to the 288 piston..... its a B piston
I am now worried that this could cause problems if its too tight for my jug, which I dont know if it will be an A or B yet.

@Gentleman, is it a lucky dip what we get when ordering a piston or is it possible to list the model number on the website so we can chose the piston size we need for the applicable model?

 

[Landmark]

I only had one known B cylinder with a A piston. I have torn down and went back with an oem Mahle AB piston and a new caber. this is a Great thread and has been a help for sure. Thanks @paragonbuilder for the read and discussion.

 

[Gentleman]

I'm not sure about that. Meteor has never asked which one we want. I think we just get whatever they send us. I checked our Meteor stock and it's a mixture of A, B,and AB's. All the 288 pistons in stock are B's. They may only make one type for each model. I've tried asking Meteor before and never received a reply.
Maybe @Definitive Dave knows about it.

 

[Definitive Dave]

If you specify which one you want they will deliver it or tell you it is out of stock and try to talk you into another variety of the same piston
Otherwise as Bruce says they seem to deliver at random, even if I have two orders in a row with the same model I might get a B in the first order and an AB or A in the next order.
The guys who want a certain version have always asked for the AB piston, that one is meant to be the universal replacement.
My understanding is that A from meteor is meant for A bore or brand new cylinders that need a new piston and that B is meant for the saws that have already had a replacement or two in their life.
Dave

For some models they only make one size and for others they make three or more, the shipment of 288s I just received are AB, but probably only because that is what I requested.
If you download the PDF catalog they show the variations for some models with the exact measurements.

I had a customer who wanted to return a 44.98mm piston because other guys had ads that said 45mm and they thought mine must be defective. I explained that Meteor is better at maintaining exact tolerances so they can advertise more precise measurements

 

[Brewz]

Fingers crossed it works

 

[MustangMike]

My 044#1 has a B cylinder, and the 440 I am currently working on has an A cylinder.

When I ordered a new piston for 044 #1 (I did not specify) it was an OEM A/B piston. As far as I could determine with my calipers, it was the same diameter as the one in the saw (which I decided to leave in it).

I think an A/B in the 440 will be fine as I had to clean up the scoring in that jug. (I'm ordering a new piston because it is 12 mm, not 10 mm).

I'm sure matching the jug to the slug will give you the best service life, but I am also pretty sure that the rings will allow a A to work in a B, and vice versa.

 

[Al Smith]

It has more to do with the process of manufacture than anything .McCulloch it had more to do with the plating process .

On auto engines for example there used to 4 different bore sizes .Honda accord at one time had 4 sizes that were selectively fit to the cylinder sizes .I know this to be fact because I installed the machines that made those pistons in 1989 .

Ford 3.5 and 3.7 are all bore grade number 2 these days because the CNC machinery is so accurate it can machine parts with micron tollerances .Something almost impossible not so long ago with any repeatability .The main bearing BTW are selectively fit .
< automotive trivia .

On chainsaw engines it's highly doubtable if using a slightly smaller piston if you could even tell there is or might be a slight diff in compression .You could damn sure know it if you tried to stuff a larger piston in a tight hole .

 

[trooney]

I got thinking about it and I had to swap over a 262 onto a new chassis. I had an A cylinder and I mated it with a B piston. Now this piston was previously mated with a B cylinder. Nothing else had changed. The A cylinder does have a small scratch but I suspected it would run fine. Tried it out and the most I could get out of it was 12k when before it would hit 13.5k no problem. No air leaks. Maybe bore too tight for piston? I had the same problem on a 262 that I got from Redfin and I got a new piston and it ran real good. Maybe switch it with a AB piston? Don't know what to think.

 

[trooney]

I'm going to put an AB piston in it. See if it helps. Also a little blowback through the carb. We'll see if that helps.

 

[husqvarnaxpman]

Keep us posted trooney please. I just bought 2 meteor pistons from hl just before this discussion came up and received B when my cylinders that i need them for are A's. Now im wondering if i should try to get A's. Thanks

 

[trooney]

Will do. I put an AB piston in it just now. Didnt fire it up as we got the little grandkid. Hes going down so I used restraint and will fire it up tomorrow nite when I get home from work about 8. I'll let you know what happens.

 

[CR888]

Where it becomes interesting is when you hone a heavily used cylinder you have the option of using a slightly bigger diameter piston to get a near perfect fit. However when Mercedes Benz invented the use of Nikasil which was later adopted by Mahle, cylinder wear is massively reduced compared to bores of the past. Nikasil is a pretty cool invention, especially for air cooled 2T OPE.

 

[Tor R]

I would prefer Meteor to use AB piston to cover both A and B jug, like they do with 254.
262 A and B piston, it's just 0.01mm in difference, but as long we can pick I want to correct piston.
Greek has them both but you have to specific what type you want else you get random choice, this probleby goes to most meteor dealers.

 

[MustangMike]

I think all Stihl OEM replacement are A/B.