RM125A v RM125B pistons?

[John Orchard]

Would anyone have 125A and 125B pistons laying around for comparison?  I know the A has a 2mm larger bore than the B, what I was interested to know is, could a 125B be bored out after the 2mm (80 thou) Wiseco with a 1st over 125A piston?

It looks like there is enough thickness in the liner to not alter port exit or timing.

Deck heights, ring stops, pin diameter's, skirt lengths etc?

[TT5 Matt]

rm125a has 56 bore by 50 stoke same as the rms125 but the rm125a has a 16mm piston pin 2mm bigger in diametter than the rms125 and the rm125b which is 14mm while the rm125b has a 54mm bore and stroke sooo wheather the rms125 piston would suit dont know but youd have to do alot of checking of things like pin hieghts/skirt clearence/port timing etc

[John Orchard]

Cool, thanks.  I might check out a 125S piston?

[Doc]

The ring locating pin maybe an issue so double check the rings don't hang up in any ports. I have heard of people using TS125 std piston but the lower ring had to be removed because of this problem.

[John Orchard]

Thanks Doc, I had my concerns about port placement.

[EML]

You could also try other makes. I remember my Honda 125 needed a piston and they found a Suzuki one to do the job as none were available from Honda-around about that time i.e RM's' TS CR MT 125 all pretty much similar.
Maybe check with Wiseco they would know. Try Serco.

[John Orchard]

Good idea, I remember wiseco use to have a chart with dimensions of all pistons that they made, anyone know of something similar around now?

[asasin]

TS 125 piston works ok , just machine the bottom as they are about 2mm longer. and the B barrel will go all the way out to 58 mm if needed.

[John Orchard]

Awesome!  Which model TS125?  Using one or two rings?

[Suzukal]

The next problem would be, you'd have to run it in the 250 class as it's outside the 5% limit for the 125 class.

Wiseco don't make TM/TS125 pistons anymore but you can use their Honda 74 CR125 pistons.
You just need to trim a couple of mm off the skirt.

[John Orchard]

That's cool, I'm not racing it anyway, I've got a few barrels if I was going to run it in a 125 class.  I'm thinking of riding it in modern lites class which is up to 250 2 & 4 stroke.

[TT5 Matt]

if thats the case why not make a cloe ratio pe175 with the rm125 box and rotor as the 175 will take 185 pistons as well,but if your sticking to the 125 ive got a new ts125 early std piston/rings and pin pm me if you want to know more

[John Orchard]

I don't have a PE engine laying around, and I'm not going to buy one  :-)

I'll PM you about the piston, thanks.

[John Orchard]

It seems all the current 125's (Yam, Husky, KTM) are running 144 kits these days; no problem running in the up-to-250 class.  I have a 2010 YZ250 2-stroke but it'd be a buzz to smoke some kids with the 'vintage' bike lol.

[bigk]

S/e pin size is different for A & B, so unless you run an A rod in your B you won't be able to run an S or A piston. Cr125M pistons can be used in S & A with small mods. Gives a compression boost as well.
K