Do A,B,C spec pistons really matter?
- Thread starter noobi
- Start date
I'd put piston which size is stamped to cylinder. I think It's 2'nd piston to that bike. My ex gasser had about same hours (and 3 years) when I did top end. It wasn't even neccessary, but I did anyway... My firs gasser EC200 -01 which was ridden alot when I bought it. No bigger piston needed at year 2009rebuid. Cylinder still in goog condition.
Off course it depends how good bike has been maintained. Clean airfilters, good premix and not too lean mixture helps to save motor against wearing. But I think thats not new thing to anyone...
stay_upright
New member
I measured the cylinder on my 2005 EC300 with a professional 3 point digital caliper.
The results were my cylinder was still slightly over size so that meant using the smallest piston (A I think) previous owner had put a B in and it had some scoring on. Also I think IanCP5 has a partial seizure on a 300 so I'd be very wary of putting bigger pistons in without the measurements to prove you need it.
The measurements on my bike seemed to show that it was much more important what size the cylinder was when originally built rather than any wear that may of happened in the last 6 years.
Are the cylinders stamped withe what pistons they need from new?
The results were my cylinder was still slightly over size so that meant using the smallest piston (A I think) previous owner had put a B in and it had some scoring on. Also I think IanCP5 has a partial seizure on a 300 so I'd be very wary of putting bigger pistons in without the measurements to prove you need it.
The measurements on my bike seemed to show that it was much more important what size the cylinder was when originally built rather than any wear that may of happened in the last 6 years.
Are the cylinders stamped withe what pistons they need from new?
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don't just guess what size of piston you're about to use! 
measure with a 3-point caliper as stay-upright says!
only then can you determine what size of piston the cilinder needs...
i allso wouldn't go back a size from B to A, the scoring may have been from lack of lubrication one time or over heating.
stick with the same size or hone the sleeve lightly out and fit the larger size if needed.
hannes.
measure with a 3-point caliper as stay-upright says!
only then can you determine what size of piston the cilinder needs...
i allso wouldn't go back a size from B to A, the scoring may have been from lack of lubrication one time or over heating.
stick with the same size or hone the sleeve lightly out and fit the larger size if needed.
hannes.
You don't say what size your cylinder is. If you have a "A" I don't think you would like the results of installing a "D". Like Hannesd said, if you don't measure first your setting yourself up for problems. Remember different pistons require different clearances too.
noobi
New member
Its just a hypothetical, I work in a bike shop and sometimes people say they just want whatever piston kit is available the quickest, usually the larger sizes, I tell them that they shouldn't do this because of everything mentioned in the above posts, but they just look at me and roll there eyes because they've been around bikes longer and "rebuilt more engines than I have", I am only 18.
It just irks me, I wouldn't work in a bike shop if I didn't know my way around a bike.
Was just wondering whether many people are like this on here, but maybe gg owners are just sensible
It just irks me, I wouldn't work in a bike shop if I didn't know my way around a bike.
Was just wondering whether many people are like this on here, but maybe gg owners are just sensible
gasmonkey
Bronze Level Site Supporter
Personaly I stick to the same size.A cylinder bore wears unevenly.Puting a larger piston in will have differnt clearances in different places(tight,tighter),causing a possible early seize.
I'd only go to a larger size if the bore has been machined and MEASURED to fit that size.
I'd only go to a larger size if the bore has been machined and MEASURED to fit that size.
I used to work at a Yamaha dealer when I was in high school. Like most two strokes, Yam stamped their cylinders A-D. What we'd find though is that when we went to order in a piston for even a 1 year old bike, the part numbers all superseded to one piston. Never new if it was an A, B, C, or D. Not being able to get anything else, we'd get these pistons for the customer, and never heard of any complaints down the road due to piston failure. Wiseco pistons.......... now thats another story. Never heard of one lasting very long in any application. Hopefully GG doesn't take the route of superseding all there pistons to one part no. Obviously there are differences if they are taking the time to stamp each cylinder differently.
Also I wouldnt use a stone hone on these cylinders,, can take too much too fast. Well I do use one but different,, I wrap my three stone hone in a large scotchbrite pad that I soak in wd40 and very lightly use that. gives a perfect pattern and cuts the glaze out without doing any "damage". If your not used to honing plated cylinders on a weekly basis its easy to screw them up,, this is a good safe way to do it for the GG owner,, who does this less as GG bikes require top ends less often than jap bikes..
stay_upright
New member
don't just guess what size of piston you're about to use!
measure with a 3-point caliper as stay-upright says!
only then can you determine what size of piston the cilinder needs...
i allso wouldn't go back a size from B to A, the scoring may have been from lack of lubrication one time or over heating.
stick with the same size or hone the sleeve lightly out and fit the larger size if needed.
hannes.
That's what I did the previous owner had put a B in it assuming the cylinder would have worn but I put an A in it as that was correct for the size of the cylinder. In fact even with an A piston I was still slightly shy of the clearance recommended by GG - but that's how they made the cylinder. I'm happier having the correct piston, it's simply going to reduce the chances of cold seizure, partial seizure and/or picking up on the piston/walls.
My advice would be put the piston in, as marked on the barrel in the bike unless you have accurate measurements to back up the fact you need a larger piston. The cylinders simply don't seem to wear. and IMO every one-else is simply guessing and cold or partial seizures seem to happen quite a lot.
desertgasser300
Banned
I cannot find a stamp on mine anywhere on the cylinder. Was it different for 97's
tm_enduro
New member
TM engines are marked too, although my '98 TM was market with ink. BTW, the '97 GG was a GG motor, not TM.
