Is there any company that makes a 2-ring piston for a 98 RM 125? My son rides one of these bikes, and after only a few hours of riding, the ring is shot. No compression. Once, it even broke a ring. The cylinder has a Wiseco sleeve in it. What do you think? Would a 2-ring piston give us more riding time between rebuilds?
2-ring pistons
- Thread starter enduroman
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MRKRacing125
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- Oct 24, 2000
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From what I know about 2-strokes, and 2-stroke motocross or dirtbike engines, I dont think I have ever seen or heard about a 2 ringed piston. I know I all the new 4-stroke motocross bikes they have 2 rings, but thats because of the high compression they want out of the 4-stroke. As for a 2-stroke, I dont think anyone would want to try a 2-ringed piston:) Correct me please if I am wrong
- Jul 31, 2000
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a lot of two stroke bikes have two ringed pistons, KDX's are a prime example. Finding one for your son's RM might be a bit of a challenge though. There could be other issues effecting the piston life such as jetting. How many hours are you getting from one rebuild?
KawieKX125
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- Oct 9, 2000
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My guess is that the sleeve was installed improperly. The ports may be too big or the port chamfer might be totally wrong. Eric will be the most help on this one.
MRKRacing125
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- Oct 24, 2000
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Now thats something I didnt know. Was that 2-stroke have 2 rings. Well some do. Why would they use to rings? More compression?
MRKRacing125
most 250 's and up have two rings stock. they give a better seal. they also help to keep the piston from "****ing in the bore ( the latter is a guess). I believe it is also a longevity issue since most of the bikes sold are for recreational riders.
most 250 's and up have two rings stock. they give a better seal. they also help to keep the piston from "****ing in the bore ( the latter is a guess). I believe it is also a longevity issue since most of the bikes sold are for recreational riders.
- Thread starter
- #8
hours between rebuilds
After the sleeve was initially installed, we got probably 20+ hours of riding. He does not do motocross racing, but with a 125, even enduro riding takes high rpm. The second rebuild only lasted about 4 or 5 hours. Since the first piston lasted a reasonable amount of time, I do not think the sleeve would be the issue. Do you think I just got a "soft" set of components from Wiseco?
The reason I was asking about a 2-ring piston was that I have a KDX also, and that top end lasts forever!
Thank all of you for your comments.:eek:
After the sleeve was initially installed, we got probably 20+ hours of riding. He does not do motocross racing, but with a 125, even enduro riding takes high rpm. The second rebuild only lasted about 4 or 5 hours. Since the first piston lasted a reasonable amount of time, I do not think the sleeve would be the issue. Do you think I just got a "soft" set of components from Wiseco?
The reason I was asking about a 2-ring piston was that I have a KDX also, and that top end lasts forever!
Thank all of you for your comments.:eek:
Re: hours between rebuilds
Did you have the bore measured between rebuilds? It sounds to me like it is just getting loose. A sleeve wears much quicker than plating, so you can't just stick another piston and ring in there like you can with plating. You have to have it measured at each rebuild. When I purchased my bike, the former owner had sleeved the cylinder. It was several thousands out of limit and had to be bored at each of the first two rebuilds. After that, I replaced the cylinder. I would never have a cylinder sleeved to repair it.
The second ring is mainly used for help transfer the heat to the cylinder walls. I CAN, stop any compression loss that the top ring let by, but ususally the top ring is more than adequate to handle all the sealing. The medium for heat transfer from the piston to the cylinder walls is the rings. More rings -->> better transfer but also more friction.
Kelsey
Kelsey
Check a wiseco piston. I just did the top and bottom on my rmx. The factory piston only has a single ring which kinda surprised me. I ordered a pro lite wiseco piston which has two rings. I just broke it in last sunday and it works well. Time will tell if the dual ring helps.
My KX 500 has two rings.
I had the same problem with an old 79 KDX 400. I had an LA sleeve installed in it. It ran great for a while, then needed new rings. Everytime I installed new rings after that, it lasted fewer and fewer hours. I finally figured out what was happening. Sleeves are made of cast iron, and this wears out. Meaning.....that you have to have it bored out and put in oversize pistons and rings. Problem was, NO one made oversize pistons for this bike. Since it was Kawi's Electrofusion bore, and couldn't be bored, why make oversize for it!!
So, what you are experiencing sounds like the same. You probably need to check your bore for wear and probably go to an oversize piston.....IF someone makes one. With so many company's doing replating these days, it's silly to put in a sleeve. And, cheaper in the long run. The plating doesn't wear out as fast, and when it does...you can replate and still have stock pistons and rings. That's lots cheaper in the long run than getting bored out until it wont take a bore job anymore and having to buy a new jug eventually.
I had the same problem with an old 79 KDX 400. I had an LA sleeve installed in it. It ran great for a while, then needed new rings. Everytime I installed new rings after that, it lasted fewer and fewer hours. I finally figured out what was happening. Sleeves are made of cast iron, and this wears out. Meaning.....that you have to have it bored out and put in oversize pistons and rings. Problem was, NO one made oversize pistons for this bike. Since it was Kawi's Electrofusion bore, and couldn't be bored, why make oversize for it!!
So, what you are experiencing sounds like the same. You probably need to check your bore for wear and probably go to an oversize piston.....IF someone makes one. With so many company's doing replating these days, it's silly to put in a sleeve. And, cheaper in the long run. The plating doesn't wear out as fast, and when it does...you can replate and still have stock pistons and rings. That's lots cheaper in the long run than getting bored out until it wont take a bore job anymore and having to buy a new jug eventually.
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