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I've been getting alot of new off-road catalogs in the mail the past few days to replace my old ones. Bob's sent me one that has replacement ring kit's for Wiseco pistons. Thing isd since this was my first piston swap in a bike last spring, how often should a piston for a bike last? Especialy a forged piston? I was thinking earlier this summer of what I needed to do this winter to the bike and could'nt decide if I should do a whole piston replacement or just rings.

What do you all think? Should I just decide after the engines torn down where I can see the piston wear before deciding or are these pistons pretty durable? Whats acceptable wear for these pistons? I can't remember if they had wear rings on them or not.

Jon.

With a KDX, I replace the piston when I'm tearing it down. They're enough work that the peace of mind of a new piston is worth it. Since I'm on a 2-year schedule with mine, it's not a big deal. My last piston was a Pro-X and when I replaced it after 2 years, the rings were only 1/2 way between "new" specs. PLENTY of wear left, but in went a new Pro-X. I'm due for another this spring but am in no hurry- the addition of the KX125 has cut back on KDX time and last winter was pretty cold and I didn't ride much, so I really don't have that much time on mine.

jafo, with your hurt knee causing less riding time, and based on an estiamte from your mentioned trail rides in the group, if I had your bike, I wouldn't even worry about changing the rings, much less the piston. I would look through the spark plug hole to check for the carbon burn on top of the piston, and if it looked OK, I wouldn't worry about it. Maybe check through the exhsut pipe hole with the pipe off (unless you can see through the pipe).

I rode quite a bit this summer sometimes every weekend for up to eight hours or more a day. This was when I was riding in the heat trying to get ready for some harescrambles then I got hurt but still rode just not as much. I rode pretty hard too. I was told that every year you should change the rings at least. That's why I wanted to ask some guys with the same bikes how often you all do this. I can tell you that the only thing that concerns me is the cold starting. It takes several kicks to get her going. where it did'nt use to. That just kind of makes me wonder if the piston rings need changed or if I should do the whole thing. A forged piston should take a pretty good beating if it's good forged piston, just not sure about the wear part. I got to pull the head off and send it with the carb to RB for the mods anyways this winter. Guess I'm answering my own question. Since I want to start racing next spring, should just go ahead and get a new piston and rings. I don't want to break down in the middle of a couple of mountains. Downhills not bad, it's pushing up the hill that sucks!

Jon.

Well, if you are going to be tearing it down anyway, just measure the ring end gaps and "there ya go".

A KDX break down?

Indawoods wrote:A KDX break down?

Its rare but has been known to happen.

I have'nt seen one break down but I don't want mine to be my first experience during a race especialy. Gotta be ready and cover all the bases.

Jason, I'll do that. I'll get the ring endgaps measured before ordering anything, I've measured plenty of ring endgaps before. But what else could cause the hard starting besides loss of cylinder pressure? Could it be the jet change? I don't remember having this problem in warmer weather, just on colder mornings we had a month ago. Maybe it's the carb and not the cylinder. Hmmm.

It is colder now, so that might affect jetting.

The pilot jet has a lot to do with starting. But the plug gap also is a big factor. put a fresh, correctly gapped plug in there and see what happens. Also, make sure your light is turned off if you have one. I sometimes have mine turned on and notice the cold start affected, doesn't really seem to make a difference when warmed up though. If it's a good bit colder out, your jetting will be lean, and make the bike quite a bit harder to start.

Thanks guys. Talking to someone about this stuff get the brain juice flowing. It must be the colder weather, but might be a combo between the cold and sparkplug. I gap mine at .028. But I've had this same plug in for the last three or four rides. Guess I'll not worry to much being the carbs gonna be taking a trip sometime soon.
Jon.