2001 RM 250 eating up piston rings... HELP!!!

[ludacrist]

I bought a used 2001 RM 250 with pipe, renthals, graphics, etc. I love the bike. However, the second time I rode it I heard a metal sound in the engine, then it just stalled, and when I tried to kick it there was no compression and then it froze. I took apart the top end and it was TORE UP. The top piston ring had been clipped off into a few pieces, and it was pieces of ring that was making that metal sound that I was hearing in my engine. What made me stall was that piece finally flattened my spark plug gap, and when it froze, pieces of the ring were preventing the cylinder from moving.

I completely tore the top end apart (what a mess), and completely built it new with a buddy who knows a lot about 2-stroke bikes. I was almost happy because I bought the bike used, and at least now I know that the motor was built right (if that was the problem last time.) I rode it twice and the SAME exact thing happened!! I just tore it apart again, and the piston looked frighteningly similar to the other piston. The top ring (only the top ring), cut into 3 pieces and found in the pipe/cylinder. When I put it back together the first time, me and my buddy were wondering if the powervalve had sluffed off pieces of the ring, but the mechanic didn't pay much attention, just had it resleeved. And since the EXACT same thing has happened to it, the only thing I can think is that it's the powervalve getting in the way of a ring. It's the only thing I can think of. It also seems like it's the exhaust side of the piston ring that goes first.

Someone said that it might be detonating and just to run higher octane gas, but I don't want to put it back together just to find out that wasn't the problem.

I have some seriously close up pictures of the ring/piston head and the cylinder wall by the powervalve, and it almost looks like there's a little of th e powervalve shinier than the rest (from hitting the ring and doing the damage?) I can e-mail pics to whoever can help. If so, is there any way to make sure the powervalve isn't loose in there? (So that it looks good and out of the way when you put it back together, only to get in the way under a load?)

It seems like the simplest problem but it's becoming a nightmare! Help Anyone!!!

Thanks!!

--James

[dirtyfingers]

When you rebuilt your engine was it bored and a larger piston fitted? If so the powervalve needs to come out and get ground down to provide the clearance for the larger piston. If that powervalve hits the piston, its throwing in a really big monkey wrench into the works.

[ludacrist]

No, I had it sleeved to stock 250cc by LA Sleeve, so that if it happened again (like it did) then I could bore it out. I talked to an established motocross engine builder and he said that it could have been detonation. And while I'm kind'a hooked on this powervalve thing, the more I am starting to believe that it could be detonating. I read an article at this site: http://www.motocrossactionmag.com/readtopten.asp?id=438 and it was all about octane. The guy said I should definately be using pure race gas for Glamis (which is lower than sea level) and a 50/50 Race gas/Pump Gas for when I go riding at 3-4,000 feet at Gormon. Now when I look at my piston head, all I can see is that the whole top of it is black. And it's black all the way to the front (exhaust) edge of the piston but there's a 1/4 inch ring that isn't burned towards the back of the piston head. Also, the piece of piston head (and ring) that got sluffed off is exactly on the front 180 degree half of the piston head. (I read that's where detonation usually happens, because the exhaust side of the chamber is a little bit hotter from the exhaust).

The more I look at it the more I think detonation, but I don't want to put it all back together, try race gas, and have it happen again (if it was indeed the power valve).

Here's a picture of both my powervalve and my piston head. It's now one of two things: 1) The powervalve is sluffing off pieces of ring from a faulty or loose powervalve, or 2) it's detonating like a cherry bomb in there because my octane is too low.

That brings up another question though, why would my bike need race gas if it only has an FMF pipe and silencer on it? Does that turn it into that much more of a "race" engine that it needs the higher octane? I know a pipe gives a dirt bike a huge power boost, but would that constitute it needing race gas?

[tiptonre]

The only thing that would cause that piston to break like it did would be something prying the rings in the upward direction. the power valve would be closest to the piston as the piston travels down the cylinder and I as for the black on the piston it sounds like you are running rich. detnation happens more often when running lean and it doesnt appear to be that by the ammout of black on the piston for only riding the bike twice. I would lean twards the power valve it needs atleast .076 clearance from the rings.

[93gsxr750]

if im right power valvce is the same thing as varible eshaust system used on polaris snowmobiles? if so try adjusting your valve sumone probably loosened it trying to get more power out of it.. check the specs on it

[RM250BS]

Make sure you put the rings with the little mark facing up, and, If I were you I would jet it richer, and check the power valve to knock off all that is on the list of possible problems. My 01 RM250 never had any trouble like that and I ran pump gas, but I jet it slightly rich.

[jswan]

I have exactly the same problem at the moment on my 02 model. I have just checked the piston by taking off the pipe and noticed it has done the same thing as before. Last time I compleatly dismantled the Power valves and even took a bit off them to make sure it wasnt going to touch the piston. When riding it though it did make some horrible noises every now and then when ringging it out and a mate that rode my bike said it sounds like it detonating. I used octane booster to my fuel and it never made the funny noises again but as I have just found out the piston is damaged. My bike is fully standard and I've never had this before. After seeing the first piston I was sure the powervalves were hitting it, but now second time around I know they wont have touched so it must be detonation.