07 rm250 Piston hitting head?????

I bought this bike about 2 months ago. My first RM. I dont know the guy I bought it from. Craigslist. Anyways, I put a new top end in the bike because I wanted to see the condition of the motor. Crank seemed fine. No "clink", no vertical play. Cylinder was in good condition with no visible ware on it. Old piston was chared on top and bottom side was the same. Looked like it had been reringed. So I put in the wiseco piston kit. Put it all together and fired right up. Broke bike in softly for first 2 hours. Never past half throttle, and stayed conservative for the next 2 hours on motor. Rode the bike on trails and track, about 50/50, total 25 hours on new top end. It ran like a raped ape for six weeks and I loved every second of it!

So the bike all of the sudden dies at idle going over a jump in midair. It starts right up, and revs and runs like a champ IF IM ON THE GAS. The second it goes to idle the piston is hitting the head. you can hear it go tick tick tick tick and then dies.

Pulled it apart and sure enough the piston is just barely making contact with the head???? its not scaring the head or the piston. its just enough to leave almost a shadow of a mark. The wiseco piston has the right part number on the top of the piston. I checked the crank and still no vertical play. WEIRD. I have set the OEM piston next to the wiseco piston and they are the same hieght(by my eyeball). Anyone have any ideas on where to go from here. I already ordered the new Hot Rods crank and OEM main bearings and seals. The piston has some odd ware on it.(from hitting the head im sure). the pin has some odd ware as well. Its killing me on the money side of things. Should I just replace that wiseco with a new one?

Sorry for the long story, just trying to eliminate needless questions to find a quick solution. Im supposed to be going to the dunes in a couple weeks.

All RM info welcome! IM NEW TO THE YELLOW FAMILY!

hmm. that is definatly weird. its possible that the head had been machined or the cylinder has been decked. that would adjust the x-dimension? but to the point where the piston taps the head? i think you might have went in the wrong direction of buying a crank. i think the problem lies in the cylnder/head/piston. does the wise-co have a dome on it? or is it flat?? do you know if the cylinder/head have had any work done to them?? im just throwing things out here.

It's got to be a bearing, my guess is that the lower rod bearing isn't what it use to be.

When you pull it all apart if the piston still looks good then you could reuse it.

The deal is it went 25 hours with no problem. Then it starts tapping the head. You may be on the right track, with replacing the rod bearing and crank bearings. Let me ask you this, is it marking the head on the intake side? If so it maybe detonation from low octane or lean jetting. If you don't think that is it, then maybe the guy before you milled the head or shaved the bottom of the cylinder. A double base, shim with base gasket on top and bottom or thick gasket would bring the ports up and mite give the clearance. I think they milled the head to much and they did not reshape the dome. As for the 25 hours, is there any way that it may have been tapping and you may not of notice it at first?

I cant remember, but was it not in 04 that Suzuki went to the flat top piston, but then went back to the dome piston? One of you 04 - 08 guys chime in on this subject.

O3-2010 take the same piston. I think 02 was the last yr for the flat top.

I'm willing to bet its detonation too if there is no bearing play....

Post pics please!

hmm. that is definatly weird. its possible that the head had been machined or the cylinder has been decked. that would adjust the x-dimension? but to the point where the piston taps the head? i think you might have went in the wrong direction of buying a crank. i think the problem lies in the cylnder/head/piston. does the wise-co have a dome on it? or is it flat?? do you know if the cylinder/head have had any work done to them?? im just throwing things out here.

HAHA. Suzuki guys dont regularly practice X dimmension. J models bolt together, plain and easy, not much to adjust. X gets set with milling the head. I dont know if anybody even makes different thickness base gaskets for an RM 250. After owning a few KTM's, I kinda wish J models could be adjusted as such.

I bought this bike about 2 months ago. My first RM. I dont know the guy I bought it from. Craigslist. Anyways, I put a new top end in the bike because I wanted to see the condition of the motor. Crank seemed fine. No "clink", no vertical play. Cylinder was in good condition with no visible ware on it. Old piston was chared on top and bottom side was the same. Looked like it had been reringed. So I put in the wiseco piston kit. Put it all together and fired right up. Broke bike in softly for first 2 hours. Never past half throttle, and stayed conservative for the next 2 hours on motor. Rode the bike on trails and track, about 50/50, total 25 hours on new top end. It ran like a raped ape for six weeks and I loved every second of it!

So the bike all of the sudden dies at idle going over a jump in midair. It starts right up, and revs and runs like a champ IF IM ON THE GAS. The second it goes to idle the piston is hitting the head. you can hear it go tick tick tick tick and then dies.

Pulled it apart and sure enough the piston is just barely making contact with the head???? its not scaring the head or the piston. its just enough to leave almost a shadow of a mark. The wiseco piston has the right part number on the top of the piston. I checked the crank and still no vertical play. WEIRD. I have set the OEM piston next to the wiseco piston and they are the same hieght(by my eyeball). Anyone have any ideas on where to go from here. I already ordered the new Hot Rods crank and OEM main bearings and seals. The piston has some odd ware on it.(from hitting the head im sure). the pin has some odd ware as well. Its killing me on the money side of things. Should I just replace that wiseco with a new one?

Sorry for the long story, just trying to eliminate needless questions to find a quick solution. Im supposed to be going to the dunes in a couple weeks.

All RM info welcome! IM NEW TO THE YELLOW FAMILY!

Is the rod discolored. Did it get hot. I have seen one of my YZ 250 rods from the 90's stretch and then the piston would tap the head. Also, check to make sure the piston isnt hitting the powervalve flap. Maybe that wore and is extending into the cylinder area.

Wiseco's are tough, I found one in a freinds KTM 300 that had been rebuilt by a shop before, they put a 250 head on it, maybe by mistake or maybe for more compression, I dont know. That piston hit the head for a long time. He raced that thing for at least a year, then I rode it and heard the noise and disassembled it for him to find the wrong head and mashed marks on top of the piston. I couldnt believe it didnt shatter, A little more forging wont hurt I guess.LOL!

HAHA. Suzuki guys dont regularly practice X dimmension. J models bolt together, plain and easy, not much to adjust. X gets set with milling the head. I dont know if anybody even makes different thickness base gaskets for an RM 250. After owning a few KTM's, I kinda wish J models could be adjusted as such.

ahhh. forgive me:worthy: im not familiar with the yellow smokers. :thumbsup:

its definitely a domed piston. the piston is tapping the head on the exhaust port side. Clears the powervalve flap just fine.

Idled and Ran perfect for six weeks and started tapping at the end of a hard day at the track. Definitely would have noticed it.

never got hot enough to boil over radiators.

I am having the new crank, main bearings and seals installed by the dealership this week. Hot Rods crank with oem bearings and oem seals.

I am pretty sure the head and the cylinder are the stock units. Still had original piston when I bought it. looked like it had been reringed but its definitely the stock piston.

The pin on the new wiseco piston has some weird ware where it sits in the piston(on the outer edges). the pin looks immaculate where it sits in the needle bearings(middle of pin). I pulled out the stock piston and pin to compare the two and the original one has almost no ware on the pin or where it sits in the piston and needle bearing. Should I replace the pin and bearings.

Yes replace them every top end.

It ain't detonation, if it only happens at idle under no load.

My money's on a worn out lower rod bearing.

can anyone help with the crank. It just got here today and it has two stickers on the box. one says hot rods part #421-4058 full crankshaft assembly 03-06. (my bike is an 07).....the other sticker says hotrods part # 421-4058 full crankshaft assembly 03-08. Does anyone have any clue if this is the right part for an 07 RM 250?????

Does anyone have a customer support # for Hot Rods????

Im confused... Did Yellow use the same crank from 03-08 or did they change it after 06???

When I was shopping on ebay there were many adds for hot rods crank assemblys from 03-08, and a few for 03-06. Does anyone know if there is a difference???

Help please Thanks guys.

Edited by 480desertrider
more information
can anyone help with the crank. It just got here today and it has two stickers on the box. one says hot rods part #421-4058 full crankshaft assembly 03-06. (my bike is an 07).....the other sticker says hotrods part # 421-4058 full crankshaft assembly 03-08. Does anyone have any clue if this is the right part for an 07 RM 250?????

Does anyone have a customer support # for Hot Rods????

Im confused... Did Yellow use the same crank from 03-08 or did they change it after 06???

When I was shopping on ebay there were many adds for hot rods crank assemblys from 03-08, and a few for 03-06. Does anyone know if there is a difference???

Help please Thanks guys.

The crank is the same from '03-'08. The '03-'06 sticker probably just indicates that that particular box has been sitting on the shelf since '06...:thumbsup:

anyone help me out with proper break in for a new bottom and top end???? been a long time since ive rebuilt a two stroke. Thanks.

I fire it up in the garage a few times letting it get warm and snapping the throttle only to 1/2 a few times each cycle. Cool down inbetween,all the way, and repeat. First ride I just cruise for a while and same thing with the heat cycling. Get it warm, then shut down to cool. Repeat a few times. Then PINNIT!:thumbsup: doing this allows the crank to find a natural position( it will actually self center in the bearings). snapping and chopping the throttle lightly lets the rings break in nicely. Heat cycles help the breakin on the piston.

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