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2002 TM250 MX rebuild :-(

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So yesterday at the track my 02 TM250 mx grenaded, it ate the ring, melted the piston at the break point, and scarred the cylinder was real good. Looking at the cylinder it seemed to crack through the liner right by the power valves. What are my options i feel that its to much damage to get by with a replate. Where can i get this cylinder sleeved, can i overbore it ? I already plan on running a 2 ringed CR250 piston, and will get the cylinder replated regardless of bore. Any guidance would be appreciated

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Langcourt Ltd. in Auburn.GA can repair a crack or a deep groove and replate the cylinder to perfect new for a reasonable price. They were the first cylinder repair company in the USA and they do terrific work.

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Langcourt are regarded as the industry standard here in the UK,

so for peace of mind I would use them.

Maybe contact all 3 for pricing / LEAD -Time ,

Charlie

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emails sent to all three. Just by looking at the prices listed on each website i think langcourt is going to be the cheapest and i will probably go with them. Now on another thought...

Do people get TM's ported very often? The power was more than adequete as it was which from what i can tell is completely stock, but if there is more to be had id like to get it. I'm going to make the change to the 2 ring enduro style piston, but otherwise what can i get out of this thing with porting, and who is known for porting TM's?

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Generally adequete does not describe a TM.

You were probably suffering from worn out motor syndrome. My Main concern is the melted piston. What type of fuel were you running? Everything I have read about TMs is that pump gas is on the ragged edge. You may be also looking at a lean condition. How is your intake manifold? Have you ever replaced the crank seals?

Any 2T of this vintage I replace the Mag side crank seal. It will suck in air, and you can not tell if it is bad just by looking. if you can, put in a picture of your piston to help us help you.

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As far as power my other bike is a cr500, so im probably just not giving the credit that is due to the 250.

Ive got a picture of the piston, im pretty sure it leaned out and started detonating due to some shitty pump gas, i was running shell power V mixed 40:1 with amsoil dominator. I plan on replacing all the seals i can in the bottom end without splitting the cases. The crank is tight and has zero up and down play so im not expecting to rebuild that for some time. Here are the pics, im trying to get it done as cheap as i can with spring tuition coming up but at hte same time need the bike out of my kitchen... lol

deathoftm.jpg

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What I see from the piston is not a lean condition, but not enough octane. This caused detonation that destroyed your piston. How does the head look? You have the same model engine as my 300 (less stroke though), so you are going to have to run a spalsh of race gas or AV to get your octane higher.

Why are you switching to a CR piston? I know that they are cheaper, but I think you are going to be opening a (bad) can of worms by going this route. You can alter your compression by changing base gaskets. there are 4 different thicknesses that you can choose from. This will not only affect your compression, but also your power band. If you change to a CR piston, all references will be thrown out the window though.

If you want to read up on squish band (what the base gaskets do), the Yamaha 2T forum has a good write up on it.

http://www.thumpertalk.com/forum/showthread.php?t=573021

Before you do anything talk to Tom at Watson Performance http://www.watsonperformance.com/

He has been building TM motors for quite along time.

Also, make sure you note or take pictures of how your power vavles fit in the cylinder. They will fit either way, but only one way is right. Good luck :bonk:

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Im probably not going to go with a cr piston, but i do plan on running the 2 ring wossner as opposed to the single ring that the MX normally has. I have taken pictures of my power valves so i should be in good shape when it comes to putting them together as well.

The head is definitely pitted and will need some work. But its really not that bad compared to some other bikes ive seen blow up.

As far as the basegaskets and squish, i need to wait to have the cylinder back before i can start making measurements. Ive gone through it before with my 500, so i know what im getting myself into. Id like to bring the powerband down a bit compared to what it was so im going to runner a slightly tighter squishband.

And having only run about 5-7 gallons of gas through this since i bought it, i guess lesson learned and ill start running 50/50 pump/AV gas. Had to do that with my old RM250, got old but was worth it.

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You can bore and replate this cylinder to 265cc. Amsoil Dominator (Synthetic) does not mix well with pump gas (ethanol). You can use the CR piston as long as your clearances are checked and set. Squish clearance/band/angle. The head may need to be machined depending on what year CR piston you use. The compression height of the TM, and CR piston are the same.

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