rmx250 piston hitting something?

[surfer4life]

bought a rmx250 yesterday and ran it for about an hour, tried to start it today, started first kick with no choke but died instantly! when i tried to kick it again the kick start was rock solid and the piston did not want to move, so i put it into gear and rolled backwards, the piston moved back but when i tried to kick it again it got stuck in the same place, so the piston isn't seized it is just getting stuck on something, exactly the same thing happened to my mates rmx250 and suspected the exhaust valve has come loose and is stopping the piston at a certain point. Has anyone else had a similar problem and how did you fix it? i think it is a 92 / 93 model

Thanks

Andy

 

[TimberPig]

Try pulling the pipe and taking a look into the exhaust port. It should be obvious if an exhaust valve has broken off and dropped into the cylinder.

It should also be equally obvious if the piston has come apart and a large piece of piston skirt is lying loose in the chamber.

Either way, the cylinder needs to come off to fix it, so you could just pull it now to examine the entire top end. If there are broken parts sitting in there, you'll need to at least clean out the crankshaft and cases as well, or it may be next. It could have been damaged from small pieces passing through it and damaging the bearings. Cleaning it may or may not prevent it from going out next if not replaced/rebuilt.

 

[surfer4life]

thanks for the advice, i took it apart last night and the middle blade of the exhaust valve had come out and was stopping the piston from moving, i am hoping not too much damage as it happened after i started with no choke the engine stopped on its own, then i think the vibration of the engine stopping made the middle blade come loose because when i tried to kick it again the piston did move slightly before it caught the blade. I will be checking damage to the piston tonight if any, fingers crossed!!!

 

[antonyp]

I will be checking damage to the piston tonight if any, fingers crossed!!!

It would be a good idea to check the connecting rod for play. You can never be too sure of the crank bearings after the piston hits something :bang:

Just my 2c. Keep us posted on the outcome :cool:

 

[surfer4life]

thanks for the advice, will check for play when inspecting the piston.

This is my first bike and only had it an hour before it went pop, so i have been welcomed into the world of 2 strokes big time, at least when it's sorted it should last 6 months before something else goes wrong.

Fortunately it wasn't me who dropped it, it was my mate who was going back to the van to get his gear on (he only had jeans and t shirt on!!! :coocoo: ) it told him to go easy but as usual he didn't listen and went screaming into a corner in 4th and apparently the back brake cylinder went so he had to use the front while turning and you can guess what happened next :yikes: he is now paying the price with severe gravel rash, fortunately my bike came off better than he did

 

[antonyp]

Good grief !!! :yikes: You don't happen to have a video of that do you ? :laugh: :laugh:

Seriously now. I hope your mate is all right. The bike can be repaired a lot easier than broken bones :whoa:

 

[surfer4life]

Good grief !!! You don't happen to have a video of that do you ?
Seriously now. I hope your mate is all right. The bike can be repaired a lot easier than broken bones

he's fine thanks, he's just going to be very sore for a while, and have a battered ego, there was a video camera there as well but it had just been turned off :bang: , i could have sent it to one of those funny clip shows and got £250, it would have paid for my engine rebuild.

Anyway I inspected the piston last night and removed the exhaust valves, the piston looks fine with a small bit of wear on the top of piston but the rings are fine and creating a good seal. The bad news for me is not only is the middle blade shafted but the lower housing is badly worn, instead of a circle the hole the pin sits in is now oblong, got a quote yesterday £53 for the middle blade and £222 for the bottom blade thats about $555 :(

a friend suggested either taking one valve out all together, or just buying the middle blade and have all three blade welded together professionally! does this sound like a good idea guys? any other suggestions to get round the problem?

i was told if i take the exhaust valve out it will lose some low end power and the power will kick in more quickly, not really what i want to happen as it already had rubbish low end for going up hills then would kick in with a bang, and i already have enough trouble keeping the front wheel down in all gears.

 

[antonyp]

My opinion is that you fix your engine with the oem parts. Modifications like the one you mentioned, although possible, are risky and potentialy hazardous for your engine. The slightest change in weight and/or size of any part in a power valve system could cause problems, namely another breakdown.

It would be much better and safer to invest in the new oem parts and once in a while (the factors of frequency are a completely new discussion), to take everything apart and clean your exhaust valve system thoroughly and re-assemble making sure those parts move freely. That will prevent another major (and costly) breakdown which could involve a lot more parts next time :yell:

Trust me :cool: I speak from experience :bang:

 

[surfer4life]

ive found the parts on a US website for around £100 just waiting for them to get back to me on delivery costs, if not i have found all the parts i need for £200 in the U.K so i am going to do it properly, thanks for the advice

 

[antonyp]

I hope you start riding soon ! Make sure you let us know of the aftermath :ride: