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Crf250 seized after top end rebuild

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Hey how's it going?

Not sure wether or not I'm in the right place.

Basically I thought I would give it a go at rebuilding my crf all went well but it didn't start it just kept backfiring with a huge bang and flame so it got striped down again found out the thing the lobes push down (tappets?) wasn't there so I got a new one with new gaskets and put it back together and it will kick over once or twice then the kickstart will go rock solid I have stripped it down and rebuilt it like 5 times but same problem.

Does anyone know what it could be as I have been quoted a minimum of 350 pounds to fix it and ATM I am struggling with money due to insurance on my car being high as I'm 17.

Any help would be much appreciated

Thanks

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The first time I rebuilt it apparently it would have started if I had that tappet in

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it didn't start it just kept backfiring with a huge bang and flame

Timing is off by (at least) one tooth.

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It really does sound like the timing. It sounds like you continued to kick it over. The first thing you need to do is make 100% sure that the timing is right on. After that, pull the spark plug out and make sure that the engine rotates without binding. If the timing was off far enough and you continued to kick it until it binded up completely, you could have done some serious damage. You certainly came to the right place to ask for help, but next time, do it sooner! Ton's of knowledgable folks on here!

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Timing... as Charlie said take out the spark plug and leave the valve cover off, then try to kick the bike by hand to make sure there is no binding.. If you can turn it over by hand and the timing marks line up then you are good.

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Rotate "slowly" by hand first any time the cam is removed, and tripple check the timing.....also check the cam lobe position.

I worked on a trx 450 for a friend that stuck a valve, turned out the cam gear journal spun on the cam shaft...only way I knew that is because the cam lobes didn't look like they were in the right position, I could feel something was wrong when I rotated the motor by hand.

Thing is I missed it during tear down.

If I would have just tried to kicked it over I would have bent the new valves.

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Hey thanks for the help it all works now but when I line the timing marks up for tdc the piston isn't 100% at the top it's about 3mm from the top but then if I put the piston as far to the top of the barell it will go the timing marks are out is this normal. As I said its only about 3mm from the top.

Thanks

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dont now much about hondas, but could do with a new cam chain as the cam chain can stretch which will make the timing out alittle bit.

carl

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You're 100% right Carl, but a stretched timing chain won't make it bind. The engine will lack power due to the timing being off. I've heard of the extreme where the timing chain finally broke and had simular issues, but unless the chain jumped on the gears and knocked out the timing way out, it shouldn't cause it to bind.

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Hey thanks for the help it all works now but when I line the timing marks up for tdc the piston isn't 100% at the top it's about 3mm from the top but then if I put the piston as far to the top of the barell it will go the timing marks are out is this normal. As I said its only about 3mm from the top.

Thanks

If you're 100% sure that the timing is correct, the bind you may be talking about may be the decompression pin hanging up like it should. If you pull the valve cover and rotate the engine, you can see where the decompression is hanging up on the exhaust rocker. When the cam comes around, and comes in contact with the roller on the exhaust rocker arm, you should be able to see what I'm talking about. If that the bind, you're fine. There could be something else that's causing it, but we will get to that part if that's the case. Just let us all know what's going on with it. We'll help you through this confusion.

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