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Hard to kickstart after rebuild

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Hi,

I have just changed piston on a 250 sx-f 2011. the engine is mounted back on the chassie, and iam having problem kickstarting it. Its feel like the decopressor is not working or something. When putting engine back together i did lock crank with the crank lock screw, and the camshafts is aligned as the manual says. Any thoughts on what i have missed or done wrong?

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Cam tensioner working right ?

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cam chain is tight, no shim's fell out. and the valves where in spec before i tore it apart

 

is there more then one crank locking location? Do i have to anything special with the camshaft before install?

Edited by melfjord

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If it was at TDC and all you did was lock the crank in, pop the head off, replace a piston and re-assemble, then its gotta be something wrong with the re-assembly process. TDC is when the two cam's marks are aligned AND the notch on the crank is exposed through the hole. Yes, its a 4 stroke motor, so there is also a position where the crank mark notch is exposed, but its NOT TDC. The cam marks are the true TDC.

Did you put the spacer back in behind the crank locking screw?

The first thing I do when the motor is done is turn it over with the kick starter without a spark plug and try to build some oil pressure with repeated kicks. I have an e-start motor, so I just tap the starter motor with a battery and crank it up. Then once you've noticed the oil jets are spraying, then you can put the cam cover back on and throw it in the frame.

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Found the problem, both rocker arms on the intake cam had broken off. any idea on what can make this happen? I tought that once you locked the crank with to locking screw(with washer off) that the piston is tdc

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Found the problem, both rocker arms on the intake cam had broken off. any idea on what can make this happen? I tought that once you locked the crank with to locking screw(with washer off) that the piston is tdc

If you align the cam's and align the crank mark, you can pull everything apart without any consequences. The crank just spins, so as long as that mark is lined up, you can simply line up the cam marks and be good to go for re-installation. So on that part, you're accurate. But its not truly TDC unless the two cam marks are aligned. Top dead center is not just a position of the piston, but its also indicating a particular part of the cycle. Its where the combustion process happens in the cycle.

Anyway, the only way you an break something is if you put the cams in wrong and the piston hit the valves whilst the cam was pushing down on them. I've never heard of breaking a rocker arm's in the 250... that doesn't seem even possible. But if you pushed it hard enough, possibly? Something needs to take up the force, usually the valves bend.

I've noticed, some of the older KTM motors (specially the 250), the cam marks don't line up perfectly at TDC (one tooth off). But you'd have to take a picture to re-align if that were the case.

Edited by tye1138

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I took the top of and the valve was okey. there were markings on the piston but no major damage done. The wierd thing was that when the crank is lined up with the marking it's almost BDC not TDC, and it not all the way. So might this be a replacement crank(iam the 3rd owner of the bike) or could the crank have twisted somehow? the crank works as it should, bike run super good before piston change.

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