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Engine help

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Recently replaced piston and cyclinder (KTM 280 kit) in 250 XC-F and did not correctly tension (translation=no tension) cam chain. Attempting to start it, the cam chain wadded up, timing jumped, piston hit the intake valves(marks visible on piston).

We put in new intake valves and seals, checked and shimmed the valves, reset the timing, tensioned the cam chain per the manual and quadruple checked it, and put everything back together. We did not replace the exhaust valves because it did not appear that they were damaged (no marks on the piston).

After all that she was extremely hard to start (had to bump start), but did fire up eventually. However, there's a loud clackalacking that seems to be coming from the top front of the head.

I'm wondering if the exhaust valves were damaged and need replacing - any thoughts?

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did you release the tension on the cam chain adjuster? You have to reach in with a long tool and release the plunger after the head is on and the chain is on the cam sprocket.

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Yes, after making the mistake of not doing that the first time, we made sure that the plunger was released and the cam chain tight all around.

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Yes - the aligning of the two marks on the camshaft gears with the dividing line between the two camshaft bearing bridges. I watched the mechanic put it back together and he didn't do this. I hadn't read the manual at the time (he said that he had), so I didn't know to tell him to do this.

Edited by fastwoodsrider

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that would be it then IMO, its easy enuf for you to do yourself now that the rest of it is together. Just rotate til its at TDC and lock the crank with the lower bolt and then remove the cam tensioner to get the chain loose. Then rotate the cams and put back together. I forgot to lock the crank once and had to do this too. On start up the tensioner popped out with a loud clunk because I forgot to release the tension like we talked about above, and all is still running well today.

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I was just wondering if anyone knows if it would be possible to slip the chain a tooth if you rolled the bike backwards in gear without the engine running on the standard ktm tensioner? I know the tensioners are pretty tough to shift but there would be no oil pressure....any ideas? I've been out today and a friend of mine has just smashed his valves, piston, head, valve guides and barrel to pieces! Only thing I can think of is a valve head breaking, possibly due to a sticking valve or the chain slipping a tooth. I noticed him roll the bike backwards on a hill a couple of times not sure if he left it facing bacwards down the hill in gear.

I'm not sure which way the chain runs now as i cant remember but I would imagine it would be on the side oposite to the tensioned side from the chain pulling the cams round?

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