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07 CRF 450 problems after rebuild

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Need help w/ my buddies bike.

Crank bearings went last year, installed new bearings, new piston and cylinder, new intake valves also as the piston had bent them when bearings went.

Now it will not run. Seems like there's not enough compression. Has spark and fuel but will not even spit, sputter or backfire when kicked or pulled. Have had it apart numerous times checking timing, valves for leaking, etc.

Any help would be much appreciated.

Thanks Shannon

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Try to pull in the hot start.That's what I had to do to get my freshly rebuilt 07 to fire.I would choke it kick a few times then pull the hot start.I believe I used too much oil in cylinder and my rings didn't seal that good,once I got her going she became easier to start but smoked when warming up.I'm currently waiting for a second set of rings and valve seals.

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Did you cut the intake seats when installed the new valves? You should always cut the seats or you will have sealing and valve life issues. What valve clearance did you set?

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Has it sat for awhile? Maybe clogged carb/idle jet?

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it does seem to be out of time. It will line up just fine but the cam lobes are not at 2 o'clock, i'd say actually they're more like 3 o'clock and it feels like the exhaust valves are hitting the piston as you turn it over by hand. Could the cam chain be loose enough to cause this? or could the crank have spun when it locked up under load?

carb cleaned, compression and leak down are good and has spark.

timed it wrong one time and it almost started but when marks are on it will not even backfire or sputter.

Thanks again for the input.

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What marks are you using? Left side flywheel or right side crank. If the cam chain is stretched there may be a discrepency etc. The hard kicking could be the Decompression adjustment out or your cam timing or both. If cam is out of time so will be the decompression adjustment etc. What was all done when rebuilt? Piston/valves/seals/cam chain/ Valve guides etc?

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both marks are on when the piston is at tdc.

it has new bottom end bearings, cylinder, piston, intake valves and gaskets.

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using both timing marks as they line up when at tdc.

It has new crank bearing, cylinder, piston, intake valves and gaskets.

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have you cleaned the carb? inspected that you have spark? checked your valve clearances?

if you have done all that, you need a leakdown test to see if the valves are sealing to the head.

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using both timing marks and a screwdriver down the plug hole. It is timed but will not fire at all. i actually advanced it now and it doesn't hit the exhaust valves and will fire but will not run. It has new everything above but the cam chain. will pick one up tomorrow.

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also replace the key on the crank for the flywheel. it may have sheared.

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There are two marks on the flywheel. One is fire and one is TDC. Are you using the right one?

If you advanced it and now it pops, Kinda makes me think you need to go further. They'll run a tooth out in both directions.

When you say advanced, if you "advanced" something and now it doesnt hit, you might have gotten it two or three teeth retarded. Meaning when the exhaust valves should have been closed, they were still hanging open. Its doesnt take much to bend a valve. If youre sure you had contact there, Id be pulling the head off to check the ex valves for straightness.

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Installed new timing chain. Now marks line up exact. The piston hitsexhaust valves at tdc. actually 1/8" before tdc it hits. it is timed correct!!!

could the new piston be too tall?

or the new cylinder too short?

even if the valves were bent, that doesn't explain why they're hitting the piston?

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Check 2 things:

Check that the cam sprocket flange is aligned to the cam properly. There are holes in the cam lobes that line up with a hole the sprocket. Sometimes the pressed on flange can rotate on the camshaft.

Secondly, rotate the engine with the bolt in the inspection cover instead of the kickstarter. It may appear the piston is hitting but is the resistance of the valvetrain. I had the same issue when changed out my camshaft. I thought it was hitting when it really was not.

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Installed new timing chain. Now marks line up exact. The piston hitsexhaust valves at tdc. actually 1/8" before tdc it hits. it is timed correct!!!

could the new piston be too tall?

or the new cylinder too short?

even if the valves were bent, that doesn't explain why they're hitting the piston?

WEIRD? when at TDC where are the cam lobes facing? They should be facing the rear of the bike and if your eye was down level with the front of the lobes they should be at about 2 oclock position. If its all lined up there should be no way for the valves to touch the piston. Unless the cam is 180 out or as stated before the cam sprocket retainer has spun? The decompression adjuster is most likely out of adjustment as well.

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the lobes are facing more like 3 o'clock but thats where the local honda dealer said they should be. I'm not for sure what you're talking about w/ tha cam retainer? the camshaft and mount are all one piece i thought?

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