Need help on 2005 yz450f new cam chain/tensioner no compression

I am working on a friends 2005 yz450f, when he brought it to me the kick starter wouldn't budge, I put it in gear and rocked back and forth and then it could be pushed down. After reading some posts, I took the valve cover off. It had jumped time. I replaced the cam chain and tensioner. Bolted everything back up and gave it a kick and no start. Did a compression check and had no compression. Took the cover back off checked valve clearances and exhaust valves were in spec at .23 "from left to right" the intake valves were way out of spec .43 .18 .25 I took some pics to see if you could tell if maybe it spun the wheel on one of the cams" if that's possible"or maybe it messed up the valves . The punch marks are lined up with the head and it is at TDC but the cam lobes look a little off.

I will post some pics in a few hours, I'm on the road right now. Thanks so much

The larger than normal clearance on the intakes is troubling.  Was there any damage in the cam bores?

Sorry for the ignorance but how would I check that ? I'm learning as I go.

When you had the cam caps off to change the timing, you should have been able to inspect the camshafts and the bores in the caps and saddles. 

I'm about to take them back out as soon as I get home. I will post a bunch of pics. Honestly nothing stood out to me when I had them out before but really didn't know what to look for.

The reason that I asked is that under certain conditions of lack of lubrication at the camshafts, a momentary seizure of the cams can cause the sprocket to slip.


Another problem that can account for the extra clearance and the compression loss is that when it jumped time, the intakes whacked the top of the piston and are now bent.

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I will take the cams back out later and post some pics of those.

Can you tell if the intake valves are bent from the pics?

No, only by removing the head. 


The timing is perfect, and the cams appear properly oriented, so a slipped cog is unlikely.  Remove the timing chain from both cams, run the engine to BDC, then apply compressed air through the plug hole.  I'll bet you'll have air escaping through the intake at a high rate.

Ok. I will do that in a bit and post the results. If that's the case, the head will have to come off for further inspection won't it?

Yes if you can air escaping through the intake port the head must come off. Lift the head off. Number and label the lifters. Using a valve spring compressor remove the valve locks retainers and springs. Then pop the gales out for inspection and inspect the seats, if it was mine I'd replace all 5 valves and have the seats professionally cut. That is if the seats are repairable and not damaged from a bent valve. At this time I'd remove the cylinder and inspect and measure the piston

Quick update, I removed the cams and chain, and watched the piston reach the bottom of its stock thru the plug hole as I turned the crank. Did the compressed air thru the plug hole and the was coming thru intake pretty fast. I guess that was correct as to how I did it. Tomorrow I will remove the head and take some pictures and post those. I don't have a valve spring compressor, is the another way to take them out without the spring compressor or should I just order one? Thanks so much for everyone's help, I really appreciate it.

There is another way to take them out, but you can't reassemble them by that method.


Set the head combustion chamber down on a bench.  Using a socket or some tubing that fits the spring retainer, place the socket on the retainer and strike it with a hammer hard enough to move the retainer about 8-10 mm.  The keepers will dislodge and release the retainer.  

Got the head off, here is some pictures. The right and left intake valves had hit the piston. The piston has a couple small places on it, does it have to be replaced? The jug looks fine. Also do you think I could get by with just replacing the valves and not having to get any machining on the head?ImageUploadedByThumper Talk1377175490.456370.jpgImageUploadedByThumper Talk1377175510.182686.jpgImageUploadedByThumper Talk1377175542.715920.jpgImageUploadedByThumper Talk1377175588.683295.jpgImageUploadedByThumper Talk1377175609.181844.jpgImageUploadedByThumper Talk1377175624.727039.jpgImageUploadedByThumper Talk1377175644.099917.jpg

The damage on the top of the piston isn't the issue.  The question is whether the skirt was deformed at all by the impact.  It probably was not, by the looks of things, but it wouldn't be unwise to pull the jug and run a mike over the skirts.

I'd personally replace the piston being as you have the head off allready and 1/2 way there. Do you have any idea of the time on the piston?

For the valve seats you really do want to get them machined. Cost is cheap compared to the valves, only $50 here locally- $10 a seat. People have just thrown in new valves without machining but I'd highly recommend it for a sure seal. Being as the valves hit the piston it could have bent a valve and damaged the seat. In that case seat repair is required as it won't seal. Take some pics of your seats and lets take a look. You don't want to throw new valves in and have them leak from the seats

Don't bother taking any pictures of the seats.  They need to be properly refinished WHENEVER valves are replaced, regardless of whether they ever touched the piston.  Just take your new valves, seals, and springs to the machine shop and have them done right. 

It's not worth tearing the head off again to save him $50. Most machine shops should be able to cut them. Just take in the bare head and new valves to show them and they will tell you if they can.

Did you ever get this resolved? Wondering what the result was and if you got it running.

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