2006 yz450f cam chain problem

Gray its smoking alot and spitting oil out of the silencer and header connection what should I check? I replaced the 2 bent valves and seals and grinded the seats with a grinding compound and a lapping tool. It smoked bad before the valves though. I bought this bike for 450.00 and Ive enjoyed working on it a lot. It basically needed everything. I'm happy to know what I have but I'm at a point where I'm just tired of taking it apart. Like I said though it smoked before I messed with the valves at all. I'm sure the rings were right according to the manual and manufacturer directions when I installed the new piston. What should I do now? Were the valve seals bad to begin with or?

You should never lap titanium valves under any circumstance, and the seats should be reground or recut with tools made for that purpose. 


That won't cause an oil control problem, though. 


How did you go about torquing the head?

O ok, the manual said to so I did but ok. This time I bought a new oem gasket, put the head on with the bolts loose with the molybdenum lube on the threads, kinda seated it by hand really well, hand tightened the head bolts back left front right front left back right then torqued to 22ft pounds loosened them all the way but left the head on and tightened them to 13 ft pounds, then made a sharpy mark on the bolts and head on each bolts and turned the bolts 180 degrees from the sharpy line on the head

The part about the lapping in the manual is an unfortunate carry-over from the days when the valves were stainless steel. 


Sounds like you torqued the head properly.  Good job.


So the next likely problem is either a valve seal improperly installed, or a problem with the oil rings.  Two mistakes can be made with them.  One is to fail to butt the ends of the center, expander ring element of the set together before adding the rails, or scraper rings, or, and you should hope this isn't it, a rolled oil ring.  This last happens when the end of a ring is snagged by the cylinder on the way together, pulled out of its groove, and folded between the piston and cylinder, and usually causes damage. 


The oil could also be residual from when it was running oily before, or maybe you just slopped it up too well on assembly and it hasn't cleared it out yet. 

Time for a leakdown test? Should give you an idea of where the problem (if any) lies.


Much quicker and easier than repeatedly tearing it open.


Regardless of what you do, good luck and please let everyone know what you find!





Ok well I did notice the cylinder was fine when I did the valves, I held it down and carefully pulled the timing chain and made the piston go down and looked at the cylinder walls. They seemed fine and from what your saying about the rings there would be lots of scratches right?. And also I remember butting the center ring not overlapping it so that leaves valve seals? Or?

Not sure how to do the leak down test but yeah I don't wanna take it apart any more. If that will help me identify the problem I'll do it.

Google something like "how to perform a leak down test" and you'll probably get more videos and articles  than you care to find.    :thumbsup:


It should give you a pretty good idea of how it works.



Good luck!

Gray I noticed a post response you posted several years ago about a crf 450 smoking and you mentioned an oil pump return problem. If there wasn't oil on the dipstick. Something about that. Is that a possibility with mine?

It will smoke if the return pump isn't working, and eventually, it will be unable to lube the cams because of it.  A CRF450 doesn't have a dry sump oil system, though, so there's no return pump on one.


To check yours, open the dip stick hole and start it. If it's healthy it will make a pretty mess as it blows return oil past the open hole and some of it escapes out the top.

Ok so yeah, it made a huge mess. What should I check now valve seals? Two were new and they were very easy to install did I miss something with the 2 new ones?

Why were only two of them new?

Why were only two of them new?


I'm guessing they were installed with the 2 new valves that replaced the 2 bent ones and the rest were left alone?

Yes, because you said if the others were fine and in good working order just let them be. Yes I just replace d the two that were bent

Or your mean the seals Gray? Like all 5 seals? I didn't mess with anything else except the two bent ones

If you removed the valves, you should have replaced the seals. All 5.

It's also possible that one or more were dislodged or tilted while reinserting the valves. Once you get the head back off, you can have a look at the rings, too.

Ok, so I'll replace all the seals. Did I ruin the other two valves by lapping them?

Don't think you ruined them per se, but you may have shortened their life.

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