Valve Shimming Question

dmount76 · Mar 21, 2008

I got into the valve cover last night on a newly purchased 05 CRF 450.
Exhast valves measured perfect, but intake valves were tight. I couldn't even get the .002" feeler in between the cam and shim (although it is pretty hard to push a .002" feeler).

Question -
I didn't tear it down any further to measure the shim that is currenly in there. I know the previous owner had never changed the shims from the factory. Is the stock shim standard so that I can purchase a few shims on either side of added .006" to the factory shim or do I need to tear it down, measure the shim and go from there.

Also - from searching it seems like many of you reccomend new valves if they are tight like this.

What is involved in repalcing the valves? How expenseive?

In case it is not obvious - I've never done this before.

Thanks in advance.

Dallas in Wyoming.

Cabot · Mar 21, 2008

Well, your going to have to take the cam off to replace the shims anways.. so you mine as well do it now so you get the right size shim. Also, some dealers do shim replacements. (so either you just trade shims for no cost, or you trade shims for a discounted cost)
taking the cam off takes about 5 minutes, just make sure you get the timing right when you put it back on!

Valves can be shimmed many times before they need replacement. If your shims are getting really small, then you might want to replace the valves. I'm not quite shir how you would know exactly, but someone else might. Replacing the valves is a pretty expensive job, and more then likely you will have to have a shop do it unless you have the right tools.

Rich Rohrich · Mar 21, 2008

Cabot said:
Valves can be shimmed many times before they need replacement.

That isn't true on the current crop of Titanium valved four-strokes. If the clearance has zeroed out (which his intakes seem to have done), then you have to replace the valves, the valve springs, and re-cut the valve seats. The YZFs are the one exception to this. You can usually get a couple of small adjustments out of them before the valves need replacement.

The reason for this is the hard facing is worn off the valve and the cast iron seat is destroying the valve face. That's why the clearance gets smaller rather than larger like you would expect when things wear. The valve face is receding and it pushes the valve stem closer to the cam, closing up the clearance.

Pulling the cylinder head is a simple job, but the valve machine work and replacement is a job best left to someone with the experience and equipment to do it right.

Adjusting the valves now might buy you an hour or two of running time, but the clearance will close back up quickly. If the valve face recedes too far the valve head can break off and drop into the engine. Ask the RMZ250F guys how much fun that is. ;)

dmount76 · Mar 23, 2008

Well I went ahead and shimmed them. Added .006" to the existing shim. could fit the .06" feeler gauge in when wiggiling the top of the timing chain and it would pullout with a bit of reisitance. Perhaps I should have added another .001". but will leave it there for a while and then remeasure.

Thanks for the advice.

Dallas

cthowards · Mar 23, 2008

On my 2005 CRF450R, at about 80 hours I did a new piston and rings, and replaced the stock valves and springs with kibblewhite valves and springs. I brought the head along with the valves to a local bike shop who basically gave me the head back with the valve train installed (they inspected the head and installed all components). From there, it was failry easy to complete the rebuild. After two hours of run time, I checked the clearances and I was way off - the intake valves were much tighter than they should have been while the exhaust valves were fine. I shimmed them and when I checked them about 2 weeks ago at about 40 hours, they had not moved at all. I was able to do the entire rebuild for about $600 by patiently buying parts online (for example I got all 4 Kibblewhite valves for $85 new in the packaging when they are normally $40 per valve, got the Wiseco high compression piston and rings for $90, etc.). If you think you may want to replace the valves, start looking online now and you may be able to slowly accumulate the parts you will need when the time comes.

Those 450s rip! :laugh:

dmount76 · Mar 24, 2008

I'll put a few hours on it and check it again. How tight should the feeler guage be? As stated above I had to wiggle the timing chain to get the .006 in. Is that too tight?

Valve Shimming Question

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Valve Shimming Question

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