my intake valve can't be shimmed. Why?

Question for the forum. 


I have a 2011 450sxf with 60 hours. 


I have the shim kit which includes shims all the way down to 1.72mm.  When I adjust the value clearances on my intake side they are too tight, even with the smallest 1.72mm shims.  The right valve is close, but under spec, but with at least some amount of gap.  My concern is the left valve, it has zero gap and likely causing my poor starting. Exhaust side is fine. Anyone heard of this before?  Why would this be case?  What can I do?    I assume if I have the seats machined and get new valves the clearance issues would continue  or become worst as I'm taking material away.   Is there anything I can do or check to put the gap more in spec? 

Edited by speedbump49

Cant you just take the shim out of the left intake valve and replace it with a thinner shim ?

cr2504life,  No, because both left and right are currently using 1.72mm shims, which is the thinnest shim available,  I think any thinner and the rocker would be hitting the value spring retainer cap.

Valve faces are likely cupped and receded back into the seat, time for a rebuild.  Are you the original owner? Those valve should last a longer than 60hr's.

highmarker, No I'm the second owner.  I know the hour meter may have been replaced and therefore the engine may have more than 60's hours but the bike is in good shape overall and it just seems hard to believe that any number of hours would cause this level of wear unless something else is wrong?  Do you think I could just replace the valves or would I need new seats too?

Edited by speedbump49

This is pretty typical, once you can no longer shim the valves it's time for a head rebuild.

johnnyballz,  thanks for the info. Does a rebuild mean new seats or re-cut existing seats?

Crf 250 used to do this with around 20 hours use

They should last 200-300 hours, so its time to rebuild send it to thumper racing.

I agree with most here, sounds like that bike has a lot more hours than you think, some of the older Hondas had valve problems but never seen one in 20hrs from new. They are more like 60-100 hrs and your in for a head rebuild. Either way your head is in need of a rebuild.

The early crf 250 could not go 20 hours of decent rider speed without a valve adjustment and new valves every other shim change was normal,the 450 was much better

The early crf 250 could not go 20 hours of decent rider speed without a valve adjustment and new valves every other shim change was normal,the 450 was much better

a valve adjustment yes, his valves need to be replaced and you said the older honda 250s did it in 20 hrs. No they needed to be shimmed, not replaced. I've seen guys get 60 - 100 on the early 250 heads ( from new until rebuild of head) and no they weren't your typical put around in the woods guys. Hell I even seen an early crf 250 flat tracker back in the day with a stock head with nearly 100 hrs or hard high rpm use on it.

johnnyballz,  thanks for the info. Does a rebuild mean new seats or re-cut existing seats?


Not necessarily.  I rode Hondas for years as did all my friends and I always did all the work on all our bikes.  It's pretty common on the Hondas to get the intake valves to where even the smallest shim has 0 clearance, for some reason it was always the left side intake valve.  I never had to install new seats in the heads, on the contrary actually.  The only thing I did was to cut the valve seat with a carbide valve seat tool which obviously actually technically removes a bit of material, but you do just enough to freshen the seat.  What most guys don't realize is that the valve face itself actually starts to cup letting the valve go "higher" up into the head and raising the stem to the point where even a thin shim will no longer work.  Fresh valves take care of this and cutting the seats is enough to freshen the seats,  The tool is about $800 for the valve seats so probably not something you want to buy for occasional use, but most shops can cut the seats for you.

I took the head off tonight. Wow, you guys are right, the intake valve is totally cupped, I'm mean really bad!  I think the previoius owner must have ground the valves.  I'm taking the head in tomorrow to my local pro shop. Looks like I'm in for new valves and seat cut. I'll let them assess further incase guides are done.  Thanks for all the posts, I was really hoping I would be riding it now and not taking it apart, but its a good thing.

Yeah it's good to take care of the stuff before it get worse.  Sounds like you are in for some new valves and a seat refreshing.  Cutting the seats is no big deal, it's a hand operated tool, there is an arbor that slides in the valve guide on which the tool head slides over and you use a t-handle type tool too simply rotate the cutting head a few times.  There are a few different cutting tools for each angle, but you can do all the seats in like 10 minutes once you know what you are doing.  The big expense is in the tool itself, but a hop shouldn't charge too much to do the seats.

Most probably the air filter was not properly seated at some point and the dirt chewed up the seats.

This is a common problem. Ktm 1190 adv do it regularly due to bad design. The sx/xc filters can be slightly rotated and not seat correctly.

This is why ktm redesigned the filter system on the 16.

Air filter and oil maintenance are imperative to the life of our motors.

I have a friend who has run 120 hours, mostly sand before a engine refresh. Surprisingly all was still kinda ok.

But he is a pedantic maintenance guy.

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