Coating on Valve Faces

[iryde]

Upon a valve check I recently discovered that my intake valve clearance was between 0 and 0.038 mm. The bike had the orignal shims, but the center digit that was stamped on the shim was not legible. Other TTer's mentioned that this is likely caused by the coating on the valve wearing away and that the valves will probably not last much longer. I reshimed yesterday, but was unsuccessful. I installed the new shims (175-L, 170-C, 175-R) and the left and right are still tight; left is between 0.076 and 0.102 mm, right is between .051 and .076 mm, and the center is between .102 and 0.127 mm. I'm planning on getting 170 for right and left and a 165 for the center.

My questions are based on statments from other threads pertaining to the coating on the valve faces wearing:

How long (hrs of operation) did you end up replacing your valves after discovering that the coating was wearing?

Did you replace both intake and exhaust valves?

What other valve train components should did you replace (springs, etc)?

[DRTYHRRY]

Closing valve clearance is a valid warning but if you don't really know the entire history of the machine I wouldn't go past 200 hrs total time. (100 hrs if there was known serious racing time, but that would probably cause valve clearance closing.) My clearances were yet to close once and I had planned to replace timing chain, all valves, springs and keepers if/when clearance closed a second time. At (my second owner guess) 200+ hrs. clearances on '02 YZ were still in spec but broke the left intake valve head with catastrophic damage! With my hard earned experience I would still replace at the second clearance closure but would use a max time elapsed as an insurance check. (See post: ANOTHER TOP END GONE

[iryde]

Did you ssay that you shimmed your valves once? If so, what size shims were you using? I'm trying to decide if I should replace the valves or try shimming. This is the first time I had to adjust, but I don't know the exact history of the bike. I've put probably 50 to 60 hrs on it mostly off-road, but a few enduros and harescrambles. What concerns me most is a comment someone made about the coating being worn off the valves. The numbers on my shims were barely legible and someone mentioned that is an indicator that the coating is worn away.

[grayracer513]

There are a couple of things to consider here. First, don't reshim the center intake. It's in spec. Going .05 smaller will make it too loose.

What you need to look at is: 1) the total amount of size change in the shim on a particular valve, and 2) the time between required adjustments.

The first tells you the total wear at the valve face. Have a shop mike the original shims so you can add this up. It's not a good idea to keep running a valve that has moved .20mm or more into the head.

The second point will tell you with reasonable certainty whether the nitride coating is worn through or not. If the coating is intact, it wouldn't be at all unusual for a YZF to go well over 100 hours without reshimming. Once it's worn through, the interval will drop dramatically to more like 10-20 hours.

I just redid the top on my '01 with an estimated 500 hours on it. I could have reused the exhaust valves, but since I have no way of knowing how long they would lest from this point on, or if they might be prone to break after all that time, I chose to replace them. Two of the intakes were heavily worn, the other less so. Replace the springs and the cam chain. It's cheap insurance.

[iryde]

Thanks for the great info. Just to clarify your stement below.

What you need to look at is: 1) the total amount of size change in the shim on a particular valve, and 2) the time between required adjustments.]What you need to look at is: 1) the total amount of size change in the shim on a particular valve, and 2) the time between required adjustments.

Would peform this after I reshim this time and then again at the next clearance check?

[DRTYHRRY]

Grayracer is spot on. What he is saying is that the amount of clearance closure since new can determine the amount of coating gone. When the coating is gone the titanium won't hold up and it is replacement time.

I am amazed that his valves made 500hrs. Mine were still in spec and no closure in the 150hrs+ that I put on it. The left intake broke at est. 200+ total hrs and made my '02 a part out project. It was raced for a few months before I got it. I'm an old guy and ride mx but don't often push the rev limiter.

My point is that loss of coating isn't the only threat to valve longevity. Mechanical cycles? Heat Cycles? I'd like to know for my '05.

[mdeleon]

ive got almost 700 hr hrs on my 250x and have no problems ,,,what is it that we can confirm we are doing differnt,,my bike is still bone stock ,,no mods ,,ca model fresno ca ,,,valves still in spec.. lots of single track riding ,,desert..and woods ..I may even have more than 700 maybe 900

mike in fresno ?

[YZ250F_Rider]

So if the valves are solid titanium what exactly are they coated with?