Valve clearance?

I'm setting valve clearance on my '99YZ400 and I have a couple questions: I have owned XR's previous to the YZ and the usually course with XR valves was initial tightening

from seating etc. then over time the valves seem to loosen. On the YZ I have noticed continued tightening: intakes .13mm X 3, and consistent tightening asymmetry with exhaust .13mm and .16mm (the latest). Is this normal,or should I see a loosening over time? The bike is very fresh and well maintained. With my XR, I would commonly set clearance at end range, predicting increased clearance with time giving longer duration in the spec zone. Can anybody with alot of hours and valve checks on their YZ tell me what to expect. Thanks, Keith.

i think that the xr valves loosen do to wear on the rocker arms and ext.the yzf does not have them so insead the only thing that makes them come out of adjustment is the valves wearing into the head whitch makes them tighten instead of loosen thats my guess


I am in the same boat your in...i have owned many XR's and I knew when to adjust the valves whenever it was hard to start and performanve started to decrease. I know that adjusting the YZ valves is a more time consuming thing (i could do my XR's valves in 15 mins) But when should you do your YZ valves? after break in? or whenever it gets hard to start and runs crappy? Since I have a 01' will I need to adjust the valves as fast since it is Ti?? I've seen many posts where everyone says that the Ti valves wont last as long due to it flexibility...

My Dad studied many metallurgy classes in college and I asked him what he thought about this matter... and he said as long as the valve seats where changed in 01' to compensate for the softer more flexible metal (which they did change for 01'...the part number is diff. and I verified that from a local well known mechanic) they should last just as long as the steel valves under the same conditions. The only difference is that Ti is lighter of course and is more resistant to expansion and contraction under extreme temperatures. Well I can sit here and quote all the metallurgist stuff in the world but that wont help...I guess we will find out how durable the valves are after we are having fun riding! Just my 2 cents



I get my kicks on a 2001' YZ426!

Friendswood, TX

I check my valves about every third oil change. I guess it depends on the type of riding you do and how particular you are about the settings. Of course, if you are modifying intake/exhaust and subsequent jetting, I think it is wise to set clearance first before making carb changes. My problem is now I have an exhaust clearance measuring out at .13mm with a 172 spacer (I had all odd sizes originally) that I had rotated from another valve. For a 99 the range is .25-.30mm which means I go with a 155 to get me to .30mm or a 160 to get to .25. This is why I ask what other people are seeing as the trend for their valves. Should I anticipate future tightening and go with the smaller spacer, thus .30mm?? Can you get spacers in odd sizes or is this just a factory deal?

[This message has been edited by kmcbride (edited 01-26-2001).]

I’ve probably checked my valves five or six times in the year I’ve had my bike, changing the shims once. The clearance decreased in a very even and predictable manner, especially over the first fifty hours or so. I swapped shims by one size only when clearances were barely out of spec., so I ended up on the loose side. That was probably 30 or 40 hours ago and at last check they had tightened some and are now approximately in the middle of the range.

So if I were you I’d get a 155.

The factory is the only source for odd-sizes, you may try your local dealer(s) and see if they have saved any odd-sized shims taken out of other bikes.

Just my two cents.

Thanks Hick, that's the way I was leaning just needed a little push, Keith.


I have about 30 hours/4 oil changes on my 01 426. The bike runs really strong, but I dont really have a benchmark for power. Do you think I should check the valve clearance now or wait a few more hours. How long does it normally take to check the clearance? Thanks,


I prefer mojo myself.

I had a 98 400 for two years of serious abuse and only had to adjust the valves once but they probably needed it when I sold it. I check the clearances about every 4-6 months or about 50 hrs. Hmmmm, I think it's time to do the 426, see ya.


An hour should be ample time to check your valves, the normal tools will suffice in addition to a set of feeler gauges with a bend in them. You need to remove the seat, tank, headstay and valve cover. The section in the manual is pretty good but it says to remove the radiators. I think this is a pain, especially if you have guards, and isn’t really necessary.

I’m still using the original rubber head cover gasket and it doesn’t leak, but that is probably because I have a new one sitting on my shelf (that whole parts mojo thing, buy a spare and the original lasts forever, this works especially well with levers).

My guess is that yours are well within spec., but I think it is a good idea to check them anyway (that maintenance mojo thing, similar in effect to parts mojo).

Is “mojo” a regional term? More urban (or literate) types may prefer “karma.” :)

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