Whats better, valves on the loose or tight side?

[Pincushion]

I checked my valves after 7hrs on the rebuild and they are all on the tight side. With one exhaust beyond the threshold @ .229.

I can shim it with a 195 pad and get it to .250, but is that a recipe for disaster? I know they will tighten over time and dont want to risk damaging the motor, if I go to a 195 pad then I'll be on the tight side, but if I go to a 190 then I'll be on the loose side. Which is better?

Also, what is the general consensus for cam cap torque? I know the manual stated specs are too tight.

Edit: all the intakes measured at .152, so hopefully being on the tight side is better and I can leave them alone.

Thanks!

[walent215]

loose you get more bottom that way also

[02YZ426]

I would rather see the valves on the loose side.. Really there is not enough difference between the 190 and the 195 for it to hurt anything. Just stick the 190 in there and you should be fine.

[SXP]

I checked my valves after 7hrs on the rebuild and they are all on the tight side. With one exhaust beyond the threshold @ .229.

I can shim it with a 195 pad and get it to .250, but is that a recipe for disaster? I know they will tighten over time and dont want to risk damaging the motor, if I go to a 195 pad then I'll be on the tight side, but if I go to a 190 then I'll be on the loose side. Which is better?

Also, what is the general consensus for cam cap torque? I know the manual stated specs are too tight.

Edit: all the intakes measured at .152, so hopefully being on the tight side is better and I can leave them alone.

Thanks!

Definitely LOOSE. If you currently have a 200 in there and are measuring .229 then a 195 would put you at 0.279 which would be perfect.

[grayracer513]

First, I fail to see how an exhaust valve that measures .229mm is a problem. The specs are .20-.25mm, so it's perfect already.

Second, anything "in spec" is acceptable. The entire range from .20-.25mm is only .0019" in the first place, which means that, thirdly, you'll never see a bit of performance difference between setting them at either extreme.

Yamaha sets them up as tight as they can make them using .01mm increment shims, probably because to do so is easier on the valve train. But as I said, there is so little difference between the high and low side that it really doesn't matter, as long as it's in the specified range.

Don't forget that your shims are in .05mm increments, not .005, and a 195 shim is 1.95mm thick, .05 thicker than a 190. If you now have a 190 in the valve that measures .229mm, switching to a 195 will reduce the clearance to .179, which is way too tight. By the same token, dropping to a 185 will give you an excessively loose .279.

Your three decimal readings are only there because the makers of your English feeler guages wanted to be accurate. .001mm is .000039" (one micron), an increment far too tiny to actually measure for with a feeler guage.

[SXP]

Gray - The exhaust spec is .25 - .30 (at least on my WR400 and I'm pretty sure it's the same on his YZ). I just double checked the factory manual. And, reading thru his post again, I'm assuming he currently has a 2.00 in there with which he is reading 0.229. So dropping to a 195 (1.95 mm) would put him in the middle of the tolerance range at 0.279 (regardless of the third decimal place).

[grayracer513]

The spec for an '01 YZ426 is called out at .20-.25, but since his is an earlier version with the stainless valves, it could be different.

[Pincushion]

I have a 2000 w/ stainless valves and it calls for .25 to .30. It must have changed when Yamaha went to Ti valves. I put a 195 in and it measures within spec now, but I'm wondering if I should've changed shims on the intake side since they were all on the tight side. I'd rather not change shims more ofter than necessary.

[grayracer513]

No, don't change them as long as they are within the specified range. They should hold that setting for quite a while.

[Matt96xr6]

loose is always better. WHy? Cause as the valve wears into the seat, it will tighten up the specs to the cam.

[grayracer513]

loose is always better. WHy? Cause as the valve wears into the seat, it will tighten up the specs to the cam.

That is true. However, when healthy, the valves in a YZF recede into the seats extremely slowly, and having them at the tight side of spec reduces the impact of both the opening and closing of the valve, which in turn discourages wear.

What you say is accurate enough, but nonetheless, Yamaha themselves set the bikes up within .01mm of the minimum as they are built in the first place. At least, that's what I have found in every one of them that I have checked early in the bike's life. I would attribute it to normal wearing in of the valves, except for the fact that they are set so near the same numbers on all of the valves. My 450, for example was, and has been, .10, .10, .10, .20 & .21.

Besides, if the choice is between .105mm and .155, only one of those numbers is in spec.

[Pincushion]

I'm on the tight side on all my valves, but all are within spec so they'll stay that way until another reshim is required (if ever). 6.2lbs on the cam caps is what you reccomend, correct?

Thanks all!

[grayracer513]

I'm on the tight side on all my valves, but all are within spec so they'll stay that way until another reshim is required (if ever). 6.2lbs on the cam caps is what you reccomend, correct?

Thanks all!

Yes, 6.2 ft/lbs. or 75 in/lbs in three diminishing steps (45, 65, 75)

[FZ1426]

loose is always better. WHy? Cause as the valve wears into the seat, it will tighten up the specs to the cam.

Yes, but the primary reason is that they get longer when they're hot. Especially the exhaust valves.

[grayracer513]

Yes, but the primary reason is that they get longer when they're hot. Especially the exhaust valves.

You don't think Yamaha was aware of that when they said that .25mm (in this case) is enough?

While you're calculating thermal expansion, don't forget that the head also expands, and quite a bit, being aluminum. The distance between the valve seat and the camshaft bore increases with heat, too.

[GrizzlyFlatter]

One of the dirt bike mags recently quoted Ty Davis(or his mechanic)saying they ran the valves on the loose end of the spec for long events for more reliability,I'll try to look for the article and find exactly what they said.

[grayracer513]

One of the dirt bike mags recently quoted Ty Davis(or his mechanic)saying they ran the valves on the loose end of the spec for long events for more reliability,I'll try to look for the article and find exactly what they said.

That may well be necessary on a Honda.

[GrizzlyFlatter]

That may well be necessary on a Honda.

I do believe the bikes were blue,Ty has ridden yammerhas for quite some time now

[GrizzlyFlatter]

Also,no slam on Yamahas intended on my part.I will likely be going blue in the near future for my 4-stroke needs,I have been riding my buddies YZ 400 quite a bit and enjoying the heck out of it,just need to work out some bike set-up quirks/preferences.I may be buying the very YZ I have been riding or go for a newer WR450