different valve shims?

I checked my valves last night, and both my exhaust valves were .01 tight.

I've heard of people shimming their valves up when they were "towards the tight end of the range." But Yamaha only makes shims in .05 incriments, which is also the acceptable tolerance range (.20-.25 for exhaust valves.) So, if you weren't clear out of this range and put in the next bigger shim, you would be out of the range on the loose end. Are there shims available in smaller incriments? And just out of curiosity, how tight would valves have to be before doing damage?

Hi,

Even hotcams valve shims are with 0.05 differences.

That .01 is so little I wouldn't bother with it. As long as there is a clear clearence you'll be safe. Too much clearence will cause excess wear on valve train and power loss.

Timo Mc

good to hear. thanks again Timo

Keep a close eye them now that they are getting tighter.

I amazed you could feel that much of a difference with feeler gages.

When they do tighten up more and you have to take it apart to re shim you will notice that from the factory you will have odd sizes like 174's 173's (increments between the .05 that Yamaha sells) You may be able to use them in other spots.

When I reshimed I only needed to buy three shims from the dealer and reused 2 shims from other valves.

Why we can't buy those shims is beyond me. :crazy:

Hi,

About that damage, it starts to happen when you don't have any valve clearance at all. Valve/s are not able to close complitely and exhaust gases will burn it. Honda has problem were valves sink to the valve seat and this way valve clearance goes to non existent, but end result is the same burned valve/s.

Timo Mc

Hi,

About that damage, it starts to happen when you don't have any valve clearance at all. Valve/s are not able to close complitely and exhaust gases will burn it. Honda has problem were valves sink to the valve seat and this way valve clearance goes to non existent, but end result is the same burned valve/s.

Timo Mc

4 out of 5 of my valves are already .01 to .02 mm tighter than spec range, so I have been thinking the same thoughts that there just needs to be clearance between the cam and lifter to still seal.

However, we are measuring cold. When the valves are hot they get slightly longer due to thermal expansion, especially the exhaust valves. Perhaps that is why they have a larger cold clearance than the intakes.

I wonder at what point leakage can occur at operating temperature even though a small clearance still exists when cold. :crazy:

If your tolerances are at or less than the min tolerance REPLACE the shim. A shim change is way easier than rebuilding your engine. Even if you are .01 looser than min spec I would consider replacing the shim. As was said before chances are that you will have many off size (ex. 183) shims that you can swap. The goal is to have all clearances as close to maximum tolerance as you can. There is a shim kit in one of the Ebay stores that has around 120 shims for about $65. Lots cheaper (over time) than the $8 per shim the dealer sells each shim for. I think it is a CRF kit but same shims as ours.

I found the items you speak of on ebay, however is it just one kit for all the diff yamaha 4 strokes, they have different listings for wrf's yzf,s' 250's and 450's etc...

My shims were about 0.05 mm too tight so I just grinded them down with some fine abrasive cloth.

My shims were about 0.05 mm too tight so I just grinded them down with some fine abrasive cloth.

This sounds good!

Tell me more about your process Johan :crazy:

I'd like to hear more about grinding down the shims too. It seems we're dealing with such close tolerances that a red scotch-brite pad or some 2000 grit sandpaper would do the trick. How perfectly flat do the shims need to be? I suppose a sanding block might be the answer.

Honda CRF 450 shims are the same diameter and come in .25 increments the CRF 250 shims are not the same diameter. Finer adjustment possible with Honda shims. I think the hot cams shim kit has the honda shims. Previous advice is correct IMO set the adjustment to the loose side of the specification you will not notice any performance differnce and your motor will last longer. If you must obsess over the valve adjustment dont worry so much about the clearance but focus on the cam cap bolt torque and cam cap fit this will get you into more trouble than the adjustment. DO NOT Overtorque the cam cap bolts

Honda CRF 450 shims are the same diameter and come in .25 increments the CRF 250 shims are not the same diameter. Finer adjustment possible with Honda shims. I think the hot cams shim kit has the honda shims. Previous advice is correct IMO set the adjustment to the loose side of the specification you will not notice any performance differnce and your motor will last longer. If you must obsess over the valve adjustment dont worry so much about the clearance but focus on the cam cap bolt torque and cam cap fit this will get you into more trouble than the adjustment. DO NOT Overtorque the cam cap bolts

Thanks for the advice! :crazy:

If its true that valves only get tighter (and that's all I've heard), its weird that the examples in the manual for replacing valve shims uses cases where the clearances have become looser (substantially).

Yep!!

The Honda shims are the ticket. That is what I used to get my valves back in line.

I started with a 1000 grit wet sanding paper on my sink and measured with a digital micrometer with a tolerance of 0.001mm. After sanding for some minutes I measured and there was almost nothing gone...

So I changed to 400 grit and have to grind for at least 15 minutes to get away 0.05 mm. The shims are very hard.

Johan: How do you know that the two sides of the valve shim remain parallel when you grind by hand? If the sides (faces) are not parallel then doesn't that concentrate load on a corner of the shim?

I just tried to make a firm pressure on the shim with my finger when I grinded them, and rotated the shim now and then. Of course ity might be a little unparallell but that must be some 1/1000 mm or less.

I got the tip from a man who had raced with cars for many many years.

GCannon and holyroller1, where are you getting these Honda shims that come in .025 degree incriments? The HotCams kit for the CRF450 is only in .05 degree incriments.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now