How do you shim valves for new cam?

[mauiguy99]

Are there any mechanics out there who want to tell us how to shim the valves when installing a new cam? This will be some usefull info as the auto decompression mod is certanly going to be a hot one. Can a Garage mechanic attempt it? I'm not sure my local Yamaha mechanics have much experience either when it comes to 4 strokes.

[YZ250F_Rider]

Well I thought about this, and here's what I plan to do. It may or may not be the best approach.

1: I plan to initially put the new cam in with the lifters (buckets) only. No shims.

2: This should let me get an exact measurement of the actual gap.

3: From this I will subtract the minimum and the maximum allowable clearances. (gap-min) and (gap-max)

4: Then I will find the nearest shim that falls within these two values. I will most likely favor picking a shim that has more gap rather than one with less.

[av]

YZ250F_Rider - Your approach to find the proper shim(s) sounds reasonable...

I'm no mechanic, haven't ventured into my engine/header yet. When you get around to doing this job, can you take some pics for us/me and show exactly what is the shim(s) ? that need to be added? Thanks.

[YZ250F_Rider]

Yeh I'll have my kid take the pics, as I point and grunt. ?

I'll do a pic test run on the gapper's leaf's (right name?) that I cut to fit for measuring the min and max gaps on the bike. I have 2 each for the intake and exhaust, as long as the max dont fit and the min does (comfortably), it's within spec.

[mauiguy99]

Am I correct thinking that the measurement would be the valve clearance EX .17 -.22 mm? (from the 02 maintenance specs). Am I also correct that "valve shims" as we have been refering to them are called pads in the manual?

[mikeolichney]

I dont think that approach is going to work. I am not sure, but I think I remember the shim (or pad) fitting down into a recess in the valve. If so, this is going to throw your technique off because the valve bucket will now not ride on the same surface as the shim. (I could be wrong, but thats what I remember).

[neWRiver]

I think you are correct Mike. There is a raised "bump" on the underside of the bucket that actually rides on the adjustment pad (shim). This raised area on the bucket allows the pad to recede below the surrounding valve spring retainer, but if you look at the assembly, it is pretty obvious that it requires a pad in there (even a thin one) to give the bucket something to rest against. Without a pad, it appears that the bucket may ride on the spring retainer and this would not be the same as a "zero" sized pad (shim).

Try it with the pads you have (noting there sizes). As long as you have any gap at all on all of the buckets, you can figure out what shims you need. If you find any with no gap, this may throw off your gap measurements on the others. This may take a little trial and error with smaller shim sizes.

[mauiguy99]

Well I'm still a little confused. Do we agree that shimming the valves is the process of finding the right size pads to place between the valve stem and the lifter?

Is adjusting valve clearance the same as shimming the valves?

[neWRiver]

Is adjusting valve clearance the same as shimming the valves?

"Shimming" the valves is the act of changing out the adjustment pads (shims). The reason you change the adjustment pads is to adjust the valve clearance into the spec range. Valve clearance is the distance between the valve bucket and the cam when not being depressed by the cam lobe (i.e., the valve is sitting closed). There is a very close tolerance on what that gap should be.

[YZ250F_Rider]

yep, I think you guys are right. It doesnt look like I can do it without using pads.

So here's another thought.

I mentioned before that the cam from the 03 was within spec when I put it into the 02. That in itself tells me that the cams are tight tolerance parts. I.E. most if not all cams should be very close to being right. The shims are not being used to compensate for slop in the cam but probably the head (most probable), valve stem length or bucket thickness. All of which stay the same from one cam to the next.

I mean the chances of the cams being ground to tight repeatable tolerances are much higher than my chances of finding the one loose tolerance cam that managed to fit.

Did that make sense? ?

[mauiguy99]

I agree with you 250F rider. It makes sense that the variables will be in the head or valve stem length, not the cam. Did you mesure the valve clearance when you put the 03 cam in your older bike?

[neWRiver]

I could be wrong, but I think it has more to do with the service life of the valves. Over time stress and wear on the valves and valve seats will necessitate some means to adjust the valves back to those tight tolerances. I would guess that there is less of a variance in shim sizes used off of the manufacturing line than you might find when comparing bikes at various stages of their expected service life.

[Crazythumpin]

Here is the big question? Why are you replacing the cam? If there was nothing else replaced or damaged other than the cam, then the measurement between the lobes and the lifter caps should be almost the same with the new cam. The reason I say almost is because the new cam's lobe clearance from the caps will be a little tighter compared to the used cam.

Are you putting an 03 cam in?

If this is what you are doing, then keep the valve adjustment pills that you were running. Go down to the local automotive parts store and pick up some plasti guage.

Set the recommended amount of plasti guage on each cam journal including the main bearing. Set the cam in the head with the marks at Top Dead Center. As you torque the cap down use a feeler guage that has your minimum clearance. What you want to check for is to make sure that your cam lobes clear your lifter caps. If you run out of clearance when you torque down the cap it will not only throw off your measurements with the plasti guage but it will also tell you that you need to go to a smaller valve adjusting pill. If this happens then you will have to stop and pick up the pills before going any farther. From my experience if you can't get a feeler guage under there at all, then you are looking at atleast two to three sizes smaller. If your clearance is larger (maximum) or slightly under the minimum then you will have to find the adjustment pill thats necessary. When I adjust my valves I like to keep the clearance around maximum .22mm for the Exhaust on a 02. This allows for wear and heat expansion.

If the clearance is not tight like I had mentioned above, then you will know what valve adjustments need to be made using the feeler guage(maybe none if lucky), and now you can take the cap back off to measure the plasti guage and compare your measurements to the specs in your service manual. Hopefully they are within specs. If they are not then you will not be able to use an 03 cam (which is what I think you are trying to do).

Just remember this, make sure when you torque the cap down that it is done in two stages and that you use a accurate torque wrench. Also torque the cap in a criss cross pattern. Make sure you Seat the cap flush by hand before you tighten anything, if you can't get it to seat then the cam is not set on the bearing surface, you may need to rock the cap side to side a little bit or try fitting the cam to the cap first and then fitting it into the head(prefered). If you don't follow this to a T then you will surely bend the cap and destroy your top end if you run the motor. DON'T FORCE ANYTHING. That is my best warning.

I hope this helps you out and gives you an idea what is involved. I'm a little tired from writing all of this so there might be some things that I left out. If you need anymore info let me know.

Good Luck!!!!!

Oh I forgot to tell you, pick up some assembly lube. Don't use it when you are taking any measurements, you want everything to be clean for accuracy. You would be amazed how much a slight film of oil will throw off your measurements. When you are ready to throw everything together for good, then coat the parts with the slippery stuff.

[mauiguy99]

excellent post, thankyou. That answered my questions to a T

[YZ250F_Rider]

newriver, I suspect the reason the shims are stamped as to what size they are, is because each one is measured to find out.

[YZ250F_Rider]

mauiguy, the 03 cam was within spec. I only measured for the two extremes though (min, max). I did not check to see what the actual gap was.

[Crazythumpin]

good deal!!! Glad I could help.

Since I have been on Thumper talk, I have been quit surprised as to how few members actually know how to work on their top end.

Believe it or not it is actually very simple once you have done the routine once or twice.

The thing you have to remember is that the clearances between the cam's and their caps is very tight. Absolutely no room for error.

How do I know this?

I learned the hard way by bending a cap, and then running the motor. Very, very expensive!!!!!!!!!!

Lucky for you the exhaust cap is alot harder to mess up than the intake when you install it.

The reason I recommend that you check the clearance between the cam journals and the head∩ is because other than the main roller bearing the other bearings are nothing but polished aluminum. Bad design if you ask me.

I believe the reason that yamaha did that is because if they had put moly bearings in there you would probably find yourself spinning a bearing everytime you spun the motor at 13,500rpm or so I believe. But if Indy cars can do it, why can't yamaha?

Thats just my 2 cents.

Anyway goodluck, if you run into any problems give a shout.

[YZ250F_Rider]

Well one thing is for sure. Yamaha will be able to congratulate themselves when this is all over. They will have single handidly created the worlds highest quantity of Yamaha valve clearance mechanics. LOL ?