Valve Clearance Shim Grinding

I would like to grind a few thousandths off of the valve clearance shims in my bike to compensate for tight clearances. Does anyone know if these shims are through hardened or just case hardened?

 

I believe they are case hardened and cannot be ground down. Member Hogfiddles runs a shim pool and all you do is swap your shims for postage cost.

 

grinding shims is something you don't want to do

 

Polock..sounds like you have a shim to grind...lol...sorry...couldn't help it...must be the lunar eclipse or something...

 

The "system" is set up so that you SWAP OUT shims for thinner ones.

They come in .05mm incremental sizes, and the spec range is similar such that one size shim, and only one size shim, will put any given valve within spec. If you have say, an intake valve too tight at .10mm, then a one-size smaller shim puts you in spec at .15mm, and so on.

If you have tight valves, swap those to an appropriately thinner shim; in most cases it's only one size; sometimes two.

They are only case-hardened, and not very deep at all. We've had this discussion more than a few times since I've been a member of this forum; and about two or three years ago a member who is a metallurgist sliced one and posted an electron microscope photo that clearly showed how "thinly" they're hardened.

BAD idea. Get ahold of HogFiddles or XJ4Ever and get some shims. Don't risk blowing up your motor to save a couple $$.

 

Thank you all for the excellent advice. I'll have to look into that shim pool you mentioned.

 

And now, for the other side of the coin. Almost literally.
I have an XJ and 3 XS 1100's and I and a couple of other members of that forum grind the shims to achieve a more even clearance between valves (Each of us happens to have access to a surface grinder)
When the shims are manufactured, they are probably done in a batch mode, with the hardening process being a bath type heating process, (Cyanide salt or gas) which will penetrate all surfaces.
The reason for the hardening is to maintain a difference in hardness of more than 5 points Rockwell between the two rubbing surfaces, which will prevent galling. The harder surface becomes the sacrificial surface because of the lapping action of hard particles imbedding in the softer surface.
Which should prompt everyone to run clean oil.
Guess which surface is harder?
And easiest to replace?
So if the wear surface of the shim does not show wear, it is probably good for a few more miles.
But notice that the pressure of the valve spring is taken by a line of contact on the cam lobe, giving us a point load of "X" pounds per square inch on the surface of the shim and contact area of the lobe.
Obviously the pressure is not enough to displace the metal, or for that matter, to rupture the oil film between the two surfaces, since if it was, they would show signs of fretting, or scouring.
Now, lets look at the other side of the coin. (Shim)
We know that X amount of force per unit area is being applied to the top of the shim, and assuming the shim doesn't bend or flex, (don't grind then too thin), the same force is transferred to the contact surface between the shim and bucket. Since there is not any relative motion between the two surfaces, there can be no wear, and the forces applied cannot be high enough to swage the metal of either surface, since the line contact of the other side is spread out over the entire surface of the shim on this side. (If someone wants to do the math on that one, I'd bet that the ratio of areas is over 500 to 1. So 1000 psi on the cam side would be 2 psi on the under side)
So the trick of grinding is to grind the face of the shim that has the size printed on it, and contacts the bucket, and when done, use battery acid to etch the new thickness value on it, being sure to rinse and neutralize the acid before installation.
I measure clearance, take that shim out, grind, remark, and reinstall in the same bucket, just to keep every shim in it's original position. Figure that those two surfaces have been working well together for a long time, and there is no sense in breaking up a good team.
Another use for grinding shims is that you can adjust the timing of the valves, (trying to get them all the same), by selective thickness grinding on the shims. (That's for all the compulsive tuners)

Personally, I would rather keep the functioning set of surfaces together, rather than throw a different used surface in, (as in the case of a dealer shim swap) into the situation.
A new shim would probably not be a problem, but since those of us that use this method can get it done in a few hours, and not have to wait for shipping, new shims seem like a waste of time and money. And swapped shims are worse than what we have in there.
My advice is if you have access to a surface grinder, and know how to use it, go for it.
CZ

 

And now for the economics viewpoint. How much is your time and equipment worth? What more productive task can you accomplish in the time it takes to grind, clean, and remark one shim? Opportunity cost is always a factor. The only time when swapping out shims is not cheaper than grinding existing shims is when there are no replacments available (from any source). In that case grinding a shim becomes feasable because it involves less cost than making a new shim in a well equipped shop.

P.S. :roll:

 

Does that include time and gas down to the dealer?

:lol: CZ

 

Yes. I live in a small town. If I call ahead they'll even deliver for no fee.

 

dear Mr. Zap, horse feathers, you can't adjust valve timing with shims. [edit] never mind i read that wrong
just in round numbers a cheap surface grinder without tooling costs about the same as 300 shims.
do you make all your nut and bolts too?

 

I don't re-use shims; I just buy new ones.

 

I truly appreciate CaptonZap's descriptive reasoning for NOTswapping shims. Obviously a fellow that finds metallurgy and machining to be thrilling and fulfilling. Congratulations on having a passion in life that can be so very helpful.

However I agree with K-Moe :roll:
:lol:

 

Well, yes I have.
The exhaust nuts on an XS11 (XJ 11) have a hex (Allen) socket in them, and are rather short, and prone to abuse from PO's that don't know that there are metric and SAE hex wrench's, and they don't interchange. And if the wrong size is used on a recalcitrant (rusted) nut, the internal hex can become rounded, which can cause consternation and foul language.
So, some coupling nuts of the proper size, drilled out on one end to a size a few thousandths larger than the distance across the flats on the wrench, and a straight section of a hex wrench ground hollow on the end, using an arbor press for a broaching machine, all become the means to make nuts that can use the hex wrenches, or a regular box end.
Now by all rights, I cant say I made the nuts, but I definitely modified them, and I have made nuts for things other than motorcycles, so maybe that counts.
While I appreciate you folks that don't want to be bothered with the, you'll pardon the expression, nuts and bolts of obtaining parts for your bikes, know those of us that do will be more than happy to take your money for supplying parts that you could make yourself. 8)
Clutch and throttle cables come to mind. But you get the point.

And if you read my original missive, you will note that I said "have access to ", which does not imply that a grinder has to be bought to be used. I'm sorry that you don't have access to machine tools, because it opens up a broad array of possibilities, and outlets for creative endeavors in the motorcycle arena.

CZ

 

New shims cost less than $10.

I have access to machine tools, but I also buy OE clutch and throttle cables.

The exhaust nuts on most XJs have an internal hex that nobody knows is there; I just buy replacements when necessary. They're available, and cheap.

Clutch and throttle cables are a matter of opinion and choice; exhaust studs are an easy fix; but a shim failure of any sort can do an incredible amount of damage. Grinding shims is an old race-tuning trick; however race motors don't have the same expectancy as street motors. The only time I've ever personally seen the spectacular results of a spit shim was in a race motor where shim-grinding was being practiced.

So grind on.

Personally, I keep my 30-year old motor maintained with "store-bought" factory parts, so I don't have to give a second thought to running it to redline whenever the mood strikes.

And I still don't recommend grinding shims.

 

Yes, and do you know WHAT caused the "spit shim"?
Correlation is not causation.
Some one putting the shim wrong side up could be a cause. Or any other number of reasons.

And your buying new parts is your prerogative.
The original poster asked if the shims could be ground, and whether they were case or through hardened.
Either way, they can be ground. They could be ground if they were annealed. Would it be a good idea? :cry:
My answer was to show that with a little thought, and to know the circumstances that it would operate in, a shim could be ground without worry. Can someone, who isn't knowledgeable about the process, cause a lot of grief? Does a bear scat in the woods?
How many riders are competent riders? Do you tell the ones who aren't to not ride?
Or do you explain the whys and wherefores of the process, and let them make up their mind as to if they should do it or not?

It's nice that you keep the newbys on a safe course of action, and the parts supplyers appreciate it too. :lol:

CZ

 

Granted; it was a race motor and there are a myriad of possibilities.

There are also a long list of valid reasons that shim grinding isn't recommended nor rarely practiced.

I keep myself on a safe course of action; then share the experience.

 

keep up the good work Zap

 

"Faint heart ne'er won fair maid".

Bunglejyme, if you have the facilities, and the know how, my opinion is that you will get a closer match on clearances by grinding, and no decrease in longevity.
Shims jump .002 in, and I can get within .0005 inch consistently in less than 10 minutes per shim. Lets see, at $10 a shim, plus mail wait time or drive to the dealer time, that equates with a shop rate of $60 an hour. Yep, I'll work for that. :wink:

CZ

 

so at 60$/hr how much you think you have in those exhaust nuts?
did you ever make any tire valve caps?