Grinding shims??

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Geezer

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As I am now being happely busy  :(  with checking and adjusting the valve clearance of my 3C I wondered if you cab grind the shims?? Five of my shims I have are too large, so tell me please.
 
You can use the flat side of a high quality VERY FINE grade stone wheel on a bench grinder if you have access to one. Have a bowl of water handy to keep things cool, rotate the shims, don't push hard let it take its time. and measure them regularly with your micrometer. Don't let them drop in under the guard if it is on the grinder. Only do it if it is a few points of a mm to take off and check that the overall thickness is over the minimum shim recommended (isn't that about 1,8mm?). It is best to use un-ground shims but reality doesn't always allow it.
 
Geezer

If you have access to a wet surface grinder it's easy. If you don't, an oil stone works but keeping the stone flat is always problematic. I have used a thick sheet of glass and sheets of wet/dry sandpaper. This allows a nice figure 8 grinding pattern to keep the shim flat, you can start with a coarse grit to take metal off quickly then switch to finer grits to get a nice polished finish, and it's cheap. Do it wet.

You can avoid sanding your fingertips off by holding the shim with a wooden dowel. What you can't be sure about is that the top and bottom surfaces of the shim will end up parallel. Exactly what will happen with a shim that's tighter on one side than the other is hard to predict. In fact, since it's very hard to measure parallelism with a 7mm ID shim we don't even know how good commercial ones are (I guess you could use a flat surface and a dial gauge with a sharp pointer). But I only grind shims today if I have to. I'd rather just put the next size known good shim in and have a valve a bit loose and a bit noisy rather than risk a cracked shim or a bent or dropped valve.

The Laverda engineers almost always showed good sense in their designs. I was always frustrated that the difference from one shim size to the next was more than the normal clearance range, but I feel that the reason was that owners were supposed to go up/down to the next size rather than trying for perfect clearance setting.

Others may disagree. There's been debate on this in the past, search the archives.

Ken
 
Within the topic: Last time I bought few shims, they appeared to be little spacious sideways. What is the right inner diameter of triple shims?

Cheers,
-Sami
 
Okay, I'll give you a reference value: Inner diameter on my new shims is about 7,6 mm. I didn't measure what it is in the original ones, less anyway. I ended up grinding the old shims and now they are back in the engine, so I'm not able to measure them anymore (not now anyway). So, I would like to know the appropriate inner diameter in case I end up buying some more?

-Sami
 
Valve stem size is nominally 7mm - 7.6 id on the shims is pretty sloppy but where are they going to go ?

I make them from 10mm silver steel and use a 7mm drill reground to a flat end to cut the recess.
 
GregT said:
Valve stem size is nominally 7mm - 7.6 id on the shims is pretty sloppy
Click to expand...

No wonder they felt a bit loose. I bought them from uk for my Jota and now they're waste. I should have given some feedback for M?lia. Well, next time I'll have to check the dimensions in advance, just to make sure?
 
On grinding the shims... If you use the side of a grinding wheel then use a center punch to hold the shim. There should (on an actual Laverda shim at least) be a small indent in the center of the pocket. If you use the center punch in this hole to hold the shim it will allow the shim to stay flat on the grinding wheel and also to turn as you grind. Keeps the face flat and even. Also makes it easy to loose the shim when it flies off so be careful!
 
I  prefer to grind them inside.... If you are proud owner of piller drill  and a dremmel stockist nearby ... You are SORTED..Just a spot of WD40 away you go !

                Timbo
 
I've found that when grinding shims, any kind of powered grinder is way too aggressive. It's too easy to take off more metal than you want to in a fraction of a second. Doing it by hand on an oilstone is much more controllable and can take off thickness quickly enough. The other problem with bench grinders is that most of them aren't flat. If you've been sharpening drill bits on them, they tend to have grooves worn in the wheel that will produce a non-flat top on your shim. Even if your shim is spinning on the point of a centre punch, the best you can hope for is a domed top. A domed shim will have a point contact on the underside of the cam bucket, which is a stress concentrator and may lead to a cracked shim.

Using a nice flat oilstone (or wet/dry emery cloth on a flat surface), rotating the shim in your fingers ever few seconds, and rubbing in a figure-8 pattern will give you a better flat surface as you're likely to get with any other method.

I made up a mandrel to hold the shim in the lathe chuck, and tried taking very fine cuts with a tungsten tool. It worked OK but I had to finish them by polishing on the oilstone anyway, so I only use the lathe if I have a lot of metal to take off.

Cheers,
Cam
 
Agree with Cam, re grinder. Shouldn't need to take much more than .05 off in reality. I use a diamond stone with WD40/CRC rotating the shim between my fingers every few figure of 8 strokes.
After 26 years of triple ownership I've accumulated a few shims so I always have one that's pretty damn close, a few licks on the stone and my tollerances are bang on. :)
 
Hi Geezer,
I am with Cam and Rob on the take it easy approach as the amount to remove is so little.
A flat oil stone is a rare item in my workshop so I have always used a piece of window glass with wet or dry sandpaper lubricated with kerosene. If you use the tip of your finger and a figure of 8 motion, it will be flat. I use some course and fine grades of paper it that order.
Hope that helps.
Cheers
Russ
 
I  prefer to grind them inside.... If you are proud owner of piller drill  and a dremmel stockist nearby ... You are SORTED..Just a spot of WD40 away you go !
Click to expand...

Not actually a bad idea when you know of some shims that are so badly made (by a British Laverda 'specialist') that they have a 'pip' on the inside... :o
 
So you have to re-shim them again then?
How long does it take for them to flatten?
 
The best shim hammering I've seen was back when we had a Superbike round in NZ.
Good rider and nice guy, Stu Murdoch - since killed in the IOM - had an OW01 with the early race kit valves in it. The ones which were rubber and stretched....Anyway the WSB meeting turned into an ordeal for him and his mate - reshimming daily.
Of course they didn't have the shims did they ? So grinding of the ones they had was required.
I could only admire the method..hammer them into the (new) Oregon bench top in their pit and use a disc grinder...much smoke and colourful language.
Various visiting riders looked on in disbelief - i remember Joey Dunlop's brother and several others making comments....
When the meeting was over - and he finished both races too - more cunning work - remove the bench top and turn it over to disguise the damage.
 
I solved the problem early on after waiting eternities for  Rickey Racer to mail spares during the racing season.  I got weekend time on a screw machine and produced a coffee can  full of shims.  I made them in thickness increments of .001" (I was a Triumph mechanic, didn't have a M&M micrometer.)  Then off to the heat treat place for tuftriding.  $25  later I had a proper assortment.
 
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