Your inputs on grinding or honing valve shims.

Hello, I would like to hear your experiences and inputs regarding grinding or honing valve shims. I have constantly seen warnings not to grind the shims that they may shatter. I have been in metal working for quite some time,and the dangers I could see is overheating the shims while grinding causing microcracks that could shatter the part,and the shims might have been in use for quite some time and by grinding it to serviceable dimensions ,extending its useful life beyond what it was designed for. It seems the shims were tempered for toughness and its surface is not too hard. Honing it even by hand wouldn't be too difficult. Would appreciate your opinion on this matter, guys.

The surface on the shim is very hard, I assume due to heat treating.
Usually heat treat affects the surface of the part, and the metal under the surface is softer. Don't know how thick the heat treated surface is, depends on the method. So grinding off the hard surface could produce a shim with a soft surface, and it will quickly wear.
Also, grinding will heat up the part. If it gets too hot for too long, then the part will become annealed, and this will reduce the hardness.

WARNING! Contrary opinion follows!

The shims are case hardened.

Who knows how deep the treatment might go. I don't see a problem grinding if you've got a good feel with the grinder and plan to inspect regularly for excessive wear. A machinist friend ground shims for his CB750. His plan is to examine for excessive wear at regular clearance check interval.

I've bought a some extras on ebay. Every once in a while a set turns up cheap. Less work and I'm not in a hurry.

-Duck

I don't know for sure that the shims are case hardened, but it does seem reasonable, one of these days I'll check and see if they are.

If they really are case hardened, then you could use Kasenit to case harden them when you are done.

But I think buying replacement shims may be cheaper, and without a doubt easier

steell wrote:

...If they really are case hardened, then you could use Kasenit to case harden them when you are done....

Am constantly amazed at all the diy info on this forum.

Post edited by: Patton, at: 2007/02/08 20:07

I sanded one down by hand. I measured along the way.
It definitely sanded down much faster after the first 20 minutes or so. I don't remember the exact numbers, but the difference was very noticeable. It came out very nice, but I never installed it because of the softness on the inside. (Nothing like an hour of sanding practice. )

Some claim to have used them after grinding, but why take a chance on destruction to save a couple bucks?

Replacement shims only cost a couple bucks... see www.z1enterprises.com for replacements. Why bother or take the chance one will fracture. You can certainly do what you want but I have SEEN the results of a fractured shim that had been ground and it destroyed the engine's top end.

Here's a picture of a shim that was ground and put in 'soft' side up...

The shim says 2.65 on the back - the center measures under 2.00mm now...

Post edited by: Jeff.Saunders, at: 2007/02/09 13:26

as has been stated, dont do it
The way the shims are made is, they are first machined to a rough state,almost to size, then they go thru a hardening process, a final grind is done to ensure flatness and thickness.
seems like a lot of work for just a shim

Thank you very much for sharing your opinions.