Sanding/Filing valve shims

[thehackmechanic]

Is sanding/filing valve shims a complete no-no? I just completed my first post-rebuild valve adjustment of my TCS, and one exhaust valve is too tight. I hate to wait the four days it took to get the last set. I've read contradictory things about carefully taking a thousandth off a shim by lapping it on a sharpening stone or emery paper. Thoughts?

[jbcollier]

By god the bleeding finger tips I’ve had from lapping down Jag shims!

You need a smooth, flat surface, fine sand or emory paper and finger tips of steel.  I use an elliptical motion, release and rotate the shim often.  Go slow.  Check it often, especially that it is staying true.

[jbcollier]

How much do you have to remove?

[thehackmechanic]

1 to 1.5 thousandths.

[TurboFource]

If they are hardened I would think having done heat treating, it has more than .0015" depth of hardness!

[jbcollier]

That little?

No problem.

[EuropaTC]

Personally I won't do it, but I have done so in the past.  I don't know if the shims are case or through hardened so I've no idea of the safe limit but I'd expect a thou' to be ok.  I wouldn't take 5 thou off, mostly because of the time involved !

But if needs must.....     use double sided tape to stick the shim to a rubber bung or something similar which you can grip easily. If you have a lathe you could easily turn something up with a shim-sized recess which would make gripping it even easier. 

I used a sheet of glass with wet/dry emery paper on top, that used to be the standard method in the olden days for preparing metallographic samples and ensuring they stay flat. As John says, rotate every few passes to keep as flat as possible. If you manage to keep it flat then I'd put that surface against the bucket rather than the valve head - larger load surface.

Brian

[4129R]

You need to grow your finger nails, put the shim between thumb and next two fingers, and use a circular motion on emery paper while listening to music on the radio.

It takes a while, but it works.

You may also get flat spots on your finger nails. 

[thehackmechanic]

Thanks everyone. All done.

[TurboFource]

Just put the sanded side away from the source of wear....

[jbcollier]

It’s the same with Ducati Desmo heads.  Shims came in 0.10mm increments, specs required 0.05mm.  Sand and curse.

My boss used to make me adjust Jag heads from an assortment of shims he had gathered over the years.  Lots of holes in the range to say the least.  Most I ever took off was 0.015”.  That took forever.  No finger prints left.  Eventually he bought a complete selection and suddenly I didn’t end up doing all the valve adjusts anymore ;-)

The important thing is to constantly change the shim’s orientation so it doesn’t go pear shaped.  Also watch your technique so you don’t “rock” the shim and take more off the edges than the middle.

Also a good suggestion to put the self-machined side against the bucket if you have taken a lot off.  No need for a paltry 0.0015”.

You do need an actual micrometer.  Callipers will not accurately measure uneven surfaces, especially where the valve stem wears a depression.

[magno_grail]

Put them on the surface grinder. The magnetic chuck will hold them.