machining valve shims ??

[RandyR]

Has anyone machined valve shims (or had machined) to a new (thinner) thickness? How about has anyone used shims that have been machined? Any thoughts on the matter?

 

I know that at least a couple of Triumph riders have had their 25mm valve shims machined which are the same shims used by our V4 Yamaha engines.

 

I see one valve & heads tool maker makes tools specifically for doing this ($500 tools).

 

What I'm thinking about is possibly buying some used automotive 25mm shims at a good price if machining them to usable sizes is possible.

 

This would also allow me to fabricate shims of sizes that aren't normally commercially available. (they are normally only available in .05mm increments).

 

Only one side of the shims would be machined and that side should be placed down in the bucket, allowing the cam to ride on a origonal side/surface.

 

Last thought. How much would/should a machine shop charge for this service?

[MiCarl]

I sell new shims (without the VentureRider discount) for $7.34. I can't imagine you could turn out remanufactured shims and be competitive.

 

The reason shims are only available on .05 increments is because the range on the spec is .04 so you can always be in spec with a standard shim.

[skydoc_17]

Hey Randy,

Because of the type of material the shims are made of, the preferred method to reduce the thickness of one of the 25MM bucket shims would be to Surface Grind them. The shims would be attached to a grinding machine with a magnetic chuck, and the grinding wheel would pass over the shims removing very small amounts off of the shim at a time. Because of the precision nature of a grinding machine, the shop time runs in the neighborhood of a buck a minute! ($60.00 per hour) Anything less than $60.00 per hour would be a "deal". Normally, I would have access to surface grinding equipment at work, but because of my injury, I don't have access to that equipment. I have ground shims in the past for my own bike with success, but to give you a perspective on how close the tolerance is on the 25MM bucket shims offered by Yamaha, they already come in increments of 1/2 the thickness of a human hair. (.05MM) To "kiss" a shim with a surface grinding machine and reduce the thickness say .025MM, would be reducing the thickness by 1/4 the thickness of a human hair, which would be "precision machining" to say the least. Micarl's offer of shims for $7.34 a piece is more than reasonable, unless you just happen to have a multi-thousand dollar surface grinding machine setting around and a extremely steady hand.

As always Randy, I like the way you think "outside the box", but in this case, the equipment needed and the skill level needed to operate this equipment makes the end result a bit "pricey".

I posted this information as an FYI, and not to discourage you from following through with this project.

Earl

[SaltyDog]

Last year on my '83 when I did the valve clearance adjustment, I had alot of the thicker shims left over when I had completed the measurement phase. I had bought a set of heads earlier for parts so I had alot of shims to swap out if needed. Since I work with some good machinists I got one of them to use the surface grinder to remove some material from the bottom (non-marked) side. I knew from my previous measurements what thickness I needed, so I ground the extra thicker shims to make them into "specials" to fit the appropriate valve buckets. I made up my valve clearance work sheet showing all the installed shim thickness and noted which ones were the "specials".

 

The shims appeared to have a thick hardened case but I made sure I put the freshly ground side down just to be safe and prevent wear on the cam lobes from the unpolished (surface ground) side of the shim.

 

With this method I got all my clearances into the middle of the adjustment range.

[RandyR]

lets say I have 100 of shims in the 2.80-3.50mm thicknesses I wanted thinned to 2.66mm +/- .02mm actually having .02 to .03 variation is ok as all of them would be mic'd for size afterwards.

 

I've also found that using a surface grinder is the most common way of doing this. followed up with a polish.

 

Here's a thread about doing it in a lathe & chuck.

 

Facing the parts to size was to be the more challenging task, since I had to face off .130 and only had about .160 to hold on to.

 

I did this work on a Hardinge HC chucker and discovered you can install the chuck over a collet in the spindle. I grabbed the previous mandrel in a collet and installed a bolt as a back stop for the shims. I used a bellville spring and a washer to back up the shim. I put a piece of brass in one of the round holders, gently chucked the shim against the backup washers, and pressed the brass against the shim while the spindle was turning. When done right I could hear and feel the runout approach zero, then I would stop the lathe, tighten the chuck, and recheck the runout. Here's the kicker, I used this procedure 8 times and I was never more than .002 different on gage depth of the shim after tightening the chuck.

 

I don't have any pics of this process, since I was busy making money, but this process is a simple, quick, and accurate for turning disc parts. These jobs are the type you can easily lose your butt on because it's not economical to turn step chucks and it can take a long time to chuck each part.

 

The secret to getting the part to chuck quickly is the bellville spring, it was sitting on a pilot on the end of the backup bolt, the purpose is to provide a gentle spring force to allow the shim to line up. It's a remarkably simple and repeatable way to chuck parts.

 

Also, discovering you could use a collet to hold a depth stop while the chuck is installed, was a pleasant surprise.

 

http://www.practicalmachinist.com/vb/general/clever-method-turning-valve-spring-shims-203589/

Edited December 3, 2010 by RandyR

[RandyR]

Having shims in additional sizes besides those in 0.05mm increments, such that one could put all the valves to the upper side of the clearance range would be useful and likely preclude ever having to do anything other than check on the valve clearance for quite a number of miles.

Edited December 3, 2010 by RandyR

[Kirby]

Years ago, when I first started work as a machinist, I worked on a job that required several thousand spacers such as this which had to be ground to within +or - .0002 inch. I would first part them all off in a lathe to within .005 inch and then put a couple hundred on a magnetic chuck for surface grinding. Afterwards I took only a couple of tenths of a thousandth at a time until I got them down to the right thickness. It was a tedious job to say the least. Every now and then the grinding wheel would spit several off the table. Having said all that and knowing what I know from working in a machine shop and tool and die shop, it's not very cost effective to do something like this. You'll be way ahead of the game to go ahead and purchase the shim set and be done with it!