Poor Man's Valve Shim Idea

The clearance on one of my 1981 XJ650 exhaust valves is .005" out of spec on the plus side (.013"). I don't want to go through the trouble of trying to find a shim to fix this so I have an idea that I am entertaining. McMaster Carr sells precision round shims which come in various thicknesses from .001" up. I believe the diameter on Yamaha valve shims is 29mm. If so, then the 1-1/8" OD shims that McMaster Carr sells should fit the shim bucket counterbore. 29mm = 1.142" and 1-1/8" = 1.125" ; therefore, the McMaster Carr shims would be .017" smaller in diameter. The McMaster Carr part number I am looking at is 3088A124. To bring my valve clearance back into spec I could add either five .001" shims or a single .005" thick shim under the valve shim. The thin shims would be captured within the shim bucket under the valve shim so there's no chance of them migrating out. Personally, I cannot think of any logical reason why this wouldn't work; however, there might be something I am missing. Please offer your feedback.

 

This is a horribly bad idea. Stacking shims will bring you plenty of trouble (all shims have a tolerance and stacking them increases the rate of error) and without a real 29mm OD shim you will spit a shim out of the bucket (the shims are a tight fit, your proposal will create a loose fit).

Get the correct shims.

 

i don't know if it would work on your bike but i do know it will never work on mine.
why don't you just go buy a shim, their not like chicken lips or anything

 

Here is something you can try. Call your local metric bike dealer. Ask if they take shims for trade. Normally you would ask the service department and not the parts counter. They may agree to trade you for your old shim with maybe charge a couple of bucks for the exchange. I did this and they didn't charge me anything at all. For shims in total. Granted, they gave me Suzuki shims by mistake the first time (29.5mm). So goood idea to take a digital caliper with to measure before leaving the shop. Yamaha, Kawasaki and BMW take 29mm shims. To be honest, the guy told me they don't even use this size on the new bikes anymore and were thinking about getting rid of them. Nothing to lose by making a couple of calls.

 

I have a supply of shims that I be willing to swap for you. Heck I will go the extra mile for you, tell me what size shims you have for each valve, and tell me what your clearances are. Then I will calculate what size shims you need for each valve, and if I have the proper size, I will trade you shims. Just cover my shipping.

 

Members here run a shim pool... If you asked them nicely enough...
(I don't mean to imply myself, it's another member!)

 

or take a look at this:
http://www.ebay.com/itm/Yamaha-750-...141-/151625433404?hash=item234d94813c&vxp=mtr
or this:
http://www.ebay.com/itm/VALVE-SHIMS...amaha|Model:XJ750&hash=item20f59b07a3&vxp=mtr
Not too expensive to start your own collection!

 

Did you ask him to call you when they throw them in the dumpster?

 

If your exhaust clearance is .13mm, the you're out if spec in the - side by quite a bit. Your exhaust clearance in- spec range is .16-.20mm

You have some choices

1. Get the right shim

2. Try do do it your way, and the when you spit out the shim and break stuff all over, you get a new head or even a new engine

 

Did you check with your local Yamaha dealer? My local shop trades shims for free.