"How-To" sand down valve shims
Posted May 11, 2006 - 08:59 PM
The bike has the same shim-under bucket design of our bikes but uses 7.48 shims rather than our big 9's. We just set a sheet of wet 400-grit on a flat piece of metal and sanded away. They are really hard and it takes about 5 minutes of intense sanding to get them down a few hundredths. This allowed us to get the clearances right in the middle of the range, which the factory .05-incriment shims prevented. We've only got a couple rides on the bike, but so far it is working flawlessly.
I'm going to save myself some money and do the same on my WR this weekend, since both my exhaust valves are .01 tight. Does anyone see any problems with this? I'd love to hear from anyone else who's done it.
Posted May 11, 2006 - 09:02 PM
Posted May 11, 2006 - 09:18 PM
Does anyone know how perfect they need to be? Our digital caliper said the were the same at all edges. My technique was to sand side to side one way for 10 seconds, rotate the shim 90 degrees and repeat until it was to the right thickness. This seemed to have kept it fairly even.
Posted May 11, 2006 - 09:31 PM
Does anyone know how perfect they need to be?
They need to be pretty much dead on. I'm pretty sure when the engineers designed these motors, the valve clearances were spec'ed out with the requirements that the shims be perfectly uniform across the top and bottom faces.
Posted May 11, 2006 - 10:40 PM
This allowed us to get the clearances right in the middle of the range, which the factory .05-incriment shims prevented.
FYI, The shims for the Honda CRF450 are identical to the Yamaha ones, and here in Australia, they are half the price as well. Also, which was more important to me, was that the Honda shims can be bought in increments of .025 mm, which allows you a bit more flexibility, when trying to get the clearances matched or in the middle of the range.
Posted May 12, 2006 - 02:00 AM
Posted May 12, 2006 - 10:08 AM
Posted May 12, 2006 - 04:20 PM
The only right way to change thickness is to surface grind them, and allway put the resurface side down.
I wouldnt recommend grinding them as that would create heat and cause the metal to loose its temper.
What you did sounds perfect. Although I have heard that a fiquer 8 pattern keeps things flatter, but who knows. You mic'ed them and they are uniform and now the right tolerance. Good job, and thanks for the tip
Posted May 12, 2006 - 05:28 PM
Posted May 12, 2006 - 07:24 PM
As far as this being too labor intensive, it takes about 8 minutes per shim if they're only a few hundredths tight. I'll have it done in less time than it would take me to run into town to buy new shims, not to mention saving a few bucks.
Does anyone who's done this have a long term report?
Posted May 12, 2006 - 08:20 PM
there was ALSO A problem with the grinding of the shims. When taking apart the motor, we realized that the valve shim buckets had aggresive swirl marks in them. This leads me to believe that the grinding of the shims that we did, is not exactly flat...causing the buckets to sit off kilter, and spin when the cam lobes contact them. All the shims were replaced with brand new Hotcam brand shims. I purchased the whole shim kit for around 60.
Posted May 14, 2006 - 01:22 PM
I HAVE DONE THIS WITH A NEW DIAMOND FLAT HONE, AND A DIGITAL MICROMETER. YOU CANNOT ACHIECE UNIFORM THICKNESS!!!![/COLOR]
My friend and i had THOUGHT we had achieved a good result, but checking the work a few weeks after, showed HEAVY swirl marks on the buckets! This means that the shimmed bucked was NOT sitting flush, and the pressure of the rotating cam lobes was causing the buckets to SPIN when the engine was running.
Spend the 60 bucks or so, and buy a hotcams shim kit. Then you never have to worry about not having the right shim when you need it.
Posted May 15, 2006 - 07:07 PM