Jump to content
Sign in to follow this  

how to clay test

Recommended Posts

where can i find some general info on the details of how to perform a clay test on a 2002 xr650r?

Share this post


Link to post
Share on other sites

It's not a very complicated process. Put strips of modeling clay ~1/4" thick over the piston's valve reliefs, assemble the top end enough to turn the crank and cam, disassemble again, and then measure how thick the squished areas of clay are. Use the old head gasket for this process.

Similar principle as this:

http://www.carcraft.com/howto/116_0701_valve_to_piston_clearance/index.html

Share this post


Link to post
Share on other sites

just to make sure that i understand...

say i put a 1/4 inch (4/16 for math) strip of clay on the piston and after the test, there is an indention of 1/16 of an inch. this would tell me that i have 3/16 of clearence before i have piston/valve contact?

if i already have piston/ valve contact, then the clay test doesnt do much good huh?

Share this post


Link to post
Share on other sites
just to make sure that i understand...

1.) say i put a 1/4 inch (4/16 for math) strip of clay on the piston and after the test, there is an indention of 1/16 of an inch. this would tell me that i have 3/16 of clearence before i have piston/valve contact?

2.) if i already have piston/ valve contact, then the clay test doesnt do much good huh?

1.) Only if you could somehow guarantee that the clay was an exact and known thickness before the impression was made. It is much more accurate and straightforward to cut the clay and measure the thinest part of the indentation.

2.) Even if the piston is hitting the valves, a clay test will tell you if the valve relieve is either too shallow or if the valve diameter is larger than the relief.

Share this post


Link to post
Share on other sites

After you do the test there should be at least .060" of clay between the piston and where the valve hit. You messure the clay on the piston after the test.

Share this post


Link to post
Share on other sites

is there any danger in having too much clearance?

im putting an 11:1 piston in with a stage2 hotcam. (this combo causes pist/valve contact, but neither one by itself does)

what i figure ill do is, whatever the difference in lift between the stock cam and the stage 2, that's how much ill tell the machine shop to cut out of the valve releifs, and that should be safe, correct ?

and after that is done, then i will clay test just to reassure that i have atleast 0.06 inches clearance

sound good?

Share this post


Link to post
Share on other sites

Depending on how much the valves are hitting the piston I would have them cut about .070" or so. If the valve just is hitting the piston then you would need .060" more clearance at that point. Then I would round the sharp edge of the valve relief cut. The smoother the less chance of pinging on 91 octane.

Share this post


Link to post
Share on other sites

And just because you cut the piston and the valve clears at the 0 mile mark will it still clear at the 10K mile mark when the cam chain has worn in/stretched?

Share this post


Link to post
Share on other sites

The clay test could be done with the cam where you want it and retarded ~6° from there to see how the clearance checks out.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×