TC Valve Protrusion

[lotusgagne]

Greetings all. The valve seat inserts have to be replaced in my TC cylinder head. In order to properly cut the seats, my friendly machinist is asking what should be the protrusion of the valves, i.e. the distance from the bottom of the valve spring well into the cylinder head to the tip of the valve stem, when the valve is fully seated. As my machinist is trying to fix the blunder of a previous machinist, he does not have a starting point. So is there a standard valve protrusion, and if so, is it the same for both inlet and exhaust?

I have a feeling that this may be a function of the head, camshaft etc. and that the only way is to go at it by trial and error and that taking measures from another head may not even be a good starting point. Any advice?

Claude

[2cams70]

When I had my head rebuilt I asked the parts supplier what thickness of valve shim I should aim for to get the correct valve clearances. They advised 0.100 to 0.110" so I bought a couple of shims in that thickness and gave them to the machinist so that he could aim for achieving the correct valve clearances by using those shims. They cut the seats accordingly.

My parts were all new however. If the valve stem lengths are non standard you will need to check for coil bind too.
Rohan is probably the best guy to help with this question however!

[rgh0]

Assuming you are building a standard big valve specification engine and the head has not been excessively shaved and your valve train components are all standard the key dimensions are as contained in the attached file.

Big valve std dimensions.pdf

(23.19 KiB) Downloaded 481 times

If you have modifications to any of the standard components e.g a reground cam with smaller base circle or the head is heavily machined then you may need to play with the standard setup to get the acceptable spring loads and shim thickness and valve position.

If the engine is using original standard or s/e specification cams then the cam base circle is slightly larger at 1.20 inches reducing the shim thickness or requiring the valve to set slightly differently.

If your building a modified engine with a high lift cam for example then you need to think carefully through the required changes.

It is rare that a head can be built to totally standard dimensions but this gives you a good starting point.

cheers
Rohan

[lotusgagne]

Many thanks guys, this is exactly what I was looking for. Indeed, I should have mentioned that I am building a standard engine for road use, so this will give a good starting point for my machinist. Cheers!

Claude