Had a set of 806's CNC milled to 60 cc, ran into some intake manifold fitment issues and had some concerns about piton to valve clearance. I finally got around to measuring it today and I have as little as 0.83" on the exhaust valve. I know minimum recommended clearance is 0.100 so what are my options? I was thinking about maybe going with a .075 Cometic head gasket but there is so much swirling around about early heads and compatibility with MLS gaskets. The heads were milled quite a bit but the notch is still present. Opinions please...

 

Just some thoughts:

1. The thicker gasket will widen the quench distance quite a bit. Not sure if you will be able to run timing required to maximize power. Best answered by someone who does tuning a lot, but likely not an optimum solution.

2. You could use an adjustable timing set and move the cam enough to open the exhaust clearance. Issues here are the timing chain will stretch some with time and may shift the clearance to a lower value. You may also lose a little power with the cam shifted.

3. You could swap out for a different cam, not sure what you are running. One with a less aggressive lobe might open up clearance to an acceptable value while maintaining the same duration you currently have. Conversely, you could also get a cam that starts closing the exhaust a bit earlier to attain the clearance.

4. You could go with different heads, something I assume you really don't want to do.

5. You could really stiffen up the valve train and run as is (a risk). Stiff pushrods (3/8) and good springs will help keep things in check.

 

you're only talking about .017 if you wanted, just touch the piston top where the valve would hit with a sanding drum. or just leave it as is. how high are you spinning the motor? auto or 6spd? cam? valve springs?

 

it is a 6 speed, small cam 222/228, PSI 1511 springs, street car probably won't spin higher than 6800. I really don't want to swap heads, I think I would replace pistons before I did that. I am short on time and not wanting to spend a bunch of money to get this thing running.

 

Ive been running 90/70 for ptv for several years with no issues.

 

I would just get an adjustable timing set and advance the cam a couple of degrees. Also get some good pushrods. Manton 11/32" if you don't want to open up the pushrod openings on the heads.