Cylinder Head Gurus-Question?
 

I am in the process of setting up a pair of aluminum cylinder heads. I am installing COMP#929 springs which measure 1.540" dia. [FYI: the springs that I am replacing measure 1.510"] The spring pockets, best I can measure, are right at 1.540" dia., about the same as the COMP springs. Question is: How much clearance is required between the the spring and the spring pocket wall? With a spring shim in, the COMP springs will rotate with relative ease. Should I have the pocket diameter reamed out some more? How much clearance is required?
Also, on the same subject; what is optimum valve to guide clearance for intake and exhaust valves? The motor is a N/A, raw water cooled. Exhaust valves are Manley Inconels, intakes are HD ss. As I said before, the heads are aluminum and have bronze guides.
Thanks in advance for any and all help, Dave.

Well, I'm no cylinderhead "guru", but maybe I can help. Your spring pockets are probably not cut @ 1.54"...more than likely, they are cut at a more conventional 1.55"...this explains why you say the spring rotates with "relative ease". This clearance may seem a little tight, but remember, the spring pocket is also locating the bottom of the spring and as long as it can still rotate, I think you'll be just fine. Anice touch in your case would be to lightly chamfer the top of the spring pocket...where the sharp machined edge is present....this will keep the valve spring from doing it for you and giving you a little more control of the metal flowing through your engine.........As far as valve to guide clearance, you won't have any problems if if you are at .0025" on the intakes and .003" on the exhaust, BUT if you get much bigger than this you are too loose....at .0015 on the intake and .002" on the exhaust you are a little on the tight side for a marine motor...so, I would use those figures as your bare minimum. I hope a real expert will jump in on this and give his opinion, but many REAL experts dont get on a public forum and air their trade secrets. Good luck and have fun.