400 head gasket mod....

[AAAltered]

What exactly does it take to run 400 copper in a 350?  What's the advantage?

[SUPERTUNE]

I machine the decks of the cylinders to 4.030 inch. (cutting out the step)
Then do a squish check and machine the heads as needed for squish clearance, calculate squish ratio and machine as needed, then cc heads pre-assembled to figure final compression ratio for the fuel your going to run.
Not real hard to do,  but does take an involved process when you setup all the right parameters.
You can grind off the locator nub off the 400 head gasket or just install them upside down as the engine won't care.
Chuck 

[Yamaha 179]

I've been running RDs since they were modern bikes; 250s, 350s, and 400s.  Raced the 350s in the early days and we machined the heads to set the squish and compression and ran the standard head gaskets.  I, and the guys I raced with never had a problem with the OEM head gaskets leaking but we were careful with annealing the gaskets and torquing them when installing the heads.  Our current racing 250s have both types of head gaskets; one OEM 250/350 style and the other the 400 style.  I think for racing the 400 style is better because you don't have the potential for bending or warping the cylinder head if you make a mistake when you are in a hurry and Chuck does a good job of making that mod.  I don't think it is necessary for normal street use, but it wouldn't hurt anything and getting the squish and compression right is a big improvement in engine life.
Lyn Garland

[AAAltered]

Thanks guys.  Exactly the members I hoped would chime in.

My heads were done long ago, and I don't want to remove my barrels and send them out at this point.   After seeing the current state of my heads, gaskets, and crowns I think I'll just anneal and reuse my 350 coppers.  It is after all a street bike.

Best
Ed

The photos below are exactly how I found the top end.  No cleaning or anything yet..

[teazer]

People seem to think that more torque helps to seal the head but the opposite is true when you goo much higher than stock.  The head warps (bows) and never seals as well.

A 400 style wide gasket makes for a better seal because the head is less likely to bow.