my slant buildup

volaredon said

I do have a question now that I have enough stuff here to actually finish assembly...
When I get to setting the valves, Oregon Cams had a tighter spec than OE. It's still a factory /6, just a freshly rebuilt one. Thermal warming and cooling should be the same as stock, maybe a bit more "heating" with the block + head shave to bump CR. My cam is still the stock cam it left the factory with, just reground. How come the lash wouldn't still be as listed "stock"? Not looking at the cam specs right this second, but I do know they list "desired lash" the same, on both intake/exhaust. I believe the number is 12-thou. Again w/o having that sheet right in front of me. using all stock/OE original pushrods and rocker assemblies.
How/why are they spec'ing a tighter lash on the exhaust? I would think that I'd want to keep that as-factory-stock. Why wouldn't I?

Click to expand...

Valve lash setting specifications for mechanical cams can vary a lot depending upon the initial ramp that is ground into the cam as part of the lobe shape. I would go with what is on the cam card. Remember the valve lash that is set into the valve train is really lost valve motion. The grind that you put on the cam is probably more of a performance grind than the OE grind is. So the performance grind is all about getting the valve open sooner and keeping it open longer. A tighter lash helps with that. Bottom line is the valves in the engine will have higher opening acceleration and closing de acceleration rates compared to the stock valves. But motor oils are also much better today than they were in the 70’s so you won’t have all that sludge built up around the rocker chamber.
Question, have you worked out the valve spring height and closed and open valve spring pressures? And did you go with positive or umbrella valve seals?