858 head rework

[Michael H.]

Re: 858 head rework

Clem,

What is the best angle for the back cut on the valves? Is that done on both the intake and the exhaust valves?

Joe

Pretty sure it was/is a 20* cut off the back side. I'll look in the book.

Remove material on the back side of the valve so the width of the 45* cut on the valve matches the width of the seat in the head.

......Found the instructions from the boys in the back room at GM.

[Joe C.]

Re: 858 head rework

This guy is one of the best:

http://castheads.com/acid_porting.php

[Michael H.]

Re: 858 head rework

This guy is one of the best:

http://castheads.com/acid_porting.php

One of the worst things for HP that can happen to an old 60's big port big block head used on the street is "enlarging the intake ports". Makes a bad design even worse.

[Joe C.]

Re: 858 head rework

One of the worst things for HP that can happen to an old 60's big port big block head used on the street is "enlarging the intake ports". Makes a bad design even worse.

Michael,

I didn't say that the intake ports should be enlarged. I do say that these folks are one of the best porters of old fashioned cast iron heads. Their website stresses SBC Chevy heads, but I believe that they are among the best with BBC heads as well.

Strike the above website, and add this instead.................I only wanted a link to Brzezinski, and the "acid porting" page came up instead:

http://castheads.com/index.php

[Duke W.]

Re: 858 head rework

Pretty sure it was/is a 20* cut off the back side. I'll look in the book.

Remove material on the back side of the valve so the width of the 45* cut on the valve matches the width of the seat in the head.

For durability on a road engine the seat surface on the valve should overhang the head seat by .010" on both the upstream and downstream side.

Duke

[Joe R.]

Re: 858 head rework

I talked to the machinist last week. The valves are stainless steel, the manufacturer is Ferrea. The viton seals are positive seal type made by P.E.P. The mfr. of the studs is PBM. Should I go back to GM studs? What is the GM part number?

Joe

[Duke W.]

Re: 858 head rework

I talked to the machinist last week. The valves are stainless steel, the manufacturer is Ferrea. The viton seals are positive seal type made by P.E.P. The mfr. of the studs is PBM. Should I go back to GM studs? What is the GM part number?

Joe

Those are probably okay. Get the part numbers and look them up. Likely the mfgs. offer data on them.

What about the valve springs... mfg.? part number? specifications? Are they a proper match for the ...143 cam?

Duke

[Michael H.]

Re: 858 head rework

Those are probably okay. Get the part numbers and look them up. Likely the mfgs. offer data on them.

What about the valve springs... mfg.? part number? specifications? Are they a proper match for the ...143 cam?

Duke

Weren't the valves .100" longer than original? May be difficult getting proper on seat spring tension if that's the case.

[Joe R.]

Re: 858 head rework

Duke,

I have already purchased GM part # 12371061 (set of 16 GM part # 3970627 springs). That's what I'll use.

Joe

[Joe R.]

Re: 858 head rework

Michael,

I don't plan on using the Ferrea valves. I'll use the Sealed Power replacements for the GM valves. I think I'll be OK on length then.

Joe

[Michael H.]

Re: 858 head rework

Michael,

I don't plan on using the Ferrea valves. I'll use the Sealed Power replacements for the GM valves. I think I'll be OK on length then.

Joe

Ok, that will work.

[Dick W.]

Re: 858 head rework

I believe that you will find that some on the top performance engine builders today use Ferrea valves. I would have no problems using them in a street engine.

[Joe R.]

Re: 858 head rework

Dick,

That's good to know. But they are not the right size for BBC. They are 0.1 " too long. The stem diameter should be 3/8 ", is 11/32 " (SBC).

Joe

[Clem Z.]

Re: 858 head rework

Dick,

That's good to know. But they are not the right size for BBC. They are 0.1 " too long. The stem diameter should be 3/8 ", is 11/32 " (SBC).

Joe

the GM BBC HP crate engines use the 11/32" stem valves and the ones GM sells now are 11/32" stems. it makes the valve a lot lighter and helps with at what RPM you get valve float. like i posted before since you are not going to be racing i would not change a thing. if you want more power build a stroker short block. you can make up the .100 length difference with offset keys and valve spring shims so you can use the GM spring.