Valve spacing and dowel shift, can someone explain??

Hey this is kinda funny but the heads I got advertise a 60-40 valve placement and a .085 dowel shift. I got the heads at the recommendation of the Guy's at AI, and I would think they know what they are doing.

But what does the 60-40 and dowel shift mean??

60-40.... Piston Manufactures are the best at showing how you get this.

Basically what that means is how much of a shift you have from the centerline of the piston. The standard placement of the centerline of the exhaust valves is 1.000" over from the center of the piston and .850" over for the intake.

A 60-40 shift takes the intake valve and moves it .040" closer to the center (.810") and the exhaust .060" farther away (1.060")

A Dowel shift is usually either using a offset dowel pin that moves the head over the set amount or you have the heads dowel holes moved over that amount to locate the intake valves that amount away from the cylinder wall.

Different motors need it done different ways but all this applies for the SBC/LT1. A LS1 can only be "shifted" with offset dowel pins, which are a PITA to make. Ask me how I know ;-)

One other little tid bit is on some motors you don't always want to offset the intake farther away from the bore but offset it CLOSER, and no it's not for a "blower motor".

Bret

60-40.... Piston Manufactures are the best at showing how you get this.

Basically what that means is how much of a shift you have from the centerline of the piston. The standard placement of the centerline of the exhaust valves is 1.000" over from the center of the piston and .850" over for the intake.

A 60-40 shift takes the intake valve and moves it .040" closer to the center (.810") and the exhaust .060" farther away (1.060")

A Dowel shift is usually either using a offset dowel pin that moves the head over the set amount or you have the heads dowel holes moved over that amount to locate the intake valves that amount away from the cylinder wall.

Different motors need it done different ways but all this applies for the SBC/LT1. A LS1 can only be "shifted" with offset dowel pins, which are a PITA to make. Ask me how I know ;-)

One other little tid bit is on some motors you don't always want to offset the intake farther away from the bore but offset it CLOSER, and no it's not for a "blower motor".

Bret


Interesting, I had seen the offset dowel for sale in summit and always wondered the purpose.

So the All-pro heads I got have the dowel pin holes themselves moved?

Wouldn't this mess with the head bolt hole alighment and everything else?

Which way are they shifted? Toward the intake manifold or toward the headers??

Thanks for the explaination!!:bow:

Here the heads I got, they are CNC'ed to 255 and on the way to AI for touching up and matching to the Vic-E intake :)
http://i20.photobucket.com/albums/b207/95ttoplt1/Daddysheads.jpg

I got a set of J2K Jesels with the heads as well so I am slowly getting a decent combo together :cool:

Piston manufactures have good pictures, this one is from JE.

http://i20.photobucket.com/albums/b207/95ttoplt1/valvespacing.jpg

Interesting, I had seen the offset dowel for sale in summit and always wondered the purpose.

So the All-pro heads I got have the dowel pin holes themselves moved?

Ask All-Pro

Wouldn't this mess with the head bolt hole alighment and everything else?

Maybe a little. You might have to enlarge a bolt hole or two.

Which way are they shifted? Toward the intake manifold or toward the heades??

Thanks for the explaination!!:bow:

Normally it would be shifted front/back, not side to side.

Interesting, I had seen the offset dowel for sale in summit and always wondered the purpose.

So the All-pro heads I got have the dowel pin holes themselves moved?

Wouldn't this mess with the head bolt hole alighment and everything else?

Which way are they shifted? Toward the intake manifold or toward the headers??

Thanks for the explaination!!:bow:

They'll bolt up just fine. Just make sure you mock up your rocker system as soon as you get the heads back. It took T&D 3 trys to get the right stands for the last set I did.

Normally it would be shifted front/back, not side to side.

Ya sure about that ;)



They shift the heads towards the lifter valley, moving the valves more into the center of the bore. It is not a symmetrical valve motor, if you shift the heads front to back you are moving two valves closer to the center of the bore, but moving the other two closer to the cylinder wall.

Ya sure about that ;)



They shift the heads towards the lifter valley, moving the valves more into the center of the bore. It is not a symmetrical valve motor, if you shift the heads front to back you are moving two valves closer to the center of the bore, but moving the other two closer to the cylinder wall.

Yep.... which reminds me, make sure they check to see if the intake face has been milled back to compensate. Otherwise you end up with the manifold ends about a half inch above the china rails and the bolt holes & ports out of alignment.

Ya sure about that ;)



They shift the heads towards the lifter valley, moving the valves more into the center of the bore. It is not a symmetrical valve motor, if you shift the heads front to back you are moving two valves closer to the center of the bore, but moving the other two closer to the cylinder wall.


That is correct, they are moved .085 toward the lifter valley, I found a little write up from a guy building a motor with my exact heads.

I bought these heads used with the rockers they were running and everything so it should all bolt right up, hopefully:p

Ya sure about that ;)



They shift the heads towards the lifter valley, moving the valves more into the center of the bore. It is not a symmetrical valve motor, if you shift the heads front to back you are moving two valves closer to the center of the bore, but moving the other two closer to the cylinder wall.

DUH! Yep, I was thinking about symmetrical heads. Thanks for the correction!

Of course, you could always move the bores instead of the heads. ;)

DUH! Yep, I was thinking about symmetrical heads. Thanks for the correction!

Of course, you could always move the bores instead of the heads. ;)

Ah I think I will just be indexing them to where they should be and leave it at that. I wanna make it a monster but I still have a budget.

Of course, you could always move the bores instead of the heads. ;)

:eek: :D

We had an apprentice at the shop for a while, and he was being trained on the boring bar - left him alone after doing the first 3 cylinders and somehow he didn't center the head over the 4th bore right and came out with a nice oval :mad: The head is auto-centering, so I am still not sure how he managed to do that one...

:eek: :D

We had an apprentice at the shop for a while, and he was being trained on the boring bar - left him alone after doing the first 3 cylinders and somehow he didn't center the head over the 4th bore right and came out with a nice oval :mad: The head is auto-centering, so I am still not sure how he managed to do that one...


Nice, some people will always amaze you with there inability's:lol: