difference between magnum and pro magnum rocker arms dimensions

[markw]

hey, im just wondering if theres any difference in the distance between the rocker pivot (ball pivot on magnum and bearing pivot on pro) and the rocker tip (at its point of valve contact) between comp pcams rocker arms for SBF (1.6 ratio) im having issues with a build on some RHS heads with magnum roller tips and getting the geometry correct.. (i have a good witness mark, but its way too outboard)

the rocker arms are the only thing different to the buildup sheet that came with the heads.

cheers,
Mark

[iwannagofaster]

No, the actual center pivot to tip measurement is the same on both rockers. The outward position would be a result of guide plate alignment more than rocker centerlines though. If you are using the 4816 guide plates, you could swap them for the 4808's and that should help bring them in a little. If you are already using the 4808's, you would need to go to an adjustable guide plate to get it any better.

[markw]

by outboard i mean exhaust side

http
://farm5.static.flickr.com/4060/4563217211_6935571b2c.jpg

everything about this head assembly is recommended on the RHS heads buildup sheet apart from the rockers, which are SBF magnum, as opposed to the recommended pro magnum - 1331-16

incidentally, the guide plates are 4502, what is the difference between these and the two you mentioned?

[iwannagofaster]

That would almost have to be in the pushrod length then. Are you using a pushrod length checker? I can't tell where you are on the stud so I dont know which way we need to go, but I would have to say pushrod length is going to be the key here. That part number is for studs, not guide plates.

[markw]

nope, its not pushrod length, the length is spot on, thats why the witness mark is where it is, the problem is elsewhere, i can come in a little (.050 shorter checking pushrod) but not any more than that and be happy, it doesnt help enough, any shorter and im getting only an outward sweep on the valve stem, and longer im getting an inward sweep only, the geometry you see is where i have good movement (out and back during the opening stroke).

someone suggested chevy sb 1.6 rockers have a shorter fulcrum than equivalent sbf ones? (this would bring the pushrod hole closer too, to maintian the 1.6 ratio) do they?

cheers,

Mark

[iwannagofaster]

Sorry for the delay, but I don' t have the resources I have during the week, on the weekend. I spoke to one of our guys here and he said that the Chevy 1.6 may be the cure. He has encountered this problem before and the Chevy rockers fixed it. I would try to find one Chevy 1.6 rocker and try that. You are correct, that will move the rocker inward and should get you were you need to be.