[Syty] Roller Rockers...

[DOlivares]

You're RIGHT about that LC2 stuff.  I've been reading too many back-issues of GM High-Tech Performance without mentally correcting for the 3800-series heads they (i.e., PAS) slapped on the Grand National LC2s for the Turbo Trans Am application.  Those heads took Corvette-type self-centering roller-rockers (I used Cranes... pedestals, no shafts) with what I remember was somewhat shorter pushrods (which I always get from Crower).  Maybe I'll try to locate some of those spares (had to buy a full set of 16) and see if I can't make 'em work.  I've never had those valve-covers off since I bought the Sy or the Ty.

For your well-deserved reward, I'll now pass on an arcane design tip for custom-engine builders (as I used to be):  When converting to Rollers, get a test-pushrod and weak-spring to mount the valve/retainer.  Vary the length of that 'rod keeping 2 key rules in mind to ensure reliability and high-RPM stability:
  1.. Keep the Rocker Arm as "low" as possible... as close to the basenut or pedestal base as possible without any part of the Arm touching it... to avoid galling, AND
  2.. At 40% of the total valve lift off its seat, the centerline of the roller-tip should be directly over the exact middle of the face of the valve tip (or lash-cap, if you use those).
When both of those conditions are met, you have your perfect length for your pushrod.  True purists and the ultra-fastidious, who don't trust replicated head geometry throughout both heads, would want to repeat this exercise for each rocker/valve/pushrod combination and then generate a screwball order for up to 12 different pushrods.  Good luck trying to keep all the matched-set markings straight!

Yes, yes, we all know about roller-rockers affording lower levels of friction and pumping losses, but they really come into their own by bestowing longevity to the integrity of your valve guides and their seals.  By rolling over the valve tips instead of sliding/grinding over the same, they virtually eliminate that ferocious side-loading of the valve stem which gradually turns those nice, tight cylindrical guide passages into nasty, OVAL'd holes which can get bad enough to cause the whole valve to rattle and wobble as it tries to seat/bounce under spring pressure!  How I wish I had converted back in '98 when I bought that Syclone!  My seals would still be holding all that oil in the top of the cylinder heads instead of being sucked down into the ovaled-out intakes....

Gotta go,

D.O.
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----- Original Message ----- 
From: Dave Goodhue 
To: Syty at syty.org 
Sent: Friday, June 15, 2007 6:59 AM
Subject: [Syty] Roller Rockers...


>What model/brand?

>I think 3.8L Buick (LC2 engine) uses the same valve gear as the Chevy
350 and the 4.3L >Vortec uses Chevy 305 gear... or is it the other way
around?

The Buick LC2 has shaft mounted rockers.   The 4.3 is similliar to the
305/350  (305 is just a small bore 350)  The 4.3 is basically a 3/4
350, sharing the same bore and stoke.  (Tidbit of info, the 229 V6
Chevy is an 3/4 oddfire 305.)

Anyway I used a Crane Gold narrow body rockers and they worked just
fine, clear the valve covers fine.  As for Vortecs, typically the
lower intake needs to be modifed (extended to cover the longer ports)
and the heads will need to be redilled as the intake bolts have a
different pattern.  Vortec also have metric screw in studs, while most
SBC aftermarket rocker are based on english threads.  The easiest
solution is have the head redrilled and tapped for the english thread,
so you can use common SBC studs and rockers.
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