Silly rocker arm question
Thread Starter
Team Owner
Joined: Apr 2002
Posts: 62,198
Likes: 1
From: All humans are vermin in the eyes of Guru VA
Cruise-In IV Veteran
Cruise-In V Veteran
Silly rocker arm question
So I am looking at roller lifters and the compcams catalog says the pro-magnum lifters require an "adjustable" rocker. and they need .002-.004 preload.
WTF is all that?
Is this the mega expensive stuff that has the little set screw in the back?
I am so confused
WTF is all that?
Is this the mega expensive stuff that has the little set screw in the back?
I am so confused
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Chevy V8 engines have adjustable rockers. You just tighten the self lock nut to do that. There is a proceedure for that but it is very simple. On some engines the rocker arms are on a sahft and cannot be adjusted. On others(like pontiac, olds,buick, you just torque the rocker nuts down tight... no adjustment available.
Le Mans Master
Joined: Oct 2000
Posts: 7,831
Likes: 5
From: Austin TX
Hey Guru
I agree with Larry.
You'll also need to look at what the cam you're looking at requires
in terms of springs. If the spring rate gets high enough you'll want
to upgrade rockers.
There are basically three types of normal rockers:
1) The factory stamped metal rockers.
2) Roller tipped rockers - rockers that have a roller wheel where the
rocker pushes on the valve stem.
3) Full roller rockers - they have the roller tip and they also rotate on
the stud using bearings.
If you're going with a reasonable hyd roller cam the best rocker is
probably the Comp Cams roller tipped rocker. They are cast instead
of stamped and the lift ratios are pretty dead on at 1.52. The stock
ones vary in ratio and are a little short of the correct ratio. So with
the comp cam rockers you'll get the full advertised lift of your cam.
These rockers are good up to 350 pounds of spring pressure.
http://www.powerandperformancenews.c...ry_Code=mgRCKR
As far as preload - what they're talking about is how far you press
the pushrod into the lifter when you adjust the valves. Lars has
an excellent write-up on adjusting valves:
http://www.corvettefaq.com/c3/ValveLashTechpaper2.doc
I agree with Larry.
You'll also need to look at what the cam you're looking at requires
in terms of springs. If the spring rate gets high enough you'll want
to upgrade rockers.
There are basically three types of normal rockers:
1) The factory stamped metal rockers.
2) Roller tipped rockers - rockers that have a roller wheel where the
rocker pushes on the valve stem.
3) Full roller rockers - they have the roller tip and they also rotate on
the stud using bearings.
If you're going with a reasonable hyd roller cam the best rocker is
probably the Comp Cams roller tipped rocker. They are cast instead
of stamped and the lift ratios are pretty dead on at 1.52. The stock
ones vary in ratio and are a little short of the correct ratio. So with
the comp cam rockers you'll get the full advertised lift of your cam.
These rockers are good up to 350 pounds of spring pressure.
http://www.powerandperformancenews.c...ry_Code=mgRCKR
As far as preload - what they're talking about is how far you press
the pushrod into the lifter when you adjust the valves. Lars has
an excellent write-up on adjusting valves:
http://www.corvettefaq.com/c3/ValveLashTechpaper2.doc
Racer
Joined: Jan 2004
Posts: 377
Likes: 1
From: Anchorage Alaska
I purchased the pro-magnum lifters, not knowing they required only .002" - .004" pre-load. This is very difficult, if not impossible to obtain without, at the minimum, a dial indicator. I spoke to the guys at CompCams several times, and they said ".......no problem. Just find zero lash utilizing the twist the push-rod method, then tighten rocker adjusting nut 1/16th of a turn." Evidently, I was not able to get this right; three lifters came apart, and two valve springs broke. I replaced the lifters with "regular" magnum lifters that require .040" - .060" pre-load, replaced all the springs, fired it up, and it sounds like I may have wiped out the cam. I haven't pulled it apart yet.
I suggest you stay away from the pro-magnum lifters unless you expect to be turning very high RMP's.
I suggest you stay away from the pro-magnum lifters unless you expect to be turning very high RMP's.
