Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - 350 Pushrod length
View Single Post
  #3 (permalink)  
Old 01-30-2013, 03:51 AM
cobalt327's Avatar
cobalt327 cobalt327 is offline
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Posts: 5,031
Wiki Edits: 1616

Thanks: 128
Thanked 616 Times in 565 Posts
Originally Posted by shane.,herold View Post
I am buildin a 74-ish 4 bolt main 350 for a racecar. it has:

double hump heads 64 cc i believe
screw in studs/guideplates set up to stock height according to machinist
1.65 harland sharp roller tip aluminium rockers
summit circle track solid lifter cam ( CT-103 )
standard deck height
fel pro head gaskets
arp head and rod bolts
clearanced crank
double roller timing set
cam degreed
.060 over bore

i have it all put together, but i went to put rockers on and they bottom out on screw in studs before they come into contact with pushrod (standard length comp). So i put my Manley pushrod length checker on it and a standard length is perfect. Yet i put an adjustable pushrod in it and set it up to where the rocker will not interfere with the screw in stud and the tip of the rocker is way far on the outside of the valve stem..

I do not know where to go from here. I could order longer pushrods, but im expecting the guides to chew out or the valves to break at the 7000 rpms im expecting to run this engine. Could my valve spring height be wrong? It has double springs set up to match the cam recommendations.

Please help!!
In your case you need longer studs. Trying to use too short studs and a too long pushrod to avoid interference is going to leave you w/the geometry whacked, as you're seeing now.

The spring and spring installed height is correct if it gives you the correct seat and open pressures, assuming there are no problems w/clearances between the various components, like the retainer to rocker arm, retainer to seal or guide boss, etc.

A 7000 rpm-capable valve train takes a fairly high spring pressure. This is often best done using a taller-than-stock spring installed height, and this can mean a longer valve stem, pushrod and rocker stud to go along w/the spring installed height.

Now, there are retainers and locks that can increase the installed height, and that could save you from needing longer valves- but whether you can get by using that or not will depend on what the clearances look like w/those parts in place. And that means a mock up, which should be done before final assembly- like you're doing now.

The pushrod slots need to be opened up for use w/the 1.65 ratio rockers/guide plates so there's no interference there. I hope you have good pushrods for this deal. What are the spring and cam specs?

A couple pages w/some general info:

Valve spring installed height
Valve train geometry
Valve train points to check
Cam break in
Adjusting hydraulic lifters
Reply With Quote