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Topic Review (Newest First)
01-31-2013 03:00 PM
cobalt327
Quote:
Originally Posted by shane.,herold View Post
I am going to take it to the machinist to look at. Im thinkin the head bosses need to be cut about .0350. And the rockers are Harland Sharp, a very high quality company, not summit. The cam is from summit, and since there are only a few places in the country that grind cams it really doesnt matter what brand they are, pick the one you want, and thats what i did. I have had excellent luck with all summit products because they are usually name brand stuff with a differnt label on them and a hell of a better price.
If the machinist was shooting to get the tops of the studs equal to where they were stock, that could account for the lack of clearance. This is because the studs have a rather generous radius between the stud and hex for strength (arrow below, ARP stud). If they made the studs at a sharp 90 degree angle there, the studs would be MUCH more likely to crack/break at the juncture of the stud and hex. Dart studs have probably the least amount of radius.



If you're using 3/8" studs/rockers, this might be a good time to consider going to 7/16".

I don't know who grinds the cams for Summit, but they have a decent reputation.
01-31-2013 02:58 PM
painted jester You can get screw in studs with no taper or hex to tighten them and you don't need to machine the bosses they have been around for many years I used them in the early 60s in gas and modified classes a good source for these are "Pioneer" Part # RM-348-16 for small block chevy and other applications. If your not using guide plates they are fine and of very good quality, and without machining the early head, You have much more thread area holding the stud before entering the water jacket cavity! The early head castings sometimes when machined because of the water jacket only left room for a few threads when tapped!!

Jester

I forgot there is no taper or hex to interfere with rocker arm movement and more thread for adjustment. Only an alternative for some reading the thread. But at over 6000 rpm you need fully race prepared heads with a very light vave train!!!!
01-31-2013 01:58 PM
engineczar Whenever I convert early Dbl Hump heads to screw-ins I touch off and remove .400 from the bosses.

The other thing to look at are rockers with a wider slot below the trunion area.

I've also seen rockers where people have chamfered the inside edge of the slot slightly to clear the radius of the stud to avoid tearing everything back off the motor.
01-31-2013 12:28 PM
MouseFink I recall that the SBC double hump heads, casting numbers 3917291 and 3782461, do not have screw in studs. Those are probably the "double hump" heads you have.

I had a pair of 3917291 heads on my '56 Chevrolet. They had pressed-n studs and were pinned. They were ported and flow tested by the late Joe Mondello in 1970. Mondello told me that they were the best of the "double hump" heads.
01-31-2013 11:35 AM
MouseFink The "double hump" heads (casting number 3991492 and 3990462) are equipped with screw-n studs and do not need any machine work. All they need are the correct screw in studs that will accept full roller rocker arms.

I thought those were the heads you were referring to when you wrote "double hump" heads. .
01-31-2013 11:29 AM
ap72
Quote:
Originally Posted by oldbogie View Post
accomodate the thickness of the plate.

Bogie
the plate and the hex head on the center of the screw in stud.

in the .300-.350" range usually.
01-31-2013 11:14 AM
oldbogie
Quote:
Originally Posted by shane.,herold View Post
I am going to take it to the machinist to look at. Im thinkin the head bosses need to be cut about .0350. And the rockers are Harland Sharp, a very high quality company, not summit. The cam is from summit, and since there are only a few places in the country that grind cams it really doesnt matter what brand they are, pick the one you want, and thats what i did. I have had excellent luck with all summit products because they are usually name brand stuff with a differnt label on them and a hell of a better price.
Were the rocker stud bosses originally machined for screw in studs?

The boss used for the press in stud has to be machined away, you can't just pull the press-in studs then tap the hole for a screw in stud. Additionally, when using guide plates under the stud the boss needs to be machined lower to also accomodate the thickness of the plate.

Bogie
01-31-2013 10:43 AM
ap72
Quote:
Originally Posted by shane.,herold View Post
I am going to take it to the machinist to look at. Im thinkin the head bosses need to be cut about .0350. And the rockers are Harland Sharp, a very high quality company, not summit. The cam is from summit, and since there are only a few places in the country that grind cams it really doesnt matter what brand they are, pick the one you want, and thats what i did. I have had excellent luck with all summit products because they are usually name brand stuff with a differnt label on them and a hell of a better price.
I was just going to say- probably need to mill the rocker stud bosses down.

And there are a LOT of places that grind cams- and it really does matter a LOT. There are only a few places that cast cam cores though and that may be what you were thinking about. Also, summits parts are not the same as name brand stuff, they are the same as the rest of the white box stuff, which SOME brands also rebox and package as their own.
01-31-2013 10:36 AM
shane.,herold I am going to take it to the machinist to look at. Im thinkin the head bosses need to be cut about .0350. And the rockers are Harland Sharp, a very high quality company, not summit. The cam is from summit, and since there are only a few places in the country that grind cams it really doesnt matter what brand they are, pick the one you want, and thats what i did. I have had excellent luck with all summit products because they are usually name brand stuff with a differnt label on them and a hell of a better price.
01-31-2013 07:55 AM
Mr. P-Body Interesting, 1.65s for a Chevy... New to me! (I make no claim to know everything, so it's not an ego hit when I say that. I LIKE learning new stuff). Since we avoid Summitt, that could explain my ignorance of their product.

We've found the vast majority of available stud/guideplate combos require .350" removed from the stud boss. Hasn't ever failed! Plenty of high-revving small blocks "out there" built here.

FWIW

Jim
01-30-2013 07:10 PM
cdminter59
350 Pushrod length

If the machinist milled the heads for the guide plates it has to be the type stud used. I would take them back to the machine shop, show the machinist what's happening. He will probably have an answer to the problem.
01-30-2013 01:19 PM
oldbogie
Quote:
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
ect.

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!!
When building a 7000 RPM engine you've got to abandon the usual practices. This is a place where you either need a .1 inch longer valve stem (above the lock groove) or use lash caps; maybe both to get the rocker up off the bottom of the stud, then dial in the push rod length for the new height based of roller sweep on the stem. It is likely that you will have to modify the depth of the slot in the push rod guide plate (not uncommon), it is sometimes helpful to use stepped guide plates that provide support closer to the end of the push rod.

One, also, cannot overlook the possibility that the rocker stud bosses were not machined as low as required causing the stud to sit too high. Fixing this if it is a problem will lead into longer studs.

You may need offset locks as well to push the spring around where the rocker body clears it. this of course leads into spring tension checking to be sure it is at spec. when installed.

What about stud girdles? I have a hard time envisioning that studs alone will provide enough support at 7000 RPM. They wiggle a lot under these RPMs and spring loads, last thing you want is a stud to break, or breakout of the head. By themselves 1.65 rockers add a lot of stress to the studs.

I wouldn't count on OEM rocker covers to fit over all this, some some tall covers might be needed.

Setting up a race engine can be a real PIA.

Bogie
01-30-2013 12:42 PM
cobalt327
Quote:
Originally Posted by shane.,herold View Post
cobalt, the hex head on the stud is where i am having interference problems with the base of the rockers.

I dont remember the spring specs its been awhile, the cam specs are
Intake Duration at 050 inch Lift: 250
Exhaust Duration at 050 inch Lift: 260
Duration at 050 inch Lift: 250 int./260 exh.
Advertised Intake Duration: 283
Advertised Exhaust Duration: 290
Advertised Duration: 283 int./290 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.533 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.553 in.
Valve Lift with Factory Rocker Arm Ratio: 0.533 int./0.553 exh.
Lobe Separation (degrees): 106
What I neglected to say was the stud boss needs to be shorter. Sorry if this was confusing. That's what can happen when posting before the coffee has kicked in!

This is briefly mentioned in the link above (Valve train points to check). I need to go back and add the cures for the various conditions listed there.

These your rockers? http://www.summitracing.com/parts/cs...make/chevrolet Hopefully you're using 7/16" studs (these rockers are also available for 3/8" studs), and as I mentioned above, GOOD (meaning stiff) pushrods. Stock wall thickness and diameter won't cut it.

A 1.65 ratio pushes the lift to 0.586" intake/0.608" exhaust. The piston to valve clearance needs to be verified, as well as the other things listed in the link above.
01-30-2013 12:40 PM
MouseFink A 350 CI Chevrolet using 1.65:1 aluminum full roller rocker arms (I assume the rockers are for a Chevrolet)

It appears to me that your poly-lock adjustment nuts are running out of rocker stud adjustment threads before you can set the valve lash. (?)

ARP offers rocker studs in several different effective lengths and Smith Brothers offer custom push rods in any length you need to correct valve train geometry. Camshafts can be ground up to .460" valve lift and use stock equipment. When valve lifts get above .460", cam grinders will grind the camshafts with a smaller base circles so the cam will fit through the cam bearings. .

Is your spring height set at 1.700"?
Taller valve spring heights will require longer push rods and rocker studs with a longer effective length and in extreme cases over 1.800", taller valve covers.

It is a solid lifter camshaft?
The solid lifter (flat tappet or roller) push rod seat can be as much as .200" deeper than a hydraulic lifter push rod seat and the cam lobe base circle of a aftermarket camshaft with more than .460" valve lift may be as much as .070" smaller in diameter, requiring a push rod that is .035" longer. Example: Smith Brothers (or equal) custom push rods that are nominally 7.435" long (.200" push rod + .035" base circle + 7.200" standard SBC push rod length = 7.435").

Before you order custom push rods, use an adjustable Comp Cams (or equal) push rod and a light weight spring to hold the valve closed. Then you can check the rocker/valve tip contact pattern which should be centered in the valve tip at 1/2 valve lift. If it is a solid lifter camshaft, it will require precise push rod length to set the valve lash. Hydraulic lifter pre-load can vary as much as +/- .060" and are more forgiving when calculating push rod lengths.

What brand and part number are the rocker studs?
If your rocker stud effective length is too short and are runnign out of adjustment threads, you will need rocker studs that have a longer effective stud length and more adjustment thread length. ARP has them in various lengths. The most common studs used for full roller rockers on a SBC is ARP 134-7104. Those studs have 1.895" effective length, 1.00" adjustment thread length and 7/16"- 14 base threads. If you are using stock screw-in rocker studs, you must use stock rocker nuts and do not use full roller rocker arms. Poly locks use 3/8-24 Class 3 threads and stock studs are 3/8"-24 Class 2 threads.
01-30-2013 11:01 AM
Mr. P-Body Not for nuttin, but 1.65:1 rockers? Are you sure? If so, you have Pontiac rockers, not Chevy. They are NOT interchangeable. This can cause all sorts of geometry problems... You need 1.5 or 1.6:1.

FWIW

Jim
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