Rocker arm stud length
 

Quick question regarding rocker stud lengths. I am going to change the stock 7/16 to 3/8 bottleneck studs on a set of 6X-4 heads in my 1978 TA. The originals measure ~1.5" long from the top of the hex head to top of stud.

The replacements I have are ARP 7/16 from a set of KRE heads that measure ~1.75" long. Will the 1/4" longer ARP studs work ok & fit under stock height valve covers?

Cam is Comp XE 268 with ~.480 lift, using the Comp 1.5 roller tip rockers & crimped type nuts but might use poly locks after converting to the 7/16 studs, but the crimped nuts have worked fine for 15+ years.

Its only 1/4" difference in length and I would guess that wont cause a problem, just wanted to be sure before I use them.

With the crimp nuts you should be fine, with the poly locks they might hit.
They make a thicker VC gasket that would help also. Butler sells them.

GT

Correction- The first sentence reads like I am actually changing "stock 7/16 studs" to bottle neck, that was describing the stock studs that are 7/16 but step down to 3/8" for the factory lock nuts...

Ok so the ARP studs being .25" longer isnt an issue, but poly locks might be. I will stick with crimped nuts for these. Just wanted to be sure the longer studs wouldnt cause a fit or function issue. I will test fit everything to be sure.

Come to think of it, a E-head motor I have uses the longer studs with poly locks & full roller rockers, the stock height aluminum covers fit with the thicker felpro gaskets.

There are some shorter polylocks Crower and Comp use with some of their SS rockers. I have some chrome repop style valve covers with E heads and a thick gaskets and HS rockers which have a slightly taller poly lock. Same thing on the 400 6X-4 in the 81 HS and chrome repop valve covers.
I think I used ARP SBC studs for both.

Pretty sure stock SBC studs are same length as stock pontiac, but these studs from aftermarket KRE or E heads are a little taller... sounds like they should be ok to use on 6x heads.

ARP has all kinds of different length top, bottoms to choose from.

I used the Comp 1.5 roller rockers with their polylocks on 6X-4 heads with the factory rocker studs and a Comp XE276HR cam. My cast aluminum M/T valve covers were about 1/8" taller than the factory stamped metal covers and would not clear the polylocks, even with the 1/4" thick Butler gasket. I had to add Butler's spacer and another gasket for enough clearance.

Then the A/C compressor didn't clear the valve cover and I had to convert to a CVF serpentine belt drive. I wish I had known about the short polylocks.:-ohwell: Those rockers wound up costing over $2000. :o

Wow, thats a lot of spacers! If youre running that big of a cam with poly locks you should consider changing to 7/16 studs... I had 1 factory bottleneck stud break with the xe268 FT cam, luckily the rocker arm & nut with the piece of stud in it just fell off to the side, I was close to home and limped it back with 1 valve being stuck closed.

I got these ARP studs for almost free so I will try to use them but for this engine stock SBC/BBC studs would be fine.

I've had M/T on the motor n the 78 TA with RAIV heads and Norris SS rockers and now E heads and HS and Crower SS and have just had to use a thick gasket.

The old kit HO Racing used to sell was just plain BBC 7/16 studs.

That is a bit concerning. The cam lift on the XE276HR is .502/.510 and the recommended Comp springs were installed with the rebuild. All the valve spring seats were milled to the same height for correct pressures. The polylocks really do stick up high on these rockers.

I may be doing a tear down soon if my rings don't seat (2300 miles on the engine and still going through a quart of oil in 600 miles), and will consider changing the studs then. Thanks for the tip.

Over .500 is pretty good lift that would justify 7/16 studs for sure IMO. Especially with a roller cam.

I kept the stock studs on these heads because on a previous 455 6x-4 motor with the same size .480 lift cam I had, I never had a problem after almost 100k hard miles. On this 400 engine I figured they would be ok too and they have been for 15+ years, but after having 1 break I will be changing them out ASAP.

Yeah 2300 miles & still burning a qt of oil there is something wrong... :eek:

Make sure you check for clearance between the valve retainer and the oil seal at full open lift. The oil seal bosses often need to be cut down lower to add clearance.

Why would changing the stock studs to 7/16 studs require checking or cutting down bosses to add clearance?

I think he was getting at the possible cause of the oil consumption.

oh sorry, wasnt sure who he was replying to

Thanks for the suggestion. I'll pop a valve cover off and take a look. I imagine I would be able to see any damage to the top of the seals.

FWIW; after doing the improved valvetrain stuff since the min 1980's, my 421 build will LIKELY use ported RA III gasket-matched 13's all stock valves, springs studs rockers pushrods, and feature the umbrella seals.

I think the Cam is modest at 0.45" lift, but will rethink all that stock stuff if big.