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My essentially new Chevy HT383 crate engine has been giving me significant grief.
I had it modified with a Competition Cams XE276 camshaft and valve spring upgrade to slightly better the performance than stock. Recently I experienced two separate rocker arm stud failures. The studs are pressed into the heads so some surgery was required to replace the broken stud. What's the deal? Crappy studs? Can such a mildly aggressive cam over stressed the studs? Can the studs be over torqued?
Are those vortec heads? If so your cam may have to much lift.
Stock vortecs usually only allow around .470 (or so) lift. While I am not 100% sure that is the issue, it should be checked, and I imagine that could stress the studs as well as other valve train components. Vortec heads can be machined to allow more lift - but return is probably negligible since they flow pretty well at lower lift. I had a set machined for extra lift a few years ago, it cost me about $50 if I recall correctly.
Maximum Valve Lift (in): 0.475 in. on those Vortecs.
That new cam has significantly higher lift so SNAP!
It amazes me that GM is still selling 'performance' heads with pressed in rocker studs in this day and age.
I'd check the lifters and cam for excessive wear/damage. If the lobes put enough force on the rocker/spring to snap studs, I'd wonder if the lifter is mushroomed or the lobes worn down, and pushrods bent.
There was no obvious rocker wear and the pushrods were straight. Only obvious damage was the broken studs.
The surprise is that studs broke instead of coming loose from the head. Anyway, I 'aint no mechanic (or tech as they are called today) but I'll know more in a week or so.
Thanks all for the input.
Just something to think about - if you're going to run that cam, either modify those heads for the extra lift, or consider new heads that flow better with the added lift.
Vortecs are great heads, but I believe they only flow well up to a certain point, so I think you will get more overall benefit from new heads - but it's easy for me to spend your money........ The cheap/easy route is probably to just rework your existing heads.
Just something to think about - if you're going to run that cam, either modify those heads for the extra lift, or consider new heads that flow better with the added lift.
Vortecs are great heads, but I believe they only flow well up to a certain point, so I think you will get more overall benefit from new heads - but it's easy for me to spend your money........ The cheap/easy route is probably to just rework your existing heads.
Thanks, but I don't need help spending my money... :-)
The C3 is a cruising car that I'm configuring to be able to drive when I'm 80 without winding up in the ditch if I prematurely punch the gas pedal. I'm in my mid 50's, hopefully I'll make it to that age. Lately I've been dropping a pile of cash into my '01 C5 Z06, goosing the engine/drive train to keep up with my C7 loving wife on the track....
Might need longer slot rocker arms? Any witness marks on the other studs?
Check the tops of the guides for interfearance but usually the pushrods would give before a stud would if you have too much lift Vortec heads are known to be lift limited in original form.
If you are going to keep the heads, consider pinning the studs. A machine shop should be able to do it for $3 per stud. I did it on both of my small blocks for added insurance. Jerry
Sorry to say but a little research and it is obvious that the cam and head modifications are a total mismatch for the heads.
The XE276 cam specs show lift of .502/.510 for intake and exhaust
The spring change looks like you put in beehive springs which have a .525 max lift but also have coil bind at 1.15 in and pressure of 292 when closed.
The vortec heads have a max lift of .475 and have stock only 1.94 intake valves.
Change the heads to a decent set of aftermarket aluminum heads with 2.02 intake valves and screw in studs.
Pinning the studs or replacing with screw in studs will not solve the geometry issues you are having with those heads.
Problem solved.
Sorry to say but a little research and it is obvious that the cam and head modifications are a total mismatch for the heads.
The XE276 cam specs show lift of .502/.510 for intake and exhaust
The spring change looks like you put in beehive springs which have a .525 max lift but also have coil bind at 1.15 in and pressure of 292 when closed.
The vortec heads have a max lift of .475 and have stock only 1.94 intake valves.
Change the heads to a decent set of aftermarket aluminum heads with 2.02 intake valves and screw in studs.
Pinning the studs or replacing with screw in studs will not solve the geometry issues you are having with those heads.
Problem solved.
Good luck
Thanks for the input. When I get back home in a few days I'll confirm the cam/spring specs to make sure it's as bad as your suggesting.
On the upside, I'm learning a lot about engine$.... :-)
Thanks for the input. When I get back home in a few days I'll confirm the cam/spring specs to make sure it's as bad as your suggesting.
On the upside, I'm learning a lot about engine$.... :-)
Hope you figure it out.
Hate to see anyone break engine parts.
Luckily all the damage is in the upper end and is fixable.
Keep us posted.
Thanks for posting the info.
Your specs for the cam show the lift height is greater than .475
The beehives are great springs but look at the closed pressure. 70 lbs over what was recommended for the 986-16 springs that Comp spec'd for the install.
Final comment...... the weak link ended up being the studs yet most times it is either a pushrod or a bent valve. I think the studs are inferior quality as indicated by the fact that they are also 3/8" press in type.
Back in the 60's we pulled those and had the humps machined and tapped for screw in studs.
Personally, on anything approaching .500 lift and aggressive pressures I use 7/16" screw in ARP studs. Too much cheap Chinese steel crap out there.
Unless going for stock look, why put money into expensive beehive springs and a better cam and then tie them to old choking iron heads with 1.94 valves?
Go with modern aluminum ones 2.02 /1.6 int/exh valves as a minimum.
IMO
Good luck.
Let us know how you make out.
Last edited by bmans vette; Jul 5, 2018 at 12:13 AM.
Never use press in studs, for performance application.
check your valve train geometry also, snapping studs off off indicates your running out of lift capability.
Crate engine blues
