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Vortec heads on racing 302

 
abeetung
I love my Chevy Chevette!
Posts: 1
Joined: 09/13
Posted: 09/10/13 07:48 PM

I'm new here and figure my question has been asked a million times, so I apologize.

We run a 302 cu in (010 casting 350 w/4-blt mains, .60 over bore, forged 3" stroke crank, 6.125" rods, comp cams .535" lift cam, "906" Vortec heads, comp cams bee hive springs, chrome moly push rods, guide plates, screw in studs, comp cams stamped steel roller tip rockers, enlarged push rod holes) in a modified dirt track car. We've run this engine in about 20 races so far with no problems to speak of until now. Since the heads were professionally prepared, we didn't do much other than check the push rod length and set the lash. The engine turns 7800rpm and will probably do even more.
First problem noticed was valve spring shims being broken and squeezed out from under the springs. While investigating this we discovered the roller tips don't seem to line up with the valve tips when in the open(ing) position. Everything I have ever read about these heads and rocker arms is to use self aligning rockers and no guide plates or guide plates and regular rockers. What really brought it to our attention was when we tried to fit aluminum roller tip rockers with a trunion mount on stud. The rockers will not line up with the valve even with no locking nut installed.
What shall we, can we, do? What causes the shims to break?
This engine has been running like a scalded cat and holds its own with much larger engines with 4 bbl carbs.  

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pepsi1
V-6 Camaros rule!
Posts: 111
Joined: 09/11
Posted: 09/23/13 11:38 AM

It sounds to me like the valve springs are bouncing off their seats causing the spring to spin, and then the valve is not being controlled by the spring any-more. I haven't had much experience with Bee-Hive valve springs at high RPM.
  One other thing comes to mind. Are the valve spring pockets much bigger then the valve spring? If they are this could also cause the valve spring to spin and move around and cause your shims to crack.
  Check the key ways for excessive wear. When a valve spring bounces uncontrollably it beats the key ways to death. Then you can drop a valve. I'm sure your using at least 7* or 10* retainers and locks. But it can still happen...
Good Luck and let us know what you find.

Bob  

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pepsi1
V-6 Camaros rule!
Posts: 111
Joined: 09/11
Posted: 09/23/13 11:38 AM

It sounds to me like the valve springs are bouncing off their seats causing the spring to spin, and then the valve is not being controlled by the spring any-more. I haven't had much experience with Bee-Hive valve springs at high RPM.
  One other thing comes to mind. Are the valve spring pockets much bigger then the valve spring? If they are this could also cause the valve spring to spin and move around and cause your shims to crack.
  Check the key ways for excessive wear. When a valve spring bounces uncontrollably it beats the key ways to death. Then you can drop a valve. I'm sure your using at least 7* or 10* retainers and locks. But it can still happen...
Good Luck and let us know what you find.

Bob  

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Mr.Mater8
I love my Chevy Chevette!
Posts: 2
Joined: 01/14
Posted: 01/07/14 01:52 PM

Abeetung,

Did you ever find "root cause" of the valve spring shim damage?

Sounds like a terrific engine build combination. I may be able to help but need more info... did you use the original small diam. GM factory valves? Do you recall the seat and open pressures your springs provided? I assume you used steel (not titanium) beehive spring retainers (such as Comp Cams 774-16)? Lastly, is this a solid flat tappet cam or solid roller?

I think Pepsi1 is on the right track. The beehive springs are excellent- I use them, but they still do have a natural frequency maybe 1000 or 1500 rpm higher than straight springs. But because of their unique, tapered design they cannot utilize a damper. I wouldn't hesitate to use these beehives to 6500 rpm, but without a very high springrate and without a damper, at 7800 you may be seeing an end to it's useful range- in fact, the valves may be limiting your rpm!. Are there any signs of coil bind in the form of a shiny line between the coils?  

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dond1965
I love my Chevy Chevette!
Posts: 6
Joined: 12/13
Posted: 01/08/14 09:37 AM

do you have guide plates? are you using self aligning rockers? you MUST use one or the other, you may NOT use both. if this is the problem you have it licked. if not, are the heads machined for high lift? are the spring pockets machined for the diameter of the base of the spring. if this is ALL GOOD, i suggest using retainers/locks to increase the spring seat pressure and eliminate or minimize the thickness of the spring shim at the bottom. if you are using a flat tappet solid lifter set up maybe consider ford shell lifters for an fe motor. you will have to disassemble and remachine the lifter bores. use tapered light weight push rods too. good luck with your hobby project.  

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Mr.Mater8
I love my Chevy Chevette!
Posts: 2
Joined: 01/14
Posted: 01/08/14 04:55 PM

Abeetung,

Sorry about all the questions... but we can probably narrow down your problem (and solution) with a bit more info.

I had a close look at a retainer on one of my heads yesterday from my beehive spring setup, and yes I see very faint indications of spring movement, but after hours of gruelling accel/decel/accel/decel... nothing indicating damage, and the headside (pocket) was fine too. But I am sure I was not exceeding the valve train's stability and ability to follow the cam.

I'm sure you didn't bottom out on the guide, as can happen with unmodified Vortec heads. The engine would have instantaneously bent the pushrod on the very first lift, no matter how good the pushrod. I'm sure you were using guide plates or guided rockers... the engine would have seen 7800 rpm for about 30 seconds afterwhich the valve tip would have been peened over and very soon running on 7 cylinders (or zero after dropping a valve).

So I willing to say this is pretty clearcut. Unless those were monster beehives, you were hopping those springs around the pocket with the shims taking a beating and getting torn up at 7800 rpm. Be careful... if you loose those retainer locks (keepers), you will immediately drop a valve and explode the piston, destroy the head, block, and rod (at best).

Any more info on the components? Thanks-  

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