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Discussion Starter #1
I just replaced a burnt cam for my 396/325 with a Voodoo 60201 with lifts of .515 intake and .530 exhaust. Stock push rods and rockers. Took it for a spin for the second time yesterday. Noticed a little knock when slowing down at an intersection. Decided to take it home before it got worse. Before I turned around the engine started backfiring similar to but not exactly the same as my first cam failure. Pulled in the first parking lot I found, called Hagerty and got towed home. Took my valve cover off and the number intake push rod now extends through the rocker. Trying to figure out what next.

First is it safe to assume the stock rockers were the weak link and failed due to the lift specs on the new cam? If not, what in the world could have been the cause? Do I need to tear the top end apart and inspect?

Second, I have original valve covers and want to continue using these. Read lots of posts here and it seems rollers or long slots would be adequate but rollers may require modifications or replacement of my valve covers. Would like some opinions. The difference in costs between the two would not be my deciding factor. Replacement of valve covers would clearly lead me in the opposite direction. I want what will work, but I also don't want to buy something that I clearly don't need.

I'll post a picture later.
 

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Stock rockers could be the cause and you might check at max lift, the clearance of the slot to the stud.

No clearance and the cam pushes up more on the rod and the stud bends. After numerous pushes of the pushrod/cam, the rocker cup fatigued. But more than likely, could be due to too thin of stamped material about the cup and the end of the arm.

Using a roller tipped arm, I believe, would fit under a stock cover. Others here who use them can advise. A roller rocker needs a higher cover. In order to use the OE covers, there is a spacer to install for added height. Paint the spacer and use longer bolts on the cover for attachment to the cyl head.
 

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Also check out your cam to see if it still has all the lobes (check the motor oil for metallic filings when you drain it) as the lack of ZDDP has made a flat tappet all but obsolete.

Stock rockers can still work if you have a long slot rocker off of an L-88 or LS-6/LS-7 BBC which used a mechanical flat tappet cam with high lift numbers. A high lift cam with the stock springs in place is an invitation to disaster. They are aged and weak to start with and were not designed to handle more lift than 0.460" to 0.480" of valve lift (L-88 which had it's own special springs was of 0.580"/0620" lift which is why they used a longer slot rocker arm). Valve springs are critical on a BBC because of harmonics in the valve train and the mass of the valves (they are actually small for the displacement, just heavy).

Larger Dave
 

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Fwiw, a stock 325hp/396 only has a .398"/.398" lift hy-cam in it and even the 350 and 360hp engines only a .461"/.480" lift if I remember right. You have to use the valve springs recommended for any cam bigger than these two small stock one's.

Hope this helps.

pdq67
 

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Discussion Starter #7
Sorry folks I guess I said something that has led everyone to believe I am using the stock springs. The springs are new and are the ones recommended by Lunati for my particular camshaft. One other piece of pertinent information, upon closer inspection I can see where the #1 exhaust valve rocker nut was loose to the point where there were no threads showing on the stud. Why this loosened up, I have no idea but I could imagine the pressure in the #1 cylinder head and what it could cause. Probably fortunate I didn't blow the head off. When I get home tomorrow I'll post some pictures.
 

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If using OE rockers and locknuts, the locknuts do become 'looser' over time from adjusting.

Buy a new rocker and new locknut and fulcum pivot comes with it. Lube well before start up.
 

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I have had failures with the stamped steel roller tip rockers. I didn't get mine from the e bay ad but they appear to be the same. I would not use them again.
 

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Discussion Starter #10
Here's the pictures. You can see that the #1 exhaust is completely backed off or loose.



 

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I guess your verily new to the BBC world - What was the Red Line for the 68 325Hp 396 - 5000rpm? That Lunati Cam now wants 5500 rpm Plus - LOL

That's a typical problem with Stock Rocker Studs and Rockers. Everette is right about the locking Nut and Stud threads weakening and causing the Tappet Settings to back off after repeated adjustments, particularly if your running a HFT Cam with over .5" lift. If you use the stock rocker system always keep Spare Rockers, Nuts, Retainers, Locks Springs and even Push Rods in the Glove Box; other words, buy ARP Studs(ARP-235-7207), descent Roller Rockers and 7/16" Push Rods. Comp Cam Pro Mags and Poly-Locks on 1.9" ARP Studs will fit under the Stock Valve Cover. You may have to double up on the Gasket but I doubt it. Make sure the Push Rod Guide clearance is minimal and centers the Rocker Roller on the Tip of the Valve stem, even if you have to cut the Guide Plates in two.

You can NOT use the OEM Rocker Studs with Roller Rockers and Poly-Locks for 3 reasons. One - The Rocker Shaft rides on the Stud Threads, Two - The top of the Stud has to be Milled Flat for the Poly-Lock to effectively Adjust and Lock and Three - The OEM Stud isn't quit tall enough to properly thread the Poly-Lock. People do it but they are asking for trouble.

By the way that ARP-235-7207 Rocker Stud works on SBC heads as well it you grind .100" off the Bottom Thread.


http://www.summitracing.com/parts/ARP-235-7207/

These are NICE. I've been running these for 4 Years in a dailey driver with set of ported 781's, SR Cam with .623 lift, 200/510 Springs, Pro Mag Rockers and a Girdle; believe me my Tappet Clearance has never changed. I know some will say I don't need the girdle with anything under .675" lift but I haven't broke anything and my tappet adjustment speaks for itself - Of course, I also run a Donovan Cam Gear Drive and Crower HIPPO's to back it up - I use my 70Z's 6500rpm Red Line Tach for my BBC ;o)
 

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Discussion Starter #13
Z15CAM, for everyone reading this, what roller rockers and what push rods? Are comp cam roller tips adequate?
 

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The Stamped Roller Tips are NO Good.

Comp Cams Pro Mag or their Stainless Hi-Tech 7/16" 1.7 Ratio Roller Rockers will fit under the Stock BBC Valve Covers. I'm not sure about Holland Sharp or Crane Aluminum Rockers as they are bulkier. I've always ran Stainless Rockers. I recommend ISKY 7/16" Chrome Moly Pushrods (Very Nice). ARP: 7/16" Poly-Lock Rocker Nuts, 7/16" Push Rod Guides and their 7/16" Rocker Stud as mention above.

The parts are not cheap but you will achieve the potential of that Lunati HFT Cam without breaking things.

Summit have these Parts. You might get lucky on eBay. Sometimes Dyno Shops will sell off these items at the fraction of the price with a few minutes of Dyno Time.

Believe me, it's nice not to be stopped on the side of the road changing out valve train components after revving your BBC - I did it for years and was usually on my way in under 10 minutes but now I'm OLD and don't look that good in public with my head under the hood of a Muscle Car - LOL

Another rather expensive alternative is to run Shaft Roller Rockers.

This is my Valve Train. I use a Jomar Girdle - You would be surprised just how much the Rocker Studs Flex at Upper RPM's. This is not so critical with a HFT or HR Cam but it's important to keep the Lash Stable through the RPM range if your running a SFT or SR Cam.

\

Here's a neat valve cover fabrication for adjusting Hydraulic Flat Tappets with the engine idling:
 

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Your issue with the rocker failure is not that uncommon. It typically happens after switching to a different cam. This is due to the old wear pattern on the rocker leaving a slight indentation in them. With a new cam & more lift, the pushrod is then moving onto a different area of the rocker that is not worn. This concentrates the load on this "ridge" & can lead to punching the seat out. It is better to swap rockers when going to a bigger cam, if the rockers have substantial miles on them.
 

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I installed CC's investment cast steel roller stock ball type jobbers along w/ new everything else. Their so-called Magnum jobbers.

Haven't lit her off BUT do feel comfortable here!

Cam is a CC 282S w/ Manton's 1.550" dia., single coil jobbers from Comp. Products from a while back.

I matched them w/ .050" taller locks to drop the seat pressure down a schosh AND I'm only looking for like 5800 rpm out of my 496 "Tow-Truck" grunt motor!

And remember that the rocker ball design is only good to like 350 per CC and PREFERABLY 330 or less UNLESS you buy the high-priced TiN gold/green plated jobbers and then I think they may be good to 400 pounds on the strip!

You check MOST "street cams" and at lift most are 280 to 300 pounds!!!!! Maybe 320??

As always just trying to help.

pdq67
 

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Discussion Starter #17
Got this sucker running this weekend. Replaced the push rods and rockers and all is good. I had a set of new roller tipped CC Magnums and just used them. From the discussion above, i realize it's probably not the best but it's better than the way it was. I do not plan on taking the car to the track so I feel pretty comfortable with my changeout.
 
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