Big Block 67

Please check the valve guide clearance. We had a car with aftermarket alum. heads. The owner was using a lead additive in the fuel. It affected the bronze valve guides and the valves would seize in the guides. It was tricky to find because sometimes the car would have a miss when first started that went away as the valves loosened in the guides. Other times it would just break rockers and bend pushrods.
TK

PAmotorman

make sure you do not have any lobes going off of the cam as this will cause this problem because if it is a exhaust lobe the exhaust pressure in the cylinder that can't get out will cause push rods to go thru the rocker arms

kimo1965

[Thanks. I am definitely going to check the lobes. That is something I have suspected as well. My buddy is bringing over a dial indicator for me to check them with. Jim

kimo1965

Whoa..you are scaring me now! I have used lead additive a while back and typically throw in some VP racing fuel, which it seems to love with the compression. Hope this is not it. If so, how in the heck would I know? Thanks, Jim

kimo1965

You guys will jump all over me for not mentioning this, I don't want to feel like an idiot, but I have had slight detonation a couple of times. I know John Z says I can run this thing on pump gas with today's fuel (and I am sure he is right), but whenever I haven't used higher octane VP in with the regular premium, it has happened. It was real slight and I got off of the gas immediately. I know it is in my timing curve and I need to address it, but I hope this hasn't caused the pushrod/rockerarm issue? I have had the heads off in the past and saw no internal damage or anything. Just thought maybe I should throw that in the mix. JIm

Avispa

It doesn't seem possible for detonation to cause any problems with the valve train. After all, when detonation takes place, both valves are closed.

You might also want to check your pushrod guide plates. I had to replace mine when I bought my engine from a supplier in California (he installed guides for 7/16 pushrods and used 3/8 pushrods...jeez.). I dropped two exhaust valves (retainer just popped off) before I figured out that the pushrods were rubbing the base of the guide fork, eventually causing the exhaust fork to break off the rest of the guide plate. A new set of correctly made guide plates solved that problem for good.

If you've had the heads off and have satisfied yourself that there is no piston to valve interference, the most likely cause of your problem is coil bind in the valve springs.

midyearvette

timing is not your issue here...good luck...something else is wrong with the assembly or wiped or mis matched parts....jmo

Big Block 67

The detonation is not causing your rocker problem. I would pull the heads and have a trusted shop check the spring installed height,check for coil bind at your cams lift, retainer to seal clearance and valve stem to guide clearance. TK

Pop Chevy

You don't need to take the heads off to check coil bind ! Just roll the engine over so a valve is full lift (verify with dial ind) and slip a feelers guage in between the spring coils. l'm guessing this is your problem but keep us informed.

kimo1965

Well guys, I have pretty much ruled out the camshaft. We checked the lift etc., today and no cam lobes worn. However, my friend brought up a good point. The rockers I have been using are GM number 10112680 and they a "O" (or maybe it is a square) cast into them. I think the originals were hardened and had a "H" (for "hardened"). This might just be the problem. I probably also need to use hardened pushrods...weren't they originally hardened due to being a HP engine? Thanks, Jim

kimo1965

Seem to maybe be getting this possibly figure out. I checked and found that the original hardened rockers are still available through GM Parts Direct.

See below:

Current GM Part Number 12368082
DESCRIPTION: ARM KIT
These 1.7 ratio hardened steel arms have elongated slots to provide extra clearance for high-lift (.600") camshafts. This rocker assembly includes arms P/N 3959182 plus the ball and nut, for use on all 396-502 big-block heads with adjustable rockers. Technical Notes: These long slot rocker arms are stamped "H".

kimo1965

ttt

jim lockwood

You've got an "interesting" problem. I just went back to the beginning to read the full history and one thing jumped out at me: the use of ARP rocker studs and factory, self locking nuts.

ARP is quite clear on this subject: Don't use self locking nuts with their rocker studs. Use Poly-loks instead.

I wouldn't be so bold as to say this is what's causing the problems you've had, but it's something that isn't quite right. I'd change it.

Jim

kimo1965

Hi Jim, I wasn't aware of that. I just bought them from Jegs I think. However, the exact same thing was happening with the original studs, so I am not sure on that. I checked and the standard ply-loks would hit the valve covers unless I had them cut down or someone sells some that are cut down. I am still waiting to see if someone can confirm that the hardened rockers and pushrods were required on the particular 427s. An old GM - Chevy issued Power book seems to indicate that they did. The springs on mine are very stout looking and I would think if the other components aren't strong enough to handle the pressure wouldn't the weakest parts give?? Just thinking out loud...I was hoping someone would know for sure. My friend seems to remember that this was a problem at one time and GM switched to the hardened ones for the HP BBs. I dunno...Thanks, Jim

muncieman

There are a limited number of things that cause this. I would be interested in the old rockers studs, did they have any cuts in them???

If the rockers binds on the stud, to much lift for a stock rocker, that will break parts. If the cam lift pushes the retainer into the top of the valve guide that will break parts, if the spring coil binds that will break parts.

The seals will get hammered by the retainer beating on it and oil control will become an issue. To fix a retainer to guide issue you need to remove the heads and machine the top of the guides.

All this stuff should have been done at the time of engine assembly so if a shop did all the work they need to fix the problem.

Guide to retainer clearence, coil bind and rocker geometry and push rod length all should have been checked, part of the deal.

larrywalk

In the picture you posted of the right bank of the engine with the valve cover off, it appears that the discoloration of the #4 exhaust and the #6 intake rockers indicates that they were running much hotter than the others. This suggests an oiling problem. Have you run the engine with the valve cover off and watched for adequate oiling through those pushrods? Perhaps there's a blockage in the lifter oil gallery?

Also, pull those lifters and put them foot-to-foot to make sure that they are still convex. If they're flat or concave, the added stress on the cam lobes has done damage.

mudbone64

I kinda noticed the same thing. Why isn't there anymore oil laying on the rocker arms and pooling up on the heads? I recently installed a hydraulic roller in my 454 and no matter how much I primed I could only get oil from 10 of the 16 rocker arms. As it turns out the end radius of my new pushrods was not compatible with my stock rocker arms. I installed a set of roller rockers and had more oil flow than I knew what to do with. I don't know how, but the new roller rockers with poly-locks fit beneath stock valve covers with only one set of valve cover gaskets.

I'm not sure how oil starvation could bend pushrods (unless the valve stem siezed up in the guide) but I could see how the additional friction and heat could lead to damaged rocker arms. Perhaps you could run the engine with the valve covers off to verify proper oiling. I use small glad sandwich bags on each rocker arm and spring to prevent oil from being squirted everywhere.

landshark 454

The H on the rocker stands for high lift, not hardened. These rockers have a longer slot. They are what you should be running. If oiling was a problem, the rocker ball or rocker should be badly worn. Factory hi perf rocker ***** had oiling grooves in them. Do yours? Do your valve covers have the drip rails in them? The factory used them to direct the oil splashed from the pushrod onto the pivot ball. I still think problem is rocker or valve guide related.

If the self locking rocker nuts are not backing off, they are not an issue.

I would run the GM "H" rockers and GM 3/8" pushrods, which should cure any oiling issues.

mudbone64

I don't know, but after looking closer at the pics of the rocker arm, it looks as blue as a gun barrel in the ball area and the pushrod pocket area. Since it would be such a simple variable to check I would definitely make sure I was getting proper oiling.

kimo1965

Hi guys. To answer some of the questions you raise. part of the reason you don't see a lot of oil is b/c I haven't started the car up in several months. I see what you say about the discoloration but I think that is the poor lighting in my garage as well as my cheap camera. In person, they all look normal colored. The lifters all look good and no concaved ones. The nuts are not backing off at all. The valve covers have the drippers. I have watched oil come through all the pushrods and the car generally has really good oil pressure. One guy suggested that I check to see if I could fit a bent paperclip up under a rocker next to the stud when the valve was fully open. I could not fit the clip in the slot underneath which seems to indicate that maybe the rocker is right up against the stud causing binding?? I have ordered new GM "H" rockers where the slots are bigger and new 3/8 GM pushrods. I also think that maybe my valve adjustment was a little lax on some of the valves. If this is not it, I think it must be a spring issue, or the retainers are hitting guides, or maybe coil bind. When I look at the springs compressed when the valve is fully open there is plenty of room (at least on the outside one that I can actually see). Not sure what is going on with the inners. I was hoping that this might be a simple matter of incorrect rockers...As to the *****, some of mine had grooves, others were smooth. The one that just tanked had grooves. My new GM "H" ones come with the new nuts and grooved ***** (man that sounds funny . Keep any thoughts coming! I will certainly let you guys know what we come up with. I keep trying your suggestions. Thanks, Jim