marky mark

Thought it was worse based on the sound I heard. I was testing out my "new" Quadrajet (The Lars Special)on a deserted piece of highway. Took the 427 L-36 big block up to red-line (approx. 5600) in gears 1,2&3 and was at approx. 4500 in 4th(a tad over 100mph) rpm with the pedal down hard when all hell breaks loose. Sounded like a rev limiter kicked in. Unfortunately I don't have one.
Got a loud popping through the carb and then a clackity sound. Pulled off the road, shut it down and waited 2 hours for AAA tow truck.

Got it home and pulled the valve covers and several tappets were very loose.I did a "temporary" adjustment on the loose ones to see if that was it and started it back up. It made no noise and it test ran o.k. So, that was it I guess.

My question is this: What would cause one or more valve tappets to come loose at full throttle? I know the answer must be valvetrain related but not sure what to do.Is it possible the timing chain might have slipped? Or that the valves were floating? I'm assuming the carb backfire must have been related to one or more valves not opening at that point.

I'm getting gun-shy on these 4th gear runs (previous motor dropped a rod bolt at 5300 rpm in 4th). Is it that big blocks don't like high rpm operation? Or that I'm getting a full dose of "Murphy's Law"?

Thanks for any feedback. Mark
:flag :chevy

Chris@VetteFinders

I would think the nuts just need replacing on the rocker arms.

marky mark

Chris, that's a great idea which I haven't thought of. Also, these heads are original so maybe the studs are stretched out a bit and won't maintain their positions once valve lash is set. Maybe new studs and nuts would do the trick?

Thanks, Mark

Chris@VetteFinders

I am certainly no expert (but that's what you get at 1 am), but I would think that is a good chance.

69 N.O.X. RATT

I would start with the new nuts and studs, if you jumped a link on the timing chain it would have most likely been catastophic, did that once pistons slap valves, push rods bend, :U etc etc

Larry B.

Are you sure they actually loosened? Hydraulic lifters CAN malfunction from lack of oil. This can happen when you have a high volume oil pump. The timing chain did not jump or the valve and ignition timing would not allowed you to re start when you got home. I do agree about replacing the rocker nuts. I know that some standard performance small blocks have press in rocker studs that pull up under high rpm but I don't remember about big blocks. That is the reason for screw in studs on hi-perengines. :yesnod:

Matt Gruber

order a set of poly locks.
Until they come in, put your nuts in a vice and squeeze them until it hurts. that will tighten them up!

MikeC

Replace the nuts,they wear out, My friend has the same thing happen to his truck when he 4X4's...... the nuts are only ment to be used a couple of times after that the thread wear and no longer provide the jam-nut effect.
..... my friend still hasn't replaced his but like they say, strong like bull smart like dump truck!

I bet if you replace your rocker nuts, your problem will go away. If it doesn't, get the studs replaced.

marky mark

I forgot this last night. The studs are old but the nuts are new. They came with the Crane cam kit.Engine has about 2K miles since re-build. Additions were heavy duty Crane "Nitro-Carb Steel" 1.7 rockers (non-roller),along with the Trick Flow heavy duty 3/8" hardened steel pushrods. I was thinking that due to the increase in weight/mass of these new parts that they may be putting more stress on the rocker nuts and/or studs.I see a set of new 7/16" screw-in studs in the Summit catalog.

Drives 61: What are the differences in regular nuts and "poly-locks"? Also, thanks for the suggestion about putting nuts in vise. :lol:

Regards, Mark

Noel Carboni

Gee, I hate to raise the spectre of Really Bad Things you could have done to the inside of your engine, but...

Is it possible that you bent your valves? Maybe you floated them so badly that they hit the pistons, and now they don't seat. That would explain the popping AND looseness.

Do a compression check before putting any time into tightening up the valve train. Gosh, I hope I'm wrong. :cry

-Noel

Barry's70LT1

Hi,
Based on your description, it sure sounds like your rocker studs are pulling out. This is assuming you still have pressed studs.
GM in their wisdom back in the old days always put screw in studs in the HP engines.
If this is not your problem, it's only a matter of time before it is.
Barry

MikeC

With new nuts, replace the studs... with screw in studs I know it'll be a pain in the butt because you'll need tall valve covers but if you like high RPM's screw in studs are a good investment. Don't forget the guidplates and hardened pushrods with that

Chuck Gongloff

Agree with Barry. Likely that the old "press fit" rocker studs pulled out somewhat. I've "been there, done that". Finally replaced all my studs with threaded ones. I used the kit, and carefully replaced all 16 on my 63 FI solid lifter car. I used modeling clay to prevent metal chips from getting everywhere. I'll bet, that if you get on it again, you'll pull the studs further out, and have the same problem. Measure the studs...see if the "loose" ones are further out from the head. Hope this helps. Chuck

Noel Carboni

If you do this, consider using big block screw-in studs. This will require matching rocker arms, but the thicker 7/16" studs are stronger and keep everything very solid. It's the way I went with my small block.



-Noel


[Modified by Noel Carboni, 6:42 PM 2/27/2002]

Flareside

I've never seen big block heads with pressed in studs. Did they make them?

Besides, that would way to easy for Mark to fix! ;)

-Joe

marky mark

Silver: normal pressure/volume oil pump installed.

Noel: Hope they didn't float that bad but it did make a racket! Compression test a smart suggestion, thanks.

Chuck, I'll remove the covers again and measure if any studs are higher than the others. That's a good suggestion!

Flare: I'm with you. I think they are screw in studs (big block stock Chevy heads). I've got to go back to work today so won't be able to do much investigating right now (valve covers are back on).

Thanks all!!!

Regards, Mark :flag :chevy

Noel Carboni

Oops. Guess I didn't read the original post well enough :bb and assumed Mark had a small block (probably because of all the mention of pressed-in studs). Sorry 'bout that.

-Noel


[Modified by Noel Carboni, 6:41 PM 2/27/2002]

Matt Gruber

mark
summit and jegs sell poly-locks(torque to 20lbs) for about $28 a set. They use an allen wrench to tighten. The stock lock nuts are junk because they create tiny metal shavings from the friction.
i am not kidding about putting your nuts in a vice. Bubba told me it fixed the new cheap nuts on my 72. Bubba's ancestor once used a hammer on them, but that is a tip from the pre-vice age(just after the ice age). :lol:

WESCH

Hi
I had a intake valve lifter rod coming out of the head cover due to a unwound lock nut on my 68 big block solid lifter.
It looks like if the stud threads in the area of the lash adjustment weare out more than in the beginning of the stud.
Even with new nuts, the running torque seems to become less once I arrive at the lash setting.
Guess the studs need to be replaced once in a while as well !
In my case , no damage occured except for a small hole in the head cover due to that it was a intake valve, so the piston just run in idle.
Make sure that the running torque of the nuts is ok, even on new nuts , and measure it near the lash setting.
Gunther
:seeya


[Modified by WESCH, 2:53 PM 2/27/2002]

marky mark

Check compression for major valve/piston damage.

If ok then install new studs and poly locks

re-adjust valves

hope for the best

sounds like a plan

Thanks again, mark

P.S. Forgot to mention that when engine is warm I have been hearing what seems to be the timing chain coming into contact with the chain cover. An intermittant thump. This has been noticed before also. I'm starting a different thread as subject is different. Any ideas on this noise?


[Modified by marky mark, 11:10 PM 2/27/2002]