Big block problems (Chevelle)

[72c20customcamper]

Got stuck again with my Chevelle same problem as before the rocker nut cracked causing a loud tic and a miss . Second one in a month first one said ok crap happens second one not so much . I’m changing them all out but it’s only happening to the exhaust rockers . Seems the builder ground down the hex head enough to clear low deck valve covers don’t know why I’ve got tall decks. My opinion is he heated them up to much taking the temper out and hardened them making it brittle. I had one at my house but I needed to be towed as it was getting dark . Not out money because it’s covered under my roadside assistance . Just pissed me off to no end .

This morning I went and got the extra at my garage about an hour from my house took literally 5 minutes to fix . The new nuts are $50 so I’m not going after the builder. Just more or less venting . But here’s a picture I took last night on the side of the road glad I always carry some tools.

[AussieinNC]

I have built way too many engines in my 69 years and can honestly say I have never seen a lock split like that....

I would be changing out all of the studs as well as the new locks, but before bolting it all up, make absolutely sure you are not getting coil bind on those exhaust valves....

Do you know what springs are installed? What is cam lift? Installed spring height? Closed pressure? Open pressure?

If the cam is 560 plus, stock bbc valve springs will equal spring bind/cam death. All the factory springs had far too much spring rate, giving them weak seat pressure and stupid (350#+) open pressure, or simply not enough room for even .500" for the newer stuff. Check your installed height and buy the appropriate single spring.

I have witnessed many times a stud will flex and snap off with coil bind, but have never seen a lock split.

Make sure the top of the new studs is perfectly flat and I always use red loctite on the locks to prevent walking...it is also not necessary to really lean on the locking screws,,,,,just make sure they are hand tight with a T wrench.

[special-K]

Darn Mark. It's a shame no one here seems to know much

Awesome advise Aussie

[RustyPile]

I've built performance engines for over 50 years and I've never seen an adjusting nut fail like that... Great advice Aussie, but let's look at it from another angle.. It appears those nuts are failing ABOVE the stud.. The only force applied to the nut in that area comes not from spring pressure, coil bind or any other force below the fracture line.. I think the nuts are failing from a combination of cheap Chinese junk and over tightening the locking screws.. Personally, I have never used locktite on the locking screws.. Just tighten them using a T-handle.. Although I don't advise it, I don't see a problem with grinding the head down for clearance..

[72c20customcamper]

Originally Posted by AussieinNC

I have built way too many engines in my 69 years and can honestly say I have never seen a lock split like that....

I would be changing out all of the studs as well as the new locks, but before bolting it all up, make absolutely sure you are not getting coil bind on those exhaust valves....

Do you know what springs are installed? What is cam lift? Installed spring height? Closed pressure? Open pressure?

If the cam is 560 plus, stock bbc valve springs will equal spring bind/cam death. All the factory springs had far too much spring rate, giving them weak seat pressure and stupid (350#+) open pressure, or simply not enough room for even .500" for the newer stuff. Check your installed height and buy the appropriate single spring.

I have witnessed many times a stud will flex and snap off with coil bind, but have never seen a lock split.

Make sure the top of the new studs is perfectly flat and I always use red loctite on the locks to prevent walking...it is also not necessary to really lean on the locking screws,,,,,just make sure they are hand tight with a T wrench.

This is the setup 496 CU IN, 650 HP, 660 TQ, 9.7 compression, 238 @ .050 hyd roller. I guess I should call the builder anyway . Guy has a stellar reputation

I'm really thinking metal got brittle when they ground the heads of the lock

[72c20customcamper]

I'm just going to replace them all ordered a set of Comp cams lockers . The rockers are a company called machine pro if I recall correctly no markings on the lockers.

Think they may have over torqued the lock set screws? As both cracked just were the set screw contacted the stud .

[burnin oil]

I am going with your theory. I run my cool nuts down pretty tight without issue. I usually gain 1-2 thousandths when I tighten the set screws. No failures. I did have a cheap set that would loosen but never a failure there either. This was a daily driver for years. Good luck.

['63GENIII]

You probably already have thought of this but when Ive had rocker nuts that were just a hair too tall, Ive used some indian head shellac between two gaskets and made one thicker one.

I agree though, that's a weird failure item and an even stranger way for it to fail.

[Keith Seymore]

Maybe I missed it, but how much lift on the cam?

Is there clearance from the inside of the rocker to the locking nut in that area? Meaning - is the cast portion of the rocker hitting the nut in that area and causing a stress riser?

Is it time for a stud girdle?

K

[Keith Seymore]

Originally Posted by 72c20customcamper

I’m changing them all out but it’s only happening to the exhaust rockers . Seems the builder ground down the hex head enough to clear low deck valve covers don’t know why I’ve got tall decks. My opinion is he heated them up to much taking the temper out and hardened them making it brittle.

I think you are right:

They look brittle.

If he only ground the exhaust nuts, and it's only happening to the exhaust nuts, that seems like a pretty conclusive result to his unintentional statistically designed experiment.

K

[BASE]

Originally Posted by Keith Seymore

Maybe I missed it, but how much lift on the cam?

Is there clearance from the inside of the rocker to the locking nut in that area? Meaning - is the cast portion of the rocker hitting the nut in that area and causing a stress riser?

Is it time for a stud girdle?

K

That would make sense. The intake and exhaust pushrod lengths are different in those things so it could explain why only the exhaust is breaking.

Just doesn't seem like a failure would happen where they are breaking even if they were heated up too much, should be breaking down where they are loaded.

[72c20customcamper]

Originally Posted by Keith Seymore

Maybe I missed it, but how much lift on the cam?

Is there clearance from the inside of the rocker to the locking nut in that area? Meaning - is the cast portion of the rocker hitting the nut in that area and causing a stress riser?

Is it time for a stud girdle?

K

238 @ .050 roller . I didnt notice any evidence of the rocker touching the nut . When I put the new one on and turned the motor over to adjust the valve with the remote switch plugs out, didnt see or hear anything either. I'll look at it closer tomorrow or Friday.

[72c20customcamper]

Originally Posted by BASE

That would make sense. The intake and exhaust pushrod lengths are different in those things so it could explain why only the exhaust is breaking.

Just doesn't seem like a failure would happen where they are breaking even if they were heated up too much, should be breaking down where they are loaded.

They both snapped exactly where the lock set screw bottoms out to the stud . Once it cracks the nut backs out from the stud

[72c20customcamper]

And of course I ordered the wrong ones 4603 comp cams poly locks . I should have ordered the 4600 the 4603 are 1.3 inches in length with .675 shank . The ones I have are 1 inch and .600 shank. So I'll have them Friday or Saturday

[Getter-Done]

Originally Posted by 72c20customcamper

And of course I ordered the wrong ones 4603 comp cams poly locks . I should have ordered the 4600 the 4603 are 1.3 inches in length with .675 shank . The ones I have are 1 inch and .600 shank. So I'll have them Friday or Saturday

Glad you Found the issue my Friend.

I have been looking at this since you posted.

And ??????

As a Machinist I thought how many threads on that nut are holding back ?

Wait for it ._____ Mark's big Foot

There was a lot of factors in play.

That set screw / Pulled the nut / TOO hard and created that crack.

Just my opinion .
And Just food for thought.

[72c20customcamper]

No evidence of rocker hitting the locker. The rockers are engine pro brand no marking on the locker . On closer inspection the metal where it cracked has a crystalline look to it. If I saw it in fracture of one my knives I would say that the temper was taken out when final shaping was done which is why I always dip the blade in water after every pass on the belt grinder so it doesn’t overheat . Couldn’t get a picture of the crystalline feature. Also the shank is only .547 according to my state of the art harbor freight calipers

[Keith Seymore]

Originally Posted by 72c20customcamper

. Also the shank is only .547 according to my state of the art harbor freight calipers

I've got some Comp Cams nuts sitting loose on the workbench. I can check them easily and see what they measure.

I can also measure the ones on the car next time I have the valve covers off, just for comparison's sake.

K

[LT7A]

I don't know enough to comment on the technical aspects of all of that, but it seems that overall quality may be an issue. The set screw is not centered which means the surrounding material will be unevenly stressed...

[72c20customcamper]

We'll the comp cam poly locks shanks are to large they dont fully seat into the rocker pivots . The wall has to go into a shouldered area.

Been conversing with the builder and his opinion is faulty parts . He is going to send a complete new valve train setup this time they will be Scorpion Racing, Amercan made . Hes even sending new studs . Hes waiting on a large order to be shipped so it may be a few weeks . He offered to pay to have them installed .

[BASE]

Originally Posted by LT7A

I don't know enough to comment on the technical aspects of all of that, but it seems that overall quality may be an issue. The set screw is not centered which means the surrounding material will be unevenly stressed...

I was hoping that’s just the threads he ground down into making it look off center, but nothing would surprise me anymore.

[LT7A]

Originally Posted by BASE

I was hoping that’s just the threads he ground down into making it look off center, but nothing would surprise me anymore.

Good point. He may have cleaned it up after grinding and put a bit of a chamfer. That may be what's making it look off center.

72C20CC, it sounds like the builder is making it right. Glad to hear that.

[K20super]

They make short poly locks for clearance under short valve covers. I have been running the crower ones for years. That way they don't have to be altered shorter.