[6t7goat]

Well today was not a good day for my 78 Trans am. I was out cruising and was at a stoplight and when the light changed I took off, not crazy but I was on it a little didnt even spin the tires. I heard what sounded like a backfire and it was all over from there. Here are some pictures of what I found under the passenger valve cover. This engine is a 74 400 block that is stroked to 461cu 4x heads screw in studs comp 1.52 rockers Tc-02 HF cam and lifters. The engine has less than 300 miles on it. What the heck happened? The screw in stud is broke clean off. I had to stick a magnet in the pushrod hole to retrieve the push rod I could barely see it. Check out the pics and let me know what you think. Thanks

[67cruiser]

Not a expert looks like incorrect valve train geomtry, incorrect length push rods or springs not matching cam, need to know a little more info. Solid cam?? How did you adjust the valves??

[71 Ventura II]

Wrong length pushrods will caue the "slot" in the rocker arm to hit the stud. It may even show an acceptable pattern on the valve tip but is a recipe for disaster. I tried to run JHB 9.350 pushrods in a solid cam setup out of a Pontiac 455 and had the same result SNAPPED off a BBC screw in stud. I swapped to ARP studs and back to my stock length pushrods issue solved. JD

[bryansMtngto]

pull the spark plug. if you got a bore- a- scope see if you smacked the piston top with the valve. could be lots of things miss aligned, wrong push rods,over tightened rocker arm nut, Even under tightened. Did you hear any ticking before this happened? could even be poor quality stud. but with out close inspection wouldnt be able to tell for sure. That will be up to you, will be interested to see what you come up with.

[screamingchief]

That happened because of those Comp Cams pushrod guideplates...

That is a fairly well known issue to some of us long time pontiac folks.

They just dont align the pushrod tip to the rocker arm cup very well @ all,the end result is they bind the valvetrain up,as that uneven alignment tends to inturn cause uneven contact with the tip of the valve,and that tends to break stuff as SOP.

Put some OE guideplates on there,and that'll almost certainly never happen again.

That or you gotta cut the CC guideplates in half leaving a little room between the halves so you can align the pushrods better,and then you just weld the guideplates halves back together after everything is lined up properly.

FWIW

Bret P.

[72LuxuryLeMansLa.]

Originally Posted by screamingchief

That happened because of those Comp Cams pushrod guideplates...

That is a fairly well known issue to some of us long time pontiac folks.

They just dont align the pushrod tip to the rocker arm cup very well @ all,the end result is they bind the valvetrain up,as that uneven alignment tends to inturn cause uneven contact with the tip of the valve,and that tends to break stuff as SOP.

Put some OE guideplates on there,and that'll almost certainly never happen again.

That or you gotta cut the CC guideplates in half leaving a little room between the halves so you can align the pushrods better,and then you just weld the guideplates halves back together after everything is lined up properly.

FWIW

Bret P.

If Bret is correct and the guide plates are indeed the culprit, this should be added to the tech tips thread.

Karl

[67 Lamnas]

Originally Posted by bryansMtngto

pull the spark plug. if you got a bore- a- scope see if you smacked the piston top with the valve. could be lots of things miss aligned, wrong push rods,over tightened rocker arm nut, Even under tightened. Did you hear any ticking before this happened? could even be poor quality stud. but with out close inspection wouldnt be able to tell for sure. That will be up to you, will be interested to see what you come up with.

X2.

It might just be an optical illusion, but in your first pic, it looks like the 2 valves might be bent and stuck in the guides, as the retainers do not appear to be as tall as the one to the left.

[screamingchief]

Originally Posted by 72LuxuryLeMansLa.

If Bret is correct and the guide plates are indeed the culprit, this should be added to the tech tips thread.

Just do a search,that info about the CC guideplates is already here in the archives.

I know it's not always the easiest thing to find something that specific in the archives,but it's often there none-the-less.

HTH

Bret P.

[screamingchief]

Originally Posted by 67 Lamnas

It might just be an optical illusion, but in your first pic, it looks like the 2 valves might be bent and stuck in the guides, as the retainers do not appear to be as tall as the one to the left.

You want optical illusions,go ahead and look @ how the pushrods are lined up in their holes relative to where the guideplates slots are lined up,and the look @ that relative to where the rocker stud itself is,and then consider how that situation is going end up affecting how the guideplates are "aiming" the pushrod at the cup in the rocker arm.

If you put one of these CC guidplates right next to an OE guideplate,you can see exactly how FUBAR they really are.

Trust me,this is not the first time this sorta thing has happened using those guideplates.

Bret P.

[72LuxuryLeMansLa.]

Originally Posted by screamingchief

Just do a search,that info about the CC guideplates is already here in the archives.

I know it's not always the easiest thing to find something that specific in the archives,but it's often there none-the-less.

HTH

Bret P.

Understood. The problem is that you don't go searching for something that you don't know will be a problem.

Karl

[77 TRASHCAN]

All the above "expert" advice is spot on. my opinion.

The price of extra power and sometimes be a little pain.

Lack of clearance in valve springs or guide to retainer clearance do same.

Who built engine??? (not knocking anyone here) you don't need to say..., Did these clearances get checked??? along w/ pushrod geometry???

A good friend of mine is a real engine builder. many times he will assemble, disassemble an engine 3-4 times, just to make sure, leaving NO room for error...

When you pull the engine, see what the tolerances are on the good cyl's....

My point being....you could have MORE than one problem biting you on this deal.....

[WDCreech]

I question the type of rocker nuts used. They appear to be the type that are torqued down, not the locking type that should be used with anything other than a stock cam.

[screamingchief]

Originally Posted by WDCreech

I question the type of rocker nuts used. They appear to be the type that are torqued down, not the locking type that should be used with anything other than a stock cam.

I dunno,they kinda look like the standard BBC rocker lock nuts (triple crimped) to me.

And those usually will work just fine with this sorta hydraulic flat tappet cam ~ adjustable rocker arm set-up,at least in my experience they do.

Main ??? here is did any of this damage the lifters or the lobes...

Might wanna pull the intake and valley pan for a closer inspection,and then put a dial indicator on there to check & confirm the lobe lift is where it should be.

Only other thing I can see happening here was maybe a lifter might've popped the retaining clip and spit it's guts out,but that usually happens @ higher RPM when the lifter pumps up.

Honestly,it still could've been "any of the above" to be honest?

But the second I see those CC guideplates they automatically become my prime suspect.

Just ask PDude about those,,,IIRC he's had problems with them in the past...

Bret P.

[screamingchief]

Originally Posted by 72LuxuryLeMansLa.

Understood. The problem is that you don't go searching for something that you don't know will be a problem.

Karl

True enough.

But the flip side of that is not everyone reads the "tech tip" thread either.

Either way,it should be a "heads-up" for all that read this thread.



Bret P.

[screamingchief]

Here is a thread I found in the archives about this after a fairly quick search.

http://forums.maxperformanceinc.com/...d.php?t=479302

Note the pic vvvv below,and how poor the valve tip alignment was for the rocker arm on the left.



And that too was using the same CC guideplates & roller tip rocker arms.

Not ideal @ all...

HTH.

Bret P.

[6t7goat]

I will be calling the builder tomorrow. He was very thorough thru out the build process I will put the ball in his court and see what he says. I did take a flash lite and give a good look down the pushrod hole it looked like I was looking at a cam lobe. I took a magnetic pickup tool and and put it down thru the pushrod hole and was able to snag the lifter. I could not get it out due to the size of the hole but when I brought it up as far as I could it was obvious that I was looking at the bottom of the lifter. I am going to see if someone at my dealership has a bore scope so I can get a better look inside.

[JimsSixtySix]

Mebbe an optical illusion.. does valve tip on right look a little oval/ oblong along wih keepers, they look like they were hit with a hammer, peened. dunno, mebbe the way i'm seeing them.
Like post # 15, mebbe how yer rockers were hitting..

[PONTIAC DUDE]

Originally Posted by screamingchief

That happened because of those Comp Cams pushrod guideplates...

That is a fairly well known issue to some of us long time pontiac folks.

They just dont align the pushrod tip to the rocker arm cup very well @ all,the end result is they bind the valvetrain up,as that uneven alignment tends to inturn cause uneven contact with the tip of the valve,and that tends to break stuff as SOP.

Put some OE guideplates on there,and that'll almost certainly never happen again.

That or you gotta cut the CC guideplates in half leaving a little room between the halves so you can align the pushrods better,and then you just weld the guideplates halves back together after everything is lined up properly.

FWIW

Bret P.

X2 Check the other rocker tips and make sure they are riding in the middle of the valve stem. Especially at max lift.


Yes it should be a sticky or warning.

[Lee]

LOTS of pressure to break one of those studs - you cam is probably ruined as well.

[screamingchief]

Originally Posted by Lee

LOTS of pressure to break one of those studs - you cam is probably ruined as well.

In a perfect world that may indeed be true.

But in the less than perfect world we all live in,that's not necessarily so.

What can happen is the incorrect pushrod alignment & uneven valve tip contact causes the stamped style rocker arm to cock itself sideways slightly on the stud,and then that'll let the rocker arm slot wear a small "cut" into the side of the stud as the stamped rocker arm travels thru it's arc,and that small cut is infact a nearly perfect stress riser,so the studs strength is severly compromised via that cut that was worn into the stud.

After the stress riser is there,the excessive rocker arm/stud side loads from the uneven valve tip contact does the rest of the work no problemo.

Now yeah,that would be far less likely to happen with a full roller rocker arm.

A full roller would likely wear out the needle bearings or break the rocker arm trunion before breaking a stud.

Though I will concede that it's also possible that the stud breakage was a secondary event after the fact,as it's almost impossible to say what specific chain of events led to what we all see in these pics.

FWIW

Bret P.