292 I-6 Rocker Arms

[ncoonen]

I have a '63 C10 that recently had its original 230 replaced with a 1965 292. The 292 was built as follows:
- bored .060 over, standard dished pistons
- crank polished
- Howard Cams 151021-10 cam with .502 lift
- head rebuilt with 12bolt.com 1.84/1.60 valve and lump port kits, stamped steel 1.75 rockers on 3/8" studs
- Langdon's cast iron exhaust headers with 2.25" dual exhaust
- Clifford ram flow intake with Edelbrock 1404 500cfm 4bbl
- eBay electronic distributor

The engine ran pretty well during and after a break-in period; idled smoothly with good throttle response. Recently while warming up in my yard I heard a huge miss develop and I quickly shut it down. What I discovered was the rear pushrod cover was bulging out and oil was running down the side. I pulled the cover and saw this.


That's the #4 intake lifter next to a broken pushrod.

I pulled the valve cover to find this.


Thats the #4 exhaust rocker broken. Here's a better picture.


My first thought was that something evil had happened to break the rocker and cause the rest of the symptoms but I pulled the head off and everything looks good. Now I am thinking that the rocker broke on its own and is the cause of all the other mayhem.

Should I be using different rocker arms on this build? The cam isn't too aggressive but it is a long step up from stock. I have looked at other similar 292 builds and stamped steel rockers seem to work okay. These rockers came out of an EngineTech overhaul kit so they aren't top shelf.

Thanks for your thought...ned.

[geezer#99]

I’ve read on another forum of similar bad rockers.
Did you check clearance to the spring retainers?

[ncoonen]

Originally Posted by geezer#99

I’ve read on another forum of similar bad rockers.
Did you check clearance to the spring retainers?

The head was machined to spec using the instructions from 12bolt.com that came with the valve kit. This is definitely something to check again now that the head is on the bench again.

[68gmsee]

Originally Posted by ncoonen

The head was machined to spec using the instructions from 12bolt.com that came with the valve kit. This is definitely something to check again now that the head is on the bench again.

Was the head damaged? I've had pushrods break before but never a rocker arm. I also just replaced them with no problem. In your case, I would suspect the combination of aggressive cam and rockers that were not up to the job. I would definitely recommend going to a better, higher quality made rocker set since at this point you don't know which one is next.

http://www.hotrod.com/articles/ctrp-...rm-comparison/

[Wrenchbender Ret]

It could be you have too much valve lift & the valve springs are coil binding.
George

[Captainfab]

With the increased lift of the bigger cam, you should be running long slot rocker arms. If you do not, the rocker can bind against the rocker stud and break. It looks to me like that is what is happening. Check the rocker stud for signs of contact from the rocker. It could also be an issue of crappy offshore cheap rocker arms, or a combination of all of the above.

[ncoonen]

Thanks for all the helpful input.

Coil bind shouldn't be an issue. The springs were set up at the proper installed height for that amount of cam lift.

The broken rocker's stud doesn't appear damaged.

I am going to get at least two new pushrods and a decent set of rockers and put it back together.

['68OrangeSunshine]

I've re-used stock GM '68 L6 rockers, and run them 250,000 miles on a second build without a problem.
I don't get it, unless they're from China.

[ncoonen]

I have ordered up a set of Elgin RK402 rockers. The Comp and Harland Sharp roller units look very nice but this engine won't see the other side of 4,000 rpm often, if ever, so they are overkill. In hindsight I probably should have used the rockers that were in the engine when I took it apart but it was a rebuild already bored .030 over so I didn't know the heritage of any of the internal parts. For sure, using EngineTech rockers with a larger cam and heavy springs seems to be a bad idea.

[GRX]

x2 on what Captainfab said in post 36 about long slot rockers and checking the studs.

Originally Posted by ncoonen

Coil bind shouldn't be an issue. The springs were set up at the proper installed height for that amount of cam lift.

Springs were checked for bind at max lift you mean? Should be 0.050" minimum between coils at full lift.

[ncoonen]

Originally Posted by GRX

Springs were checked for bind at max lift you mean? Should be 0.050" minimum between coils at full lift.

Not exactly. The head was rebuilt with this kit from 12bolt.com. The kit advertises compatibility with up to .525. We eyeballed the springs turning the engine over by hand on the engine stand and it did not appear that coil separation was even close at full lift. I didn't check any further because my cam had .502 lift and planned to use stock ratio rockers.

[D13]

.502 is a lot of lift. My bet is on the rocker either hitting the stud, the stand, or just plain failing. it still has the guide slots in the head, correct?

Unfortunately long slot rockers for the L6 are not readily available, and roller rockers require guide plates and hardened push rods. You may be into the 'lengthen your own slot' zone.

If you keep your on evilflay NOS rockers come up fairly often. Other name brands too. A little grinder and polishing work ashould help. You may also want to make a solid dummy lifter to check clearances.




unfrotunately

[mattfranklin]

Just guessing, but here are a couple of possible postmortem analyses...

GUESS 1
Broke rocker
push rod moved to a bad position
then got bound up, bent and then broke.
Maybe?

Another thought...
GUESS 2
Looking at the push rod, the lower end of the broken long part remaining, it looks kind of shiny.
Is it possible it started rubbing on something
got worn and weakened
then it bent at the weak spot.
But that wouldn't explain the destroyed rocker.

I think I like GUESS 1 the best.

I'm about to use Crane stamped rockers (https://www.summitracing.com/parts/crn-11800-16) on my 1970 V-8.
Hopefully I'll be OK.

[mattfranklin]

I just looked again. Did you really mean that your rockers had a 1.75 ratio? Isn't stock ratio 1.5? So your cam that has 0.502" lift with stock rocker arms has 0.586" lift with the 1.75 rockers?

That seems like a lot.

[mattfranklin]

Originally Posted by ncoonen

Not exactly. The head was rebuilt with this kit from 12bolt.com. The kit advertises compatibility with up to .525. We eyeballed the springs turning the engine over by hand on the engine stand and it did not appear that coil separation was even close at full lift. I didn't check any further because my cam had .502 lift and planned to use stock ratio rockers.

Your springs cover a max of 0.525" lift, but your cam and 1.75:1 rocker combo give you 0.586" lift. This is the answer. A quick solution is stock 1.5:1 ratio rockers. Even 1.6:1 will be a problem with these springs.

EDIT: I accidentally typed "lifter" instead of "rocker" the first time.

[ncoonen]

The stock OEM rocker arm ratio is 1.75:1. I have measured OEM rockers and the all of replacements I have and they are all 1.75. I seriously doubt that the stud geometry would allow switching to 1.5 ratio rocker.

The head rebuild kit with the heavy springs allows for a cam with up to .525 lift using the stock rocker ratio.

mattfranklin: where do you see that stock rockers for this generation of Chevrolet inline 6 are 1.5 ratio?

['68OrangeSunshine]

"The nominal ratio is 1.75 to 1 on both the intake and the exhaust rocker. The stock stud diameter is 3/8''.
L. Santucci, ''Chevrolet Inline Six Cylinder Power Manual," P. 99, paragraph 2. (C) 2002.

And I have built two 292s. Never built a V8, though. Easier just to buy them from the dealer.

[mattfranklin]

Originally Posted by ncoonen

The stock OEM rocker arm ratio is 1.75:1. I have measured OEM rockers and the all of replacements I have and they are all 1.75. I seriously doubt that the stud geometry would allow switching to 1.5 ratio rocker.

The head rebuild kit with the heavy springs allows for a cam with up to .525 lift using the stock rocker ratio.

mattfranklin: where do you see that stock rockers for this generation of Chevrolet inline 6 are 1.5 ratio?

Rock Auto lists the Sealed Power R832 as a stock replacement for a 1965 292 I-6...
https://www.rockauto.com/en/catalog/...ocker+arm,5656

Summit lists the Sealed Power R832 as having a ratio of 1.5...
https://www.summitracing.com/parts/slp-r-832

You could well be right. Rock Auto doesn't always get it right. Same for Summit. I do not have hands on experience with the 292. Only the 350 V-8. At the very least if there is a difference in information from the sources it's something to dig into.

So if you have better information, like a stock shop manual then that might be truth.
Hoping we get to the bottom of it and get you back on the road.

EDIT: accidentally pasted a bad link

[mattfranklin]

I dug a little further...
Federal Mogul says 1.7 for the Sealed Power R832
https://www.fmmotorparts.com/fmstore...B#.Wwc7ZUgvyM8

I trust them (and your measurements) more than Summit.

[mattfranklin]

Originally Posted by '68OrangeSunshine

"The nominal ratio is 1.75 to 1 on both the intake and the exhaust rocker. The stock stud diameter is 3/8''.
L. Santucci, ''Chevrolet Inline Six Cylinder Power Manual," P. 99, paragraph 2. (C) 2002.

And I have built two 292s. Never built a V8, though. Easier just to buy them from the dealer.

Interesting, thanks!

[ncoonen]

I have seen that 1.70:1 ratio rockers pop up once in a while as a usable substitute because they are easier to find since the early big block chevy V8s used them. The geometry difference is well within the casting tolerances of these 50 year old heads!

Rock Auto is a good place to find oddball stuff but you have to verify parts cross-references. I have learned that the hard way but I still buy a lot of parts from them. I'm just more careful now.

[mattfranklin]

So what's your next step? More premium materials?

[ncoonen]

Originally Posted by mattfranklin

So what's your next step? More premium materials?

I showed the broken rocker (came from an EngineTech kit) to a few folks and the consensus was "cheap metal" so I bought a set of Elgin stamped steel rockers that I am going to install as soon as I get the pushrods into place. I am also replacing all the pushrods with new Sealed Power pieces.

I will share the results of this effort here in the next week or so. Other stuff is keeping me busy at the moment.

[mattfranklin]

Originally Posted by ncoonen

I showed the broken rocker (came from an EngineTech kit) to a few folks and the consensus was "cheap metal" so I bought a set of Elgin stamped steel rockers that I am going to install as soon as I get the pushrods into place. I am also replacing all the pushrods with new Sealed Power pieces.

I will share the results of this effort here in the next week or so. Other stuff is keeping me busy at the moment.

Good to hear. I know how that "other-stuff-is-keeping-me-busy" goes. Oh, how are you dealing with fitting that back pushrod in with the firewall in the way? Good luck with everything.

[Mike_The_Grad]

Any update???