A while back I had a rocker slide off the valve on my 70 L46 350 because it had worn a notch in the stud. Fortunately, it happened while the car was idling in the driveway so no serious damage was done, just had to replace the stud and bent pushrod.

Since then I've been keeping an eye on those studs to make sure no others end up in the same condition. I tend to drive my cars hard (high revs) and I'd hate to have the same thing happen at 5000 RPM. I noticed that a couple of the rockers seem to not be centered on the valve tip. In the picture below, you can see one of them. The rockers do seem to have a little side to side movement, which I don't think is good at high RPM. I'm not real knowledgeable on GM engines, most of the engine work I've done has been on Mopars. Even stock Mopar engines have shaft mounted rockers and they can't get sideways like this, so maybe it's normal, but it scares me.

I have decided that at some point I'm going to switch to screw in studs, solid roller cam/lifters and roller rockers, but that's probably a year away.

I have another engine at the machine shop right now and was asking the owner yesterday about the cost of machining for the studs. He said that until I'm ready to do it, I might check to see if later SBC rockers that are self-aligning may work. I guess these came on late 80's-up 350 engines and have indentations on the rocker tip for the valve tip to sit in. They seem to be available pretty cheap. Can I use these on mine until I get the shaft mounted rockers?

 

You will not be able to use them on your heads without modifications. The rockers that are on now use the head as a guide, and thats why your rockers are off a little bit. Where the pushrod goes through the head needs to be drilled out so no binding will occur with the guided rockers.

 

It did NOT happen in your driveway but rather over a long period of time. It all started with the tip of the valve wearing crooked which then caused the rocker arm to run crooked which wore a groove in the side of the stud which wore the slot in the head egg shaped. If you look closely at your head you will find it needs to be replaced because of the egg shaped slot.

 

I understand that the metal wore over time, I just meant that it finally let go in my driveway.

If the head was new, would you get no side-to-side movement of the rockers? And would the rockers would be centered on the tips? If so, then all of them are worn to some degree, as they all have a little movement. Some more than others.

So can I just pull the heads off and open the pushrod holes up a little with a die grinder, then use the self aligning late 80's rockers? I imagine I'd have to do that anyway when I go to the shaft mounted rockers, right? I'd be using guide plates then.

 

the correct thing to do is switch to screw in studs with push rod guide plates.

 

I don't recall push rod guide plates ever being made for the smaller 1.93" X 1.50" valve heads with a 1-3/4" valve spacing.............only the 2.02" X 1.60" heads because those have a wider 1-7/8" valve spacing and require guide plates.

 

Did you read that the engine is a 1970 L46, they came with the large valves!

 

That's what I ultimately planned to do, but I was just looking for an interim fix for a year or so as I'm working on another project. Maybe I'll just have to bite the bullet and do it now.

 

Been awhile since I've messed with them, but that rocker pivot ball looks pretty worn, is it an exhaust valve one? Sounds like an oiling problem caused your part failure. Crane Koolnuts or Pioneer 850008 help oil the pivot and your studs better. They also make grooved pivot ***** that some like and others don't, they are suppose to help hold oil and reduce wear. I imagine those who don't like them are pushing the loads to the max and the reduced metal surface area doesn't help. A valvetrain oil deflector or stud girdle is another option.

Speedway has cheap $70 1.6 stamped rockers if your looking for a bit of extra pep if your gonna replace all the pivot *****(they have those as well).

Some decent pushrods & springs would be a nice upgrade as well if you want some more rpm.

 

I'm on the other side of the camp...... why add uneeded parts to an engine (guide plates,) when you can buy guided rockers and ensure they stay on the valve tip. I have seen several engines with damaged pushrods/guide plates over the years which has added unknown quantities of metal shavings into the mix. They are more expensive, but worth it in my opinion.

 

Thanks for the suggestions. What springs and pushrods would you recommend? The rocker is an intake.

 

sstocker, what would be the correct method to open up those pushrod holes? Is it something to be done at the machine shop, or can I grind or drill them myself? How big should they be?

 

How big the hole needs to be is related to your rocker ratio. Mine uses a 1.6 ratio and IIRC it was enlarged to 1/2" hole. If you stick to the 1.5 ratio a 3/8-7/16" hole should do it. It just needs to be big enough so the pushrod doesn't touch the edge of the hole during a complete valve movement.
I drilled and ground out my own heads (Vortecs) although they were off the engine when I did it. It's an easy job, but I'd recommend you remove the heads to do it.

 

Yeah, but the head shown in the picture isn't a "large valve" head because the large valve heads all came with 1/2" diameter holes for push rods and push rod guide plates because of the wider 1-7/8" center-to-center valve spacing. You did know the large valve heads had a wider center-to-center valve spacing, didn't you?

Maybe the engine started off with large valve heads in 1970 but someone has replaced them with the smaller 1.93" X 1.50" valve heads in the last 45 years that used the smaller 1-3/4" center-to-center valve spacing that all the small blocks used from the 1955's thru 1962's until the 340 hp 327" came out..

 

Depends on your budget, but I'll assume low buck since your not talking roller rockers. Proform moly 7.8 pushrods and some z28 springs are decent budget upgrades. Normally I measure for the exact pushrod, but if your using stock cam even with the 1.6 rockers the 7.8 will be fine.

https://sdparts.com/details/scoggin-...-center/sd1004

http://www.ebay.com/itm/Proform-66891C-1-Piece-Pushrod-Set-5-16-in-Stock-Length-Clamshell-Package-/131020669351?_trksid=p2141725.m3641.l6368

 

Small block lifters are spaced 1-3/4" apart so they used the same 1-3/4" spacing for the valves and slots in the heads to guide the push rods. That worked just ducky until the larger 2.02" X 1.60" valve heads came along in 1962 with their 1-7/8" valve spacing so they required 1/2" holes in the heads and guide plates to guide the push rods.

 

I bought this car long distance and paid an NCRS judge to inspect the car before I bought it. He said the engine was all original, minus the exhaust manifolds which had been replaced by headers.

I just measured between an ex valve and it's corresponding intake valve and, center tip to center tip, is 1 7/8".

 

You know little about Corvettes and are demonstrating it here. The picture shows a 186 casting# head, these were used interchangeably on most 4bbl 350 Chevy motors and can be found in 1.94/1.5 valve, and 2.02/1.6 valve configurations...they are also used on Z/28 motors. The head in the picture is about 100% a 2.02/1.6 L-46 cylinder head, the rocker arms are "special" "O" type hardened rockers found on HP motors meaning Z/28, LT-1 and L-46 350HP motors. You should check the pushrod hole in the cylinder head for wear, pushrod straightness, rocker arm wear and valve tip flatness. It is not uncommon to find studs with wear slots in them, you can get a replacement stud in STD or oversize fitment from a auto machine shop. If the rocker is shot PM me, I might have one or two spare "O" rockers around my shop, they are decent parts.

DO NOT put a self aligning rocker on your motor if you don't open up the push rod opening in the cylinder head, it can cause misalignment and valve failure....even possibly dropping a valve into the cylinder. I personally don't care for the later self aligning rockers they cause more guide wear than the earlier hardware.

 

OK, thanks. I'd definitely take them off. I may go ahead and have them machined for the screw-in studs at the same time.

 

Solid, I'm not sure if you are directing this to me or or toobroketooretire, who you quoted. I will acknowledge that I don't know much about Corvettes, or Chevys in general for that matter. That's why I'm asking in the first place.

As I mentioned in the initial post, I've already been down the road of stud replacement, and I understand I'd need to open the pushrod hole as it's been explained by sstocker.

Thanks for the offer of the rocker, that nice of you. But if I'm understanding the info I'm being given here, my problem is the pushrod holes have been worn over time and are allowing the rocker to get off-center. As I understand it, my only option, short of replacing the heads, are guide plates or self-aligning rockers. As I mentioned earlier, I want to upgrade the entire valvetrain after I finish my current project, but I want to keep driving the Vette while I do it. So the SA rockers are just a stop-gap until then. I'll probably rebuild the heads anyway then, so new guides will be installed.