I was directing my comments to the quoted poster that was giving you misinformation.....not you. You need to check you push rod passages in your cylinder head for wear......I doubt the passage has opened up and until you decide to go the a guide plate/threaded rocker stud set up like used on LT-1 motors you shouldn't open up any push Rod holes in your heads. The early Vettes and 67-69 Z/28 motors didn't use guide plates they came about on 1970 LT-1 motors, your L-46 did not have guide plates. The head can be easily checked and compared to an adjacent cylinder for push Rod fit, given the surface area of the slot, I doubt it has opened up. I think you should check the push Rod for straightness by rolling it on a flat surface and if every thing checks out....put it back together like it was from GM. I use a little #680 locktite on press fit rocker studs when I replace them.

I have worked on motors for 40 years now and have seen cut studs more than once, it is not a rare occourance and I've never come across a cylinder head with a drastically loose pushrod passage causing the stud failure. The rocker studs can be easily replaced by stacking washers up and pulling them out with their own threads, you have to be careful that the replacement stud is properly aligned before driving it back into the hole and make sure to clean the hole of all objects/fluids.

 

I'd check all pushrods like said ^^^^ and the rockers, they could be the slop. I'm not a fan of oem press-in studs and from my experience once you start pulling them and then pin them to stop it, then they bend. ARP screw in studs are much better. Still idk bout how you feel on modding your 70, I have no problem changing my common 77. Heads can always be swapped out and back.

Also I sometimes forget that c3's once had decent power so I'm not even sure about the cam specs of your engine.

 

As I have reconditioned at least 1000 small block cylinder heads in my lifetime I would bet I know a LOT more about them than you'll ever know. The only small block heads that ever got the push rod guide plates were the 2.02" X 1.60" heads because they used a wider 1-7/8" valve spacing which is 1/8" wider than the 1-3/4" lifter spacing. You see, you can't put a 2.02" valve next to a 1.60" valve with the standard 1-3/4" spacing because they'd clobber each other. The #186 casting number head you see in the picture does NOT have the larger 2.02" X 1.60" valves but rather the smaller 1.93" X 1.5" valves because the 2.02" X 1.60" valves REQUIRED guide plates because of their 1/8" wider spacing. Sorry but you're dead wrong.

 

Solid, I will check all of the pushrods for sure. Last night, I started pulling each rocker one at a time. Only got through four as I ran out of time, but I found another stud that has a slot developing. I did use the stacked washer method to remove the other one so I'm familiar with the process. I also put the pushrod from the valve with the slotted stud against a straight edge and found a little daylight showing. It was minimal, but it wasn't perfectly straight either.

Several of the rockers are like the one in the picture, cocked off to the side of the valve tip to some degree or the other. I know logically that millions of GM small block motors have traveled billions of miles with these stock valve trains, but this just seems unstable. Especially given my nature to rev my engines.

How should I measure the pushrod holes? None of them show blatantly obvious wear, but maybe a couple thousandths make a difference? I can measure the width of the holes or the side-to-side play at the top of the pushrod, but I'm not sure what they should be.

Maybe the slop is in the pushrods and rockers, as you mention. You mentioned that these are special hardened rockers (with the "O"). Will the stock-style aftermarket replacements work? Like these:

http://www.summitracing.com/parts/su...make/chevrolet

http://www.summitracing.com/parts/cc...make/chevrolet

Boot77, though I plan to keep this car relatively stock, I don't mind modifying a few internal engine parts to make it last longer, especially the valvetrain. This engine does have good power, not like the later smog/low compression motors. I have a couple of those too, and there's quite a difference.

toobroketoretire, I don't know what to tell you man. I have found several references on the web that the 3927186 heads had the 1.60/2.02 valves. Here's one:

http://gearheadgeek.com/ghgj/index.p...head-casting-s

And as I mentioned earlier, I measured the spacing myself, 1-7/8". And these have never had guide plates. The stud bosses are not machined.

 

In 1970, the L46 DID have 2.02" X 1.60" valves and DID NOT have guide plates.
In 1970, the LT-1 DID have 2.02" X 1.60" valves and DID have guide plates.

 

If i were going to stay with the original head I'd install screw in studs, open the push rod slot's and use guide plates as was mentioned already ecspecially since you want to swap to a solid roller camshaft which between the spring pressure's and the aggresiveness of the camshaft would probably pull the studs, but since you want to swap to a solid roller have you thought about upgrading heads to a good set of aluminum which would be set up in that manner and work better with the camshaft upgrade.

 

it isn't the rocker arms, studs, or guide plate-slots. you have a bad valve guide. the valve stem is flopping around and pushing the rocker off the tip...

 

Thought about the aluminum heads, but I'm not looking for big HP gains for this car. I have a couple other ones for that. If I can ever get them built anyway. I mainly was wanting to do the valvetrain update for reliability more than power. Of course, if the new cam makes it faster, that won't bother me! This car is already pretty quick, but every time I wind it up it scares me knowing whats going on under those rocker covers.

 

Oh, no! Another reason to look for! I've got my work cut out for me figuring out this one.

 

For reliability stick with a hydraulic cam, why use a solid cam if max power isn't the objective?

 

you can probably grab that valve spring and rock valve side to side...i have a set of Dart sportsmans and one rocker was falling off side of valve. i couldn't believe how much that valve could wiggle. and this is a boat engine. no real amount of running time compared to a car engine.

 

Well, I did say I wasn't going for big power gains. My main objective was going to be two things. One, stabilize the valvetrain for frequent high-rpm use, and two, basically change this to an LT-1 engine. I've always wanted an LT-1 but can't afford it. This engine already has a Performer RPM manifold, which I'm hoping is close to the LT-1's. If I add the solid lifters and an LT-1 cam (or some modern equivalent), I was hoping to get the LT-1 feel.

Plus I just like solid lifters.

 

I have 2 HW 1969 Corvette L46 engines, both are very originale, both engines have 186 heads.
Both set of heads has 2.02 x 1.60 valves, non of them have guide plates.

 

But have you done 100000000's of valve jobs?

 

I've done some, here is my valve grinder

 

What a nice machine to own, gets the job done !!

 

Isn't this fun??

I can't begin to count the number of original 2.02/1.60 heads I've seen over the years without guideplates. Never saw a 327 with them from the factory and quite a few had big valve heads. Same with early Z-28's.

Not too wild about carving on the heads to convert to valve guided rockers either. First...you better have some good valve stem tip above the retainers or you're going to be pressing on keepers/retainer instead of the tip.

I'd be looking real close at the valve/guide etc. to see what has moved. They weren't mega-precision from the factory and the ball fulcrum rocker allowed for some inconsistency. Maybe this one was out of whack for years and finally wore into the stud?

I wouldn't spend the money to convert a set of 186 heads to guideplates and whatever else they needed. Might as well buy some good ehads and be done with it and make some power.

Yep...I've done some headwork over the years too. Also have my own Sioux valve machine and seat cutter equipment at home...but the Serdi stuff is awful nice! Hard to tell in the above video because I wasn't standing there...but I'd have left as much meat on the valve as possible since the seat area was already cleaned up and do that last final part with a 30* back cut. As you cut valve...the diameter decreases and the seling areat moves closer to the edge. Then when you cut the seat..the hole gets larger and moves the sealing area even closer out to the edge. Leaving as much on valve as possible increases flow, leaves material on valve so it won't sink into the seat as far (and hurt flow even more) and all is good.



JIM