Rocker arms for �66 L79

[Gary B.]

Thanks,


Gary

[Duke W.]

[Gary B.]

[Jim L.]

I know the original rockers arms for 64-69 smalls blocks, GM 3843359, were long ago discontinued and eventually superseded by GM 10089648 (which are the guided type)


Thanks,


Gary

Note that if you decide to use the guided rocker arms, you MUST enlarge the pushrod hole in the head. If you don't, you could end up with the pushrod guide in the cylinder head fighting the rocker arm guide for proper alignment of the rocker arm.

[Gary B.]

[Duke W.]

[Jim L.]

That's true if the heads have pushrod guideplates, but I've never heard opening up the pushrod passages in the heads was required for the self aligning rockers. They should keep the pushrods in the center for the passages.

Duke

Nope. It's either keep the pushrod holes the stock size and use normal rocker arms or open the pushrod holes if you want to use the self guided rockers.

[Joseph S.]

[Gary B.]

Gary, We use the Sealed Power R826 for most of the small blocks we rebuild. No issues to date. I can't say how many miles are on customer's cars, but we've used those rockers for 15+ years.

[Joe L.]

Joe,

Thanks. That’s exactly the kind of feedback I was hoping for.

Gary

Gary------


The Sealed Power R826 are completely adequate for your use and will serve you perfectly for as long as you or, even, possible future owners are going to need them. One slight concern, though, is that older stock examples of these rocker arms that I've seen appear to be nitride treated (i.e. surface hardened). However, more recent examples I have seen do not appear to me to be nitride treated. Either way, they are going to perform and last as long as you will ever need them to, even if you drove the car day-to-day. However, for stock-type rocker arms I prefer nitride treated pieces. The original GM rocker arms were nitride treated.

In order to ensure obtaining high quality, non-guided, nitride-treated. stock-type rocker arms I used to recommend Crane Nitro Carb rockers. However, Crane is now out-of-business and, apparently, its assets have been taken over by Comp Cams. Comp Cams offers nitride-treated, stock type rockers and I believe these are the equivalent of (or, even, the same as) the old Crane rockers.

Now, I'll go a little further and describe what I did many years ago relative to this issue when I rebuilt the original 300/350 engine for my 1969. (Incidentally, this engine has never been run and awaits possible future re-installation in my car):

First, I had the original heads machined for flange mount rocker studs. I absolutely abhor stock-type, pressed-in rocker studs. One reason is that field replacement is extremely difficult and if one is a long way from home on a road trip and loses a rocker stud, one is in trouble. Another reason is that press-in studs can crack the stud boss and, sometimes, ruin a cylinder head. At a minimum, it's my opinion that non-flanged, thread-in studs be installed when heads are rebuilt. These offer the additional advantage of not requiring the stud bosses to be machined down so the "finished product" appears virtually the same as pressed-in studs. But, I still prefer flanged rocker studs so that's what I did.

I installed the flanged studs with guide plates and used GM #3974290 rocker arms. I had and have plenty of these [none for sale].

After some time and more thinking, I decided that this might not have been the best solution. GM went to the guided rocker arms for a reason. They certainly did not do it because the 3974290 worked just as well. So, I decided to remove my 3974290 rockers, remove the guide plates, install hardened washers of equivalent thickness, re-install the flanged rocker studs, and install GM #10089648 guided rockers. These are high quality, PRODUCTION-validated, nitrided rocker arms.

I did not enlarge the pushrod holes in the heads. My pushrods center perfectly in the holes and there is no interference at any point when the engine is hand-cranked through complete revolutions. As an additional safeguard, consider that stock GM pushrods have hardened tubes and the heads are decidedly non hardened, so even if there were some slight interference it would not prove catastrophic. However, I am 100% confident than there is no interference in my engine. Could there be in others? I suppose considering possible core-shift in castings there could be but the pushrod holes are machined into the castings in heads having holes.

One other point on this: GM discontinued the 3974290 rocker arms and replaced them with the GM #10086948. This means that GM considers these rockers SERVICEABLE for all applications for which the 3974290 were once used in PRODUCTION or SERVICE. The 3974290 were used in PRODUCTION for all 1970-1986 small blocks and SERVICE for all 1955-69 small blocks. The use of the 10086948 rocker arms does make it difficult to feeler gauge adjust those applications with mechanical lifters but it can still be done and that was not GM's preferred method of adjustment for these applications, anyway.

Attached is a photo of my installation. You might be able to see that the pushrod is perfectly aligned in the hole in the head. All the others are the same.69Original350rockerchamber.pdf

[Gary B.]