Olds 425 Super Rocket valvetrain question

[Russell]

My best friend has a 67 Olds Delta 88 with the 425 Super Rocket olds big block in it. He recently blew both headgaskets on it, and I've been helping him re-assemble it. Prior to the teardown, he had two cylinders with 180PSI, four with 140ish, and two at 60 (aka, blown headgaskets ).

We tore the engine down, and took the heads in to be machined as they were slightly warped, and had a few hammered valve seats (too many 5000rpm passes). The machine shop milled the head to block surface, and also the intake surface to make everything match up correctly. The machine shop took .060 off each head to make them true again along with repairing valve guides and valve seats.

This engine has pedestal type rockers on it. Each rocker has a bolt that passes through a pedestal that passes through each rocker. I assumed that the engine was similar to my 6.2L diesel, and that there was no adjustment in the valvetrain. So, I re-assembled the valvetrain, and simply tightended the pedestals right down. However, doing so actually opened each valve slightly. When I checked compression with the pedestals tightened right down, I am at 165 PSI per cylinder, and if I leave them right when they reach zero lash, I get 180 PSI per cylinder.

My guess is that the milling on the mating surface dropped the heads down far enough to throw the whole valvetrain out of whack. I don't think a guy is supposed to adjust the preload by not tightening the pedestals right down, so I was hoping someone could give me some advice on where to go from here.

Does a guy have to add shims under each pedestal to raise them up, get shorter pushrods or what?

The engine runs with the valves tightened right down. There is no valve to piston interference. Infact, the engine runs very strong (easily roasted my 365hp / 700 ft/lb Duramax off a boosted launch) but I can hear it popping through the intake and exhaust at idle, and it is taking way more timing than I think it should (approx 18 BTDC without any vac advance applied). I am also hearing some slight valve train noise that actually sounds like a loose rocker arm on a SBC.

Any thoughts or suggestions?

 

[original balzer]

425 is a nail head correct? If so I have no helpful info lmao deffinatly a cool engne to have though.

I dont think olds/buick blocks are either small block or big block but consitered a mid block???

sorry I know nothing useful here

 

[3 on the tree]

Buick's 425 was a nailhead.

I would go with adjustable length pushrods. Shimming the pedestals MIGHT cause interference problems with the valve cover.

 

[dyeager535]

Never had to deal with that on my Olds, but I don't think I'd have a problem shimming them.

You can also convert to "adjustable", I've got some Small Block Ford rockers on my 403.

 

[Russell]

Do you have any details on what is involved with converting to adjustable rocker arms?

Since the head and the pushrods are all pretty much parallel, I think I am going to try shimming them up with some .060 washers and see what that does for me. If not, I found a local hotrod shop that can have push rods custom made if I measure them out first.

 

[80' 427]

Your sure its not just the lifters pumped up a tiny bit that opens the valve but lets it close once the oil is pushed out right? We shimmed a dodge no adjustable setup without a problem.

 

[dyeager535]

It's been a few years since I cracked the valve cover on this motor unfortuntely. Pretty sure they are pro-form rockers.

I don't recall if I needed to add pushrod guideplates or not, but I suspect yes, since nothing holds the rockers stable. Not much more than adding studs and guideplates though.

If the head was machined, I would think shim-stock of the exact height to be required...otherwise you'd be losing lift, with no way around that. Scott has probably dealt with similar issues.

 

[wasted wages]

I would reshim the rocker stands .060 ...moving the heads lower on the V of a V-8 motor also changes the fulcrum point on the rocker to pushrod and valve tip as well...shimming the stands will get it back to where it belongs..

 

[Russell]

Well, shimmed em up and everything is good now. 180 PSI +- 3PSI in every cylinder, running 14 degrees of base timing and took a good tune about where I'd expect it to. No more popping in the intake or exhaust, idles smooth as a baby's backside.

I think she is ready to rock n roll again! Definitely picked up a bunch of power, it is downright tough to catch any traction with the open rear diff now, bad enough that I actually beat him with my d-max cause I can hook up (locked rear) and he can't, haha

 

[4X4HIGH]

Guess i'm a little late on this one. Shimming the pedestals was the proper thing to do. I have NEVER seen a head that required .060" to be machined off to make it straight again though. That definately raised the compression in that engine and your friend needs to keep a very good ear for any detonation and might need to run premium fuel now.

 

[tRustyK5]

No sh!t, .060" is a ton!!!

The BOP motors were always great for torque down low, but all managed to make great power up top too. My first car had a 401 nailhead and it'd pull 6500 rpm without complaint and without fading away. Down low it made ridiculous torque too. Fun car...and I eventually found a factory 3.23 posi trac diff for it that made it that much more fun.

Sounds like it worked out...

Rene

 

[Russell]

My buddy has always run premium in the engine. I believe they came with close to 10:1 compression right from the factory. We eased into the engine to listen for pinging, slowly advanced the timing from the factory 10 degrees initial until we hit 16 degrees, where I started to hear it ping. Dropped it back to 14, and all seems good.

I thought that was a lot to cut the head down too, and chances are I probably wouldn't have either (those particular heads are still relatively easy to find at a decent price), but I didn't know how much they were cut down until after we got them back