Rebuilding original cylinder heads 1969 z28

[asm69]

I'm in the process of having my original cylinder heads rebuilt.  Machine shop indicated that he would use umbrella type of valve seals on intake valves with the "O" ring seals too, and just the "O" ring seal for the exhaust. He will have to modify the head for the umbrella seal. There have been comments on CRG that if possible do not use pressed in valve seats as well as to have cast iron valve stem guides installed.

Is there a thread or information as to what the best practices should be used to have the original number matching cylinder heads rebuilt?

[Stingr69]

The O-rings are for stock OEM spring retainer and external metal umbrella shield setups.  Nobody seems to use them much anymore. The OEM setup is not that great but did get the job done until the warranty was over.

The O-ring seals the valve stem/retainer setup from the oil that would otherwise run down the valve stem.  They deteriorate over time and loose their ability to complete the seal. The intake valve guides will also wear and allow the oil to get sucked down the guides into the intake tract.  That it the reason for the modifications he mentioned.  Not much worry about oil on the exhaust valves as they do not suck anything in, and even if oil was to go there it would not be that big of an issue.

There are rubber umbrellas that can be used inside the springs that accomplish the same function without cutting on the heads.  Just another option.

As for cutting the seats, that is a crap shoot.  Might work fine, might junk the casting altogether.  Risky, but maybe you really do require it.  I would think real hard about weather you need to do that or not on a car that gets maybe limited usage.  The heads might just outlive you without all the extra effort. I don't anticipate putting 100K miles on mine before I pass it on to the next caretaker.  Any machine shop will want to do what it takes to go 100K miles as it is the right thing to do 99% of the time on other cars but maybe you don't need it to go that long?


Cast iron guides are fine if you need them. Better than just knurling the guides and needs to be done before the seats are finished.

-Mark.

[bcmiller]

I would not use the O ring seals if you are having the heads redone. I would also probably not have the heads cut for positive seals.

As stated, the umbrella (or "Ford" type) valve seals would be fine if you are not concerned about emissions and the car gets limited use.

[asm69]

I prefer not to have the stems cut for oil control. But, I want the head rebuild to be done properly using acceptable standards. I don't want to go cheap on this. Don't want to go through the whole process and then have oil burning after some time. Heads are numbers matching correctly dated, don't want to make them unusable as well.

[bcmiller]

Express your concerns with the engine builder and see what he says.

[X33RS]

I don't build an engine anymore without using the positive seals on the heads.  I like my engines sealed up tight, and when you're pushing octane limits with todays pump gas, oil usage, even a little bit complicates things.

Valve guides should likely be replaced.  I find that after about 70k miles on most engines the guides and/or valve stems have excessive clearance.  If you have 46 year old heads that don't need them, your lucky.  Which type to use varies among engine builders.  A lot of them don't even like to use iron guides nowadays because unleaded fuels don't agree with them (no lead for lubricity)  It's just something you'll have to discuss with your machinist and see what they like to use and why.

I know you say your heads are original and you don't want to cut on them, but my thoughts are do it once.  A top engine builder shouldn't have any problems working those heads over with no ill affects.

We are finishing up my DZ302 now.  Heads got completely reworked.  I wasn't leaving any stone unturned.  Had a few valves with worn stems, guides were excessive, and valve seats were sunk.  Plus they are 46 years old anyway.  Decided to go with Ferrea stainless valves throughout, all new guides, all new hardened seats, a nice valve job to help off the seat flow numbers, heads are cut for positive seals on all valves for better oil control, and we are using a lighter weight retainer setup for a little better valve train control.  I want to do this once and be done with it.  Sometimes you just have to grin and bear it, do it right.  Mine are numbers matching too.  I had to draw the line with no port work though, keeping the heads virgin in that respect.  By the time they were all done, I could have bought a really nice set of aluminum heads, lol.
 My short block was no different.  I'm not using 46 year old pink rods in a matching numbers engine after all the stress they have been through lol, even if they are resized with good bolts.  Would make me sick to loose one and take the block out, and I don't want to be afraid to spin this thing up when I want.  Went with good Lunati rods, 11:1 JE pistons,  small ring pack and lots of other tricks inside to make a little more power and do it reliably.  That's the key, I want it to stay buttoned up for many years to come.

I'm of the thought process that none of this hurts value, and actually for me, it increases value in my eyes knowing the engine was done properly, better than it was when new.

[asm69]

I like what you say. I already planned to use valve guide inserts of some type. Some type of umbrella seals for the valves. Probably a new set of swirl polished stainless steel valves for intake and exhaust. If possible no valve seat inserts. Heads already have screw in studs (previous owner). So, I may opt for push rod guides.
But, for sure want to do it right the first time.

[X33RS]

I like what you say. I already planned to use valve guide inserts of some type. Some type of umbrella seals for the valves. Probably a new set of swirl polished stainless steel valves for intake and exhaust. If possible no valve seat inserts. Heads already have screw in studs (previous owner). So, I may opt for push rod guides.
But, for sure want to do it right the first time.

Ah yes, that's another thing we are doing I neglected to mention.  We converted the heads to screw in studs.  Why GM waited until 1970 to do that boggles me.  We wanted a little more strength in the valve train and with the rpm capability it will have along with a little more spring seat pressure, it's a little piece of mind.  Also nitride the DZ camshaft for hardness and running the new solid flat tappets with an oil feed hole on the face for some extra insurance.  Good quality oil and it won't be a problem but again, I like to do everything possible for a long happy life.  I don't want to rebuild it again.

[z28z11]

I used Perfect Circle seals on my original 186's back in '75 - rubber based with a tension ring around the outside, teflon seal on the stem. The fit right over the casting without machining, installed by hand, and perfomed perfectly for the five years (30K miles) that I drove the car after I rebuilt the motor. Still on the heads, to be exact. Never had any oil sucking into the chambers, even as hard as I ever flogged the car (plus drove it back and forth to school on the interstate for a couple of years with 12.5:1 Manley pistons and an Erson Hi Flow IIH hydraulic cam, 4.11 gear). Machine shop warned me I would pound the mains out of it in 10,000 miles, but they came out looking new, and the original crank is still std/std. I installed umbrella seals on my LS5 heads a couple of years ago, and they dry rotted before I could get the motor assembled (replaced them before I finished the motor and sold the car).

I polished the rods, had bronze bushings installed, everthing was balanced and then assembled by yours truly. I, too, debate using 40+ year old parts now that things have gotten a lot more expensive and scarce, but unless you plan on strip use, I'd bet the old parts will keep on slugging. At least they're not Chinese -

Regards,
Steve

[X33RS]

Gotta watch the Chinese stuff.  Lunati is here as far as I know and came highly recommended from the shop I'm using that does a lot of high end stock eliminator builds as well as pro-mod stuff.  I'm much more comfortable with the choice. 

You are right about the stock stuff.  If this were just a show queen that hardly got driven and was pampered when it was, I'd have no issue at all using the stock rods.  I do however have some occasional fun with the cars, and this Z won't be a stranger to the dragstrip once in a while either.  I'd like to at some point set it up for the PS drags but that will have to wait until the car is restored completely.  The other issue I have is that these blocks are getting crazy expensive, not something I want to replace.  So it's going together with good quality high end parts.   The only DZ piece I'm using in the block is the 1178 crank and even that isn't out of my engine, it's a spare I got from a Traco engine.

[asm69]

z28z11, is your use of bronze bushings to make the connecting rods full floating?

[69Z28-RS]

I like what you say. I already planned to use valve guide inserts of some type. Some type of umbrella seals for the valves. Probably a new set of swirl polished stainless steel valves for intake and exhaust. If possible no valve seat inserts. Heads already have screw in studs (previous owner). So, I may opt for push rod guides.
But, for sure want to do it right the first time.

Ah yes, that's another thing we are doing I neglected to mention.  We converted the heads to screw in studs.  Why GM waited until 1970 to do that boggles me.  We wanted a little more strength in the valve train and with the rpm capability it will have along with a little more spring seat pressure, it's a little piece of mind.  Also nitride the DZ camshaft for hardness and running the new solid flat tappets with an oil feed hole on the face for some extra insurance.  Good quality oil and it won't be a problem but again, I like to do everything possible for a long happy life.  I don't want to rebuild it again.

When I purchased my car in '76, one of the valve covers had been cracked (from underneath/inside), and half-a$$ welde up.. When I disassembed it, one of the rocker studs had also been pulled out and 'welded' up.  So apparently it had been 'over revved' in the past, yanked out a press in stud, which broke the valve cover as well.   Fortunately that was all that was damaged, so I replaced the heads (angle plug at the time with screw in studs).. Later when I realized I needed to have original heads, I traded the angle plugs for some stock 186.  When I had those rebuilt, I had them install a 'screw in' stud which *appeared* to be a press in (ie. it didn't have the 'nut' portion on the stud)...