Owner #1 did some performance upgrades back around 1999 to my 1973 L82 4-Sp car. Upgrades consisted of World Product (WP) Heads, Comp Cams CL 12-246-3 (110 C/L), Edelbrock Torker intake and 600 Holley carb.

Car came to me in a poorly running condition that turned out to be a bent #7 intake pushrod that owner #2 had no knowledge of and I’m guessing owner #1 also had no knowledge of. Given what I know about the car and owners 1 & 2 It’s a safe bet less than 1000 miles have been put on this car since the 1999 performance upgrade. Car currently has 43,553 miles on it, when owner 1 sold the car it had 43,227.

I sorted out the bent pushrod issue, installed new pushrods, self-aligning rockers and put the original intake and Q-Jet back on the car. Car currently runs on all 8 now, smokes on startup (leakdown and compression tests are good) and has a rough idle due to the 110 C/L cam that is installed.

My plan going forward was to replace the cam with the OEM GM 3896962 and replace the heads with the original heads that came with the car. Now I’m thinking of just going for the low hanging fruit and do the cam swap and keep the World Product Heads and replace the valve seals.

Here’s what I know about the heads, they are S/R (Street Replacement) I-052 dated July 1999 with stampings on the front that read 4266 / CN8A. I’m assuming the WP part number is 42660-1 and all I have been able to find for info is that this head was offered under that part number as a S/R Torquer with 2.020/1.600 valves and either 67cc or 76cc chamber volume.

My WP heads don’t have guide plates and per the WP website these heads are not machined for guide plates. I came across a tech paper that stated If desired .125" would need to be milled off the stud bosses and the push rod holes opened up. Even more confusing is a note in both the 2015 & 2020 WP catalogs that says this head requires pushrod guide plates.

Question today on this head is 1) do I need guide plates, 2) should I use the stock valve stem seal and a positive stem seal, 3) should I replace the springs with OEM L82 springs during the cam swap.

Going to call WP tomorrow to figure out what 4266/CN8A means but not going to hold my breath on that being these heads are 22 years old.

Sticking with low hanging fruit I have a couple options

#1 – Change out the valve seals and intake gasket first to see if the smoking goes away.
#2 – Do option #1 and the cam swap at the same time.

Anyway, throwing this out here for consumption as the marble rolls around in my brain.

 

If the pushrod holes are already "round", then the guided tip rocker arms will get the job done - Keep it simple. If the pushrod holes are "obround", then you do not use either guide plates or guided tip rockers. Do not use both guide plates AND guided tip rocker arms at the same time either way.

99% of original GM heads from the era used obround holes to guide factory pushrods and align the conventional rocker arms. 1970 and newer SHP engines (LT-1, L-82's) used large round pushrod holes (too big to guide the pushrods) along with guide plates and screw-in studs to retain them. The GM guide plates fit tight on the studs and tight on the stock diameter pushrods so not much adjustability there. Did not need them to adjust much as the factory machine work was very reliable. Just bolt them on and run it.

Aftermarket guide plates typically have larger stud holes for alignment adjustability and the pushrod slots are sized wider for specific (larger than stock diameter) pushrods.

I would suggest you leave the heads where they are for now. You can pop off the valve springs and check the guides for wear (slop). Put new seals on it and rule that all out. Even if the guides are marginal, a set of inexpensive rubber umbrella seals would just drop in and stop the oil burning if it is guides. I suspect it is from somewhere else. Intake port gasket leaks are a frequent issue.

Cam swap is a good idea while you have it all apart.

 

Thanks Stingr69, I'm not going down the guide plate rabbit hole with these heads. WP tech sheet says these head have umbrella valve seals, I'm assuming these are just the basic black rubber one and not the positive seal type.

 

I had the SR Torquers from that period, good heads but the umbrella seals are no good-everyone got chewed up. I believe this was an issue with the WP heads I was going to machine them for positive seals but sold them instead.

 

Mr D,
One more thing you might want to do before diving in too far....a compression check. Not a lot of time or money here but it is worth doing. You had some trashed pushrods. Pushrods usually get damaged by some sort of mechanical interference. Something jammed in there and the pushrods are the thing that gives. It is possible that a valve may have touched a piston. Bent valves will make the car loose compression and run bad even with new pushrods. We just do not know what was interfering at that time. Better to know if you need to take the heads off before you get too far into the job.

EDIT: Did you ever figure out why #7 compression was so low?

 

Sting69, been there and done all that. Leak down test on all cylinders is 2.7% to 11.4% (6.3% Avg), this was verified twice. Compression is 170-180 on all cylinders.

As for the bent #7 intake pushrod I have inspected, researched, endoscoped and theorized why this happened and all I have come up with is that when this WP heads were installed the original non-guided rockers were used vice guided rockers and the #7 intake rocker loosened up causing the event. There is no internal visual indication that a mechanical interference event happened.

Just got off the phone with World Products as I suspected didn't learn much more than I already knew. He did say that very few heads (as in single digits) go out the door assembled and that places like Summit, Jegs etc. have them assembled. If they were to assemble a head it would get a Pioneer OS450 umbrella seal which is the same one Gary was referring to in the above post.

So knowing all that I won't really know for sure what I need or can use in the way of positive / umbrella valve seals until I get the springs off. I came across a YouTube video of a guy using Fel-Pro SS72527 (intake) positive valve seals and SS72526 (exhaust) umbrella type seals on a stock 305 head. Looking at the pictures the 305 valve guide boss area looks the same as the S/R I-052 but no way of knowing for sure. I will go with the stock seal at the top of the valve stem and black umbrella type seal if a positive seal is not an option.

Comparison picture (not my I-052 head)

 

Agreed new umbrella seals are probably your best option.

Do pull a spring, to test and see if the valves have too much clearance/wobble due to worn valve guides, (Open the valve 1/2" and then see if it wobbles.) and also to see what shape the top of the valve guides are. That will determine your seal type.

Also that cam is a bit much for a low compression L82. The 230/236 duration in a hydraulic is as much as an LT-1 cam in a solid. And the 110LC is going to make it idle rough and kill vacuum. For street use it would run better with something in the 224 range. Similar to the L82 / L46 cam spec.

Maybe your CR has been raised with those heads?

 

Leigh, I agree on the cam and it's why I plan to replace it with the OEM L82 cam. I think the guides will be fine as the heads have very few miles on them.

From what I know about owner #1 the Johnny Hot Rod parts he was talked into paying for were based on bad advice by a bad mechanic and given the poor performance of those dollars spent he never enjoyed the car enough to keep it. Owner #1 was a high end high yield commercial farmer with a stable full of classic cars.

The original heads are PN 330545 and are 76cc, the S/R I-052 are 67cc so yes a slight bump in compression ratio.

 

i had a pair of dart heads circa 2000. ran on a boat i bought. one valve guide was so bad i could wigle it side to side with the spring on and the head on the engine. so loose the rocker fell off the top of the valve. these were very low time heads. and still had standard 76cc chebby chambers so not really any upgrade over stock stuff. so see what these heads are and in what shape before committing to them.

 

I would just sell those heads and get some nice aluminum heads. The old stock replacement heads have horrible flow.

-- Joe

 

I have the original heads that came on the car, if replacement comes into play those will go back on the car after a rebuild.

 

Those heads flow maybe 195 CFM. Stock heads would be the wrong way to go If you want more power.

So far it looks like you have an XE series cam that is not wiped. Sounds like a good idea to get it out of there before it does if that's where you're going anyhow. Stock L-82 cam for replacement? I don't know about that. If I was going through the trouble of replacing cam I'd at least get one that is good for the CR and makes good torque down low too, a more modern grind in the 270-274 range with 220ish @.050. The L-82 grind may be the same @ .050 but long slow opening ramps lead to lots of loss torque down low vs modern more aggressive openings.

 

A stock 1973 Corvette L82 as delivered off the showroom floor would run down the road at 70 MPH all day long. That's really all I'm looking for here, my Hot Rod days are behind me.
I will also be putting the AIR pump back on the car, oh the horror.

 

So, while I'm waiting to retire next month and pull the trigger on this cam swap I thought I would pull a couple springs on the OEM heads and measure the valve guide boss. I was surprised given what I know about the car that positive valve seals were on the intake valves and umbrellas on the exhaust valves. They appear to be FEL-PRO SS72527 & SS72526 or similar.

Heads are 330545 dated May 23 1973

 

Someone has been in there before. A good sign. Maybe the heads will not need much work?

 

you probably have good valve guides then. what do the seats look lie? i have done some backyard a$$hole seat lapping with a drill on the valve stem. grease the guide up good and you won't hurt anything.

 

I didn't look at the seats, this was just a quick spring removal to measure the valve guide boss. If I end of doing a head swap these will go into the shop for a valve job.

 

I started the cam swap this weekend and while waiting for help to remove the hood I pulled the springs on #1 to measure the valve guide boss. As I suspected the WP heads had the Pioneer OS450 black nitrile umbrella seals but was surprised to see no upper valve stem seal (o-ring) was used. Personally, I would have used both.

The WP valve guide boss measures .582 and the OEM head was .567 a difference of .015, I think the Fel-Pro SS72527 positive intake valve seals will work on these heads.

 

The factory O-ring seals work with factory style 2-groove valve stems so you need those to start. You also would need those HEAVY factory valve retainers and the factory metal umbrella shields. If don't have all 3 of those items, the original O-rings will not seal anything.

 

I could never understand the use of those cheap, junk "O" Rings for stem seals. They never stay where you put them. They do not handle hot oil well. And eventually become brittle, useless and collect in the oil pump screen.

It's my understanding that one should never "double-up" on stem seals. And that is exactly what happens when someone has an "O" Ring plus an umbrella style seal.

Every valve stem in every head regardless of make, has to have some lubrication. You can not deprive a stem & guide of absolutely no oil. Doing that will make the guide short-lived. Thats metal on metal, dry, with hundreds of strokes per minute, equals rapid wear, overheating guides and failure.

Good Valve stem seals are designed to allow a small amount of oil to pass by into the guide. That is a must. That is normal.

The best umbrella type seals are about $30 for 16 pcs.
The "O' rings are 100 pc for a dollar?
Guess which ones to use. But never both.