[steve25]

X2, it’s a 5.

[mgarblik]

Car has a shipping date of 6/25/73 from Norwood. Interest from 7/19/73. Per PHS. I think I am correct that all the 73 SD cars were built in a batch over a short time period and the production was delayed. I assume the time frame for this car is pretty early?

[Held for Ransom]

The SD was released for production in late May '73. Hard to say when, in line, it was produced as far as SD's go.

[steve25]

They cast the 1973 heads first in 72, hence the 485 prefix to that part number.
The heads where cast well before there was a dedicated SD production block.

As far as I know 485 was only used in late 72.

The blocks for both 73 and 74 had the later 490 prefix which was only used in 73.

[steve25]

What’s very interesting is that McCarthy’s last book list The 73 SD heads as being part number 485216, but as I posted before that last digit sure looks like a 5 to me.

[PAUL K]

Original part number was 485214

[Held for Ransom]

Originally Posted by PAUL K

Original part number was 485214

How were those sold, bare heads or what?

[steve25]

Always bare over the counter and you ordered Or bought whatever else you needed.

[mgarblik]

Originally Posted by HWYSTR455

Did SD heads come with 1 piece valves? Honestly don't know that.


.

Took a closer look at the valves. The intakes look like a nice 1 piece valve and the entire valve is magnetic. The exhaust valve is a 2-piece design but nice looking. The head is non-magnetic and about 2" down the stem. Then the rest is magnetic. No visible sign of the friction weld like many 2-piece valves.

[PAUL K]

Mike the intake valves should be tuliped with a small dish on the face. The part numbers are usually on the valve near the lock and oil seal groove.... Are those what you have?

[mgarblik]

I will look for part numbers on the valves. They have the visual look you described. They look original to me. I do have a question for the cylinder head experts. For the SD engines, what spring pressures are you comfortable with on these heads. I will test them of course. They look to be original springs and of course several have been compressed for over 40 years!. All the springs had shims under them from the previous rebuild. .030" was the least and several had .090" in shims. I have no problem replacing the springs. Just looking for nice target numbers that won't kill the flat tappet cam. The heads do have straight 7/16" BBC studs which make the valve train adjustable. Thank you.

[Gary H]

Originally Posted by mgarblik

Few more pics. Sorry some of these pictures are sideways. Don't know why it does this or how to turn them.

My heads are cast the same as your, no "16" on the exhaust ports, but has the full part number on ridge below the valve cover edge. My intake was actually cast in November of 72'. The car was built the 2nd week of June. Brewster Green with Beige cloth interior. Sold here at Coggin Pontiac in Jacksonville.

[steve25]

Supposedly due to EPA catching Pontiac trying to pull the emissions wool over theres eyes there where no SD cars made before Apr of 73.

[steve25]

Mike I can look up the stock specs later, but with a stock cam and the power range it has a spring with 125 on the seat should do it.

[Gary H]

Originally Posted by Gary H

My heads are cast the same as your, no "16" on the exhaust ports, but has the full part number on ridge below the valve cover edge. My intake was actually cast in November of 72'. The car was built the 2nd week of June. Brewster Green with Beige cloth interior. Sold here at Coggin Pontiac in Jacksonville.

Couple of pictures of the head code and trim tag

[mgarblik]

Originally Posted by Gary H

Couple of pictures of the head code and trim tag

Those cars might have been on the line together. That would have been a great color picture. Your heads look the same as mine. BTW, I looked very closely between the seal groove and lock groove on the valves and did make out what looked like possibly a number or two on a couple of the intakes. Nothing on the exhaust. That was with my camera and a 10X magnifier glass. So no good on part numbers. 99% sure they are the original valves. They do not have enough margin to be new valves. They are certainly usable IMO.

[PAUL K]

I hope the OP doesn't mind but I thought these pictures would be of interest.

A picture of an GM SD valve showing it's tulip and dished face.

A picture showing where the PN is usually stamped on the valve stem

A picture of where I believe the head of the valve is mated to the stem

[mgarblik]

Originally Posted by PAUL K

I hope the OP doesn't mind but I thought these pictures would be of interest.

A picture of an GM SD valve showing it's tulip and dished face.

A picture showing where the PN is usually stamped on the valve stem

A picture of where I believe the head of the valve is mated to the stem

After looking at your pics I again looked at my valves. It's possible there are some extremely faint numbers on the stem, but not readable. In my pics, look at where the magnet is stuck. The intake valve is fully magnetic everywhere. The exhaust valve, look at where the magnet is stuck. If you move it any further toward the valve head, it falls off. Toward the stem it is magnetic. A little surprising I guess. Pic 1, fully magnetic intake valve. Pic 2 possible joint for 2 piece valve, but really can't tell. pic 3 tulip head intake. Pic 4 point where magnetism ends on exhaust valve stem. Valve head and part of the stem, non-magnetic.

[steve25]

Here’s what I get from looking at the specs for the springs on these heads.

Closed = 117 lb

Open = 292 lb, but this was stated with what was the original cam that had .470” lift, which is not what the production 323 cam had.

The 323 cam only had .406” lift!

Now with no info on what the actual springs rates where my best guess is a open pressure with the .406” lift of 260 lbs .

This to me would be marginal with with the valve weight of even the 4.980” length valves, no less the longer heavier valves in the SD motor.

Just to make a comparison the 1968 428 HO motor had springs that provided 129 on the seat and and 272 open @ .414” .

What do you folks think?

Mike do you still have the stock springs to do a check on?

[mgarblik]

Thanks for looking all that up. I have the springs that were installed. I assume they were the stock springs. Also based on the amount of shims they used, they are likely pretty tired. I will get installed heights, current pressures for reference and go for there. May get them back together in the next week, 10 days. Unless I need new springs and they prove to be difficult to get. Never know in the new post COVID world. once the heads are together it's paint the engine and install for the most part. May still try to dyno it but not likely. We have a chassis dyno as well and I can run it on there pretty much anytime it's not being used by students.