Valve seals

[68LAlonghorn]

Hi All,

I've been reading this amazing forum since I purchased my '68 C20 Longhorn about four months ago.This is the first time I've done any work on a truck, so definitely a newbie, but mechanically inclined, so been able to do a lot already thanks to the amazing information I've been able to find here, so thanks so much to all of you!
My first post is to ask about valve seals. I've read a lot of good things about the Fel-Pro SS 72527 for the intake and the SS 72526 for the exhaust, but when I look into purchasing them, it shows as not compatible with my '68 327 and shows the SS 10058 as the correct seals. My question is, can I use the positive seals or being an older engine I should use the older umbrella type seals for both intake and exhaust?

Thanks in advance for any help.

[Accelo]

The felpro ss10058 umbrella seals go on your valve stems without machining the head.

These are a supplement to the original seals. (Use oem o-ring and the umbrella style together) This seal doesn't fit onto the head like a positive style seal. It rides on the valve stem and acts as an (umbrella) so that the oil doesn't make its way through the guides in the head. Hope this helps. You have to purchase seperatly the stock style "O" rings for the top of the valves.

[68LAlonghorn]

Thanks so much for the info Accelo. I had read about the machining, but was not too sure what that meant. I will go ahead and order the 10058 and the O rings, which I think are the FEL-PRO SS 5112.

Thanks again.

[68LAlonghorn]

Hi Accelo and all,

So I removed the intake and exhaust springs on cylinder one, as I thought I saw blue under the spring, and I was correct. On the exhaust valve there was a positive seal by KOK, model M046C, very similar to the Fel-Pro SS 72527, on the intake another positive seal, not sure of the make and model. Neither had the OEM rubber O rings on them. I've attached some pics, as I'm not sure these seals fit correctly. the one on the exhaust valve had one of the rings on it loose above the seal. Not sure if my heads have been machined to be able to use these type of seals, so any feedback would be much appreciated.

Thanks in advance.

[Accelo]

To my knowledge GM never machined the valve guide for positive seals. So yes they have been machined. I believer this set up is superior to the ones you were considering. Purchase the new seals for the machined guides and enjoy. It appears you have identified your issue. BTW you will still need to replace the OEM style "O" rings.

[68LAlonghorn]

Thanks so much Accelo. I should still go with the umbrella SS 72526 for the exhaust, instead of using positive on both valves correct?

[68LAlonghorn]

The more I look online and look at the pics the more I think the heads have not been machined to fit the positive guides. The guides don't make it all the way to the bottom shoulder of the guide, which watching some videos seems like they should.

[Carl Spangler]

I replaced the original (50 YO) OEM O-ring style seals on my L6 engine and all trace of startup smoking vanished. Additionally, the engine is WAY less sensitive to fuel octane issues.

I used this spring compressor:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[Accelo]

68LAlonghorn
If the heads are 1968 they have been machined.
I have always used the same seals on the intake and the exhaust.
However, I doubt it would make much difference if you wanted to use both styles.
Any seals will be an improvement over what you have.
BTW nice pictures.
Cheers.

[68LAlonghorn]

Hi Accelo,

So after a bunch of investigative work, it seems that my heads may not be the original ones. I checked the casting numbers on the heads (3998993 H3 2), and they seem to be from 72. Not sure if there is a difference between 68 and 72, but maybe they machined them before installing them? Still not too sure how to tell if they have been machined or not, would the positive seals fit if they were not?
Anyways, I've ordered the positive fel-pro seals and will try those out.

Here is a pic of the casting number on the head for your enjoyment!
Thanks so much for your help.

[ohboy321]

Here is a link to a site that can help decode SBC heads: http://outintheshop.com/faq/casting/heads.html

[68LAlonghorn]

Originally Posted by ohboy321

Here is a link to a site that can help decode SBC heads: http://outintheshop.com/faq/casting/heads.html

Thanks so much!

[Accelo]

I can assure you they didn't come machined like that. You have 76-CC heads on a 327. These typically came with heads with 64CC chambers. I have included a picture of the tool they use to machine the heads for the type valve seals you have.
Cheers.

[68LAlonghorn]

Thanks so much Accelo.

Got the positive seals today so I'm going to work on it this weekend and see how it goes.

[68LAlonghorn]

Well, have a couple more updates on the valve seal replacement job. Seems like the previous owner did the valves for the left head with positive seals on both intake and exhaust and the right head with the fel-pro black umbrella type. Also the right head has completely different looking machining on it, which looks a bit strange to me (photo attached). Finally when going to do the 7th, cylinder, I realized that the spring was broken (pic attached), so I just ordered a whole set and will redo them all.

Should I worry about the different machining on both heads? I wonder if the broken spring has something to do with the truck dying at every stop, or the vacuum gauge jumping around when testing.

[bry593]

I'd measure both sides to determine the difference. I bet that broken spring was on the shim. Probably found to be weak during the rebuild and they cheaped out and did not replace the set. Sure doesn't build confidence seeing two different machine works and seal styles.

Yes, the vac gauge will jump around if a cylinder has a valve that is leaking. You can't have vacuum or pressure if there is a leak....

Might also think about dropping a set of the Summit (Dart) iron heads on your motor. These are damn good for the money. Will bump your compression (72cc), flow well (2.02/1.60) and be solid castings (Dart USA). I use them and have 20k+ miles on one set without a single issue.

[68LAlonghorn]

Thanks Bry593. Yes, the different machining does not make me feel too good about these heads. Those Summit once look really nice and affordable, but I've never replaced heads, although I had never done valve seals either till a week ago, so maybe I could do it. Can you change the heads without doing any changes to the pistons? just remove the heads and install the new ones? I wonder how my stock 327 would do with those.

As I already have springs coming in, I think I will install them, install the new intake, carb, and HEI distributor and see how she runs and if it's still not happy I may just go ahead and get those heads.

Thanks.

[bry593]

I'm with you. Might as well see how these things run before dumping $700 into new heads. Maybe the spring and some leaky seals were the only issues? If so, you saved some money to be used for other improvements (or gas and food as prices rise).

Yes, the Summit heads bolt right on a 327 and will not cause detonation issues. They are not HotRod heads, but do flow better than any OE old school head. You simply can't go wrong using these on a driver.

By the way, are you sure its a 327? Did you run the casting number on the driver side rear of the block? You might be surprised at what you find. When I bought my truck was told it a 350. When I got it home, found it to be a '76 305....

[Accelo]

I checked a block in a C10m for my daughters boyfriend. He was told it was a 327 when he purchased the truck.
Well two out of three numbers taint bad. It was a 307.

The large CC chambers have dropped the compression substantially. It's easy to spend your money but the replacement heads could really wake up your motor with both a increase in breathing and compression.

Or just put the springs and seals in and enjoy the ride. One has to remember "it ran before!"
cheers.

[68LAlonghorn]

This are the numbers I have:
engine casting on drivers side: 3914678
Heads: 3998993
front of passenger side: VO7I5YS.

I"ve looked at all this numbers and I'm still not sure. Depending on what page you check, It seems the engine number could be either a 327 or a 350, and in some sites even a 302?

Is there a sure way to tell what it is?

[Mnguy]

YS suffix with that casting number shows a 68 327 4 barrel manual trans. It is the same block as a 350 so it's always possible it's been crank swapped at some point in the last 50 years.

[68LAlonghorn]

Thanks so much MnGuy, I was having problems figure it out.

Well guys, it seems like I may need new heads after all. Check the pics attached. Went to do the springs on cylinder #2 and found that, which to be honest I'm not surprised. Didn't see the piece anywhere, so not sure how long it's been like that, but I don't think that can be a good thing.

Now have to figure out how to swap heads, back to Youtube!

Thanks so much for all the info and help guys, it is incredible having this type of support when you do something for the first time.

[Accelo]

You got this far so doing the head swap it well withing your capabilities.
A great opportunity to upgrade the efficiency and performance of your truck.
Lots of options.
The GM Vortec heads are good options but require an intake change.
If you go with an aluminum head you will be able to run a point higher compression than with iron. Which every heads you will be pleased with the results, including the lack of smoke.

[68LAlonghorn]

Been looking at heads for the last couple of hours and it's crazy how many options are out there. Assuming my engine is stock, I'm currently between the Summit SUM-152123 Cast Iron, which I think is the one Bry593 suggested and the Edelbrock 5089 aluminum heads, but already reading stuff about them warping or not mating well with iron blocks, so still reading up.

Any additional head suggestions are welcomed.

[BigBird05]

Go look at Engine Masters videos. They did a comparison between Iron and Aluminum SMB chevy heads. Bottom line Aluminum always won if you can afford the increase in price.