Valve Guide Seals for Big Block

[Joe L.]

Re: Valve Guide Seals for Big Block

Attached are pictures of my springs, etc. The valve seal is about .630 in diameter. The ID of the spring is about .6875. These are not OEM springs, correct? They actually have three springs, an inner, outer and a flat center spring. OEM do not have the outer spring from what I have seen. If these are non-OEM as I believe, and I change to the OEM 3970627 do I leave the shims in place? Any other thoughts?

Thanks.

Larry------


I think what you have here are the GM #3989354 springs. You cannot use these with umbrella-type seals and that's probably why someone previously installed the PC-type seals. Personally, I would not use this for a street engine IF the cam is a stock L-72. If you want to keep using these springs you will have to stay with the PC seals, although I'd install new ones.

I think I'd just go back to stock----not all the way back to 1966 stock, but with the late 1969+ valve springs and retainers which are also SERVICE for 65-E69. You can buy a set of the 3970627 springs, retainers, and seals under GM #12371061 for about 250 bucks, GM list.

Will you need the shims? Well, the only way you'll know that if you change the springs is to measure the installed height as clem suggested. If you go back with the springs you have, I'd install the shims that were under each spring, just as you found them. Then, measure the installed height to confirm it's right.

[Joe L.]

Re: Valve Guide Seals for Big Block

All------



By the way, the L-88 and ZL-1 valve spring is none of the springs that have been discussed here. The L-88 and ZL-1 spring is GM #3916164.

[Clem Z.]

Re: Valve Guide Seals for Big Block

[quote=Joe Lucia (12484);484657]Larry------


I think what you have here are the GM #3989354 springs. You cannot use these with umbrella-type seals and that's probably why someone previously installed the PC-type seals. Personally, I would not use this for a street engine IF the cam is a stock L-72. If you want to keep using these springs you will have to stay with the PC seals, although I'd install new ones.


i dont think they are the 354 springs because the spring in the picture is black and shiny where the 354 springs were made from shot peened wire and had a rough surface. i would take the spring to a shop with a spring tester and see what the installed height poundage is.

[Wayne M.]

Re: Valve Guide Seals for Big Block

...I think what you have here are the GM #3989354 springs. You cannot use these with umbrella-type seals and that's probably why someone previously installed the PC-type seals. Personally, I would not use this for a street engine IF the cam is a stock L-72. ....

Joe -- I think you're right (see pic # 1); the spring retainer underside is the same contour as shown in Larry's pics.

Here's a couple of shots of the low-horse BB spring and retainer '65-69 with passenger 396/427, Corvette L36 / L68. These were removed from an early calendar '68 cast set of "215" oval port heads [which seemed stock, unmodified]. Note the "T" stamp on the retainer. The cap/retainer is 1.41" OD, and the spring OD is 1.510". In the 3rd shot you can see the flat damper coil and the underside of the retainer.

[Larry T.]

Re: Valve Guide Seals for Big Block

Larry------

I think what you have here are the GM #3989354 springs...Personally, I would not use this for a street engine IF the cam is a stock L-72.

I think I'd just go back to stock----

Will you need the shims? Well, the only way you'll know that if you change the springs is to measure the installed height...

I do not know for a fact that the cam is a stock L-72. I assume, and I know that can be dangerous, that it is because everything I do know about the engine (and car) is OEM. Block, heads, intake, carb, ignition, etc. Of course, then there are these valve springs.

Under what circumstances, if any, is changing to the 3970627 springs possibly a bad idea? What material are the valve seals in the kit #12371061 made from? Clem says the old style rubber ones will dry up and fall apart. Is it fair to assume these will hold up better than that? One more thing to throw into the mix, my rocker arms have an H on them. I believe that is a long slot arm, is that correct. Also, is that the correct arm for my application?

Thanks.

[Joe L.]

Re: Valve Guide Seals for Big Block

I do not know for a fact that the cam is a stock L-72. I assume, and I know that can be dangerous, that it is because everything I do know about the engine (and car) is OEM. Block, heads, intake, carb, ignition, etc. Of course, then there are these valve springs.

Under what circumstances, if any, is changing to the 3970627 springs possibly a bad idea? What material are the valve seals in the kit #12371061 made from? Clem says the old style rubber ones will dry up and fall apart. Is it fair to assume these will hold up better than that? One more thing to throw into the mix, my rocker arms have an H on them. I believe that is a long slot arm, is that correct. Also, is that the correct arm for my application?

Thanks.

Larry-----


The GM #12371061 kit contains 16 of the GM #3970627. The GM #3970627 is a valve spring assembly + cap and seal assembly. The seal is a NYLON umbrella seal which is attached to the cap. A photo of one appears in the book excerpt posted by Wayne. These are the SERVICE valve springs for all 1965-72 Corvette big blocks except L-88/ZL-1. They were also used in PRODUCTION from later 1969-72. I HIGHLY recommend the GM #3970627 springs, retainers and seals. This set-up is "tried-and-true" for over 40 years now.

I don't think your original rockers would have had an "H" embossed on the pallet end of the arm. Your application originally used GM #3860308 rockers. These rockers have an "X", "Z" or an "L" embossed on them. The "H" rockers are the GM #3959182. These were originally used for 1969 L-88 and ZL-1 applications and later used for 1971 LS-6. So, I'd say that when the valve springs were changed, these were changed, too. Who knows what else might have been changed?

[Clem Z.]

Re: Valve Guide Seals for Big Block

if your main objective is just to reduce the oil consumption i don't think going to umbrella type seals is the answer. i would measure the lobe lift on the cam before i would just change springs to make sure you don't have a higher lift cam than the 627 springs are good for.

[Larry T.]

Re: Valve Guide Seals for Big Block

I think for the short term my objective has changed. Currently I want to be sure I am not using any parts that may cause, or may have caused, damage or premature wear to the engine. Or further be affecting the performance of the engine.

The first thing I am going to do is measure the lobe lift. If that checks out for L-72 spec I will assume I have the correct cam and it does not have excessive wear. Then I will change the springs. If the lobes are too high or low I will regroup.

Is there a reason to change rocker arms back to the original configuration, instead of the long slot ones I have, if I determine I have the L-72 cam and use the OE 627 springs?

[Clem Z.]

Re: Valve Guide Seals for Big Block

I think for the short term my objective has changed. Currently I want to be sure I am not using any parts that may cause, or may have caused, damage or premature wear to the engine. Or further be affecting the performance of the engine.

The first thing I am going to do is measure the lobe lift. If that checks out for L-72 spec I will assume I have the correct cam and it does not have excessive wear. Then I will change the springs. If the lobes are too high or low I will regroup.

Is there a reason to change rocker arms back to the original configuration, instead of the long slot ones I have, if I determine I have the L-72 cam and use the OE 627 springs?

the rocker arms will be fine.

[Joe L.]

Re: Valve Guide Seals for Big Block

the rocker arms will be fine.

clem and Larry------


Yes, I agree. The 3959182 rocker arms can be used on any big block. The slightly longer slot will cause no problems. In fact, I do not understand why GM hasn't just replaced all other big block rocker arms with the 3959182.

[Clem Z.]

Re: Valve Guide Seals for Big Block

clem and Larry------


Yes, I agree. The 3959182 rocker arms can be used on any big block. The slightly longer slot will cause no problems. In fact, I do not understand why GM hasn't just replaced all other big block rocker arms with the 3959182.

they also may be of a better quality than the std rockers

[Joe L.]

Re: Valve Guide Seals for Big Block

they also may be of a better quality than the std rockers

clem------


The GM #3959182 was discontinued in November, 1997 and replaced by GM #12368082. The latter is a KIT which contains one 3959182 rocker arm + rocker ball + nut. The 3959182 part number was just the rocker arm by itself.

The last available SERVICE rocker arm kit for all applications other than L-88/ZL-1 was GM #10112680. It's now discontinued and I can't find a replacement part number at the moment, but it's possible it was replaced by the 12368082. I'll check on that later.

Now, here's the really strange thing: at the time the 10112680 was discontinued it carried a GM list price of OVER TWICE the list price of the 12368082. Of course, the difference might be due to a difference in volume of sales; I'm sure the 12368082, being the successor to the 3959182, sold quite briskly while the the 10112680 was likely a slow seller. That MIGHT be the reason for the price difference. However, there might have been other reasons, too.....

[Clem Z.]

Re: Valve Guide Seals for Big Block

i have been told that the later rockers were stamped in a reduced number of steps causing them to break easier. if i had to used stock rocker because of the rules i rockwell hardness tested them to make sure of the heat treat. never had a BBC rocker break but had some SBC ones break in race engines with stiffer valve springs.

[Larry T.]

Re: Valve Guide Seals for Big Block

I checked the cam lobes and found them to be consistent in lobe height with the L-72 cam. Using a dial indicator and measuring the lift of the push rods with the head on the lobes were all .302 to .307. L-72 is .3057 +/- .002.

I have decided to change to the GM 3970627 spring as part of the 12371061 kit suggested by Joe in lieu of the current heavier L-88 look alike. When I do so, should I leave a positive stop seal in place on the head along with the umbrella installed on the retainer as part of the kit? If not, would I be better off replacing the included nylon umbrella with a more modern, taller, hi temp silicone umbrella? I checked the installed height of a couple of the springs and they were nearly perfect at 1.88". I will check the rest as I go, but should I anticipate that the new retainers may be thicker or thinner requiring further adjustment with shims? If so, what is an acceptable tolerance for installed height?

Thanks for your thoughts.

[Joe L.]

Re: Valve Guide Seals for Big Block

I checked the cam lobes and found them to be consistent in lobe height with the L-72 cam. Using a dial indicator and measuring the lift of the push rods with the head on the lobes were all .302 to .307. L-72 is .3057 +/- .002.

I have decided to change to the GM 3970627 spring as part of the 12371061 kit suggested by Joe in lieu of the current heavier L-88 look alike. When I do so, should I leave a positive stop seal in place on the head along with the umbrella installed on the retainer as part of the kit? If not, would I be better off replacing the included nylon umbrella with a more modern, taller, hi temp silicone umbrella? I checked the installed height of a couple of the springs and they were nearly perfect at 1.88". I will check the rest as I go, but should I anticipate that the new retainers may be thicker or thinner requiring further adjustment with shims? If so, what is an acceptable tolerance for installed height?

Thanks for your thoughts.

Larry------

I would not use both the stock umbrella seals (attached to the retainer) with positive-type seals. For one thing, the 2 seals might "collide" and destroy each other. For another thing, the double seals might cause too little oil to get to the valve stem. Some valve stem lubrication is necessary.

For the past 40 years, or so, the stock umbrella seals have proven to be pretty effective at oil control on these engines. However, GM did finally go to a positive type seals on the last big block, the 8.1L. These are GM #12555601. If I were going to use positive-type seals on a big block, I think these are the ones I would use. However, I don't know what valve guide OD they require.