Replacing big block valve springs in L78, L71 & L72�s.

[Gary C.]

[Joe L.]

My valve springs have lost their tension which isn’t surprising after all these years!

What do we use these days to replace, springs 3970627, Retainers 3859909 & collets 3947880 as these are no longer available?
The seat pressure should be around 100 LBS (96-106) as quoted and 320-370 open.

Thanks,
Gary

Gary-----

It depends which valve springs are on the car now. If you have the original springs, they will be a single spring with a damper. If the springs have been replaced since about 1970 with new GM springs, they will be dual springs.

The best replacement is the GM #3970627 spring and valve cap kit. These are the dual springs. Unfortunately, these are now discontinued. Replacing the spring component of these kits is easy------use Sealed Power VS-708. These are identical to the spring supplied as part of the aforementioned kit. The problem is the valve cap (retainer) which was supplied with the kit and also available separately under GM #3964264 are no longer available. These were discontinued in August, 2013 and are not available in the aftermarket, now or ever. These valve caps have an attached umbrella shield of nylon material. So, if you have the replacement 3970627 valve springs/retainers, all you have to do is to replace the springs with the VS-708 and replace the nylon shields with Fel-Pro SS-72513 and you're all set.

However, if you have the original 1965-69 valve springs and valve spring caps, that's a big problem. You cannot use those retainers with the VS-708 springs and you can't buy the 3964264 valve springs caps.

The GM #3947880 valve keys are still available from GM. These are not the ones originally used for 1965-68 big blocks but they will perfectly replace the originals and are improved from the originals.

[Gary C.]

https://www.parts.com/index.cfm?fuseaction=store.morePartInfo&PartID=130 9190&catalogid=7682&keyword=&Title=GM%20Performanc e%20Parts-Big-Block-Valve-Springs-PartNumber-12371061

[Joe R.]

[Joe L.]

Thanks for your help Joe.
I found this GM Performance parts kit 12371061 on the web. What do you think?
https://www.parts.com/index.cfm?fuse...umber-12371061

Gary-------


Two problems.

First, this is a unit of 16 of the valve springs that were supplied with the 3970627 kit. You can get the same valve springs under Sealed Power VS-708 for less money. Unfortunately, the 12371061 does not include the 3964264 retainers. If you don't already have them, neither the 12371061 or VS-708 will do you any good.

Second problem: I believe the 12371061 is discontinued.

[Michael F.]

[Gary J.]

[Joe L.]

So if you go with aftermarket, what do you go with for a stock configuration for a '66 427/390?

Gary-------


Here's another option for you: use valve springs Federal-Mogul/Sealed Power VS-657. This is a single spring with damper. These can be used with your original retainers and original style umbrella shields.

This would not be my preferred option but it does allow you to replace the original springs used for 1965-69 big blocks with NEW springs pretty much equivalent to the originals. Hopefully, these will be improved from the GM originals which were very prone to breakage. I would expect that Federal-Mogul has solved that problem with the VS-657 springs.

The dual springs that I mentioned above were the 1970-72 PRODUCTION springs which were also SERVICE for 1965-69. These were the "fix" that GM developed for the breakage-prone, original 65-69 springs. However, as I mentioned, they can only be used if you have the matching retainers.

[Gary C.]

[Joe L.]

[Wayne M.]

All-----
By the way, when replacing stock-type umbrella seals used with original 1965-69 big block valve springs (except L-88) or when using the Sealed Power VS-657 valve springs I previously mentioned, use valve seals Sealed Power MV-1912. These are VITON seals and are superior to other materials.

Joe -- would those VITON seals work on these "842" aluminum heads I have ? Cast June or Aug 1967; (hard to make out the year numeral). Probably these valve guides were machined by previous owner, but it sure looks like it's "factory" to me. Did the L88/89 heads use a different guide (& seal) ?

[Joe L.]

Joe -- would those VITON seals work on these "842" aluminum heads I have ? Cast June or Aug 1967; (hard to make out the year numeral). Probably these valve guides were machined by previous owner, but it sure looks like it's "factory" to me. Did the L88/89 heads use a different guide (& seal) ?

Wayne------

These guides have been machined for positive seals. You could still use the standard umbrella seals I mentioned above but, since the guides have already been machined, positive seals would probably be a better choice. These had to have been field-machined since no '842' heads were ever originally of the configuration you show. Many different positive seals are available.

L-89's originally used the same umbrella shield as most other big blocks. Originally, these were GM #3866612 and later GM #460483, now discontinued without supersession. The Sealed Power MV-1912 is better.

L-88 and ZL-1 used a different valve seal. This was a small nylon seal which attached to the valve spring cap in a manner similar to the 1970-72 (and SERVICE for 65-69) valve spring cap GM #3964264. These were GM #3879613. However, the seal was much smaller than the seal used with the 3964264. It had to be to fit within the smaller inside valve spring used with the L-88 valve spring. Personally, I do not consider these seals suitable for a street engine and, in fact, they were never intended for a street engine since Chevrolet did not consider L-88 and ZL-1 as being street engines.