Sorting out early big block valve springs

[Duke W.]

From what I can tell the early BB valve springs - the ones with a propensity to break -were a single spring with damper and used an O-ring seal - essentially the same setup as the SB.

The force data listed in the '67 AMA specs is 94-106 pounds @ 1.88", and 303-327 pounds @ 1.38". Using the center of these ranges, the rate works out to a whopping 430 pounds/inch. Geez, no wonder they broke a lot!

My '77 vintage Corvette P&A catalog lists "second design" components; 3970627 "spring unit" that must be used with 3964264 "cap unit" (retainer), and no seal is called out.

My 2006 GMPP catalog lists the above spring (described as dual) and retainer along with a 460527 seal kit, which I crossed at napaonline.com, and it appears to be a set of silicone rubber "umbrella" seals. Does the 264 "cap unit" differ from the 1st design, by having a provision for retaining the umbrella seals? The Chevrolet Power Manual (4th edition, Fig. 28 page 3-12), shows a photo of of production (which I assume are the second design) and racing spring and retainer, and the production retainer appears to be a two piece design with either a built in shield or seal retainer. The photo caption describes the spring as "valve spring and damper", but looking closely at the photo indicates a dual spring though it's tough to tell.

The 627 data in the GMPP catalog is seat force, 105 pounds @ 1.88" and a rate of only 267 pounds per inch, which seems low.

So can anyone verify the above or fill in the blanks and resolve the ambiguities?

The point is to restore a L-72, which may still have the early setup, to the later more reliable setup. No hot rod (or L-88/ZL-1) parts will be used - just second design production from GM or OE equivalent like Clevite or Sealed Power.

Duke

[Clem Z.]

Re: Sorting out early big block valve springs

3970627 is what you want for a stock lift cam. i have not bought any for 4/5 years but that part # got you a dual spring and retainer with a snapped in place nylon cup type oil shield which could be removed if you wanted to use a positive type seal.

[Clem Z.]

PS i replaced the 3964264 reainer which was

a PM powered metallurgy material piece with a 3879613 1st design L-88 retainer because it was a machined,heat treated billet material which would be stronger. the snap in nylon oil shield could be installed in the 3879613

[Duke W.]

Re: Sorting out early big block valve springs

Thanks, Clem. Are you saying that when you order 3970627 you get both the dual spring assembly and 3964264 retainer in the same box, or do the retainers need to be ordered separately.

I assume that the LS6 used this spring and retainer, but did they also have an additional separate oil seal? I'm also considering going with positive type valve seals on both sides.

The cam will be a 143 clone or maybe a custom with slightly different indexing and maybe a 30-30 lobe on the exhaust side depending on how the exhaust flow ends up after head massaging including opening up the exhaust seat for a 1.88" valve. (As OE built I'm amazed how restrictive the exhaust side of these early rectangular port closed chamber heads is. The top end is constipated, big time. ) BTW, my understanding is that the Speed Pro CS-165R doesn't have the rear groove, so that will have to be machined unless someone knows of a 143 clone that does have the rear groove.

The 30-30 lobe actually has slightly softer dynamics than the L-72 (143) lobe. The combination of the L-72 lobe on the inlet side and 30-30 lobe on the exhaust side is the same setup as the LT-1 cam, and EA says the best SAE net torque curve is with the same 110/122 indexing as the LT-1 cam. It's pretty amazing - like GM designed the LT-1 cam for the BB and then put it in the SB!

Duke

[Clem Z.]

when i ordered them 4/5 years ago the reainer

with the shield was in the box with the spring. i change my new 70 454 450HP reainers to the 1st design L-88 because of the reason i posted above and the retainers on the 454 engine had the nylon oil shields which i moved to the L-88 retainers

[Clem Z.]

exhaust port flow

i would look into installing exhaust seats with a venturi effect. i will look to see if i still have the drawing that was sent to me back in the mid 60s. the later aluminum BBC heads had this type of exhaust seat insert. the open chamber cast iron heads flow a lot better than the closed chamber ones. we made 20+ more HP over a closed chamber head even leaving in the closed chamber pistons which lowered the CR to about 11:1 from 12.5:1 with the closed chamber heads

[Duke W.]

Re: when i ordered them 4/5 years ago the reainer

Did the 70 LS-6 have a separate valve seal of any kind, or was the shield built into the retainer the only oil control provision?

Okay, so the first design retainer is 3864900 (stamped "O") which was used with all early ('66-69) except HD (L-88/ZL1), which was 3879716.

I take it that the 900 retainer was designed for a single spring with damper, and the 716 (and 254) retainers are designed for dual springs.

Is that correct?

Also, it appears that the "fix" for the early valve spring issue did not go into production until '70. Is this correct?

Duke

[Clem Z.]

Re: when i ordered them 4/5 years ago the reainer

3879613 for the first design L-88 retainer and the LS-6 retainers are 3964264.there was a 3879613 single spring with a damper in between the orignal HP 396 spring and the 3970627 dual spring. the only oil seal was the nylon shield on the 450 HP 454 70 chevelle engines. the single spring with a damper used a umbrella type seal on the stem and i guess the reason it took so long for the duel springs was coming up with a oil shield design to replace the umbrella which would not fit with a dual spring

[Wayne M.]

This might help -- 1972 article

in "How to Hot-Rod BB Chevs"

What I'd like to know is if the 3859911 was such a weak spring for Hi-Perf BB chevs, then why did GM continue to specify it for the non-L88 versions at least thru Jan 1970 ? (except '70 Corvette [454, exc.H.D.], which calls for the 3970627)

[Duke W.]

Re: This might help -- 1972 article - EXCELLENT!

I'm trying to pry that first edition away from a buddy for a few days because I figured it has some good info.

Not being that close to BBs over the years, I'm surprised that is took literally five years for Chevrolet to "fix" the early SHP spring breakage problem.

It looks to me like combination 2 is the way to go for a L-72 restoration with the OE cam. (Comb. 3 is too much force and is only necessary for the racing cams.)

My buddy - who has considerable BB experience, but is no longer "into it" - said the early umbrella seals (Comb. 1)work okay, but they look Micky Mouse to me.

I think Comb. 2 - the setup for the '70-'71 LS6 is the way to go for an earlier vintage SHP BB restoration. But I'm thinking of eliminating the built in umbrella on the inlet side retainers and going with positive seals. On the exhaust side you want some oil flow, so the umbrella is okay by me.

When completed I want this engine to use a little oil - say a quart every 1500 in normal driving. These big guys generate higher internal component temperatures than SBs if run hard, and they need some oil into the top end to lubricate the guides and top ring - and enough flow through the exhaust guide so the oil doesn't stay around long enough to carburuze and wear the stems and guides! That's probably why the HD setup has what appears to be a less aggressive oil seal setup.

Is their any info on massaging early rectangular port closed chamber head for more flow? Any flow data?

Duke

[Duke W.]

Re: This might help -- 1972 article PS

At some point GM dropped the early parts (Combination 1) from service. My '77 P&A catalog calls out "second design" (Combination 2) parts for all earlier SHP BBs. I don't know when they made the P&A catalog changes because I don't have an earlier edition.

It could be they waited awhile until the new design was proven in the field. Then maybe they decided to let the stock of the early ****t... springs be depleted by sales rather than scrapping them. They must have sold FAST!

Early on the BB developed a reputation for being no where near as reliable as even the hottest OE SBs, and now I see why. Waiting five years for a decent valve spring setup that wouldn't break is a long time, but the later SHP spring setup (Combination 2) appears to be the way to go for a SHP BB restoration and not have to worry about breaking valve springs.

Duke

[Wayne M.]

1972 article - Heads and Flow/Porting info

Duke -- the cylinder heads section of the "How to Hot-Rod BB Chev's" book is 19 pages long. I could scan and email. Most of the mods are done on the (relatively new in 1972) open chamber ZL-1 heads, but I see that one flow chart compares stock hi-perf closed chamber (2.19 / 1.72" valves) with the same ported by Bob Joehnck.

Let me know if you'd like a few of these pages scanned.

[Mark #28455]

Why no L88 springs?

While the LS6 spring has a seat pressure of only 105#, it is rated at 450# per inch compression, so at 0.500 lift, it has 330# "over the nose".

The L88 spring has a seat pressure of 116# and is rated at 317# per inch, so "over the nose" is only about 275#.

All numbers per the Chevy Perf Parts Catalog.

So, although it is a common misconception that the L88 spring is more likely to provide excessive wear of the cam lobes, the truth is that the "high perf" LS6 spring is actually HARDER on the cam.

Go figure!

Mark

[Duke W.]

Re: 1972 article - Heads and Flow/Porting info

Thanks for the offer, Wayne, but since I'm still in the Internet stone age with just a dial up connection...

Anyway, Clem sent me what appears to be that chart, so if there is no other info on the early closed chamber heads, then I probably have everthing worthwhile from How to Hot Rod BB...

I do find that chart confusing. First, as is often the case, the flow test depression is not listed, so the data has no context.

Next, the peak inlet flow is well over double what I would expect, so they must have used a substantially higher test depression than the typical 28" H2O.

One can get virtually any flow you want by increasing the test depression, but it takes four times the depression to double the flow!

Duke

[Duke W.]

Re: Why no L88 springs?

One thing I have learned over the years is that catalogs, techical specs, etc. are FULL of errors, and GM is no exception. Then there is the NY Times and the Washington Post, but that's a whole other issue...

As I believe I posted earlier, the '67 AMA specs list 427 spring force data which computes to a spring rate of 430 pounds per inch. Of course those are for the first design springs, and for comparisons sake the SB 068 springs are 267 lb/in.

Now the rate listed in the 2006 GMPP catalog for the second design 627 dual valve spring is 267 lb/in - same as the SB. What a coincidence!

And if you believe that I have a bridge to sell you.

Whenever I run across something that doesn't make sense I seek out other sources for corroboration.

The '70 Corvette CSM or AMA specs may have technical data for the 627 springs, eventhough the LS6 was never released for Corvette. It was planned! And the '71 CSM or AMA should also have the data. So if anyone has these documents can you please post the spring force data.

As far as the L-88/ZL-1 springs are concerned, I expect that they have a higher rate than the SHP spring, but again, some sources have suspect data including the GMPP catalog. I believe these springs went through some design change interations with new part numbers assigned after '67, so the rate may have even changed.

The '67 AMA specs say nothing about the HD engine, but there should be some data in the '68 and/or '69 CSM and AMA specs, and I'd also like to see the HD engine valve spring data from those sources.

Duke