300 H.P. valve springs

[Kenneth F.]

I have a CS-274 Sealed Power camshaft, and Sealed Power VS-521 valve springs. The machinist is asking for specs to set the valve spring installed height.

Would someone have the valve opening measurements for this camshaft? I found .390/.410, but want to make sure.

Would a spring installed height measurement be available?

There is no information with the camshaft.

Ken

[Joe L.]

Re: 300 H.P. valve springs

I have a CS-274 Sealed Power camshaft, and Sealed Power VS-521 valve springs. The machinist is asking for specs to set the valve spring installed height.

Would someone have the valve opening measurements for this camshaft? I found .390/.410, but want to make sure.

Would a spring installed height measurement be available?

There is no information with the camshaft.

Ken

Ken------


The VS-521 is equivalent to GM #3735381. The latter is the valve spring applicable to all 1955-66 Corvettes with small block V-8. The installed height spec for this valve spring is 1.66"

The VALVE LIFT specification for the CS-274 is 0.390" intake and 0.410" exhaust. This is assuming that rocker arms with an exact 1.5:1 ratio are used. Most stock-type, stamped steel rocker arms will not measure out at exactly 1.5:1, though.

[Kenneth F.]

Re: 300 H.P. valve springs

Joe, This information is appreciated. Thank you for taking the time.

Ken

[Duke W.]

Re: 300 H.P. valve springs

I recommend you exchange the VS-521 for VS-677, especially if the 677 is cheaper. The 677 is identical to the 3911068 valve spring that went into production in 1967 along with the new "300 HP" camshaft of which the CS-274 is an exact duplicate. The '57-'66 base camshaft (and spring) is obsolete and has harsh dynamics compared to its replacement.

The VS-677 was used on all small blocks - from 2 bbl. 283s to the LT-1 - from '67 to at least '79 other than those with exhaust valve rotaters, which require a different geometry spring with the same seat force and rate. This 677 has slightly higher specs than what it replaced - a rate of 267 lb/in, and 80 pounds force on the seat.

If set up for .090-.100" coil bind clearance the valve train limiting speed is at least 6500 with OE hydraulic lifter cams and at least 7200 with OE mechanical lifter cams.

Duke

[Joe L.]

Re: 300 H.P. valve springs

I recommend you exchange the VS-521 for VS-677, especially if the 677 is cheaper. The 677 is identical to the 3911068 valve spring that went into production in 1967 along with the new "300 HP" camshaft of which the CS-274 is an exact duplicate. The '57-'66 base camshaft (and spring) is obsolete and has harsh dynamics compared to its replacement.

The VS-677 was used on all small blocks - from 2 bbl. 283s to the LT-1 - from '67 to at least '79 other than those with exhaust valve rotaters, which require a different geometry spring with the same seat force and rate. This 677 has slightly higher specs than what it replaced - a rate of 267 lb/in, and 80 pounds force on the seat.

If set up for .090-.100" coil bind clearance the valve train limiting speed is at least 6500 with OE hydraulic lifter cams and at least 7200 with OE mechanical lifter cams.

Duke

Duke-----

I agree. The VS-677 would be a somewhat better spring. However, I figure that if he already owns the VS-521, there's no reason to go through a lot of trouble to try to exchange them (if it can even be done in his situation). The VS-521 should work just fine. Also, the VS-677 is slightly larger in OD (1.24" versus 1.22") which may or may not be a problem if pre-1967 heads are being used. In addition, if the stock 1955-66 valve caps (retainers) are being used, they should be used only with the VS-521 springs. The VS-677 requires a different cap. It is GM #14003974 or Federal-Mogul #VSR-7021. All small block valve caps are NOT the same.

If the VS-677 is used, the installed height is 1.70".

[Kenneth F.]

Re: 300 H.P. valve springs

Joe and Duke, Thank you for sharing your information. This helps me a lot. The machinist should do well with these specifications.

Ken

[Duke W.]

Re: 300 H.P. valve springs

Joe - I know the 677s have been successfully used in pre-'67s with the original first design retainers, but now I'm wondering what the differences are. Are there any dimensional differences or maybe the '67 design used different material spec or heat treatment? Do you or anyone else know?

I can't find any dimensional data for the VSR-7021 or a Sealed Power part number for the early 3729363 retainer. Does the VSR-7021 service both?

Respective 677/521 spring OD, ID (not including damper), and coil bind height are 1.238/.880/1.150 and 1.22/.880/1,125, so it appears the 677 wire diameter about .018" larger, but they fit the early spring pockets without problem, and there was probably sufficient clearance that the '67-up heads were machined to the same diameter as earlier years.

Duke

[Joe L.]

Re: 300 H.P. valve springs

Joe - I know the 677s have been successfully used in pre-'67s with the original first design retainers, but now I'm wondering what the differences are. Are there any dimensional differences or maybe the '67 design used different material spec or heat treatment? Do you or anyone else know?

I can't find any dimensional data for the VSR-7021 or a Sealed Power part number for the early 3729363 retainer. Does the VSR-7021 service both?

Respective 677/521 spring OD, ID (not including damper), and coil bind height are 1.238/.880/1.150 and 1.22/.880/1,125, so it appears the 677 wire diameter about .018" larger, but they fit the early spring pockets without problem, and there was probably sufficient clearance that the '67-up heads were machined to the same diameter as earlier years.

Duke

Duke------


I have no doubt that the 67+ springs could be used with the 55-66 valve caps. In fact, lots of valve caps (retainers) might be thought of as "interchangeable". That does not mean that they are functionally correct, though; it just means they APPEAR to fit OK.

The VSR-7021 was never specified by Federal-Mogul for a pre-67 small block application. In actuality, Federal-Mogul only lists them as equivalent to the GM #14003974 which is the 1979+ valve cap. However, the 14003974 replaced the 67-78 cap, GM #3896934, for SERVICE so, presumably, the VSR-7021 is applicable to the 67-78 applications.

The GM #3729363 was replaced for SERVICE by the GM #10038209 which remains available from GM. Federal-Mogul offers no equivalent for either of these valve caps. There's absolutely no reason to believe that the VSR-7021 is applicable to the 55-66 applications.

I would think that if the 14003974 was functionally correct for the pre-1967 applications, then GM would have by now cataloged it for those applications and, thus, eliminate the need for stocking the current 10038209. But, they have not done that, 50 years after the last car using the 3729363 forerunner was built. There's just got to be a message in that. Plus, even the aftermarket has not consolidated part numbers.

I have many NOS examples of all of the 1955-82 small block valve caps. I can't get at them at the moment but I did once-upon-a-time compare them. I do recall that there were differences but I just don't recall right now what they were. Do these differences rule out interchangeability between the 1955-66 and 67-82? I don't know but, apparently, GM and Federal-Mogul think so.

[Joe L.]

Re: 300 H.P. valve springs

Here are some photos of the 67-79 valve cap, GM #3896934, and the 1955-66 valve cap, GM #3729363:


DSCN3263.jpgDSCN3264.jpgDSCN3265.jpgDSCN3266.jpg

[Kenneth F.]

Re: 300 H.P. valve springs

Joe and Duke, There is an old machine shop nearby. I explained that I needed to lower the spring height on a 327, preferably without taking the heads off the engine that is in the car. He said different retainers might help, and showed me where to look. I originally had retainers on my engine with a V. The machinist suggested retainers with an H, that shortened the height .045, but the overall height of the H retainer is tall enough that I was concerned that it could come too close to the aftermarket oil seal, and this retainer is heavy. I ended up with a set of retainers with a symbol that resembles a fancy X. I shortened the height .045, and this retainer is .180 shorter in height, and is much lighter. This set of retainers came off a 1962, 250 H.P. 327. The machinist looked at the valve stem locks that came off my engine. He let me try 2 different style locks, and I was able to lower the height another .050. The .095 gets within .005 of 1966 GM specs. for a 327. I have 2 valve springs on this first head that need to be shortened another .030, and plan on using a shim.

Thank you for all of your help,
Ken

[Duke W.]

Re: 300 H.P. valve springs

The early cap (GM terminology) is listed in the P&A catalog as having a stamped "H" and is 1 3/16" OD. The symbol in the photo might be some sort of stylized "H", but I can't tell for sure.

The late cap is listed in the catalog as 1 13/16 diameter - but it sure looks like about the same OD as the early cap - and is stamped "A", but it looks like "V" to me.

So, Joe can you verify the stamped ID codes and so some dimension checks. One thing that might be hard to measure is the height of the spring mating surface relative to the valve stem when installed, but other than that they look basically the same in the photo other than the late cap having a little less material on on the lower end, which may make it a little lighter and that area is not under load, so it's a more efficient design.

Ken, do the caps you have match Joe's photos or are they something else?

I'm trying to get an understanding of the difference(s), and I'm beginning to think it's only the height of the spring mating surface relative to the valve stem tip, which would impact the shim stack to get the target installed height.

I recall on a '67 Special 300 HP rebuild that it took so many shims to achieve the target installed height that the valve was out of the pocket, so a couple of shims have to be installed between the cap and spring, which is not ideal.

So maybe the early cap is best to use if you are looking for minimum installed height. Does that sound like a correct conclusion.

Duke

[Kenneth F.]

Re: 300 H.P. valve springs

Duke, The caps I replaced look like the GM 3896934. The caps from the 1962 327 heads I used to shorten the height .045, have an artistic X, the top of the cap is 1" wide and .125 thick. The overall height is .325. The caps with the C are 1" wide, .125 thick at the top, and the overall height is .460. The C mark caps would have also shortened the height .045. I have extra C caps, and V caps if you could use samples.

Ken

[Duke W.]

Re: 300 H.P. valve springs

So, I understand that you are saying the '62 caps you have do not appear to be the same as Joe's photos of the early 37... cap.

Can you post a photo of what you have?

I recently viewed under the valve covers of a '64 FI and the cap is as described in the parts catalog with H clearly stamped. They do not look the same as in Joe's photo. I can't save and crop the photo for some reason, so Don, can you post the photo?

Duke

[Joe L.]

Re: 300 H.P. valve springs

The early cap (GM terminology) is listed in the P&A catalog as having a stamped "H" and is 1 3/16" OD. The symbol in the photo might be some sort of stylized "H", but I can't tell for sure.

The late cap is listed in the catalog as 1 13/16 diameter - but it sure looks like about the same OD as the early cap - and is stamped "A", but it looks like "V" to me.

So, Joe can you verify the stamped ID codes and so some dimension checks. One thing that might be hard to measure is the height of the spring mating surface relative to the valve stem when installed, but other than that they look basically the same in the photo other than the late cap having a little less material on on the lower end, which may make it a little lighter and that area is not under load, so it's a more efficient design.

Ken, do the caps you have match Joe's photos or are they something else?

I'm trying to get an understanding of the difference(s), and I'm beginning to think it's only the height of the spring mating surface relative to the valve stem tip, which would impact the shim stack to get the target installed height.

I recall on a '67 Special 300 HP rebuild that it took so many shims to achieve the target installed height that the valve was out of the pocket, so a couple of shims have to be installed between the cap and spring, which is not ideal.

So maybe the early cap is best to use if you are looking for minimum installed height. Does that sound like a correct conclusion.

Duke

Duke------

From what I've found, the earlier versions of the 3729363 may have been stamped "H". I don't know what the symbol is on the 3729363 I have. However, I'm certain that what I have are the GM #3729363. Also, based on the box, they're quite old----possibly around 30 years.

The OD of the 3729363 is 1.199"
The OD of the 3896934 is 1.197"

The "first step" OD of the 3729363 is 0.780" note the "first step" OD is the OD which centers the valve spring
The "first step" OD of the 3896934 is 0.749"

overall height of the 3729363 is 0.472"
overall height of the 3896934 is 0.495"

thickness at outer perimeter of the 3729363 is 0.125"
thickness at outer perimeter of the 3896934 is 0.107"

[Kenneth F.]

Re: 300 H.P. valve springs

DSCN1243.JPGDSCN1244.JPGDuke and Joe, The photos might not be as clear as needed, but the retainer on the left came off the 1962, 250 H.P. The retainer on the right has the C marking.
Ken