Valve Spring Part Number

[Joe C.]

Looking for the original GM valve spring installed in 1963 327 engine. This spring was superseded by 3911068.
I see 3735381 in the archives. Was there any other?
Thanks in advance.

[Joe L.]

Re: Valve Spring Part Number

Looking for the original GM valve spring installed in 1963 327 engine. This spring was superseded by 3911068.
I see 3735381 in the archives. Was there any other?
Thanks in advance.

Joe-----


GM #3735381 is the part number of the original valve spring used for all 1963 Corvette engines. It was also used for all 1958-66 Corvette small blocks as well as most other 58-66 small blocks. It was NOT superceded by the GM #3911068 valve spring used for most 1967-1991 small blocks. In fact, the GM #3735381 is still available from GM to this day.

Was there any spring used prior to the 3735381? Yes, there was. 1955-57 small blocks used spring GM #3837002 (yes, that's the part number and not a mistake). It was superceded by the 3735381.

[Joe C.]

Re: Valve Spring Part Number

Joe-----


GM #3735381 is the part number of the original valve spring used for all 1963 Corvette engines. It was also used for all 1958-66 Corvette small blocks as well as most other 58-66 small blocks. It was NOT superceded by the GM #3911068 valve spring used for most 1967-1991 small blocks. In fact, the GM #3735381 is still available from GM to this day.

Was there any spring used prior to the 3735381? Yes, there was. 1955-57 small blocks used spring GM #3837002 (yes, that's the part number and not a mistake). It was superceded by the 3735381.

Thanks Joe.
I was successful in tracking down the needed info in my "Reference" library, in my "garage archives"........in printed form.
Guess what, as expected..............your information is just as good now, as it was in 2003!!!!!!
Here's a link to the original thread.........good stuff, Joe:

https://www.forums.ncrs.org/showthre...ement&uid=5587

[Timothy B.]

Re: Valve Spring Part Number

If the 3735389 spring is still available why is it recommended to use the later 068 spring. What is the difference in these springs?

[Joe C.]

Re: Valve Spring Part Number

If the 3735389 spring is still available why is it recommended to use the later 068 spring. What is the difference in these springs?

Very little difference. The 068 has virtually identical seat force as the 381. The 068 has about 25# more force in the open position than the 389. Back then, with the very gentle cam profiles, 25# spring force increase may have been a large amount for a production engine. Also, they were dealing with pressed-in spring studs. The 25# force difference MIGHT have been useful in preventing float with the "new" "high-lift" 3849346 camshaft (.485/.485) which replaced the old Duntov 3736097 (.395/.401). Of course, with today's fast lift rollers, even the mildest of them may use seat spring force in the vicinity of 140 # and full open force as high as 300#.
The following Joe Lucia reply, from the aforementioned link:


Duke----

Not exactly. The GM #3911068 spring never "officially" replaced the GM #3735381. The GM #3735381 was originally used for all 1958-66 Corvette applications with small block. It replaced the GM #3837002 which was originally used for 55-57 Corvettes.

The GM #3735381 is a valve spring/flat damper assembly which has the following specs:

OD--------------1.228"
free length-----2.097"
wire diameter---0.169"
closed pressure as installed----76#
open pressure @ 1.26"-----------175#

The GM #3735381 valve spring assembly remains available from GM to this very day.

In 1967, Corvette and other Chevrolet small blocks changed to valve spring assembly GM #3896931. This spring was used throughout 1967 PRODUCTION but not thereafter. It was discontinued from SERVICE in March, 1968. I don't have specs for this valve spring, but I think that they are very similar, if not identical, to the GM #3911068.

Starting with model year 1968, the GM #3911068 valve spring was used for all PRODUCTION small block applications. The GM #3911068 also became the SERVICE valve spring assembly for 1967 small block applications which originally used the GM #3896931 valve spring assembly. However, it did not then become nor is it now the SERVICE valve spring for 1955 to 1966 Corvette small block applications. It can be used for 55-66 applications, though, and may even offer some slight advantage over the original springs for these applications. The specs on the GM #3911068 valve spring are as follows:

OD----------------1.239"
free length-------2.027"
wire diameter-----0.177"
closed pressure as installed-----80#
open pressure @1.25"------------200#

From 1968 through the 1991 model year, the GM #3911068 valve spring was used for ALL Corvette small block applications. It was also used for most other Chevrolet PRODUCTION Gen I small block applications right through the year 2000. This also included ALL 1968+ Z-28 PRODUCTION applications (1967 Z-28s originally used spring GM #3896931 which was replaced for SERVICE by the 3911068).

GM never used a valve spring on any PRODUCTION Gen I small block with a higher spring pressure than the GM #3911068. Other, higher-rated valve springs were used on SERVICE-only engine assemblies or otherwise available seperately in SERVICE. The GM #3927142 valve spring is one of these and is the one which is often referred to as the "Z-28 spring" since it was used with the "Z-28 off-road" camshaft GM #3927140. This spring has an OD of 1.273" and has a closed spring pressure of 110#. This spring can be used to advantage in a high reving small block, but at the expense of camshaft life.

The FM 739R spring has specs similar to the GM #3927142.



Here is something that I find very "queer":

GM's 3927142 spring (the so-called Z28 spring), which was sold OTC for GM's 3927140 camshaft (1st design "off-road" cam, used in race prepared Z28's, especially with cross-ram and dual quads), advertises MAX LIFT as .490. Similar springs from Federal Mogul (VS-677) also advertise MAX LIFT as .490. In both cases, the margin to coil bind is 0.100. GM's 140 cam has lift of .493/.512!!! FM specifically states that the VS-677 should be limited to .485 valve lift, which incidentally, barely qualifies it for ultra high RPM use in conjunction with the 3849346 camshaft.

[Michael H.]

Re: Valve Spring Part Number

Very little difference. The 068 has virtually identical seat force as the 381. The 068 has about 25# more force in the open position than the 389.

The new valve spring for 67 was designed for the new hyd lifter cam for 67. Slightly different ramp speed on the 67 cam required the slight additional pressure.

[Duke W.]

Re: Valve Spring Part Number

The new spring was released for the '67 model year concurrent with the new 929 cam, which has milder dynamics than the previous base engine cam.

Why did GM release this new spring(s)? I don't know the exact reason, but GM learned a lot about valvetrain dynamics beginning in the early sixties when they started studying valve train motion with the Optron. This research also yielded milder dynamics and greater asymmetry in lobe designs.

It's curious that the earlier spring remains available, but in any event, I recommend the 068 for all engine restorations, and they are okay with pressed in studs.

Duke

[Bob S.]

3735381 Discontinued?

In talking to my 2 closest Chevy dealers this morning, I'm told their 'systems' show 3735381 has now been discontinued. Does anyone have any info saying this isn't true?

Thanks,
Bob S.

[Clem Z.]

Re: Valve Spring Part Number

Very little difference. The 068 has virtually identical seat force as the 381. The 068 has about 25# more force in the open position than the 389. Back then, with the very gentle cam profiles, 25# spring force increase may have been a large amount for a production engine. Also, they were dealing with pressed-in spring studs. The 25# force difference MIGHT have been useful in preventing float with the "new" "high-lift" 3849346 camshaft (.485/.485) which replaced the old Duntov 3736097 (.395/.401). Of course, with today's fast lift rollers, even the mildest of them may use seat spring force in the vicinity of 140 # and full open force as high as 300#.
The following Joe Lucia reply, from the aforementioned link:


Duke----

Not exactly. The GM #3911068 spring never "officially" replaced the GM #3735381. The GM #3735381 was originally used for all 1958-66 Corvette applications with small block. It replaced the GM #3837002 which was originally used for 55-57 Corvettes.

The GM #3735381 is a valve spring/flat damper assembly which has the following specs:

OD--------------1.228"
free length-----2.097"
wire diameter---0.169"
closed pressure as installed----76#
open pressure @ 1.26"-----------175#

The GM #3735381 valve spring assembly remains available from GM to this very day.

In 1967, Corvette and other Chevrolet small blocks changed to valve spring assembly GM #3896931. This spring was used throughout 1967 PRODUCTION but not thereafter. It was discontinued from SERVICE in March, 1968. I don't have specs for this valve spring, but I think that they are very similar, if not identical, to the GM #3911068.

Starting with model year 1968, the GM #3911068 valve spring was used for all PRODUCTION small block applications. The GM #3911068 also became the SERVICE valve spring assembly for 1967 small block applications which originally used the GM #3896931 valve spring assembly. However, it did not then become nor is it now the SERVICE valve spring for 1955 to 1966 Corvette small block applications. It can be used for 55-66 applications, though, and may even offer some slight advantage over the original springs for these applications. The specs on the GM #3911068 valve spring are as follows:

OD----------------1.239"
free length-------2.027"
wire diameter-----0.177"
closed pressure as installed-----80#
open pressure @1.25"------------200#

From 1968 through the 1991 model year, the GM #3911068 valve spring was used for ALL Corvette small block applications. It was also used for most other Chevrolet PRODUCTION Gen I small block applications right through the year 2000. This also included ALL 1968+ Z-28 PRODUCTION applications (1967 Z-28s originally used spring GM #3896931 which was replaced for SERVICE by the 3911068).

GM never used a valve spring on any PRODUCTION Gen I small block with a higher spring pressure than the GM #3911068. Other, higher-rated valve springs were used on SERVICE-only engine assemblies or otherwise available seperately in SERVICE. The GM #3927142 valve spring is one of these and is the one which is often referred to as the "Z-28 spring" since it was used with the "Z-28 off-road" camshaft GM #3927140. This spring has an OD of 1.273" and has a closed spring pressure of 110#. This spring can be used to advantage in a high reving small block, but at the expense of camshaft life.

The FM 739R spring has specs similar to the GM #3927142.



Here is something that I find very "queer":

GM's 3927142 spring (the so-called Z28 spring), which was sold OTC for GM's 3927140 camshaft (1st design "off-road" cam, used in race prepared Z28's, especially with cross-ram and dual quads), advertises MAX LIFT as .490. Similar springs from Federal Mogul (VS-677) also advertise MAX LIFT as .490. In both cases, the margin to coil bind is 0.100. GM's 140 cam has lift of .493/.512!!! FM specifically states that the VS-677 should be limited to .485 valve lift, which incidentally, barely qualifies it for ultra high RPM use in conjunction with the 3849346 camshaft.

the 140 cam lift is .469/.485. you may be thinking of the 754 cam

[Duke W.]

Re: Valve Spring Part Number

"Gross lifts" are phony numbers derived by multiplying the gross lobe lift (including the clearance ramps) by the phony "design" rocker ratio. This is how you get the 0.485 "gross valve lift" for the 30-30 cam and .491/.512" for the 140, but that's not what's happening inside the engine.

You have to subtract lobe clearance ramp height from gross lobe lift and multiply by the result by actual peak rocker ratio of about 1.44:1. This yields .440" actual valve lift for the 30-30, and I estimate actual valve lift for the 140 as .448/.468".

The nominal installed height of 068 and 142 springs is 1.70", with coil bind at 1.15" and 1.16", respectively, so they will handle .450/440" actual lift with 0.100" coil bind margin, but you can probably get away with .050" as long as the springs don't get into a significant surge mode.

Both spring/lobe combinations were designed for production rocker arm geometry. "High ratio" rocker arms could get into coil bind and they will definitely reduce valvetrain limiting speed.

Duke

[Joe C.]

Re: Valve Spring Part Number

"the 140 cam lift is .469/.485. you may be thinking of the 754 cam"

Clem:

The specs I have are as follows:

140.....................257/269......................493/.512...............112
754.....................262/273......................488/.509...............112

of course, @ .050, with the mythical 1.50:1 GM "design" ratio.

[Clem Z.]

Re: Valve Spring Part Number

"the 140 cam lift is .469/.485. you may be thinking of the 754 cam"

Clem:

The specs I have are as follows:

140.....................257/269......................493/.512...............112
754.....................262/273......................488/.509...............112

of course, @ .050, with the mythical 1.50:1 GM "design" ratio.

the GM power manual lists the #140 cam, dur @ .050 256/268.max lift with 1.5 rockers .469/.483. the #754 cam, dur@ .050 262/273 and max lift with 1.5 rockers .488/.509. 112 lobe centerline for both

[Joe L.]

Re: 3735381 Discontinued?

In talking to my 2 closest Chevy dealers this morning, I'm told their 'systems' show 3735381 has now been discontinued. Does anyone have any info saying this isn't true?

Thanks,
Bob S.

Bob-----


It's very possible that the 3735381 has been recently discontinued. GM dealers should have "up-to-the-minute" information on this. My information "lags" by up to a month or two. The only thing that surprises me is that GM offered this part for so long in SERVICE. I mean, it's been 42 years since the last one of these was used in PRODUCTION.

[Duke W.]

Re: Valve Spring Part Number

the GM power manual lists the #140 cam, dur @ .050 256/268.max lift with 1.5 rockers .469/.483. the #754 cam, dur@ .050 262/273 and max lift with 1.5 rockers .488/.509. 112 lobe centerline for both

The Power Manual specs for SB mechanical lifter cams are different than most other sources. The durations and lifts appear to be top of the clearance ramp to top of clearance ramp with actual valve lift (at 1.5 RR).

For example the LT-1 cam .050" duration is listed as 229/237. Most sources quote the gross duration at .050", which includes the clearance ramps, of 242/254. The tops of the clearance ramps are .012.017" above the base circle. My .050" duration above the tops of the clearance ramps measurement (.062/.067" lifter rise) based on the detailed GM lobe data is 231/239. These are the durations you need to use when comparing mechanical lifter cam duration to hydraulic lifter cam specs.

Duke

[Clem Z.]

Re: Valve Spring Part Number

The Power Manual specs for SB mechanical lifter cams are different than most other sources. The durations and lifts appear to be top of the clearance ramp to top of clearance ramp with actual valve lift (at 1.5 RR).

For example the LT-1 cam .050" duration is listed as 229/237. Most sources quote the gross duration at .050", which includes the clearance ramps, of 242/254. The tops of the clearance ramps are .012.017" above the base circle. My .050" duration above the tops of the clearance ramps measurement (.062/.067" lifter rise) based on the detailed GM lobe data is 231/239. These are the durations you need to use when comparing mechanical lifter cam duration to hydraulic lifter cam specs.

Duke

they also list a duration @ lash point 300/312