3970627 valve spring measurements

[Joe R.]

Duke, et al,

I had three 3970627 (BB) springs measured. The length measurements did not include the retainer. The inner and outer springs are the same height. The springs were tested assembled with the retainer and seal. All three were within a pound or two of each other on every measurement. Here's the results:

120 # at 1.88 "
347 # at 1.38 "

So, if I understand this correctly, for a linear spring the spring rate is:

2 (347 - 120) = 454 lbs/in

Coil bind set in at 1.28 ".

Joe

[Joe R.]

Re: 3970627 valve spring measurements

Joe,

I don't have any dogs in this fight but the specs are listed for the 627 spring are 105# @ 1.88, solid height @ 1.28" and 450lb per inch.

Your pressure with the 627 @ 1.88" installed height is closer to the 164 spring as it's listed at 116# @ 1.88". The 354 spring is listed at 128# @1.90".

JR

[Clem Z.]

Re: 3970627 valve spring measurements

Duke, et al,

I had three 3970627 (BB) springs measured. The length measurements did not include the retainer. The inner and outer springs are the same height. The springs were tested assembled with the retainer and seal. All three were within a pound or two of each other on every measurement. Here's the results:

120 # at 1.88 "
347 # at 1.38 "

So, if I understand this correctly, for a linear spring the spring rate is:

2 (347 - 120) = 454 lbs/in

Coil bind set in at 1.28 ".

Joe

that is what the chevy power manual says

[Duke W.]

Re: 3970627 valve spring measurements

Wow, I always thought the 450 lbs/in rate that I've seen published was in error, and the fact that the rate is listed as 267 lbs/in in the GMPP catalog gives further rise to suspicion. Most of the other BB springs listed in the above catalog are quoted in the low to mid 300s. For example, the 3916164 L-88/ZL-1/LS-7 spring is quoted as 116 lbs at 1.88 inch with a rate of 358 lbs/in. Go figure!

With those spings and the mild dynamics L-72/71/LS-6 cam the valvetrain should be good for over 7000 revs, but make sure you use C-category oil!

I express the rate formula as (347-120)/0.5 (the difference in readings divided by travel between the two readings), but if your measurements are based on one-half inch travel, multiplying the difference in readings by two gets you the same thing.

By comparison the SB 3911068 spring is 80 pounds on the seat and 267 lbs/in.

Thanks for verifying by having the ...627 springs tested!

Duke

[Clem Z.]

Re: 3970627 valve spring measurements

dual spring should be test separately not together.

[Joe R.]

Re: 3970627 valve spring measurements

dual spring should be test separately not together.

Clem,

But only if you use C-category oil!

JR

[Bill M.]

Re: 3970627 valve spring measurements

Wow, I always thought the 450 lbs/in rate that I've seen published was in error, and the fact that the rate is listed as 267 lbs/in in the GMPP catalog gives further rise to suspicion.
Duke

247@1.38 calculates to 254 lbf/in...

[Duke W.]

Re: 3970627 valve spring measurements

What......................?

[Bill M.]

Re: 3970627 valve spring measurements

What......................?

I'm questioing the accuracy of the data. 450 lbf/in makes no sense.

[Duke W.]

Re: 3970627 valve spring measurements

Look at Joe's original post. I don't see any data or test procedure issues, however it would be interesting to see each spring tested individually and see if the sum of the rates is also 450 lbs/in.

Duke

[Bill M.]

Re: 3970627 valve spring measurements

Look at Joe's original post. I don't see any data or test procedure issues, however it would be interesting to see each spring tested individually and see if the sum of the rates is also 450 lbs/in.

Duke

Duke:

I don't see any obvious data issues. But the conclusion of 450 lbf/in makes me question the data.

I calculate the L-88 (164) rate at about 330 lbf/in. I think the 627 spring is a single spring with flat damper inside. The L-88 is a true dual spring. Just doesn't make sense to me.

Bill

[Duke W.]

Re: 3970627 valve spring measurements

The ...627 is a dual spring assembly that includes the retainer and umbrella seal. It went into production on all BBs (except L-88/ZL-1/LS-7) circa '69/'70, and replaced the earlier single spring/damper that had a high failure rate. I recommend the ...627 for all Mark IV engine restorations.

I always questioned the 450 lb/in rate that is quoted in some sources (but quoted at 267 lbs/in in the GMPP catalog), which is why I asked if someone with a ...627 set could have a few tested.

Compared to the L-88 spring rate I agree that 450 lbs/in for the production spring "doesn't make sense", but I don't see any problems with the data or test procedure, so I have no choice but to accept it unless new information pops up that reveals a data or test procedure error.

Duke

[Bill M.]

Re: 3970627 valve spring measurements

The ...627 is a dual spring assembly that includes the retainer and umbrella seal. It went into production on all BBs (except L-88/ZL-1/LS-7) circa '69/'70, and replaced the earlier single spring/damper that had a high failure rate. I recommend the ...627 for all Mark IV engine restorations.

I always questioned the 450 lb/in rate that is quoted in some sources (but quoted at 267 lbs/in in the GMPP catalog), which is why I asked if someone with a ...627 set could have a few tested.

Compared to the L-88 spring rate I agree that 450 lbs/in for the production spring "doesn't make sense", but I don't see any problems with the data or test procedure, so I have no choice but to accept it unless new information pops up that reveals a data or test procedure error.

Duke

The 627 must have been developed after I left Tonawanda. I don't remember us dyno testing a dual spring on the street mechanical cam engines. I do remember replacing a lot of the singles.

I installed 164s on my 396 because of the problems with the original springs. I had to remove the umbrella seals to install the 164, so I get more oil down the guides than I like.

Sounds like I should get a set of 627s, but I would be very nervous about installing 627s based on that spring rate!

Maybe friction between the springs is the issue?

Bill

[Duke W.]

Re: 3970627 valve spring measurements

The ...627s were used on all subsequent production Mark IVs after they were phased in and solved the excess failure problem of the early single spring/damper, so they are proven.

I still have nagging doubts about the rate, but nothing to hang my hat on to challenge the data.

Friction between the springs (if they actually do interfer) creates a damping effect and would not effect static spring rate measurements.

The flat wire dampers on typical single springs create a damping effect to mitigate spring surge, but the flat wire dampers used on SB springs contribute virtually nothing to the rate.

Duke

[Clem Z.]

Re: 3970627 valve spring measurements

450#/inch would mean 234# over the nose at .520 lift. #627 are dual springs but the are not interference fit so friction does not enter into the calculation. the inter spring is progressively wound so put the closed end down.