The Stovebolt Site Forums The Shop Area Engine Shop GMC Inline Six Valve Spring Questions

I have two GMC motors I am working on, a 228 and 302. I have a few questions regarding valve springs. I do know that GMC used the same springs from their 228 all the way up to the 302, to include the 248 and 270 as well. I have read in several places that the springs are all the same for the Chevy inline sixes as well as the GMC's, they can be used interchangeably. So I purchased a new set of SBI springs, part number 160-1116, and the vendor told me "they should work for your GMC".

When I received the springs in the mail today, I noticed these springs are about an 8th of an inch taller then the original springs that came off of both the 228 and 302. I wanted to see if anyone on the forums had used these springs before without issue? I did contact both the vendor and SBI directly, and both claim they show no listings for ANY GMC inline six cylinder, only the Chevy motors.

Next I went onto EGGE's site to see the specs for the springs that they sell in their GMC kits. Their part number for their valve springs is 160-1126. The specs between SBI's and EGGE's springs are close to each other as shown below:

SBI 160-1116
Free Length: 2.250"
Outside Diameter: 1.341"
Inner Diameter: 0.969"
Wire Diameter: 0.182"
Solid Height: 1.390"
Closed Pressure: 78lbs @1.858"
Open Pressure: 192lbs @1.462"
Material: A877


EGGE 160-1126
Free Length 2.160"
Outside Diameter 1.344"
Inner Diameter 0.980"
Wire Diameter 0.182"
Solid Height 1.375"
Closed Pressure 65lbs @1.858"
Open Pressure 163lbs @1.530"
Material A877

As you can see the numbers are close. What makes me question it is the open/closed pressures. I would hate to wipe out a cam lobe. What are your thoughts?

As a side note, a reputable machine shop that completely rebuilt another 228 I have, used Sealed Power valve springs, part number VS424, a common spring. The only spec I could find for them online was the free length, which at 2.250" matched the SBI springs I just bought. I also found that VS424 interchanges with 160-1116. So as I sit here typing this, I just realized that I may have answered my own question, that yes in fact the SBI Springs 160-1116 will work, as they are currently being run on my other 228, and have been without issue since 2013. I guess now the question is, will my other 228 with the VS424 springs need a new cam shaft soon???

I'd still like to hear your thoughts. This post is also cross posted on the GMC tech site. Thank you in advance.

Those spring specifications are so close to each other that the cam will not have a problem with either one. Just be sure the space between the coils does not go away with the valve fully open. The old school method of checking for coil bind on the race engines we built was to use the end of a bent paper clip inserted between the spring coils as the engine was turned over by hand after adjusting the valve clearance to spec. If the wire doesn't get pinched, you're good to go. It's a shade tree method, but it has worked for me for 60+ years.
Jerry

For the V8 engines, you can buy offset valve keepers to raise or lower the spring hight like these, http://www.classicenginesupplies.com/assets/classic-keeper-flyer.pdf. They may also fit the GMC, you would just need to know which valve stem configuration you have.

The SPI springs increase spring pressure by approx. 14.25 lbs for every .050" increase of compression. All you need is about .040" longer installed hight to make the installed hight pressure match. Since this isn't a race engine, I would lean towards the weaker side to save wear and tear on the cam and lifters.

Spring hight checkers are easy to use and getting cheaper, something like this, https://www.ebay.com/itm/4929-Valve...-600-2-200-Most-V8-Measurer/124302909410

SPI springs are likely for the newer inline sixes with slightly more aggressive cams, they just happen to fit the older engines with not quite the correct spring pressures.

Spring pressure, poor machining practices, cheaper material, and incorrect oil all can kill a camshaft, so you are right to be concerned about it. If you changed camshafts or lifters, ask the dealer about it.

Check the hight of each valve stem before getting too worked up, you may find there is enough clearance to set them where needed for the pressure you want. It's not all that hard for a shop to cut the spring pockets on the head just a touch deeper if you find that's what is needed, with the correct tool, it can be done as a DIY project.

Joe

One other consideration- - - -regrinding a valve seat sinks the valve deeper into the head, and also lengthens the installed height of the spring. There are ways to check and correct that situation that any machinist worthy of the name should be able to do. It's entirely possible that installing those springs without shimming them to the specified assembled height might be a fudge factor that will work in your favor. Nothing beats hands-on measurements instead of speculation on "possibilities" in a chat room, though! I've used the quill on a drill press and a bathroom scale to check spring pressures at times! LOL!
Jerry

Duly noted........ Bob C