GMPP Hot Cam Kit question...

[jnkman61m]

Greetings from a newbie to this fine forum. I am building an engine for a client and have chosen a GMPP 12480002 Hot Cam Kit for this build. My question pertains to the valve springs included in the kit, which are GM #12551483 springs.

I am concerned about coil bind after doing the math......

Installed height 1.780"

Spring "Solid Height" 1.215"

Valve lift using the supplied 1.6 rocker arms in the kit is .525"

1.780" - 1.215" - .525" = .040" remaining clearance.

I am thinking minimum accepted coil bind clearance is .060" in most publications.

ACTUAL coil bind has not been measured as the heads are not assembled and are at the machine shop awaiting my decision regarding use of these springs.

My machinist is pointing out that SOME builders will use a tight coil bind spec on some builds and get away with it, however he and I are both puzzled as to whether this will be an issue considering that this is a very popular cam kit and neither of us have seen any information in print or internet based regarding a coil bind situation being common with this kit.

Any ideas or input are welcome and appreciated. Thank you for taking time to read my post.

[FlowSpecialist]

1mm is tighter than I'd ever want to use and it's so close to coilbound you'd need to check every single spring for fitted height and actual coilbind length by squeezing them up in a vice. It's common to find about 0.5mm tolerance on the actual coilbind length of a set of 'identical' springs.

I'd aim for 1.5mm minimum as you've already surmised but if the valve seats are being recut you'll probably end up at that anyway.

It's looks to me like they designed the kit for the 1.5 rockers and decided they were going to risk trying to get away with it with the 1.6 rockers when what they really needed was a different spring. No one with half a brain designs a spring to go as tight as 1mm on a fit and forget road kit. That's just bloody stupid.

Maybe on a money no object 'everything's going to be individually shimmed anyway' race engine. Production tolerances on the springs, valves, valve seat heights, factory spring seat machining depth etc could wipe that 1mm out very easily. 2mm is the rock bottom minimum you'll ever see on an OE head and it's usually closer to 3mm or 4mm.

Dave

[rookie]

Searching hear,
http://search.msn.com/results.aspx?q=Valve+spring+%2312551483&FORM=MSNH
I found this
http://www.gmpartsdirect.com/perform...mlCATID=2.html

Also try, Pace Performance.com
or call them at
1-888-748-4670

I dig your Avatar

[jnkman61m]

After assembling the heads at the shop and compressing these springs in a vise as a test, it appears I should have adequate coil bind clearance. Picking up the heads later today and will do another mockup on the short block this weekend and confirm what the clearance actually is AS INSTALLED instead of whining about unknown issues,lol.

If there is still an issue, I will select a different spring combo to be safe and will update the thread. Thanks to all for reading and replying.