427 BB Valve Spring Part Numbers

[Ken K.]

I have a pair of 1966 427 heads. I'm looking into replacing the valve springs on them. (Weak??) I think the original part number was 3859911 and this was replaced by 3970627. Is this 3970627 number correct, or is there a later part number I should be checking into? Does anyone have any recommendation on what type of spring to use with the stock cam.
My other question is about valve spring washers. (Spacers) When I removed the valve springs from the heads, they all had a harden washer/spacer under them. Is this factory correct? Or did someone add them to help the weak springs work better? If so, I'm assuming that I would leave them off when the new springs are installed. Thanks again for the help and advice. Ken

[Michael H.]

Re: 427 BB Valve Spring Part Numbers

Ken,

The 3970627 is the replacement for all 65 and later big blocks (exc L88 etc) and it's an excellent spring. The original design was a single coil with a flat coil damper and that design proved to be prone to frequent breakage which often resulted in complete engine destruction. If I remember correctly, the 3970627 is an assembly which includes a new design cap and seal. I've had the 627's in my 425 HP 66 for over 20 years and probably 30,000 miles with zero problems.

I don't remember a shim being installed in production but I suppose it's possible they may have had the thin SS shim. It would be a good idea to check the dimension for each valve/retainer and shim if necessary but only to factory specs. I can look that up if you need it.

It's also a good idea to replace all of the locks too. This was yet another problem with early big blocks.

[Bryan L.]

Re: 427 BB Valve Spring Part Numbers

I just bought the springs, retainers, and locks from Competition Products to replace the originals on my 427. I ordered off their website. I was going to go with GM pieces but they were approx 3 times as much as the aftermarket stuff.

BL

[Clem Z.]

make sure the keys are hardened

use a file to see if they are hard. the installed spring height is 1.880(1-7/8") you should use a "hardened" shim between the valve spring and the head because the cast iron will be "eaten in to" by the spring and even worse the flat wound damper that some springs have.