Source for correct distributor advance springs?

[G B.]

I'm pulling my hair out over this one. I can't find any source of moderately stiff advance springs that give anything close to the original advance curve of a late sixties Corvette performance distributor.

Chevrolet no longer sells any advance springs for pre-HEI distributors. The junkyards have passenger car advance springs, but these are far too stiff.

The aftermarket spring kits (such as those made by Mr. Gasket) usually contain three different sets of springs. However, they're all too soft. The advance curve with aftermarket springs always starts below idle speed and peaks too early. I've tried a combination of one aftermearket soft spring and one passenger car stiff spring. That gives a curve that is close to stock for a factory performance distributor. The problem is that the mid-range advance with this combination is wrong.

Can someone help me out here? Where can I buy some new STOCK advance springs for sixties Corvette distributors? Is there a source who will sell them in volume?

[John M.]

Re: Source for correct distributor advance springs

Jerry,
If you can give me some dimensions, wire size, OD and length I can probably get you the spring that you need. Or, if you have one that you could send me I could do it that way. We use a lot of different size extension springs in our business and have some of them custom made. Also, check with Lee Spring to see if they have an on-line catalog and compare sizes and dimensions.

[Joseph T.]

Re: Source for correct distributor advance springs

Jerry

Do you restore 1957 FI units and Distributors.?

If so... can you give me an idea of the process you use, time involved and general price range.

I have a complete original 4360 unit with tach drive 889 distributor.

Kindest regards,

Joe Trybulec
479-435-1855

[G B.]

A nice offer

John, it's very thoughtful of you to offer help.

I don't think any spring company is going to have old stock GM distributor advance springs in their current inventory. If they did, some Corvette supply house would be offering them in their catalogs. I do know that Jim Thorpe in Iowa has tried to have some reproduced without success. He believes it will be very tough to get a spring manufacturer to tool up for anything so tiny in a relatively small quantity.

I do have 4 NOS service springs #1883498 that "look" about right. I don't know if this part number corresponds to any particular assembly line distributor application though. I'll put a pair in a '63 FI distributor and map out the advance curve with stock #37 weights, #724 point cam, and #54 advance cam. If this curve comes anywhere close to right for a '63 FI distributor, I'll send you one spring on loan as a sample. Who knows, maybe you could sell a billion or two. Or maybe 50 over ten years.

[G B.]

It's best that you phone.

I'm sure it would violate some international law/treaty if I used this board to describe my FI work.

My Top Secret phone number is (251) 478-4003 from 8 am to 9 pm Central Time. If you lose my number, you can find it listed in the phone book and in my NCRS Board profile. That number you see on bathroom walls at swap meets is for another FI repairman that I shan't mention by name.

[Mike M.]

Re: Source for correct distributor advance springs

joe: what's the serial # of your 4360? thanks, mike

[Clem Z.]

Re: Source for correct distributor advance springs

back in the 50s and 60s we used the springs from the 6 cylinder chevy distributors because they allowed full advance at about 3000 RPMs in a V-8 distributor

[Duke W.]

Re: Source for correct distributor advance springs

Most of the OE curves start at about 700, which is below the reasonably acceptable idle speed for mechanical lifter cam engines regardless of what Chevrolet said, so it's "normal" to have the centrifugal start at below idle speed on hi-perf engines.

The rate that you can get it in is basically a function of detonation, which is a function of fuel octane.

With the exception of the two engines listed above, most of the curves topped out at 4-5000, but were mostly in by 3000-3500. On the two referenced engines it was all in at 2350.

I think with some combination of aftermarket springs you can get a curve you can live with, but having it start below normal idle speed is just part of the deal with SHP/FI engines.

Duke

[Clem Z.]

Re: Source for correct distributor advance springs

try just one of the heavy springs and see what the curve looks like. put a "E" ring on the weight post without the spring to hold the weight in place. been there done that

[Art A.]

Re: Source for correct distributor advance springs

Mike, I think it's #132

Art

[Art A.]

Re: Source for correct distributor advance springs

Duke If it's the one I'm familar with, the engine that goes with Joe's 57FI unit is anything but stock. It's a Chevrolet Engineering built RACE engine.

Art

[Duke W.]

Re: Source for correct distributor advance springs

Ah, a racing engine - very different animal than a street engine. For an engine that is meant purely for racing a vacuum advance is not necessary. For a racing SB I would recommend limiting centrifugal to no more than about 22 degrees, then set initial timing at 14-20, which will yield 36-42 total at maximum centrifugal advance. Experimentation should yield the initial timing level that gives the total advance that yields best average power over the normal racing rev range.

Since a racing engine usually has a very high compression ratio and is not usually expected to deliver much power below 3000-3500 I would delay full centrifugal with a fairly mild tip-in until this rev range to help preclude detonation, which is mostly a low rev issue unless the fuel is of totally insufficient octane level.

Duke

[G B.]

Thanks for your posts

I appreciate the time everyone took to respond.

I'll keep looking for a source of new springs. Maybe I can have some made. We'll see.