Distributor Advance Spring Choices

[Larry B.]

I purchased a stock distributor weight and spring kit from one the popular
suppliers for my '61 283/315. It has two sets of springs, a light set of yellow springs and a tighter set of silver springs.

The instructions are very general and say most hydraulic cam engines should use the yellow/light springs and most solid cams should use the silver/tighter springs. The old springs in the car seem to be of the lighter variety. Which spring would be most beneficial for my car?

[William C.]

Re: Distributor Advance Spring Choices

The springs that come with most "Kits" are absolute BS, and the weights do a very poor job of imitating the GM products. Take all the parts to a shop with a distributor machine and have the shop match the parts (or use some off their "spares" ) to the curve from the shop manual (or the shop can look the curve up from the in-house references) If they can't do that, find another shop.

[Clem Z.]

Re: Distributor Advance Spring Choices

make sure the aftermarket weights are hardened because a lot are not and they will wear the cam on the center post.

[Gene M.]

Re: Distributor Advance Spring Choices

I find that most of the stock GM advance are much slower than what the spec calls for in the books. I verify on my Sun machine. Another note there is a lot of slop in the no advance position on most distributors.

Take Bill's advice and take it to a speed shop to be set up correctly on a machine.

[Duke W.]

Re: Distributor Advance Spring Choices

Install the lighest springs, but use the OE weights.

Set the initial timing to achieve 38 deg. sum of full centrifugal plus initial. Check the service manual and/or AMA specs for the maximum advance and max advance revs. (You can download the AMA specs from the GM Heritage sight.)

If it doesn't detonate, you're okay, but it's best to verify the current spark advance map with a dial back timing light, and then again with the light springs. If it does detonate, install ONE of the next heaviest springs and repeat the test. Continue this do loop until you find the lightest spring set up that results in no detonation.

In order to check the amount of full advance, some engines may have to be free revved to a bit over 5000 RPM. It shouldn't hurt the engine, but some guys chicken out. Unless the fan disintegrates, you won't get hurt and I've never heard of an OE fan disintegrating at high revs, but I have heard a few stories about aftermarket flex fans disintegarting at high revs.

The faster you can bring in the centrifugal advance - without detonation - the more torquey the engine will feel and this will also improve fuel economy in normal driving.

While you're at it, you should check the vacuum advance for proper function against specs, but in your case the OE dual point dist. doesn't have a vacuum advance.

I think your dist. only has about 20-22 degs. total centrifugal, so you will need to run about 16-18 initial, but CHECK THE SPECS AND TEST IT. On a non-vacuum advance dist. the more initial you can run, the less the tendency for the engine to run hot in stop and go driving.

Duke

[William C.]

Re: Distributor Advance Spring Choices

Duke, the 315 hp FI dist is a typical GM unit with the top mounted weights and springs, easy to change.

[Duke W.]

Re: Distributor Advance Spring Choices

Thanks for that. I thought all the dual point distributors had the weights/springs below the breaker plate, but looking at the IPB I can see that only the '55-'56 dual point distributor had them below the breaker plate.

For '57 to '62 they were located under the rotor just like the single point distributor, which makes it easy to change springs.

Now I know.

Duke

[Clem Z.]

Re: Distributor Advance Spring Choices

if you want a quick check to see if lighter springs will make your corvette run better just remove one of the two advance springs and this will speed up the advance.

[Michael H.]

Re: Distributor Advance Spring Choices

Larry,

I wouldn't be in a hurry to throw the original springs and weights in the trash. You may later decide that they weren't so bad after all.

[John H.]

Re: Distributor Advance Spring Choices

Thanks for that. I thought all the dual point distributors had the weights/springs below the breaker plate, but looking at the IPB I can see that only the '55-'56 dual point distributor had them below the breaker plate.

For '57 to '62 they were located under the rotor just like the single point distributor, which makes it easy to change springs.

Now I know.

Duke

Duke -

The 891 distributor (internally-adjusted dual-point, no vacuum advance, used on all carbureted applications from '57 thru '61) had the weights and springs below the breaker plate.

[Larry B.]

Re: Distributor Advance Spring Choices

Thanks Guys! Michael, I sure won't be throwing anything out! Everything goes in the spare parts box.

[Duke W.]

Re: Distributor Advance Spring Choices

Duke -

The 891 distributor (internally-adjusted dual-point, no vacuum advance, used on all carbureted applications from '57 thru '61) had the weights and springs below the breaker plate.

Now I'm confused, again. So does this mean that all '57-'61 FI dual point distributors have the weights/springs under the rotor, and same for ALL '62 dual point distributors?

Duke

[John H.]

Re: Distributor Advance Spring Choices

Now I'm confused, again. So does this mean that all '57-'61 FI dual point distributors have the weights/springs under the rotor, and same for ALL '62 dual point distributors?

Duke

Duke -

Bill Clupper knows the details and distributor numbers better than I do, but in general, '58-'61 fuel injection distributors had the weights/springs under the rotor, as did all 1962 distributors. '57-'61 carbureted applications used the old-style bowl distributor with the weights/springs below the breaker plate.

[Tim S.]

Re: Distributor Advance Spring Choices

Install the lighest springs, but use the OE weights.

Set the initial timing to achieve 38 deg. sum of full centrifugal plus initial. Check the service manual and/or AMA specs for the maximum advance and max advance revs. (You can download the AMA specs from the GM Heritage sight.)

If it doesn't detonate, you're okay, but it's best to verify the current spark advance map with a dial back timing light, and then again with the light springs. If it does detonate, install ONE of the next heaviest springs and repeat the test. Continue this do loop until you find the lightest spring set up that results in no detonation.

In order to check the amount of full advance, some engines may have to be free revved to a bit over 5000 RPM. It shouldn't hurt the engine, but some guys chicken out. Unless the fan disintegrates, you won't get hurt and I've never heard of an OE fan disintegrating at high revs, but I have heard a few stories about aftermarket flex fans disintegarting at high revs.

The faster you can bring in the centrifugal advance - without detonation - the more torquey the engine will feel and this will also improve fuel economy in normal driving.

While you're at it, you should check the vacuum advance for proper function against specs, but in your case the OE dual point dist. doesn't have a vacuum advance.

I think your dist. only has about 20-22 degs. total centrifugal, so you will need to run about 16-18 initial, but CHECK THE SPECS AND TEST IT. On a non-vacuum advance dist. the more initial you can run, the less the tendency for the engine to run hot in stop and go driving.

Duke

I'll vouch for this! Made a big seat of the pants difference in my 62 340hp!

Tim