nastee383

Yesterday I posted what I thought was my timing curve and asked opinions on what to do about it. It was 18 initial, 27 @2500rpms and around 40 before it peaked at 4000rpms. Well come to find out the timing wasn't returning all the way to the initial setting after the rpms had been raised. I assume the weights may be sticking but if someone else knows another possible cause I'd appreciate the input. Anyway, my actual curve is 14 initial, 24@1000, 27@1500, 29@2000, 31@2500, 32@3000 and 34@3500. Much better than I thought but still a little slow to full advance.

Jvette73

Use some anti sieze lube under the weights and on the mounting pins. Just a tiny bit and spread it on thin. Sometimes the springs are to light or worn out and wont pull it back at idle. I found that when I installed my curve kit, what worked best for me was a combination of one medium and one light spring. You could bump your timing up 2 degrees to get 16 initial and 36 total. Overall the curve looks pretty good.

Paul 75 L82

nastee383- I've been watching your post as i have the same HEI from Summit. I think that I'm going to try out the lighter springs as soon as I get around to changing them. All in All i do like the Summit HEI.

nunus79

On my HEI, the Summit weights would fling under the rotor "ledge" and sometimes get stuck. It cause all kinds of misdiagnoses. So if your advance mechanisms look ok, take a look at the underside of the rotor cap and note where the weights are contacting the rotor ledge. If at or near the edge, then this may be your problem. I built up the ledge with JB weld and it seemed to have cured the problem. I have since switched back to stock weights that have built in weight stops. If your Summit distributor uses their curve kit, then likely the weights use the rotor cap to limit the advance. Hope this helps.


[Modified by nunus79, 5:08 PM 12/27/2001]

yellow 72

FWIW the only suggestion I can make is to play with the weight springs to get it all in by 2500 :smash:

Blkblt

Conjur up LARS the professor on timing curves. Good beer usually brings him around, but in this instance I will shoot him an e-mail.

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Jeff
Ô66. Modified L72
ÒThe Silver BeastÓ
Keep on :cool: :cheers: :cheers:

dually4wd

Hi Nastee,
Good advice on cleaning and lubricating the advance weights; just don't go overboard and have grease slinging around inside the cap. Also, are you running vac advance? If so, make sure it's free to move too.

That sounds like much too lazy of a curve for your use. Shoot for having all your advance in by 55mph cruise rpm at the most, preferrably 45 if it doesn't rattle. Are you pulling another 4 deg. out on the spray? Reading the plugs?

When you make a full pass on clean plugs, look at the ground strap. It should be heated to the point where it joins the plug base, but no bluing or rainbow effect. That's what's going to determine exactly how much timing your motor wants. Judging by the numbers you're runnig, it's obviously close.

BTW, did Santa bring you any new horses? :crazy:

nastee383

Thanks for all the replies. I'll try lubing the weights.

Dually, I have an adjustable vacuum advance. Right now I have 17 degrees of vacuum advance so @ 60mph (2000rpms) I have about 46 degrees of advance. To be honest, sometimes I take 2 degrees out on a 125 shot of N2O and other times I don't. It seems to run the same with no noticeable detonation. My motor is only 9:1 compression. I have looked at the plugs after a run before but its not a routine thing. My understanding is if you don't shut off immediately after the run reading the plugs is useless. The times I have looked at them (a couple) they were clean. I didn't get any extra horses from Santa, but I did get a nice helmet. The graphics match the color of my car. BTW, you know anyone locally that does distributors well? I have an extra HEI I'd be willing to experiment with.

American Boy

I got the same problem this summer. The mecanical advance wasn't returning to it's position. It was causing bad idle and detonation. My problem was the distributor shaft. There is a piece that rotate on top of the shaft, where you attach the spring and weight, in my case, this piece was not rotating freely. This with some light spring and you're in for trouble. I got a brand new from GM and it solved my problem.

Great idle now. :D

Stephan

dually4wd

Nastee,
I don't know of anybody locally doing distributors, but they're not very complicated; you could call around to see who has a machine for setting the curve, and put the parts in yourself. I would like to see what one would do with one of those MSD modules and a hot coil.
With the plug readings, driving back to the pits makes it very hard to read mixture, but if the motor runs clean you can still see the heat marks for the timing. When are you gonna break in the new helmet?

Richard Burt

I believe another possible cause of variable base timing is too much play in the end of the distributor shaft. My experience: After an engine rebuild the original distributor was reinstalled by the rebuilder. I broke it in with original timing. Because I had about 90,000 miles on the original and lots more power now, I decided to "upgrade" to an Accel HEI unit. When setting the timing, I found I had variable base settings after runs! The local speed shop guy told me to pull the distributor and check the end play - he said it should be about 0.015". Well,I had over 0.060" on the new Accel unit! He got me another one and it had over 0.040" end play!!! So, I shimmed the thing to 0.014" with a shim kit they sell for such things and reinstalled the new unit. No more problem with base timing moving around. I guess the shaft had enough end play that the gear could ride at different positions on the cam gear, so advancing/retarding the timing as it pleased. BTW, I called Accel tech line and they confirmed the clearance should be 0.012 - 0.015" (as I recall) but offered nothing more than "we'll send you another one to try". As always, buyer beware. :mad

Richard Burt

I forgot to add that I have since asked other people about the distributor shaft end clearance issue. I've been told it is common for small blocks to have well over 0.020" end play straight from the factory and not show problems with wandering base timing. So, I am not sure how important the spec is. Maybe the gears wear in and find a neutral spot, and then stay put. I guess you would set the base timing after break-in and it would be stable. Anyone know for sure? Maybe my problem with the first Accel distributor was sticking weights after all.

nastee383

Guess what? I have an MSD module in my HEI and I have a Hypertech 53000 volt coil too with an ACCEL 300+ box. I'll break in the helmet early in 2002.