hi guys i have a 79 elky a regular non ccc hei ignition. mild 350 engine 350 trans... had no mechanical advance took it apart the weight bushing are shot the weights jambed so i ordered a recurve kit should i put in the advance stops that comes in the kit ? which springs to use ? the shaft bushings are good no wobble . how much up and down play should i have at the gear i can shim it now while its all apart thanks in advance
distributor advance
- Thread starter jcelk
- Start date
The weights typically have a ton of play in them and it's not a big deal. If the bushings are completely shot then they need replaced, and some kits provide them. I'm unsure what kit you bought so I don't know what advance stops you're referencing - I use a cheap kit that's just springs and weights. Some people only use the springs since the cheap kits have weights that are inferior to stock ones. What springs are correct is entirely dependent on what your engine wants but a common combo is is 1 light and 1 medium spring. Here's a PDF that explains a few things: https://www.google.com/url?sa=t&sou...oQFnoECCwQAQ&usg=AOvVaw2VXjE9osL-Ko4Ih7gZyjnD
the kit i bought is from ebay so its a cheap one in the picture there are 2 bushings that look like the weight bushings i need and 2 other bushings which i thought were advance stops i never messed with the weight or springs so i;m trying to learn thanks for that article johnny i will have to reread that a couple of times to understand it
How To Re-Curve A Distributor, And Why!
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Could be, things are always slightly more complicated than they seem. It'll run but won't necessarily be perfect. Making gas explode is easy but using three ways to vary the ignition timing opens many ways to either mess up or remedy the situation.
For instance, I'm currently running ported vacuum to my distributor and I've always ran and prefer manifold vacuum. I'm doing this because if I set my timing with manifold vacuum I run into issues when I shift into drive since my torque converter stalls a tad low. My idle drops, causing the vacuum to drop, causing erratic advance. I could simply change the advance canister but this way works too, especially since I currently have an Accel distributor with adjustable vacuum advance. However.....it causes other issues due to being set at 18° initial. Detonation would be a real issue on an engine with more compression than mine but I get away with such initial timing with ported vacuum by running stiff advance weight springs and not driving at WOT. The springs and vacuum can are things that most people have to play with for quite a while before finding what THEIR engine wants. I don't mean to overwhelm you but here's a taste of what's out there.
Dont use the aftermarket weights and springs kits, from what i've read, they are more suited for racing applications.
Why mess with an old and used unit since the aftermarket HEI distributors are more than reasonable prices like ones from amazon, but as far as quality goes, its a "roll the dice" kinda thing.
I would go for someone more reputable like "blueprint engines", i bought one not too long ago, for backup use only, just too see how they fair out of curiosity since they use the very same on their own crate engines, its a nice peice.
Personally, i got away from HEI destributors that uses weights and springs, lots of trial and error trying to dial it in since every engine requirement is different, initial and total timing wise, the one i currently use is by "progression ignition", its all electronic that is bluetooth controlled by cell phone or tablet, lots of features and very versitile, if you can afford one, i'd go that route.
Link - https://progressionignition.com/
Why mess with an old and used unit since the aftermarket HEI distributors are more than reasonable prices like ones from amazon, but as far as quality goes, its a "roll the dice" kinda thing.
I would go for someone more reputable like "blueprint engines", i bought one not too long ago, for backup use only, just too see how they fair out of curiosity since they use the very same on their own crate engines, its a nice peice.
Personally, i got away from HEI destributors that uses weights and springs, lots of trial and error trying to dial it in since every engine requirement is different, initial and total timing wise, the one i currently use is by "progression ignition", its all electronic that is bluetooth controlled by cell phone or tablet, lots of features and very versitile, if you can afford one, i'd go that route.
Link - https://progressionignition.com/
Understanding vacuum advance or any kind of advance of timing is a little bit of a learning curve. If and when you ever get into building engines you will see where the piston is at the advance where you set your base distributor advance. A lower compression engine needs more base timing, while a higher compression engine needs less. The older engines that were higher compression and typically prior to unleaded fuel started base advance anywhere between four to eight before top dead center. As an example if you have a vacuum can that's pulling 20° of advance and you set your engine to 12 BTDC then you have 32 degrees of advance once that can comes full in. As you go to wide open throttle you drop your vacuum advance if you're hooked to manifold vacuum. If you're hooked to Port it vacuum your advance comes on later because it's not until the port that is connected to the Venturi starts to draw vacuum. Those are two main things that you have to understand.
After that when you go to mechanical advance with weights and springs that becomes your curve as far as how much at higher RPM does your advance come on. Seeing that you loose manifold vacuum as you go to wide open throttle. You lose vacuum to the can so the weights and the springs take over so you have a transitional area. This can cause a bog. The heavier the weight and the lighter the spring, the quicker you get advance, if you go with heavier springs and lighter weights, it's the opposite. So this relates to your timing curve.
When you start getting into cams with lower LSA and you have longer duration and significantly more overlap where your intake valve is closing just before or a little after where you throw your spark, you can start having problems with the development of the flame front. When you start going to .50 to .60 valve opening with longer duration at .050 and you're around 30° mechanical advance as far as where the piston is, you can still have the intake valve open when you have air fuel and spark. On a race engine some of that's not so bad but on a street car you can have a loss of power and other problems. So on a street car that is basically OEM 8.5 static CR, you have an LSA of around 110 to 114, intakes opening at about .330 at .050 with standard 1.5 ratio rockers, and base timing starting out at around 12° BTDC typically isn't a problem.
If you want the engine to get back into it's Max advance which should be around 36° before TDC for a small block Chevy you can use heavy weights and light springs. If you get into detonation you can use lighter weights and heavier springs. Typically most modifications of the curve is exactly what Johnny said. One light spring and one heavier spring, medium weights. The truthful answer to this is you have to drive the car. Does it drive the way you want it to? Does it detonate? Does it have a bog? These are the things you have to do your own homework on and figure it out for yourself.
As far is the Amazon level of HEI distributors I have purchased several from a source that currently don't remember, but I'll look that up and post the information here later. You have to understand what you're buying for the money. Even the OEM HEI starts to fall down on itself after the RPMs go up. That's why higher quality units command the price that they do.
On the books for the 327 I have going in, is the purchase of the progression ignition unit. Haven't purchased one yet but that's on the list and from what I've seen, that one seems to be a good solution for the money.
The biggest issue with the older points distributor made by Delco which would be a pre-1972 engine was the cam. The cam would wear out and the points wouldn't open properly and at a minimum they would open inconsistently. The biggest issue with the HEI distributor even the OEM made by Delco is the wobble in the shaft will cause inconsistent spark because of the pickup is getting inconsistent signal. You cannot have a sloppy distributor either with excessive end play or wobble in the shaft and expect to have consistent firing of the spark plugs.
Now on tuning you need to get your air fuel ratio proper at curb idle. The best way to do this is shut the plates all the way shut to where the engine barely runs, if not it probably quits. If that's the case open the plates just enough so it barely runs hook up your vacuum gauge and adjust your fuel mixture screws to get your best manifold vacuum. As that increases then you can increase (or change) your idle setting so that in drive you're somewhere around 750 to 850. A test for this is with the automatic transmission typically a Turbo 350 is to put the car in Drive and let it Coast, it should creep forward. It shouldn't be going 30 and it shouldn't be shifting into second. If it is doing that then you need to adjust your idle speed down to where it needs to be.
The closer you get the plates to the base of the primary bore means you're drawing the maximum amount of vacuum you need to pull the fuel out of your idle ports. The plates should not be into or covering the transfer slot. As fuel quality gets worse and now we're using unleaded fuel and you have an engine that's over 30 years old it's quite possible that you might need to have your throttle plates open to where they are getting into or covering the transfer slot. If that is the case, then that's the case.
Once you get your idle where it needs to be now advance your distributor to where you get your maximum manifold vacuum. Place your hand on the top of the distributor back it off (retard) it just a hair, ...about an eighth of an inch and lock it down and go drive the car. This of course, is an assumption that you have a clean carburetor, you don't have garbage in the float bowl, you don't have a float that's saturated, you have the proper size jets, you don't have emulsifier tubes that are plugged up. And you don't have weights and springs that are sticking, and you don't have a distributor that's wobbling, or you don't have a distributor with excessive end play.
Barring no other issues, like a vacuum leak somewhere or a bad torque converter, or some other things.... You should now have a runnable streetable car.
After that when you go to mechanical advance with weights and springs that becomes your curve as far as how much at higher RPM does your advance come on. Seeing that you loose manifold vacuum as you go to wide open throttle. You lose vacuum to the can so the weights and the springs take over so you have a transitional area. This can cause a bog. The heavier the weight and the lighter the spring, the quicker you get advance, if you go with heavier springs and lighter weights, it's the opposite. So this relates to your timing curve.
When you start getting into cams with lower LSA and you have longer duration and significantly more overlap where your intake valve is closing just before or a little after where you throw your spark, you can start having problems with the development of the flame front. When you start going to .50 to .60 valve opening with longer duration at .050 and you're around 30° mechanical advance as far as where the piston is, you can still have the intake valve open when you have air fuel and spark. On a race engine some of that's not so bad but on a street car you can have a loss of power and other problems. So on a street car that is basically OEM 8.5 static CR, you have an LSA of around 110 to 114, intakes opening at about .330 at .050 with standard 1.5 ratio rockers, and base timing starting out at around 12° BTDC typically isn't a problem.
If you want the engine to get back into it's Max advance which should be around 36° before TDC for a small block Chevy you can use heavy weights and light springs. If you get into detonation you can use lighter weights and heavier springs. Typically most modifications of the curve is exactly what Johnny said. One light spring and one heavier spring, medium weights. The truthful answer to this is you have to drive the car. Does it drive the way you want it to? Does it detonate? Does it have a bog? These are the things you have to do your own homework on and figure it out for yourself.
As far is the Amazon level of HEI distributors I have purchased several from a source that currently don't remember, but I'll look that up and post the information here later. You have to understand what you're buying for the money. Even the OEM HEI starts to fall down on itself after the RPMs go up. That's why higher quality units command the price that they do.
On the books for the 327 I have going in, is the purchase of the progression ignition unit. Haven't purchased one yet but that's on the list and from what I've seen, that one seems to be a good solution for the money.
The biggest issue with the older points distributor made by Delco which would be a pre-1972 engine was the cam. The cam would wear out and the points wouldn't open properly and at a minimum they would open inconsistently. The biggest issue with the HEI distributor even the OEM made by Delco is the wobble in the shaft will cause inconsistent spark because of the pickup is getting inconsistent signal. You cannot have a sloppy distributor either with excessive end play or wobble in the shaft and expect to have consistent firing of the spark plugs.
Now on tuning you need to get your air fuel ratio proper at curb idle. The best way to do this is shut the plates all the way shut to where the engine barely runs, if not it probably quits. If that's the case open the plates just enough so it barely runs hook up your vacuum gauge and adjust your fuel mixture screws to get your best manifold vacuum. As that increases then you can increase (or change) your idle setting so that in drive you're somewhere around 750 to 850. A test for this is with the automatic transmission typically a Turbo 350 is to put the car in Drive and let it Coast, it should creep forward. It shouldn't be going 30 and it shouldn't be shifting into second. If it is doing that then you need to adjust your idle speed down to where it needs to be.
The closer you get the plates to the base of the primary bore means you're drawing the maximum amount of vacuum you need to pull the fuel out of your idle ports. The plates should not be into or covering the transfer slot. As fuel quality gets worse and now we're using unleaded fuel and you have an engine that's over 30 years old it's quite possible that you might need to have your throttle plates open to where they are getting into or covering the transfer slot. If that is the case, then that's the case.
Once you get your idle where it needs to be now advance your distributor to where you get your maximum manifold vacuum. Place your hand on the top of the distributor back it off (retard) it just a hair, ...about an eighth of an inch and lock it down and go drive the car. This of course, is an assumption that you have a clean carburetor, you don't have garbage in the float bowl, you don't have a float that's saturated, you have the proper size jets, you don't have emulsifier tubes that are plugged up. And you don't have weights and springs that are sticking, and you don't have a distributor that's wobbling, or you don't have a distributor with excessive end play.
Barring no other issues, like a vacuum leak somewhere or a bad torque converter, or some other things.... You should now have a runnable streetable car.
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Yes you can shim the lower gear to limit end play. Generally I shoot for as much initial timing as I can put in it and not have starting problems. Try for a total of mechanical timing of 34-36 and see where you wind up. The issue with some stock distributors is the timing AMOUNT of advance. If you can dial in 12-16 initial and then advance to 34-36 by 3000 you're good. I've had them where they kept advancing to 44-46. This is where you will have to limit the advance by blocking off the slot that the shaft moves in. The more timing you can put in at idle the less carburetor opening it will need to achieve the same idle. I bet your stock distributor might have only advanced to mid 20's in the rpm range it was working in. Just a simple timing adjustment can probably find 10 hp or more by moving it up. I found 4 hp on the dyno on my 540 dropping the timing from 40 total to 36.
thanks all i have been doing a lot of reading
im going to keep my hei dist when my kit comes in i will put the new weight bushings in with my original weights i;m unsure of what spring to install any insight of what rpm the total advance should max out not including vacuum advanse as for the end play i have 42 thousands i will check when installed to make sure i have a little play i have a 350 engine 8.5 compression ratio mild cam peak torque is probably around 300 lb at 3000 rpm and a auto trans i have a new timming light with didital advance and tach built in and am ready to play the nice thing about retirement is i got the time thanks for all your help
im going to keep my hei dist when my kit comes in i will put the new weight bushings in with my original weights i;m unsure of what spring to install any insight of what rpm the total advance should max out not including vacuum advanse as for the end play i have 42 thousands i will check when installed to make sure i have a little play i have a 350 engine 8.5 compression ratio mild cam peak torque is probably around 300 lb at 3000 rpm and a auto trans i have a new timming light with didital advance and tach built in and am ready to play the nice thing about retirement is i got the time thanks for all your help
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