Distributor Rebuild Project

[Ernest]

I plan on rebuilding the HEI distributor thats currently in my ZZ4 crate engine, the distributor that came with the engine is not original, the prior owner said it went out a year ago, to what extent, i didnt ask, but he took it some garage and they replaced it with a brand new aftermarket unit that was bought locally. After pulling it out of the engine and reading the info engraved on the shaft, i finally found out that its a "Spectra Premium GM08", the center plate and outter weights are shaped just like the original GM, but with no numbers and made of a different material, looks to have medium tension springs, and the engine pings slightly mid throttle with this out of the box setup. I picked up a brand new in box ZZ4 center shaft(GM 1894379) with the #375 center plate and #41 outter weights that gives a total of 22degrees, along with its stock heavy springs, total advance @ 4000rpm according to the ZZ4 pdf file, i plan on swapping the new center shaft over to the spectra distributor, replacing the generic ignition module with a brand new "GM 990" unit, replacing the generic pickup coil with a brand new "Standard LX302" unit, replacing the generic ignition coil with a brand new "Standard Blue Streak DR31" unit and finally, replacing the adjustable vacuum advance can with a brand new napa "Echlin VC1703" 10degree vacuum can that starts @ 4'' hg and full in @ 8" hg, tested with actron vacuum pump(CP7830), and as for the advance springs only, i plan on using the Mr Gasket set(928G) to hopefully dial in 36degees by 2800-3000rpm, i'll have to reshim the dist gear to housing, currently .032 when it should be .020 gap, and no machine/speed shop with a distributor machine in my area, so im on my own for now.

In another post, i mentioned that i just bought a Progression Ignition HEI distributor, i do plan on using that, and soon, the one i just described will be a backup, besides, i bought all the parts long before the progression unit.

Can anyone here can direct me to someone they know or a shop where they live that continues to use a SUN distributor machine to dial in everything for my engine?

Heres a couple of before pics for now.

 

[Ernest]

Well... its done, from aftermarket GM08 to ZZ4 status, will be installed soon and tested, will be reusing brass can and rotor, still in great shape.

Example third picture shown is a great idea if you cannot locate a spiral roll pin, the typical single GM spring tension roll pin is 3/16'' x 7/8'' and split on one side, you can make it stronger by putting an even smaller roll pin inside, M2.5 x 30 to increase the overall strength, my GM08 dizzy already had one like it, an inner and outter roll pin, you can carefully remove the single roll pin it with an old 3/16'' drill bit(smooth shaft side) and reuse, or you can buy a 3/16" tap for it.

 

[Ernest]

She's up and running... with a little help from my friends(tools) to set everything straight, i also made sure to oil prime the engine after sitting for 2weeks, ran the primer tool for 30sec with my 1/2" cordless drill, worked fantastic, i've had it since the mid 90s, purchased from a machine shop thats sadly no longer around, newly bought vacuum pump w/guage and seperate vacuum gauge, to further tune the carb/engine.

Kick the auto choke on along with its squirt of gas, starts and runs normally, nothing special, just using better parts now IMO, took the car out for a moderate test drive, no WOT runs, feels good, cant figure out whats causing the part throttle pinging still when it shouldnt, no where near advanced timing with original heavy springs, 22* distributor, plus 10* initial and 10* vacuum can on full vacuum, im hitting 42* total, way under the typical 52* max, depending on engine, and im running 93octane pump gas.

My plugs(MR43LTS) are clean, but with that extra advance at idle, its looking more lean than before now, hard to believe this engine being lean with a presumeably stock 770cfm vac/sec street avenger carb. GM recomended timing for ZZ4 engine is 10*(idle), but running 20*(idle) instead, thanks to running the vacuum advance can off the full vacuum port at the base of the carburator, you can use a port off the intake as well, i've always ran ported before, just thought i'd give it a shot to see how it feels. Using full vacuum has a greater benefit for more radical camshafts, advances your timing at idle, raises idle rpm, and less chance of having to open up the primary throttle too much if you decide to run ported vacuum that would uncover the idle transfer slots rendering the idle mixture screws useless, running full vacuum is what GM did back in the performance 60s, along came the 70s and switched to ported due to emissions requirements.

 

[69hurstolds]

Are you running 20 degrees initial? If so, that's too much, IMO. If it's initial plus vacuum can to manifold vacuum, then it's just about right from what I was told. I'm not going to claim to be an expert by any stretch, but ironically, me being an Olds guy, I do have about 5 minutes worth of experience fugging around with a touchy (backwards-running from what I'm used to) distributor as a ZZ4. So anything said after this point- I may be just talking out of my azz.

I got a new GM ZZ4 distributor for my 502 because it didn't come with one out of the crate. I had a Chevy-head friend who loved building 383 engines for whatever reason (before the LS craze) and putting them in everything and that's the distributor he said to get. I picked his brain for tips to set mine up because out of the box, I tried using Oldsmobile logic and that doesn't work well on a BBC.

I recall setting it up with his recommended 12 degree initial timing, and with a 22 deg mechanical limit, it needed to be all in 34 degrees (vacuum can shouldn't even be involved when setting initial timing or under load anyway) all in by around 3000-3200 or so. It's like the distributor was GM tuned for advance to come in at higher RPM for some reason when you didn't need it. Maybe that was one of the issues. I wasn't getting it there, and I pulled it back down to 10 degree initial. It helped some, but still, something wasn't exact. I suspected the springs, but I wasn't there yet with those because the ZZ4 was supposed to have a "good curve" built in already.

I set my end play to 0.017" or .019", can't recall for sure, but it was less than 0.020". Spec I was recommended was 0.015"-0.020". If that is too tight, well, fugg it. It felt pretty solid at that point. There's a lot of slop in that distributor end play out of the box. Can't speak for the aftermarket housing, though. Your vacuum advance can may be messing with you as well. My friend always used those adjustable vacuum cans so he could adjust and limit the vacuum advance to his liking. I never got around to that, but that may be the issue with your distributor. There's also something about those stock distributor springs that seem kinda slow though. Ran pretty good, and I believe if I mucked around with the mechanical springs and put some lighter ones in, I'd have been able to get a bit more out of it sooner. Again, I quit playing with it when I got it where I was just ok with it. It was better, so I quit mucking with it. Still, I wonder what I was leaving on the table.

In the upper mid-60s, GM started using thermal vacuum switches (TVS) on the intake coolant passage for distributor vacuum and started using ported vacuum for NOx considerations. Even my 69 H/O has a simple 3 ported TVS on it for this. The distributor vacuum can was connected to this thermal switch, and both a ported vacuum and manifold vacuum tubing was ran to the switch. If the car started to get too hot, say, idling at a stoplight, the TVS would reach setpoint of 226 degrees, and switch the vacuum from ported to full manifold vacuum. This gave the advance can vacuum and increased RPM to increase coolant flow, and fan flow (air side). The thermal clutch would likely already be engaged at elevated temperatures, so the result was faster flows, which equates to faster heat transfer, and hopefully, a quick cooldown. When the TVS temperature cooled below setpoint, the vacuum got switched back to ported. This was entirely a work around for trying to have their cake and eat it, too. When emission hammer came down, they started using TVS for EFE, and EGR as well.

Good luck with it. I know these kind of things can drive you bonkers sometimes.

 

[Ernest]

By GM's design, they like to keep their engines from easily going full retard to have them working conservatively within the warranty period.

All the ZZ distributors come with heavy springs, so the total advance happens at or after 4000rpms, which makes the engine feel lazy, just to keep the uneducated with a heavy foot from breaking their engine, heck, even MSD distributors come with heavy springs out of the box.

I set my engine to 10* initial, plus the 10* vacuum can connected to full manifold vacuum, 20* total at idle, not 20* initial, then 10* vacuum can, then with the 22* centrifical, for a grand total of 42* total advance at or after 4000rpms of because of the heavy springs in using at the moment, but i do plan on testing the medium springs that came originally with the GM08 distributor, one at a time and check total timing that way, medium plus heavy, then medium and medium for quicker advance.

To be honest, Im not too concerned with getting this mechanical distributor dead nuts accurate, its basically a spare/backup that i'd like to get running good enough to get the most potential out of this ZZ4 engine, this is actually the long block version, not the shortblock version, its the earlier engine with the L98 pre fastburn heads. I've actually got an electronic distributor by the name of PROGRESSION IGNITION that i plan on using for the long haul, it runs off BT straight from your cell phone or tablet with an their specially designed app, and im hoping this will cure, or somewhat have better control of the part throttle ping i've been experiencing sine i've own the car for the past 6months, so no more spring/weight/advance guessing.

The thing about the pinging, as i've been reading around the web, theres probably nothing i can do, others with the ZZ4 have the same issue, even with the required 92 octane fuel use, again, im using 93 octane, it appears to be a "quench" thing, since this is a brand new block, the piston sits .025 in the hole and uses a .051 head gasket to acheive the 10:1cr, the tighter the quench, the better for more efficient/complete and trouble free combustion.

 

[CopperNick]

You can "fix" the spring issue by scoring a Mr. Gasket aftermarket advance weight kit. This kit comes with pairs of springs that have various tensions. Be aware that while you are buying a complete tuning kit, you are only buying the kit for the springs. The advance weights and centre cam are generic and mostly shapeless when compared to their factory counterparts. Based on my personal experience with the 41's, as compared to other sets of GM factory advance weights, they are what I would term, "heavy". It would take a small triple beam balance or weigh scale to actually discover the weight in grams for the various sets. With a set of stock heavy advance springs, it would take a fair amount of engine rpm to get them to open and advance the timing. A lighter set of springs will let them open sooner. When you want the advance to come in kind of depends on what you are doing with the vehicle. Around town commuting with lots of stop and go, or just periodic trips to the coffee shop or a show and shine usually mean you are just running on the carb primaries and just need enough advance off idle to pull away cleanly. Oh, and don't assume that what Napa says the vacuum advance is supposed to be doing is what it actually is doing. That adjustable can and a Mity-Mite vacuum tester will tell you if it is functioning as advertised.

When you say your plugs are "clean", do you mean they look white or are just devoid of any oiliness or carbon? A plug that is burning cleanly usually displays a light tan color on the insulator. A pure white or ashy white color is indicative of a lean burn. Ping.. You may have to give some thought to the jetting in your carb to get it just that hair richer that the engine seems to be telling you it needs.

Thing here to remember and appreciate is that you are not running, it seems, any type of ECM or ECU that, in a straight from the factory setting, would be automatically tweaking the timing and advance at the distributor to eliminate the ping. Minus any electronic baby sitter, Getting rid of your ping is all on you AS 69HurstOlds pointed out, this dialing in process can be a frustrating experience and a mind bender but hey, if we wanted simple, we'd be walking.



Nick

 

[Ernest]

I've already bought the Mr Gasket kit(928G), its the springs only, those will be next in line to use.... the kit with the weights are usless on typical street driven vehicles, from what i've read, they are more set up for the race track.

Since the timing is conservitive at the moment, bumping up two jet sizes at a time couldnt hurt, thats the norm, two sizes, up or down to acheive the desired goal, what i'd like to do in the near future, attach an AFR guage kit, just to help zero in what the engine likes and doesnt like.

But again with the quench area of this engine being larger than recomended( .035 to .045), a very good chance it is causing the pinging, i might be beating a dead horse trying to elimnate it, but if i could have better control over it, that would be most helpfull in the longevity of this engine. Figure the better way around this, going with cast iron heads with slightly larger intake/exh ports, 64cc chambers, which would drop my 10:1 to roughly 9.5:1 compression, using larger valves(2.02/1.60 vs 1.94/1.50) for increased breathing, and using coated steel shim .015 thickness head gaskets to tighten the quench, while still using 93octane thats available locally, i'd be content with that, but thats somewhat of a stretch nowadays, at least at the moment, with most the performance parts shortages.

Over all, who knows... i enjoys the tinkering though, its not a daily driver, so i dont mind the minor inconvinience of not being able to drive it on the weekends when its nice out.

 

[Wraith]

I went with MSD Digital 6 and Pro Billet distributor to fix the pre ignition on my ZZ4 back in 99', easiest way at the time to set the right ignition curve. I've always hated those HEI recurve kits.

 

[rwd_pete]

I have a ZZ4 in a hot rod. I was reading up on the specifications. Although it has a vacuum advance on page 4 under Ignition Systems it recommends to not use it. I wonder why?
"Set spark timing at 32º before top dead center (BTDC) at 4000 RPM with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32º of total advance at wide open throttle (WOT). The HEI vacuum advance canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve."

 

[Ernest]

I've never been to fond of using CD boxes... last time i used one(MSD 6A) back in the mid 90s, was on a street/strip, well, mostly street driven '75 chevelle i once had, 350hp 355cid, it didnt seem to make much of a difference IMO.

I have the same ZZ4 PDF.... the recomendation of not using the vacuum advance is beyond me, unless GM performance knew the engine was going into detonation, eliminate the vac advance, eliminate the ping. Again, it needs to be .035 to .045 to be more effective on making power and not having to worry about detonation and its not possible with this engine out of the crate. You would want the vacuum advance for the street and cruising speeds, its easier on the engine and its better for fuel mileage, leave the disconnected advance can or locked out distributor for the strip.

I'll see what i can accomplish with my current distributor..... if at any point i feel content enough, i'll switch over to my PROGRESSION IGNITION HEI distributor and be done with it.


Thanks to everyone for their input!