UPS delivered my timing light today. I didn't waste any time. I'm not sure I've done things correctly, though, so please if you have the time and expertise, take a look at what happened and give me some feedback. Thanks.

I selected the spark plug #1 wire, on the driver's side of the car. I didn't actually follow it down to the plug (since it's not jacked up and I couldn't see it easily from above). Instead I noticed which wires were the 1357 set (the ones going to the driver's side of the engine)... and using the 18436572 firing order, could figure out which wire must have been the 1. The pattern is 1..3.57., so the plug that came before two wires going to the other side must be the 1 plug. I'm presuming the distributor rotates clockwise (right?).

Question #1: Does the distributor rotate clockwise?

Oh, I should mention that my distributor has a bright orange pertronix ignitor. That was the work of the mechanic I took it to just after purchase (and prior to any knowledge). I don't have the points system, he tossed all the old parts. I wish I had known to keep hold of it. (maybe he kept it for another car!).

I disconnected the vacuum from the distributor vacuum can, and plugged the hose with a nail punch. I took off the cap and rotor and removed the springs from the centrifugal advance. Then reassembled, with no springs.

I started it up. No backfiring. It seemed to run okay, but choppy, as usual, like it was experiencing atrial fibrillation (by feeling the car body, I could feel powerful thumps usually in a steady pattern, but not always). I let it warm up.

Question #2: Should the engine at idle seem smooth, or bumpy and jumpy?

The timing line wasn't always showing up in the same spot. Sometimes it would jump around by 12 or 14 degrees, maybe even more. If I revved the throttle, it would advance, and get a lot more steady, but it was never really solid steady unless the RPM was up around 3000 or more.

Question #3: Does the timing line at idle jump around normally? Or is my distributor sloppy or something?

Anyhow, when I revved it (it didn't need much to get all the timing advance to come in) the total timing was coming in at 44 degrees BTDC! Yes 44. From what I've read, I should expect that sort of timing to cause detonation, shouldn't I?

Now, this engine was rebuilt at 70k, and it now has 85k on it... so it's only got 15k on the rebuilt engine. The oil is clean as (that's Kiwi for "very clean"), and seems to stay clean for a long while. Anyhow... maybe the guy who rebuilt it didn't line up the timing marks right. It does seem like the timing mark thingy was a new one put on later (it looks too shiny to be original).

Question #4: Do you think it really was at 44 degrees? Or has the harmonic balancer slipped?

So I retarded the total timing back down to 36 degrees. Doing so caused the idle speed to fall.

Question #5: If the idle speed falls when you move the timing, does that mean I'm reducing performance?

Next I put the original springs back on the centrifugal advance and checked the timing again. Even at 5500 RPM, I was not getting the entire advance curve to come in. So the stock springs are pretty strong.

Next I tried several pairs of other springs. The kit I got (accel) had three pairs of springs: stiff gold ones, medium silver ones, and light black ones. The gold ones were too stiff. I tried the black ones, and they allowed the centrifugal advance timing to come all the way in at about 2800 RPM. So I didn't even bother with the silver ones.

Actually, that's not true. I originally thought the silver ones were the right ones. But the coil part of the springs is longish, and when I put them on, it seemed like they weren't holding down the advance at all for the first part of the turn of the rotor... like they were just slightly too long. I could twist the rotor by hand, but it wouldn't revert to the starting position. So I didn't even bother with them.

Question #6: The rotor was rubbing very lightly on the pertronix ignitor thing (I think). Is that normal?

Question #7: Is a small amount of friction on the rotor, that prevents it from retarding all the way after twist-advancing by hand, anything to worry about?

Question #8: After locking down the distributor cap, it wiggles ever so slightly. Is that anything to worry about?

Next, I checked the timing at idle speed, just to see what it comes in at. That was 5 degrees.

Question #9: Is 5 degrees at idle reasonable/normal?

Finally, I hooked up the vacuum (manifold vacuum), and took it for a drive. There was no detonation, and I didn't expect any. When I'd punch it, there was a very slight lag, which I didn't used to have. Also it seemed like the whole process has caused me to lose power... the car seems more like a ford now. Of course, I'm not certain that it has less power... it's very subjective. But it does seem that way.

Anyhow, I went ahead and hooked up a vacuum gauge, adjusted idle to 750 (according to specs) and tried to tweak the mixture for maximum vacuum. Both screws started at 3 turns out from the lightly seated position. Well, I was getting a steady 15" of vacuum, and turning the mixture screws up to 2 turns in either direction doesn't seem to do jack.

Question #10: Why might the mixture screws be generally impotent?

I'm thinking about getting a 14mm bolt and verifying TDC.

Comments appreciated.

 

Hi,
I would check TDC on No.1 as a priority. Doesn't sound like the numbers you had to start with were right although it obviously ran OK.
So does point to a moved TDC mark - perhaps.

Petronix unit shouldn't bind on anything. Minimum 10 thou clearance if memory serves.

I'm suprised that the timing marker jumps under the strobe light. Since you have a constant vacuum at idle. Mine jumped - but fixing the vacuum issue sorted that (It was a badly adjusted exhaust lifter).

It might be that you are not getting a great signal to fire the strobe from the No1 wire. Try moving the pickup a bit. (Assuming it's an inductive pickup it has to go the right way round).

Otherwise, 5 Deg init. looks low - and clearly the drivability is worse so something ain't right.

Jeremy.

 

you can mix the advance springs to adjust the advance. the weights are mechanically attached, so they move as a unit.

 

metheglin

Try using 1 silver spring and one black spring. It doesn't matter which side of the weights you install the springs on.

"Timing scatter" occurs at higher RPM's as a result of end play in the distributor shaft. You may want to pull the distributor and if it is sloppy, install some shims to take up the slack. Should be within 10 - 20 thousandth, I believe.

Replace the Distibutor cap if it doesn't fit tight. There should be no "wiggle" on the cap.

Any reason you went to a Pertronix unit? A well set up conventional points type of ignition system works beautiful. Just curious.

There is a great paper in corvettefaq.com edited by Lars Grimsrud that goes over the proper sequence of setting up the distributor/timing on these cars. Lars was over last weekend and I had the pleasure of having him do this on my car along with 4 other cars. All of the cars ran MUCH better after he removed, cleaned, changed out the springs, took out the end play and adjusted the carb after the igniition system was dialed in. You can also refer to Barry K's sticky at the top of the Corvette Forum on timing. Pretty much the same thing that Lars' paper is about, written in an easy to understand manner. Good luck

Tony

 

My timing was jumping all over the place last year. Discovered it was a broken weld on the distributor. Might want to check that...

 

It sounds like this happened at the whim of this mechanic a while back... when the Pertronix "Ignitor" was installed... we're talking HEI here, right?

#1: http://boxwrench.net/specs/chevy_sb.htm

#2: The engine at idle should seem consistent under normal conditions, but with the springs removed from your dist. weights it's hard to say what might happen. It also sounds like you might have some old bushings on the weights themselves. A mech. adv. kit should include new nylon bushings for the mechanism.

#3: Same as #2, my guess is that your mech. adv. weights are flopping around because it's running without springs. also the previous poster's description of timing scatter related to improper dist. drive gear/shaft shimming... who knows.

#4: It's hard to say why you're reading 44deg. Perhaps the ring has slipped or the mechanic who set the timing didn't line up the marker with TDC, or just mentally remembered that TDC showed up at the 4 or 6 deg mark on the indicator, or perhaps it really is running with 44deg of total advance and you have a weak vac. adv. can so you just don't notice it at idle (i.e. vac can is only putting out 4-8 deg of adv.) But this is all guesswork. you should 1. verify TDC and where that corresponds on the timing marker. 2. test your vac. can by pumping it up with a vacuum pump while the car's at idle, and compare the timing signal to what you read at idle with the can disconnected. Also inspect the neoprene/rubber ring on the balancer for any obvious cracking or deterioration... balancer rings certainly can slip.

#5: Idle speed will change as you adjust timing based on what your current fuel / air settings are at idle. Once you've established that all your timing is set straight, then you'll want to go in and adjust the carburetor for those correct timing settings.

#6: previous poster is right on, depending on which spring kit you bought (some kits have different colors), try combinations to get your total advance to come in around 2800-3200 RPM.

#7: I would inspect that rotor to find out why it's rubbing. where is it rubbing? are the rotor mount screws torqued down too hard, distorting the rotor? does the chip unit have too much dielectric buildup underneath it? I can't remember what parts can cause interference wiht the rotor, but you should look at where the rubbing is occurring.

#8: Inspect the base mounting ridge on the cap and mounting flange on distributor base for debris. The cap could have warped after modling as well... I've never seen that before though. As long as it's not rocking very easily, the spring tension on the hold-down clamps should keep it in place.

#9: 5 deg... well that all depends on what vacuum can you have installed. maybe that's why you have 44 deg of total timing advance. Seems to me like the car would be much happier with less total advance and more initial advance. you might need to replace the mech. advance central body, which is shaped according to how much total advance will be produced. again, if you purchase a full "mech advance kit" it will include bushings, springs, and the mech adv. weights and central body.

#10: depends on what carburetor you have... could have gummed up mixture needles or passages depending on when the carb was last rebuilt / serviced... or a number of other things. focus on the timing and get that dialed in, then work on the fuel and air. Unless setting it to proper timing causes the idle to drop below stall speed, then you'll inevitably be motivated to start diagnosing the carb mixture settings.

Just felt like answering all your questions since you obviously put a lot of time into organizing them... Hang in there, you'll get this all sorted out, and when you're done you'll feel like a million bucks when you get out on the highway and goose the throttle a bit and feel all the performance you've been missing out on due to current engine tuning.

and definitely check out the corvettefaq page, there's tons of good info there.

good luck brother

the blonde weasel

 

iNdigo,

Must have missed the part about the Pertronix being installed by someone else earlier. My bad!

 

sent PM

 

Thanks for all the help.

Now I can't remember if the initial 5 deg. was without the vacuum hooked up, or with the vacuum. So that number is suspect.

Also, I don't see clear evidence of the rotor rubbing on the pertronix.. it just looks like the clearance is very tight. Maybe that's normal? I was just noticing how if I didn't tighten it down all the way it would definately not clear.

And yes, it wasn't exactly my decision to replace the points... I was in the hospital experiencing atrial fibrillation (for the first time ever), and told the mechanic to "go ahead" with whatever he thought needed to be fixed or replaced. Usually a bad thing to do, but hell, I was kinda concerned about other things at the time.

So once I can find a 14mm bolt, I'll verify TDC on No 1 next. It sure seems like it's off by 8 degrees or so.

Thanks.

 

I was wondering when you were going to respond to this!

 

Ok I pulled the distributor.

End shaft play is .018" according to my feeler gauge.
Service manual says it should be shimmed to .002" to .007", so I've got shims on order. I'm also ordering a new felt washer, lower gear roll pin, plastic housing seal, and mount gasket, and 20W non-detergent oil.

I suck-tested the vacuum advance, and it does work... but I'm not certain how many inches I was sucking. If I could tee the hose to my gauge, I would know, so maybe I'll order a tee and hose (or stop my my local shop).

The bushing that stops the centrifugal advance looks to be installed on the underside of the main shaft.. and it appears that I do need to knock out the roll pin and disassemble the main shaft in order to replace it with the bushing that came with the new springs/weights. Is that correct, or am I looking in the wrong place?

I've also now gone back to my original statement - the rotor is definately rubbing on the pertronix ignitor II... there are plastic shavings all over the place and it has definate wear marks on it. I'll have to adjust the mounting on that, and maybe get a new rotor.

As for the 14mm bolt - no one locally sells that size.. they jump from M12 (12mm) to M16 (16mm) so I guess I'll have to order a piston stop from the states (summit or elsewhere) for six bucks plus much more in shipping (to New Zealand).... but I'm checking with a fastener co. in Auckland.

This is going to take a while to get the parts I need, so I suspect this thread will fade out until then, and I have some more hard data to discuss.

Thanks everyone!

 

metheglin,

So far, so good. You are definitely going down the right path! You will want to knock out the roll pin, disassemble the entire distributor, clean off any old grease and lube the shaft with a thin coat of high-temp wheel bearing grease, including the cupped area around the base where the shaft meets the base of the distributor housing and the tach gear drive, install the shims and grease seals, and do any other repairs or changes while it is apart. Make sure you place the gear at the bottom of the shaft back togather the way it came off. If not, you will be off by one tooth. While you have it apart, you may want to consider putting in a conventional points type of ignition back in there. Just a thought.....

Good luck and resurrect your thread once you get it back together and let us know how it turns out.

Take care,

Tony

 

The saga continues...

I got a top-dead center locator/bolt. Low-and-behold, the timing mark is right on the money.

I fixed the "rotor rubs on pertronix ignitor II" problem.

I also fixed the timing jumping around at idle... or, actually, I realized that it was just because I was timing without springs on the cent advance.

NOW I WANT TO LIMIT THE CENTRIFUGAL ADVANCE.
Let me explain...

When I first tested the timing on this car, set by some US mechanic, and it was running well, very powerful, very punchy, it was set like this (as I put in my first post): Idle Timing = 12 degrees, Total Timing = 44 degrees.

Everyone on this list seems to think that's too advanced, and so that's why I verified the timing mark placement... which is right on.

I adjusted it down to this: Idle timing = 4 degrees, Total Timing = 36 degrees. Now it runs, well, less impressively, but runs well and maybe even smoother.

I'd like to try it like this: Idle timing = 8 degrees, Total Timing = 36-38 degrees...... in order to do that, I believe I need a new bushing for the centrifugal advance (so it tops out sooner?) Can anyone explain where that bushing goes, and do I have to take apart the distributor to change it out, or just pop the cap?

 

Hello metheglin:

Pardon me for laughing...... .....but when you said that you "weren't certain of how many inches you were sucking" ....well, I just lost it. Here in the states you would get a good ribbing for such an innocent comment.

That being said, I have no remedies for you, except that you can make your own piston stop by using an old spark plug and removing the porcelain and center ignitor. The way I did mine was to break the porcelain where it meets the hex head. You can then use a band saw, or a hack saw to cut the crimped end where the porcelain attached to the hex head. Just cut enough to allow you to remove the ring, then you can push out the ignitor and you will have a hollow hex head with threads. I then obtained a piece of metal rod of slightly smaller dimension and fit it so that it protruded about 2 inches from the front of the threaded portion of the old spark plug. Just to be sure that the distance remained consistent within the cylinder, I peened the rod so that it would go no further than the 2 inches, or whatever distance you detrmine to be correct. The further into the cylinder the stop goes, the more the spread when you do the clockwise and counterclockwise rotation. Just make sure you turn the crankshaft slowly by hand, so that you don't put a hole through your piston. (Don't mean to imply that you are ignorant, but it's always best to write objectively).

Let me know if this works, or if you found another method....

 

Metheglin,

You can limit the centrifigal advance by installing new bushings. The original bushings may have been removed at some point and it might be a matter of re-installing the bushings. Read Lars' paper on timing or Barry K's sticky regarding timing at the top of the forum.... You are getting really close, hang in there, OK?

Tony

 

Thanks everyone for the helpful comments. I'm a slow learner, but once I learn, I never forget. This forum is amazingly cool.

Ok I found a brass bushing with my spring kit. I pushed it onto the peg that is on the underside from the centrifugal advance mechanism. Without taking the distributor apart, I can't hammer it into place, so I just squeezed it on with pliers. I re-timed it to run at 36 when all in at 2800RPM, and that meant that initial is now at 11 (instead of 4). MUCH BETTER. Now it runs punchy and powerful again!

I'm not entirely done with fixing the timing. I have distributor parts on order, including shims, and I'm going to rebuild it, if for no other reason than to shim it and clean it up.

But until those parts arrive, I'm going to use the new timing as the pretty-much-there basis for minor tuning of the carb. Right now I'm having various idle speeds. After a nice highway run, it was idling at 1500... Then after the surface streets to my garage, it was idling at 500... same trip, no tweaks. It was definately warmed up for both stops. I'm at a loss, I don't know which way to turn the idle screw!