Distributor Problems...
 

Hi folks. Most of you know I just recently bought a '72 911 RS clone with a 3.0L in it. This thing was built in a hurry (for the German AutoFest), and still has a few issues that I'm trying to work out. One of them is the distributor.

The first thing I did was ditch the points and install a Pertronix Ignitor. This is a very good upgrade, and I really feel I should have featured this in either one of my books, but I overlooked it.

Next, I tried to set the timing, and I checked the advance. Seems that the distributor wasn't advancing enough, which leaves power on the table. If the distributor isn't advancing, then that means the weights inside are not expanding fully, right? Wrong.

What appears to be happening is that the springs have become weak and the distributor has started advancing *too early*. So, at idle, the distributor is already advanced 10-15 degrees. When it gets up to 6000, it's supposed to have a full advance of 31-38 degrees (2.7 distributor). I'm finding it's only advancing about 15-20 degrees total.

So, the springs appear to have been weakened. I'm trying to source some new ones (not an easy find, as these were never sold separately - when I find them, I will either stock them or let everyone here know where to get them). Then I'll install them in the distributor, and check the advance.

The bottomline? Your distributor is very important to gaining power out of your car - if it's not advancing properly, you may be leaving 10-20% of power "on the table." Most people look at the distributor and assume it's working, without checking. One way to check to see if it's advancing when it shouldn't is to check the timing with a timing light by cranking the engine *only*. Set the timing to TDC while cranking (disconnect fuel pump or CD box, etc). Then start the engine up and check the timing at idle. If it's the same, then you're distributor is not advancing prematurely. If it reads advanced, then you need new springs.

This applies only to 1965-83 911s, as the 1984 and later cars didn't use a mechanical advance mechanism...

-Wayne

Wayne, What motor and dist? The SC dizzys did not have much advance and usually require a recurve. I am using a 78 dist. with carbs and it does not seem to be quite enough. The total advance is about 19 +/- 2 deg if i remember correctly. i have mine set at 12 BTDC at idle which gives me about 30 BTDC at 6K. not ideal.

I don't see how you can have a 2.7 dist in the car. It would spin backwards in the 3.0 even if the gear was changed.

You can mill a bit from the plate using a dremmel to increase the total mechanical advance.

Usually you want less mechanical advance than more...

The idea is you put cams or carbs on the thing and the engine wants more timing at lower engine speeds. Rather than the 5 or 10BTDC degrees it normally has, you add 5 to 10 initial while keeping the same total. It should really help wake up engines like I've described.

No, if you replace the crank gear and use a 2.7 distributor, then it will spin clockwise. The distributor rotation is determined by the interaction of the two gears (crank and destributor shaft). On the SC, those two gears spin the distributor counter-clockwise. On the 2.7, those two gears spin it clockwise. Basically, as long as the crank gear matches the distributor, then it will spin in the direction that the distributor originally spun...

-Wayne

I did not realize you changed the crank gear. I was thinking about changing the pinion on the dist itself. There was a dist. rebuild kit on ebay last week. Springs were included.

When I tore into my SC dist I found that one of the springs had no tension until the weight was almost half out on its travel. this would induce a few degrees of advance at idle. I bent the tab back to increase the tension slightly. It really helped.

Send your dizzy to pelican, I think they can have it fixed for you ;)

My limited knowledge of mechanical advance is as follows:
The springs and mass of the weights work together to determine how early and how quicky the advance happens, the slots in the weights determine total advance.
Assuming the dizzy is mechanicaqlly sound as far as play/wobble, stronger springs will solve the problem as you described.

Sounds like we need to find a dizzy shoup that can spin and measure and map everything. I had a contact years ago but he specialized in "merican iron, I have no idea if he can do German stuff. I think I'll try and find his phone number if no one else has a place.
I've been thinking of sending mine out to have it checked, the other day I was setting the timing and it was wavering about 3 degrees.

Wayne, you could send it down to me and I could put it on my machine and map it. I can set total and perhaps secondary spring engagement.

Your primary spring is the weakest link. When they are small they tend to weaken at a more advanced rate.

Or you can stop by on a weekend if you are so inclined.

Interesting!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7939679750&catego ry=33690

I don't see the springs though. I have never seen anything like this...

I know of several places that can recurve this, however, I want to find a source for the springs so that I can offer them to you guys!

-Wayne

The E-bay auction link that Wayne listed above was won by me!!! I too suspect that that my distributor requires some maintenance and this looked like a 'cheaper' possibility because the true rebuilds are quite expensive. Springs are not part of the package I purchased.

if that rebuild kit has a Porsche number on it please post it so I can check in to ordering one.

thanks

One more reason why I am going to a distributorless ignition system on my 930.

Isn't that PartWerks new ID though? Didja get the part?

"I want to find a source for the springs so that I can offer them to you guys!"

Wayne,
Try Century Spring in downtown L.A. (also huge website, www.centuryspring.com). They have a huge inventory of springs, but you may have to have them custom made if they don't have one that fits off-the-shelf.

BTW, the early S distributor curve provides the majority of advance at relatively low rpm (10º static and ~20º distributor) for a total of around 30º crankshaft.

It'd be nice to have a distributor machine so one could verify and tweak the curve.

Sherwood

Wayne,
The 84' 3.2 distributor does have advance weights on it too, this doesn't have the trigger wheel and mag sensor on it however,that's a function of the motronics., I think that the springs on the 3.2 distributor are the same used on the 3ltr.,I'll check my notes for a spring source, 'cause I bought some years back.,cheers,Antonio.

I'm sure I could find springs to fit, but then how would you know which ones worked for the proper curve?

-Wayne

Yes, it does, but this is simply to rotate the distributor so that the rotor and position on cap line up when the timing advances. These weights don't actually control the firing of the cylinders, and as such, they don't need to be precise or calibrated at all.

-Wayne

Wayne, have you talked to Ron at MotoParts (800.745.1531)? They dont like to recurve anything, but maybe they know where to get the springs.

I'd never heard anyone stress getting a distributor rebuilt, but this one had been sitting for a while and I figured it would be good insurance.

In my book, I emphasize checking the total advance - if it's not advancing all of the way, then you're just leaving power on the table. If the advance is broken, then it's time for a new distributor or a rebuild...

-Wayne

".....but then how would you know which ones worked for the proper curve?"

You would have to obtain a set of springs from a distributor assembly with a known advance curve (given equal centrifugal weights), then have the spring company replicate the physical dimensions and spring rate.

This may not be as accurate as one would like, even with replacement "factory springs". Even an ever-so-slight error factor (manufacturer's tolerances) could result in a less-than-desireable advance curve.

Perhaps a kit with a mix of springs labeled "normal tension" as well as "+1", "+2", "-1", "-2" might work for the owner (or tuner) to mix and match.

or..... tackle this from another direction and somehow add weight to the existing centrifugal weights to change the advance curve. As you know, the shape and weight of the mech. advance weights also determines the advance rate.

In each case, a distributor advance machine would be ideal to verify the modifications. Short of that, a test procedure with an advance-type timing light could be devised to verify and record the resultant advance curve.

Ideally, a preliminary spark test on a chassis dyno will reveal the maximum advance/rpm for your particular engine (all engines are not the same, even factory engines). With that data in hand, one can proceed to change the distributor advance curve per the dyno test.

Sounds like a viable project.

Sherwood

I thought of that. But even if I obtained a brand new distributor, I wouldn't be 100% sure that the springs weren't already stressed (if it was NOS, but 30 years old). I suppose I could check the advance and spring rates, but that wouldn't necessarily be a guarantee...

-Wayne

Well, you have the factory specs to go by, and if you have a brand new distributor and a distributor machine, that would verify what it is versus what it should be.

Even the spring attachment points can be tweaked (I think) to change the effective spring rate (and thus the advance curve).

Sherwood

One can check the advance on the motor with a timing light. All you need is the advance graph. If the curve doesn't match the graph change the springs. Summit sells an assortment of advance springs.

Dean

I just received the package today and although no Porsche number is present, this is the Bosch part number 1 237 011 034.

Wayne,
If you must retain something as paleolithic as a mechanical advance dizzy, then there is no substitute for having it set up on a dist machine. This after insuring the bearings and advance are clean, corrosion free, in spec, and lubed. A seemingly tiny flaw in this simple device can turn a good engine into a dog.
Phil

Useful info - did the package contain the springs?

-Wayne

Wayne,
No springs... New O-rings (2), snap rings (2) , several different screws (5), and the six-fingered star apparatus plus the holding pin. I haven't even opened the plastic covering yet since I want to keep everything intact until I plan on installing. I needed another snap ring which was the actual reason I purchased this kit plus I had slightly bent one of the six legs during my initial attempt at the distributor disassembly.

Yes, I got this kit yesterday. Big disappointment for me - no springs. Sortof useless if you ask me.

Oh well, the hunt continues!

-Wayne

Hmmm,

Well, you know what the current springs are delivering, so you want something incrementally stronger. Have you considered purchasing an assortment of ultra-precision springs from McMaster-Carr and doing the old Trial and Error method?

I figured I'd try sourcing the original springs before the time-consuming trial and error method. I have a few better things to do than to mess with springs :) (remember, I have a five-month old).

:)

-Wayne

Wayne,

Are you certain the tabs the springs are attatched were not bent in by the PO? It's very hard to imagine that those springs could have lost there tension with so littlle force acting on them. It seems more likely that the tabs were adjusted as I have done many times to get my advance to come in earlier.


Of course if you bend the tabs in too much you end up with the situation that you describe...what appears to be weakend springs.


-Joe

Quote:
One way to check to see if it's advancing when it shouldn't is to check the timing with a timing light by cranking the engine *only*. Set the timing to TDC while cranking (disconnect fuel pump or CD box, etc). Then start the engine up and check the timing at idle. If it's the same, then you're distributor is not advancing prematurely. If it reads advanced, then you need new springs.

How can you get a read on your timing light if the CD box is disconnected when cranking? I can understand to disconnect the fuel pump (Relay) but the CD box? Help!
SmileWavy

That's a good thought, but one I hadn't looked at - I'll have to take a look at that over the next week...

-Wayne

Yes, I wasn't quite thinking straight when I wrote that. Of course, you can't get an inductive read on your timing light when you're cranking, if you've disconnected the CD box. Pulling the fuel pump relay / fuse works too, which is what I did this week.

Incidentally, the distributor didn't advance at idle, nor at cranking speed. I'll have to rethink this one...

-Wayne

Disconnect the vacume lines. If your centrifcal (sp) advance is working, when you rev the motor the timing will advance. So all you do is hook up a timing light and note the advance from idle to 4000 rpm and plot it on a graph and compare to the factory graph. If it advances too fast put stiffer springs in and recheck. If it advances too slow put weaker springs in.

Dean

Yes, that's the procedure. Now, is there a source out there for stronger and/or weaker springs? I haven't found any...

-Wayne

Wayne, I would assume a distributor shop somewhere could give you a tip on where they source their springs for recurving distributors.

Summit racing or Jegs sells a small assortment of dist. springs. The assortment usually contains 3 sets of springs. Do a search on the respective sites.

Dean

You'd think that, but they don't really want me to start selling them so that others can rebuild their own distributors...

-Wayne

Any luck on this quest? Send the measurements on the OD, length & wire d, plus a picture and I can calc the numbers so you can ballpark it from a spring catalog. A photo too and, oh yeah, is it magnetic?

I also got the same indications as Wayne (insufficient advance at high rpm and apparent early advance at idle). My distributor was fine, springs were good – it was another problem.

BACKGROUND
My car uses vacuum to retard ignition at idle (you leave the hose connected to the pot during timing). As soon as you press the gas pedal, you lose vacuum and this advances ignition by 15 degrees. As you accelerate, mechanical advance moves it another 18 degrees through 4000 rpm. For me, using the starter as Wayne suggested earlier (which is a great idea) to check early advance doesn't work because I need vacuum at idle.

CONCLUSION
My problem was that I was not getting sufficient vacuum to the pot at idle. Once I unblocked my vacuum port into the throttle body, I was OK (used copious amounts of carb cleaner).

TIDBIT:
This is probably something everyone knows (so feel free to correct me if I don't have this right), but it was a revelation to me: I realized when you look at the distributor vacuum advance curve for your car, you need to double the amount on the graph to get ignition advance. For example, for my car, the graph below tops out at 9 degrees total mechanical advance at the distributor. This is 18 degrees ignition advance.

[Every 1 degree of rotation at the distributor drives two degrees of ignition advance (distributor rotates once for every two turns of the crank.]


http://forums.pelicanparts.com/uploa...1104509308.jpg