Distributor Problems...

[911pcars]

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

[dean]

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

[fireant911]

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

thanks

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

[tctnd]

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

[Wayne 962]

Originally posted by fireant911
I just received the package today and although no Porsche number is present, this is the Bosch part number 1 237 011 034.

Useful info - did the package contain the springs?

-Wayne

[fireant911]

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.

[Wayne 962]

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

Oh well, the hunt continues!

-Wayne

[viejopatron]

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?

[Wayne 962]

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

[stlrj]

So, the springs appear to have been weakened.

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

[Gunter]

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!

[Wayne 962]

Originally posted by stlrj
Wayne,

Are you certain the tabs the springs are attatched were not bent in by the PO?

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

[Wayne 962]

Originally posted by Gunter
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!

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

[dean]

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

[Wayne 962]

Originally posted by dean
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

[350HP930]

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

[dean]

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

[Wayne 962]

Originally posted by 350HP930
Wayne, I would assume a distributor shop somewhere could give you a tip on where they source their springs for recurving distributors.

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

-Wayne

[viejopatron]

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?

[TurboBert]

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.]