• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Distributor Alignment

WillySLC

NAXJA Forum User
Location
Bountiful, Utah
Wow, this is interesting...

I was just browsing through my AllData section on the '88 Cherokee. There is a rather detailed discussion on how the "self-aligning" Distributor mounting tab apparently doesn't self align very well. The document explicitly describes a process of cutting off the end of the Distributor Locating Tab that usually "hugs" the ditributor hold down bolt. The idea is to allow manual rotation of the distributor for timing types of operations. It then also describes a process by which you would "statically tune" the distributor by taking a sacrificial distributor cap and cutting a hole or window in it around the #1 spark plug post. You then manual crank the engine so that the timing mark on the dampner is at 0* top dead center and the distributor rotor is suppose to be at .020" past the #1 spark plug post. Hey, why doesn't anyone make a clear distributor cap anyway? :rolleyes:

This is critical information for anyone who is replacing a distributor. I guess you can't depend on the locating tab to do the job for you. This might explain my recent rash of sporadic misfires that have been plauging me.

Though you all might want to know.

WillyS
 
This has been mentioned many times. It's usually called "indexing" the distributor. Often necessary with a rebuild if you use a non-factory camshaft because the after-market cam grinders don't necessarily set up the distributor drive gear to perfectly match the way a factory cam is set up.
 
If im not mistaken, the problem with indexing on a 4.0 with a renix computer is that the computer will advance or retard the manual change in distributor timing. A slight adjustment can be made, however will be retarded (at least at low rpm) This has been checked with a timing light. I could easily be wrong and would like to be corrected on this issue if I am. After cutting off the indexing tab, and major adjustment will cause quite a bit of bucking and or missing. (In stock trim engine) -Steve
 
XJ-ARMOR said:
If im not mistaken, the problem with indexing on a 4.0 with a renix computer is that the computer will advance or retard the manual change in distributor timing. A slight adjustment can be made, however will be retarded (at least at low rpm) This has been checked with a timing light. I could easily be wrong and would like to be corrected on this issue if I am. After cutting off the indexing tab, and major adjustment will cause quite a bit of bucking and or missing. (In stock trim engine) -Steve

You are correct about the computer changing the timing back (true of post-Renix as well), and major adjustment might well cause starting problems. For example, with my 87 advanced a notch on the gear, it started badly, acting as if hydrolocked, yet ran perfectly once the computer kicked in and corrected it. However, the indexing issue here is not for basic spark timing, but to ensure that the rotor hits the post at the right time. Remember that a distributor is really two gadgets in one case: one times the occurrence of a spark, and the other sends it via rotor and cap to the correct plug. The latter function is something the computer cannot adjust, so if the cam timing is off relative to the distributor, that perfectly timed spark may come up the rotor and find that there's no cap post there, or be past the post before it has finished sparking.

If you have an indexing problem it might show on an old rotor as conspicuously off-center pitting on the edge.
 
this could be the problem I'm having. just had the engine rebuilt with an after market rv cam. it sputters and coughs with an occasional backfire starting at 1900 rpms and up. perhaps this would solve the problems.
 
Thanks Willy for posting that info. Turns out thats what my problem was all along. went out and checked after I read your post. cut a tab off that allowed me turn the distributor just a little bit. smoothed everything out. just needs a little fine tuning. Thanks
 
Back
Top