63 L84 distributor problem

[Michael G.]

I was out driving and my black 63 L84 car and had gone about 70 miles when it suddenly started missing badly on acceleration. I figured maybe I had fouled a plug, so I limped back to the my office and changed them.

Didn't help. Car seemed to idle smoothly, but as soon I accelerated it again missed badly. As the acceleration was the the trigger, I guessed maybe the vacuum advance wasn't working right. I took off the distributor cap and found that the rotor seemed to be fixed, i.e. it was no longer spring loaded, it just didn't rotate at all by hand.

I suppose I can take the distributor out and inspect it, but frankly that's not my area of expertise, so I wouldn't know what to look for. I think I'm going to learn a lot about that device here pretty soon, but since I'm currently clueless, maybe someone can tell me what to look for.

Thanks,

[Duke W.]

Re: 63 L84 distributor problem

Did you check dwell/dwell variation and the spark advance map?

If the rotor won't turn, remove it and inspect the centrifugal advance system underneath.

The distributor is a simple device and once out of the car can be field stripped as easily as a typical 9mm pistol.

All you need is in the 1963 Corvette Shop Manual.

Duke

[Michael G.]

Re: 63 L84 distributor problem

Duke, I didn't check the dwell, I will tomorrow. I removed the rotor earlier, after I found it wouldn't move. The center portion does not turn by hand. (It does on my other car). I'll pull the distributor and check the manual.

[Timothy B.]

Re: 63 L84 distributor problem

Michael,

If the advance inside the distributor turns out NOT to be the problem when is the last time the engine had a tune up.

Cleaning the spark plugs along with a check of all the secondary ignition parts paying attention to those spark plug wires will most times cure the problem.

[Jim T.]

Re: 63 L84 distributor problem

Michael you do not have to pull the distributor to clean the advance system under the distributor's rotor. Just remove the two springs and remove the advance weights and clean. This part of the distributor without cleaning and light lubrication can freeze up.

[Duke W.]

Re: 63 L84 distributor problem

One thing everyone should ask: When was my distributor last overhauled? Or perhaps a better question: Has my 50 year old distributor EVER been overhauled?

It's the most overlooked component on the engine. Many are run until they fail, which is often the tach drive. Though "lubed for life" when assembled by GM, they didn't think in terms of 50 years.

In the case of a FI distributor, failure of the pump drive would not be a pleasant thing to deal with.

So whenever one finds a significant problem, the best bet unless you know the maintenance history is to pull the distributor, disassemble and clean everything, and assemble it properly including using a proper grease in the upper bushing grease well, tach and FI drives, and setting up proper end play. If you can do most maintenance and minor repairs you can overhaul the distributor. It's not a challenging job, and the procedure is in the 1963 Corvette Shop Manual and later Chassis Overhaul Manuals. Just remember to install the drive gear with the dimple in line with the rotor tip. None of the service manuals mention this little, but important check.

In some cases it may not even require new parts other than some nickel and dime items, but fresh grease and proper clearances should insure it performs well for at least the next 10 years - maybe 20 if you don't accumulate more than a few hundred to a few thousand miles per year.

One common thing found is the centrifugal advance clogged with grease. It doesn't need grease. GM applied no grease. Clean components wiped down with WD-40 is all that's necessary for the centrifugal advance.

If you search threads started by me you'll find one about a "blueprint overhaul" of an L-79 distributor late last year and what we found.

Duke

[Michael G.]

Re: 63 L84 distributor problem

The whole ignition system has maybe 2000 miles on it and I replaced the plugs after the problem cropped up. The wires are MSD, so I'm not thinking that's an issue. The distributor was rebuilt in 2010 by one of the best. It's not a matter of poor maintenance. The distributor cam should move independent of the main shaft and it doesn't, so something is preventing the distributor cam from advancing. I took the distributor out will disassemble it to try to ascertain what is causing this.

If I were more familiar with the internals of the distributor, I could probably guess what's wrong now, but I'll know when I get it apart.

thanks,

[John D.]

Re: 63 L84 distributor problem

Mike, Call Don Baker in Sandwich, ILL for help. 815-498-9522. John

P.S. What Duke said was/is a real mouthful. It's like pulling teeth trying to get FI owners to have their distributor properly restored soup to nuts.
Then when the engine runs like crap the FI unit is the culprit when in fact most of the time it's the ignition system.
With Baker restoring the FI distributors that problem is eliminated. But there are other factors in the ignition system but I won't go there.

[Michael G.]

Re: 63 L84 distributor problem

Thanks John, I'll get with Don to help sort this out

[Timothy B.]

Re: 63 L84 distributor problem

Mike, Call Don Baker in Sandwich, ILL for help. 815-498-9522. John

P.S. What Duke said was/is a real mouthful. It's like pulling teeth trying to get FI owners to have their distributor properly restored soup to nuts.
Then when the engine runs like crap the FI unit is the culprit when in fact most of the time it's the ignition system.
With Baker restoring the FI distributors that problem is eliminated. But there are other factors in the ignition system but I won't go there.

Same with carburetors, John, as soon as there is engine trouble owners start turning screws on the mixer. Many times it's in the primary/secondary ignition system and those lean mixtures are hard to lite. High voltage will always take the path of least resistance to ground and many times it's not across the plug gap.

We are spoiled with today's cars, I just changed the original spark plugs in a Sable I use with 120,000 miles and the plug tips were wore to a stub with at least .125+ gap, I couldn't believe it and the car still ran fine.

[William C.]

Re: 63 L84 distributor problem

I'm betting the shaft has locked onto the cam plate due to old or lack of lubrication. Relatively easy fix, but requires dissambly of the main shaft from the distributor, separation of the weight plate assy from the shaft, cleaning, and also the use of a special lube to lube the shaft/weight plate interface.

[Duke W.]

Re: 63 L84 distributor problem

What special lube?

All I do is put a thin film of GM 1960954 Distributor and Starter Motor grease on the shaft adjacent to the cam assembly to lubricate that interface.

There is no meaningful load and very slow velocity between the football, weights, and the top of the cam assembly... same with the pins that the weights pivot on, and these parts are all hardened steel. I just clean these parts thoroughly and wipe them down with WD-40 that makes the surfaces slippery and provides minor corrosion protection, but won't attract dirt, which is all that's needed.

I've seen the top of centrifugal mechanisms literally buried in wheel bearing grease. All this does is completely gum it up.

The centrifugal advance mechanism is somewhat akin to an old mechanical clock movement. Do you load up a clock with wheel bearing grease? Certainly not!

Duke