Distributor and Caps
 

Hi,

during my last tour the engine (zz502) did not feel so smooth in low rpm, I decided to take a look inside the distributor, because
I didn´t for a long time. It´s a original TI distributor which I run with MSD AL2. So the engine looks stock and the box is hidden.

Well after some years the MSD has completly burned the carbon pin in the cap.
The metal of the rotor has half meltet out of the plastic.
Time for new parts, no big deal.

Still had bad feelings and pulled the complete distributor out.
Now the lower gear teeth have only half thicknes, they are eaten by the camshaft.
The lower bearing is also worn.
I assume the oilpump of the zz502 is too much load for that old stuff.

Now I think about replacing the distributor with a new MSD unit.
But I dont want to put new plugs on my wires.
Does the normal GM cap fit onto a MSD distributor?
MSD offers already such a dark red cap for normal plugs.

AFAIK ... ZZ502 comes with a Steel Roller Cam AND GM instructions inform owner it Requires Melonized Iron Distributor Gear.

Perhaps you can use a Hi-Performance cap & rotor on your TI ... Accel, Mallory etc.

Maybe you have not, maybe you already have swapped TI gear to Melonized.

- edit -
QUOTE from GM install instructions
Distributor Gear A melonized distributor gear must be used in these 502/502 engine assemblies. The deluxe 502/502 engine assembly comes with a melonized distributor gear. For the base 502/502 engine assembly you must install an HEI distributor, part number 93440806, with melonized gear or install a melonized gear on your distributor. Use part number 10456413 gear for 31/64” diameter distributor shafts or use part number 10493532 gear for 27/64” diameter distributor shafts.

Bigger concern to me would be....where did the metal chewed off the distributor gear go?

Oil and filter inspection - cut it open after removing.
Maybe drop the pan also.
Sooner than later.

Good luck :thumbs:

Thanks for your response.
I just took the TI distributor as it was on the old engine.
Did not know what kind of gear was on it. I took it out one year later
when I installed the MSD, back then the gear looked good.
So I let it run for years and now comes the bill :D

Because the lower bearing is also worn I would like to go MSD
and have enough time to get spare parts for the TI and restore it.

It´s good idea to always have a spare distributor I think.
But does a MSD take a stock cap?

If you aren't running a bronze distributor gear or a melonized one then I would worry that the shavings are going to cause problems...

Whatever you run make sure it has a vacuum advance if you are on the street... it will run better and cooler.

The shavings fall down into the sump, go through the oil pump and are catched in the filter.
Only if they would pass the filter there would be a problem. I always use the big K&N filter btw.
And as mentioned before, this setup runs for years, tenthousands of miles, now.
I guess all metal gone out with the anual oil change.

But my main question was if the MSD caps can be replaced by the stock type.

Well ... you left out a large part of the shavings pathway.

Unless you have blocked your OE bypass (integral with oil filter mount), Not ALL oil goes through oil filter.

From the oil pump ... shavings are pushed through the cam bearings, the main bearings and the rod bearings.

The bypass opens only when the filter is clogged. (11psi back pressure)
But so far I have no problems with the engine since years.
When an issue will occure I can´t change it anyways and have to deal with it.
But I will not take a good running engine appart just because there could be
something somewhere. It has to run until theres a real need for taking it appart.

Your car, your choice.

Taking off a $8 filter and cutting it open is CHEAP compared to spun bearings 2 yrs from now. No one is saying tear down the engine now but some minor investigation now will certainly save you later. If your filter gets clogged from metal shavings, the relief valve will dump the oil pass the filter. How will you know that has not happened?
You just found the trashed distributor gear.
And you only change your oil annually?

Red flags all over the place.

Good luck. I'm out of here.

Which MSD distributor are you using?
M

I just went through all of this as well and had the destroyed cap and rotor as you did

Yes stock caps fit, but will they handle HEI power and will the stock rotor last? Another thing is the MSD distributor has the geardrive offset so you cant clock it the same way as stock, you may have to either buy the adjustable MSD rotor (Which may not work with a stock cap) as well or move all the plugs over a tower or 2 to get the tach drive cable to not interfere with the coil as well as the vacuum tower not hitting the fire wall, or the intake at the carb, or the shielding bracket.

When I bought my MSD-8572 (1996 FYI) it came with a cap with Female terminals.

SO, you can ask MSD if they still make that.

I now have the the same distributor and the MSD cap with the Male terminals since that's what my new engine uses for spark plug wires. (The distributor is now locked out, tach drive removed, vac adv removed- using it with EZ-EFI 2.0 --- but the internals and body are the same. I already owned it so I just used it when I got the EZ-EFI 2.0).

Also, when I was going to install the RamJet 350, with it's roller cam, I asked MSD if the gear was ok to use with that roller cam... and they said it was good to go.

Distributor gear wear is very gradual and metal particles are very small. Not much to worry about with that. It will get picked up by the filter sooner or later. Some small particles may get imbedded in the bearings, but they are made to handle the small stuff. Again, not to worry.

If you have some kind of quick metal failure of a component...where pieces are much larger and irregularly shaped...that's when you need to worry about engine damage.

Thanks to all.
So i guess they made their caps matching.
I will just order new plugs for just in case it won´t fit.
My intention is to have the old distributor as spare part for quick exchange, so ist must be fully compatible.

I would take another TI unit, but it´s double the price. So I prefere to go with the MSD, it´s hidden in the ignition shield anyways.

About the worry guys, I just did oil change 200 miles ago, there´s no chance to find anything in the filter.
And even then, what would I do with this information? I know where the material comes from and how much is missing.
I change oil all 5000 miles, but have to add that during this period the engine burns 5-7 quarts. That´s from the low
tension piston rings, issue since I have the engine. The zz502 is known for that. Bottomline: theres always fresh oil in the engine.

The Stuff arrived today.
Cap is interchangeable with the stock type.
Rotor has also the same dimensions.
But the MSD stuff is made of much thicker plastic.
It seems the MSD gear I also bought will fit on the old TI dizzy, but didn´t try jet.

And recomendations where I should drill a vent hole into the cap?
I had the TI restored some year ago and now it´s fully rusted inside.
The mus have come moisture inside and did not go out.

Update:
The MSD gear does not fit onto the stock dizzy. The shaft of the dizzy is ~0,2mm thinner. So there would be a sleeve needed to make it fit.

I don´t know why they made the design of the MSD distributor so different from the original one since this is advertised as special for corvettes.
To have the tach drive right aligned the vacum canister comes out at a different location, directly above the clamp down screw.
So I could not use my adjustable canister that sticks wide out of the dizzy. Luckily the MSD has very similar ratings to my adjustet one, so I went with the MSD canister.
The trigger cable also comes out at the other side of the dizzy.

But setting up was really easy. I knew the values I needed from my old modified TI unit. 18-36° @3000rpm. It startet on the first attempt
had just a little adjustment to do and came out at 18° at idle. Checked at +3000 and reached perfect 36°. That´s the fun part.
You can trust in their setting diagramms.

The engine runs now stable again at low rpm. Jerking caused by worn internals has gone. Expensive, but successfull job.

My MSD distributor cap came with a vent system(mine was a male post type cap on an MSD-8572). Are you asking about the MSD cap?

Yes, found that syphon style vent hole on the one with the male towers. I just drilled at the same place into the other cap. The ignition shield covers the whole thing.

The distributor has to be 10% different to avoid patent infringement laws. If you are running the stock shielding and an MSD you can either mod the passenger side mounting bracket or buy the adjustable cap to clock the distributor. I dont know if the adjustable distributor will fit a stock dizzy

Simple on the cap vent hole.
If you need to order a new gear from MSD order one of their Marine distributor caps.
They come with a vent that allows moisture out but is one way and won't allow gas fumes in.
Think about that before you start drilling holes into the distributor cap.