HELP! MSD Distributor Gear Shredded

[Cobra#1]

Ok, I have a 351W with an MSD #8485 Distributor. I was driving my car when all of a sudden it backfired and the engine shut off. After much trouble shooting (will save you the details), I determined the rotor was not spinning and pulled the distributor. When I did, the teeth on one side of the gear are eaten away. I am concerned as to why this would happen and am not sure what to do next. Obviously, I need to get a new gear for the distributor, but am curious as to what would cause this. Ideas?

[davecobra]

Well I offer this,
1. bad gear msd had some problems with composite gears
2. Cold engine high oil pressure, lot of load on the gear
3. Binding on the dist gear to block.
David

[Cobra#1]

Thanks . . .I can rule out #2 as the engine was well warmed up . . had been driving for 20 min. Would be happy if #1, and concerned about #3.

[Three Peaks]

A little more information may be helpful-

If this is a roller cam, you will need a steel distributor gear to match the steel cam gear. Iron gears don't hold up to the billet steel used in the roller cams.

If you are running a High Pressure oil pump, you are putting undue pressure on the distributor gear causing premature wear. Ford small blocks don't really need a high pressure oil pump to work properly, even under relatively rough use. Keep in mind a High Volume pump isn't the same as a high pressure pump.

Try to make sure you get as much of the ground up metal out of the engine as you can before putting it back together and firing it up. Getting all of the metal in your bearings can cause a huge problem later on.....

Bob

[nymathboy]

This might be off topic but MSD is on my fecal list right now. I had a MSD box give up the ghost recently.

I will echo the types of gears used as a previous poster has stated.

[blykins]

I like using the Comp polymer gears when the application allows it. I also use bronze gears.

I would look first at the material combinations. As Bob noted, the distributor gear has to be compatible with the camshaft gear.

[Jamo]

Becoming an vintage story around here, but I have several bronze gears on my desk as paper weights and letter openers (sharp teeth...yanked them before FUBAR hit). Had a sold roller for a year, not hardened cam gears at the time (2003-4) so bronze gears was it application-wise. A very disposal item in such applications (save the cam). Finally went to a solid flat tappet...nice iron gear has lasted since 2004 (I still have the habit of pulling the damn thing and checking twice a year). And yes...high output oil pump.

The polymers were just coming out...

Do NOT forget to drain every damn oil line, including the oil cooler (get it flushed, then do it again, and then do it again).

Find out what the cam company wants on the distributor.

[FWB]

for what its worth.....when the oil pump picks up debris it will seize. the pin on the distributor gear will shear shutting down the motor. if the gear was weaker than the pin, then it will shear. just make sure when the dissy is out you can spin the oil pump drive

[Jamo]

...and drill the shaft/gear to accept a Chevy pin (thicker).

[charles roybal]

This happened to my 408w MSD composit gear(1,420 miles)...KC changed it to bronze gear(

JEGS Bronze Distributor Gears - JEGS

Had to flush engine with diesel... ran new oil & filter for 250 miles then change both.Need to keep an eye out on ware of bronze gear.

[Jamo]

Geez, I hope that's just your camera...otherwise I've got to get a better brand of taquilla.

[charles roybal]

Originally Posted by Jamo

Geez, I hope that's just your camera...otherwise I've got to get a better brand of taquilla.

Might consider not drinking any more taquilla.

[Jamo]

Hehehe...actually, I barely drink. Maybe that's the problem.

[bobcowan]

A picture of the gear would really help.

But, a coupple of quick answers would also help: Type of camshaft (roller or flat tappet). Part number of distributer. How many miles. What does the cam gear look like.

[RICK LAKE]

Cobra#1 Pictures of the gear would help, Here are some failures of why
1 Wrong gear material to camshaft.
2 Too much endplay of camshaft causing gears not to mesh correctly. Need to measure this before reassembly of motor, could happen again.
3 IMP DON'T enlarge the pin for the distributor. This just gives less material of the shaft to turn the gear with if it runs the oil pump. If the motor has a different oiling system,( drysump or crank driven) there should be no problem with needing a bigger pin.
Failure of this pin in an FE distributor happened in my car. I have a 100 pound spring and cold run 135-138 psi at idle. 15-40 Rottela oil 13 quarts. The problem was not leting the oil warm up before running. Let car run at 1,100 rpm for 2-3 minutes and drive it. Pressure is under 90. I tryed a bigger pin and broke the shaft at the hole. Also this pin breaking may save your motor from metal getting into it and eat itself alive. I have seen this.
4 There is no oiling to this part of the motor and these 2 gears rely on oil spray, mist, or splash to lube the area of the gears. If you have a oil galley behind the distributor you can put a .005"-010" hole in the plug. You will loose 5-8 psi of pressure depending on hole size. This will give you oiling to the part of the motor and help stop wear of the gears.
5 Alignment of the distributor assembly into the block and contact of the 2 gears to be 90 degrees and centered. The block may need to be remachined and have a spacer installed to center the distributor square over the camshaft.
6 Check 2 things before reassembly of the motor, pull the oil pan( I know this is a pain in the ass) find the other parts of the pin and check for damage. Cut open the oil filter and again check for metal or any weird partials. Motor should be ok. Unless you have or find all 3 parts of the pin DON'T run this motor, unless you have a spare. We did this at Run&Gun 3 years ago with installing a new pin to make a couple of runs, On the 2nd lap the car quit. The piece of pin from the oil pan got through the screen and locked up the oil pump. No damage to the motor except for a 6,500 rpm backfire. Any way good luck with your repair. I have tryed to cover all ends. Rick L.

[mreid]

An msd 8485 is for a 4 cylinder volkswagen, so that could be your problem!

Assuming you mean an msd 8584, as it is for a 351w, it comes with an iron gear and unless it was changed will not last long on a steel roller cam. However, there are some steel roller cam blanks that use an iron gear. You need to make sure that the gear is made of the material called for by the cam manufacturer.

[Jamo]

Rick, for crying out loud...what the hell sized pin did you use?

Come on, think it through buddy...how come all of the MSD shafts for Chevies don't break? It's not that much bigger.

I'm gonna tell Boghosian what you said...he'll take a wrench to your head with his one good arm.

[patrickt]

This was a pretty good thread on distributor roll pins over on the GT40s forum. Broken distributor gear roll pins? - GT40s.com

[Jamo]

Nothing to disagree with, but using a standard Chevy pin ought to provide the "fusible link" (as it presumably would in...for example...a Chevy) while providing a bit more strength where Ford went skinny.

Not talking about putting a tree stump in there.

Seems to me all MSD did was just use the stock diameters from the mfgs...not sure of what "thought" went into that anymore than the thought MSD put into that assinine little blob of carbon in their caps.

...just sayin

[FWB]

the same thought they used to use a GM height housing in an FE so your wires are smashed up against a 2x4 carb set up......