Mallory Distributor Tip

Argess · #1 (**permalink**) 10-12-2009, 09:18 AM

The problem with Mallory Distributors, at least the YL units, is that the drive gear 1/8" roll-pin can shear. I queried Mallory about it and was told the failure is normally associated with using a high volume oil pump.

What I did to resolve the problem was to re-drill the roll-pin hole through the drive gear and dist shaft with a #22 drill bit. I then pressed in a 5/32 roll-pin (the split kind, not the rolled up kind) with the split up (down also works) and then nested a 3/32" roll-pin inside the larger one, but with the split 180 Deg apart.

Despite the fact that a loose drive gear to shaft fit is also a problem with the Mallory (you get more bending of the pin), the mod has not failed me since, at least 4000 miles ago.

bobcowan · #2 (**permalink**) 10-12-2009, 02:00 PM

That's a problem with all distributers. I've never had that problem with any Mallory Unilite I'v ever used. But it happend to a friend of mine at atrack day. He had a brand new MSD; he got 1 and 1/2 laps before it sheared.

NRP/MN · #3 (**permalink**) 10-13-2009, 08:33 AM

On my way to a local car show, blipped the throttle on a downshift off a freeway ramp and the engine died. Took of the distributor cap and found the rotor wasn't turning as I spun the engine. Flat towed the Cobra the last 6 blocks to the car show- I had the only Denali powered Cobra there! Pulled the distributor to find the dreaded roll pin failure. Trip to the local hardware store and 27 cents later it was running again. It still screwed up a perfectly good day, or at least a couple hours. Drained the oil when I got home into a very very clean drain pan and found part of the pin, stuck a magnet into the drain on my Aviad pan and pulled out another piece. Installed a magnetic drain plug and hope to catch the rest. Mike

Jerry Clayton · #4 (**permalink**) 10-13-2009, 08:44 AM

If running a big pump---you can double/triple pin the gear by drilling more holes---of course then you run the risk of stripping the teeth off the cam gear

Gunner · #5 (**permalink**) 10-13-2009, 09:00 AM

Aren't there roll pins (or rod material) with a higher shear strength?

Argess · #6 (**permalink**) 10-13-2009, 11:09 AM

Quote:

Originally Posted by Gunner

Aren't there roll pins (or rod material) with a higher shear strength?

I looked into that, but there really wasn't anything I could find at the time. Seems to me, when I looked into it, those spiral roll-pins are even weaker. With solid pins, like tool steel or titanium, you may have a problem keeping them installed unless you have an expertly machined and "very tight" press-fit.

The big problem is the Mallory gear is a loose fit. The pin flexs every time it goes around and eventually fatigues and breaks. Ford distributors have an interference gear to shaft fit, and with the same size pin, there are a lot less failures as the pin is in direct shear with no bending moment.

It's also difficult to cross-pin the gear as the existing hole is in the middle of the available space, so another hole, even at 90 degrees is too close and weakens the dist shaft.

PaulProe · #7 (**permalink**) 10-13-2009, 05:10 PM

When you change a distributor or its drive gear, it is essential you set the proper end-play. If you don't it and the drive pin is subject to higher than design forces.

Going to a larger drive pin is just a mask for an improperly located drive gear. That is the reason they come to you un-drilled, with a pilot hole. If installed properly, all the forces of the gear and camshaft are absorbed by the boss in the block, not by the drive pin.

Here is a link to the Ford bulletin: Distributor gear installation

Paul

Argess · #8 (**permalink**) 10-13-2009, 05:50 PM

Quote:

Originally Posted by PaulProe

When you change a distributor or its drive gear, it is essential you set the proper end-play. If you don't it and the drive pin is subject to higher than design forces.

Going to a larger drive pin is just a mask for an improperly located drive gear. That is the reason they come to you un-drilled, with a pilot hole. If installed properly, all the forces of the gear and camshaft are absorbed by the boss in the block, not by the drive pin.

Here is a link to the Ford bulletin: Distributor gear installation

Paul

That's a different problem. Note that in the link you provided, it states "press the gear on the shaft". With a Mallory, it's loose. No pressing. That's a problem. I even thought of getting the shaft or gear knurled to help things, but just went with a pin upgrade. I am absolutely certain, in my case, there was plenty end-play clearance left after the dist was clamped down.

Michael C Henry · #9 (**permalink**) 12-29-2009, 12:04 AM

My Mallory distributer had a !/8" x 3/"4 spring pin. It failed in my alley once when I reved the engine leaving the yard with cold oil. I replaced it with a true roll pin I sourced from MSD.When you drill larger holes or multiple holes you have moved the weak link in the system to somewhere else. Just read the stories about the high volume pumps with really high releif preasures. Read the storiy about Brent and the Heli-coil piece that got left in the oil pan and stopped the pump. His distributer drive shaft looked like a peice of ornamental iron, and the bearings that got damaged. I can see the high volume pump with a realistic releife pressure a slight step up to the roll in. If something happens, everything just coasts to a stop no damage other than halving tp remove the distributer, replace the pin and then reset the ignition again retiming again
I'd think rather than going with an absured releif presure that assureing flow would be a better focus. Large hoses , large fittings , gentle bends ,in and out of block matching bearing and block oil holes and in particular, a large capacity oil filter or if you are going to run Ford style filter elements, Try a filter bracket that lets you use two elements in a parrallel arangement to increase flow and not restriction

chas427fe · #10 (**permalink**) 12-29-2009, 11:00 AM

My pin sheared after rebuilding my 428. Like Argess, I drilled it out and put in the larger pin. That was 5000 miles ago and it is still going fine. Chas

Michael C Henry · #11 (**permalink**) 07-25-2017, 04:05 PM

This time I suspected the pin because I knew that I had over revved the engine with cool oil. Once I removed the distributor I found that wasn't the case. But I messed it up from there. I should have left it alone and just reinstalled the distributor. The moving up to 5/32 in. pin sounds good if there is ever a next time. This time it was me, over my head. Turns out that I just ran out of gasoline , but it did run great for that short instance.

Gaz64 · #12 (**permalink**) 07-25-2017, 04:37 PM

Quote:

Originally Posted by Jerry Clayton

If running a big pump---you can double/triple pin the gear by drilling more holes---of course then you run the risk of stripping the teeth off the cam gear

I'm glad of your response here Jerry.

Others seem to not realise that the roll pin only needs to be strong enough, but still the weakest link.

Michael C Henry · #13 (**permalink**) 08-13-2018, 11:17 AM

Mallory was taken over, CRAP. I found better true roll pins at ZORRO. They have different materials and strengths pins. I bought a bag of a hundred pins. The original roll pin was a great failsafe. If it sheared the engine stopped and no damage done and easy to fix. Bigger pin takes away from the shaft thickness and moves the weak link some where else. The distributer gear was drilled so it can and would only be reinstalled the one one way. The gear and shaft pin hole was slightly off center and angled downward slightly.