Sheared distributor gear pins caused by thick oil?

[Big O Dave]

I have a customer who has a '71 Mustang Mach 1 with a 351 Cleveland. He runs 20W-50 in it.

He came in to my shop a couple of days ago with a sheared distributor gear pin, so we pulled the distributor and replaced the pin.

He indicated that this car has had a propensity to shear distributor gear pins, and that this is not an uncommon problem with 351 Clevelands. When I heard this, I began to query him about running overly thick oil in cold weather - it has gotten into the low 30's lately - my goal was to find out if these pin failures have occurred primarily in cold weather, or if this wasn't a factor.

My thinking is that running 20W-50 in 30F weather makes it much more difficult for the oil pump to pump oil when the engine is cold, thus causing the distributor pins to shear. Ford used hollow formed pins, as opposed to solid pins to secure the distributor gear on the distributor shaft.

What do you think - could the 20W-50 be causing these failures?

Thanks, in advance, for your comments and thoughts.

 

[expat]

As someone who has (in the past) used 20w-50 in winter, and even with added STP in old, British 4 cyl engines, I don't think it likely. But why else it would break a pin?.
I don't know

 

[OVERKILL]

It is very likely. It happens with oil pump drive shafts on the Windsor engines too, where "you have to run 20w50 because its the BEST!!!!!!!!!!"

But the guys running 5w30 never seem to have that problem

 

[aquariuscsm]

I say no way! Just a bad design is what caused the problem.

 

[Doug Hillary]

Hi,
yes it is possible in certain conditions - it is also possible to shear oil pump drive mechanisms

 

[SteveSRT8]

A known problem on old Mopar 273/318/340 with too thick oil. They would break the driver. Hardened parts do the trick.

Should be able to make something to do the job.

 

[TFB1]

Cause for the Ford's is a loose fitting gear, if the "fit" is correct you can just about run the dist without a pin, it's common for rebuilt dist to have this problem... I have a buddy who went through four or five rebuilds before he got one that didn't shear the pin in in a few hundred miles...

 

[Big O Dave]

When you say "loose," how loose do you mean?

Doug, the "right" conditions would be really cold weather, correct?

Thanks for all of the comments, guys!

 

[Doug Hillary]

Hi,
Big O Dave - Yes! Oil too viscous, revs and etc!

 

[Big O Dave]

Thanks, Doug!

 

[ac_tc]

And maybe a high pressure/ high volume pump...

 

[Shannow]

Originally Posted By: TFB1
Cause for the Ford's is a loose fitting gear, if the "fit" is correct you can just about run the dist without a pin,


Yep, in design, the pin/keyway etc. should really only be along for the ride, unless you really want them to be the trigger.

Most of my playing was with Holdens back in the day.

The grey motors, people would increase oil pump relief pressure, and shear the pin, through too much pressure (or as per Doug, viscosity and pressure).

 

[Jim Allen]

Sheared pins or oil pump driveshafts are relatively common on old Ford Windsors, Clevelands, 385s (429/460 BB) and FEs. It's always oil related, one way or another. I can see high viscosity oil shearing the pin. CHeck out the oil fitler section to see what happened when high viscosity oil and cold temps combined to blow up a filter.

 

[OVERKILL]

Originally Posted By: Jim Allen
Sheared pins or oil pump driveshafts are relatively common on old Ford Windsors, Clevelands, 385s (429/460 BB) and FEs. It's always oil related, one way or another. I can see high viscosity oil shearing the pin. CHeck out the oil fitler section to see what happened when high viscosity oil and cold temps combined to blow up a filter.


I always thought of it as a fuse. On the Windsor, when the shaft would break, the distributor would stop working, so the engine would stop, LOL.

Every time I've heard of this happening, somebody is running 20w50 in the bloody thing, or 20w50 and a high volume oil pump.

I've never heard of it happening with the Ford-spec'd 30-weight oils (10w30/5w30).

And high volume oil pumps on a Windsor are a waste of money.