I was going down the road today, found a nice stretch of smooth road and opened up the throttle. All of a sudden a loud backfire and no more go, uh oh. Once home and doing some checking pulled the dist cap and turned the rotor by hand, oh crap what happened. It was the roll pin, sheared right off. What causes such things? Cheap parts, defective material? 1 question though, are these ordinary pins or a hardend type?
Oh yea more info always helps. :p Chevy 250 mostly stock HEI dist bought new from napa about 6 yrs back, 2bbl rochester 2GC, 200-4R, 4:11s,
Hope your day was better than mine.
Jason

make sure the pump turns smoothly with a screw driver. weird problem. tom

On my hot rods I replace the roll pin with a piece of 1/8 d TIG welding rod, which is pure, has high ductility, and high tensile strength. I broke one myself and have heard of others who experienced the same problem. Be sure you get all the broken bits out of the oil pan even if you have to pull the pan to do it. Good luck.

Roll pins are made similar to a spring in that they are tempered but not hardened. Ideally they are a few thousandths of an inch smaller than the hole so their springyness ( new word ) holds them from slipping out. Normally they should last longer than yours did but any extra strain or binding can bring a failure as Tlowe points out regarding an oil pump problem. How does the gear teeth look on the distib? Any excessive wear pattern that might indicate a high loading from the oil pump?

Solid pins like a dowel pin are generally hardened and mostly used for alignment of parts rather than as a fastener for assembly because they offer no tension to keep themself in place like a roll pin does.

Like so many other things there can be differences in quality of roll pins depending where they were made. Be nice if after you checked things out you didn't find any problems with the oil pump and could blame it on a 2nd quality roll pin.

Thanks for the replies, Tom the oil pump turns nice and smooth. Frenchtown you said you use rod in place of a pin does it have a snug fit, nothing in the pan, could it be in the filter? Mike the teeth look to have "normal" wear to me no deep groves or anything.
I have a pin that fits the diamiter but the length is to long, can i grind it down or find one that fits all dimensions?
thanks

Dear Jayson;

There's a lot of bogus "offshore" stuff out there.

I think the "welding rod idea" is the best. A Welding Shop would probably give you a left-over piece too.

Good luck.

The welding rod should fit snugly. Before installing it I heat one end with the TIG torch to create a little ball of metal on one end to prevent the pin from coming out. Then I insert the pin in the gear/shaft so that it protrudes out the other side about 1/8". Then I heat that end with the TIG electrode to form another molten ball on that end also, permanently locking the pin in place. Be sure that the ends of the pin do not stick out more than the root diameter of the gear teeth or you may have trouble installing it past the cam gear.

You can also grind down the longer pin, but I would take care not to heat it up so as to lose its heat treat.

DO NOT use drill rod as it is too brittle and may break. Good luck.

I've removed quite a few distributors from Chevy 235's and GMC inlines.The stock gear pin appears to be a soft steel pin,peened over.Most pins where a little loose too.I've also messed around with Hei's from Chevy 250's and home modified Chevy 2.8 V6 Hei's for use in the old 6's.The gear pins were the roll pin style,some were double roll pins,one inside the other,some where a single roll pin,some where solid soft steel pins like the older 6's.
Anyways,on a street engine,there may be some thought to the gear pin shearing if the pump jams to avoid chewing up the cam drive gear.
When I assembled my GMC 302,I made an oil pump test fixture to adjust the oil pump relief valve to the pressure I thought was proper,about 65-70 psi with room temperature 10-40 oil,which worked out to 55-60 psi in the running engine with 20-50 oil.I used a 7 amp industrial Metabo drill on low speed(1200 rpm) to spin the pump.When the pressure got over 60 psi it bogged the drill and I had to really have a firm grip on the drill.I can't say how much torque or HP the oil pump consumes,but V-8 Chevy pump running 60 psi uses about 5 hp from what I'm told.There is probably dynamics of vibration that also affect the drive gear.

Any idea what the flow rating of the GMC pump is? I prelubed/flushed an engine using an external GMC oil pump and it smoked my B&D 3/8" drill.

It takes a few seconds for oil pressure to come up on my Reo six and you can hear it load the engine down. That pump is 15gpm at 3200rpm. It is probably approaching the limit for a right angle helix drive.