Distributor roll pin (again)

I love Jack and Judy. This is one place where my dear friend and I disagree. If the roll pin has lasted 132,000 miles without failure its not going to fail.

The roll pin failures are a result of installation of the "non-original" heavy duty oil pump shafts ... period. If your car's engine is equipped with a standard oil pump drive shaft, the standard roll pin is not going to fail. Its a well engineered system. How many millions of Ford vehicles have traveled more than 100,000 miles per vehicle without failure of that roll pin? Without stranding the drivers and passengers? What has the last 132,000 miles taught you?

If the 351C has original valves, that's a far more precarious situation.

Thank you George .. you've replaced one worry with another .. hehe. I've had a couple of rebuilds .. I'll have to check my records on valve replacement. I suppose the "it lasted 132,000 miles with no problem" philosophy doesn't apply to valves.

quote:

Originally posted by Robbie:

I suppose the "it lasted 132,000 miles with no problem" philosophy doesn't apply to valves.

Unfortunately no.

I wish I knew what factors were involved, if so it might be possible to predict what the chances are of the valves failing based on the history of your car's engine.

This is not a problem peculiar to the 351C. There are other vehicles (cars & motorcycles) which have had similar "brittle valve" issues over the decades. The stems of the "brittle valves" develop microscopic cracks, those cracks develop into larger cracks, and every once in a while a crack becomes so severe that the valve head separates from the stem. Some folks think the development of microscopic cracks is related to the constituents of the fuel you burn in the engine combined with environmental factors like humidity. Some believe extended periods of non-use are a contributing factor. But those are just conjectures, no solid studies have been done to my knowledge.

If you take a normal valve, clamp the stem in a vice, and grab the valve head with a pipe wrench you can bend the valve 90 degrees without breaking it. Do that to a 351C valve and you'll snap the valve head off. The 351C valves are brittle.

Robbie, my intention was not to scare anyone into not driving their car. The distributor gear roll pin in a 351-C is undersized by comparison to other high-performance small blocks- there's no denying that. But there are several things that must happen to actually overstress the 351C pin. I was not familiar with the Pantera in the article that failed its pin so I didn't speculate on the cause, only described what happened. This is NOT uncommon, either.

The stock 351-C gearotor oil pump is extremely intolerant of any debris in the oil, and the #1 cause of pin-overstress/cracking is dirty oil. With clean, well-filtered oil, most pins will not be overstressed. The second cause- which you may qualify for with 132,000 miles on the engine- is the stock umbrella valve 'seals'. These things if present aren't really seals but in fact are umbrellas that ride up and down with the valves as they open and close, and shield the guides from oil cascading from above. The problem is, the umbrellas (or even cheap real-seals from rebuilder kits) are made of neoprene plastic, and soaking in hot oil for decades, they harden, go brittle and break into small bits that are washed down into the pan. There, they get battered into hard pieces small enough to fit through the oil pump inlet screen. Long periods between oil changes causes this to be worse. A tiny piece of hard plastic debris that fits thru a pump screen will jam the oil pump at least momentarily, which overstresses the roll pin enough to break parts off it, as happened in the subject engine.

The third thing that can overstress that roll pin is high rpms. If the oil is clean and engine revs are kept low, the stock pin is adequate; it's when the motor is asked to exceed maybe 6000 due to a tempting open road, a stoplight challenge from another car or even a missed shift. Then, even with clean oil and with your lucky socks on, an old pin may let go just from the sudden extra strain of high-rev pumping. Of course, installing a high-pressure or high-volume pump will push the pin closer to failure even if everything else is OK and the revs are more reasonable.

As George mentioned, the hexagonal pump driveshaft is the second weak-link in oil pump or distributor pin failures. Once the roll pin is strengthened, the stock driveshaft is soft mild steel and repeated encounters with debris and a strong enough pin may visibly twist the shaft. Close examination may show the straight lines on a stock hex driveshaft are now spirals. 100K+ miles might also be enough to wear the drive hex on the pump end of a stock shaft rounded so the oil pump slips under sudden load. So just strapping up the pin might not be a cure-all; some engines need an aftermarket 4130-steel pump driveshaft, too. Not all upgraded shafts are identical, either. I like the one Ford sells.

Both the above mods are simple insurance, not high performance changes, are cheap and it's up to each owner to decide if the history of his engine and his driving style warrants a closer look at what parts make up his engine. Good luck- J DeRyke