Quiz, May 1997
Copyright 1997, by Harry Pellow, All Rights Reserved.

As the Maestro was cleaning and inspecting the parts of a 1963 356B Super, he was always on the alert for Anything Out of the Ordinary.

..... So, when he checked the Inner Bearing Surface of the #4 Main Bearing and found a whole buncha scratches in the center of the bearing, he was not surprised.

..... This was not unusual- many #4 Mains have more than a few "scratches" in the middle of the bearing from Foreign Particles vacationing in the engine.

..... But when the Maestro ran his Magic Finger Micrometer over the scratches in #4 Main Bearing he was Absolutely Amazed! Those "scratches" were damn deep GOUGES! "WHOA!" said the Center of Higher Reasoning, Porsche Pathology Division. "Were did these Grand Canyon-like Gouges come from?"

..... But no Foreign Particles called the Maestro's Hot Line at (408) 727-1864 to take credit.

..... So the Maestro hadda figure out what happened himself.

..... He eyeballed the #4 Main Bearing more carefully- and found a "Wowie" (Technical Term) at the end of the lead-in groove in the middle of the bearing, where something Too Big to get through the gap of the crank/bearing Running Clearance tried anyhow, and got ground into submission and the bearing too.

....."AHA!" cried the Maesttro. "A Wowie!"

.....Then, the Maestro eyeballed the Crankshaft's #4 Main Bearing Journal and sho' 'nough, there was a corresponding "Wowie" on #4 crank journal too!

..... Ok, so what was the cause of the "Wowies"?

..... The Maestro thought about the problem, but nothing obvious jumped into the his somewhat twisted brain.

..... "Well," he thought. "The Oil Supply for #4 Main Bearing comes from #3 Main Bearing so that might be a good place to look. I'd better check that out."

.....So he got out the Engine's Main Case Halves and checked out the #3 Main Bearing area in the Case.

..... And what did he find?

..... He found what looked like an attempt to ream a SECOND DOWEL PIN HOLE IN THE CASE, for #3 Main Bearing! Well, ALMOST a Second Dowel Pin Hole- the "new" hole in the case was offset only a couple of millimeters from the Original Hole, meaning both the "new" and the "old" dowel pin holes overlapped.

..... Of course, in the process of Reaming a new dowel pin hole in the Case, some metal was lost from the Case. And THAT was the source of the wayward particle that caused the "Wowies" to #4 Main Bearing/Crankshaft Journal.

..... But how did this attempt at reaming a second dowel pin hole for # 3 Main Bearing happen? Nobody in their right mind would ever do this on PURPOSE. So it must have been accidental. (Lets give the previous rebuilder the benefit of the doubt, shall we.)

.....So ifin it 'twer accidental, how did it happen?

.....That's the Quiz, Part 2.

..... Maybe like this?

..... The engine first failed from two spun rod bearings. Being cheap, the owner neither replaced nor reconditioned the rods. He just put in new rod bearings and reasaaembled it.

..... During assembly, he put the 356B 50mm crank into the case, initially placing the #3 Main bearing on its dowel pin properly. But for some reason, he pulled the crank out slightly, which is when the Dowel Pin for #3 Main Bearing became STUCK in the BEARING and was pulled out of the Case with the crank when the crank was pulled out of the case.

.....THEN, when the guy went to put the crank back INTO the case, the Dowel Pin on #3 Main Bearing didn't quite go into its dowel pin hole properly but rather rested on top, offset a millimeter or two from the original dowel pin hole.

.....As the guy torqued the Case together the dowel pin reamed a new dowel pin hole in the Case. And the chips from this "machining" operation went Downstream, straight to the #4 Main Bearing, causing the Grand Canyon-like Grooves and the Wowies!

..... Incidentally, although the 356B crank was still "Standard" (meaning it was Original and had never been ground), it was, sadly, CRACKED at the second rod in from the pulley end. By the Heap Big Torque produced by reaming a new dowel pin hole in the Case cause the crank to crack? Only the Porsche gods know.

..... And now you know why there's such a Strong Correlation between problems with #3 Main Bearing causing problems with #4 Main Bearing.

.....Anything that #3 Main Bearing sluffs off, #4 Main Bearing gets to eat.

..... How'd that Tom Lehrer song go? "What they flush into the Bay at noon today, they drink the next day in Sambo Se."

..... Or: Why You Don't Want to be Downstream from the Outhouse.

..... Such things you find out when you:

KEEP THE 356 FAITH!

The Maestro
 

 

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