Over the years, it has been our experience that if a TR-4 type engine
>>> experiences oil starvation for any reason, number 2 rod bearing will be
>>> the first to fail. Exactly why number 2 should fail and not number 3 rod
>>> bearing, I cannot say, but none the less that is what happens.
>>> To help prevent this what we do is use great oil. We like PennGrade 1
>>> racing 20/50 best. We have also successfully used Torco and Chevron Delo
>>> oils.
>>> We set the main bearing clearance at .0025 to .00275". The crank will
>>> flex at high RPM and high power outputs. By giving it more clearance, it
>>> can flex without rubbing on the bearing surfaces. On one high output
>>> engine, increasing the main bearing clearance from .00175 to .0025
>>> lowered the engine oil temperature when running on an engine dyno over 50
>>> degrees F. In fact, we had to shut off the oil cooler blowers and put and
>>> insulating shroud around the allow oil pan to get the engine oil
>>> temperature up over 180 degrees F while running on the dyno!
>>> We set the rod bearing clearances at .003" when using "carrillo" style
>>> machined steel rods. We have used more with race prepared stock rods
>>> which do not stay as round as the aftermarket rods do. We prefer to use
>>> Vandervell VP-2 rod bearings for racing. They are the best.
>>> Unfortunately, for the most part there are not many left around and they
>>> have been out of production for many years. We did have ACL make up 100
>>> sets of trimetal .010" undersize rod bearing a number of years ago. We
>>> still have some left. They do not have the load carrying capacity of the
>>> Vandervells, but they are the next best thing, and they are available.
>>> We drill out the oil holes in the two center main bearing shells so
>>> that they are the same size as the holes in the block that feed them.
>>> We modify the oil intake hole in the main bearing journal by grinding
>>> a "leading" scoop the same width as the oil groove in the main bearing.
>>> When looking at the crank from the front, with the oil hole in the main
>>> bearing journal facing up, all of the grinding should be to the right
>>> side of the oil hole. As the crank rotates, you want it to scoop oil out
>>> of the reservoir of oil that is in the groove in the bearing and force it
>>> down the drillings toward the rod bearings. ( Volkswagen 1600 air cooled
>>> engine cranks were manufactured this way, it wasn't my idea!)
>>> We modify the oil pickup so that it's opening faces down against the
>>> bottom of the oil pan, with about 3/16" clearance between the bottom of
>>> the pan and the screen on the bottom of the pickup.
>>> We measure the oil pressure in the main oil galley running down the
>>> side of the block, not at the original location at the oil filter head.
>>> This is very important. The original measuring point is right at the
>>> output from the oil pump. You want to measure the pressure just before
>>> the feed to the bearings so if there were a blockage anywhere in the
>>> system before the bearings, you would see it.
The Engine Room
Morgan & Sports Car Specialists
Santa Cruz, Calif. 95060
831 429-1800
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