VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 216 Rear Main Bearings

It was time for me to drive to Virginia to diagnois a deep noise in the engine which was heard in cousin Dale's 1948 216 engine. The engine was recently rebuilt ( new rings, new connecting rods, new mains, etc. )by us and has less than 3 hours running time all in the car in the garage.
We then pulled the engine out of the car, and looked at the main bearings. Each main bearing had been set to .002-.003" clearance. Upon inspection, the rear main bearing has ALOT ( 3/16" x 1/4" area ) of babbitt material that appears to have been "wiped" off by the crankshaft. The material was at the opposite ends of both rear main bearings where they touch each other. The crankshaft was checked with a mic prior to initial assembly and it was determined that standard main bearings could be used. The crankshaft did not appear to be out of round.
The rear main bearing is made by Clevite and is 1 5/16" in width. The bearing is not as wide as the rear main bearing cap. Is this ok ?
Help! What do I do next.

If the rear bearing was set to the same specs as the other three it did not fail from being too tight.The other probable cause could be lack of oil.Does the oil hole in the insert (upper) line up with the oil feed hole in the block?..Is the oil pasagge restricted?..You could blow thru the oil pump feed line and see if air flows thru the feed hole for the rear main-would also blow out any deposits.Is the crank still in the block?..Would need to be removed to inspect.The fact that the insert is not as wide should not cause a bearing to burn out.!948 Engineering picture of the "new" for 1948 mains and crank shaft show bearing as wide as the cap-but as long as the oil holes index and grove in center of bearing insert line up should make no difference.Who adjusted the bearing originally?The good part is that they are a precision main bearing and just the rear can be replaced.The shaft should be OK seeing it hasn't been driven....isn't restoring old cars fun :confused: ...And how is your rear main leak doing?and your 3.73 rear.?.

Also check markings on the back of the insert to be sure that it was standard size.The fact that the sides or where the inserts meet went out it sounds as if it may have been too tight in that area.Adding the shims would have put clearence in the top and bottom but not the center.(sides).....still thinking..... :rolleyes:

Thanks Chev Nut for responding. I adjusted all of the mains to .002" - .003" when I built the engine a year ago. All of the mains are marked "STD" - standard on the back. We did notice that when we pulled the crankshaft out last night, one of the two rear main oil holes in the engine block appeared bone dry. This was the larger of the 2 holes which is on the side of the upper rear main bearing cavity, ie. opposite of the camshaft. Is the larger hole the oil feed line for the rear main bearing? We will be checking tonight to see if there is an obstruction in either of the two oil holes in the rear main. Oh by the way, is the larger hole the oil feed line ( under pressure ) to the rear main? Is the smaller hole in the rear main cavity a pressure line to the camshaft or just a gravity drain hole?
" up to my elbows in grease........."

More updates on the main bearings. The standard main bearings are made by Clevite. From front to back, their numbers are MB1175P, MB1176P, MB1177P and the rear main is MB1535P. Is this rear main bearing the correct one? Should it be MB1178P?
All of the oil feed holes were clear with NO obstructions in the lines in any of the 4 main bearings.
The front 3 main bearings have almost a slip fit on the crankshaft. The rear main bearing has a mild light press fit. This is even after all of the wear on the rear main. The rear main is the only one which shows wear to the point that it looks like brass is showing under the babbitt material. In other words, it is worn ALOT for 2-3 hours of operation. As of tonight, all 4 main bearings mic .001" with plastigage.
Our next step is that a new set of main bearings has been ordered for tomorrow. Any other suggestions ?

I am not familiar with the 216 bearing setup but most slipper bearings need to fit with the locating notches together. Is it possible you fitted that 1 with the cap end for end.
Considering that the tunnels were probably originally machined after the caps were faced and bolted together.
I make it a practice not to mix bearing caps. If this is the case you probably will need to have the main tunnel closed and honed to bring all parts back to correct alignment.
I hope this is not the case for you.

TonyW the rear main cap is unique to its position in the engine .
Toolman , do you have an update as to what happened in your engine ,, was the rear main fitted with a wrong undersize bearing ??

I would be wondering why the bearing is not the same width as the cap machined area.