Quote:
Originally Posted by bettlesr
When I had to change a piston on my original engine in the car when I bought it ('28 block), I checked all the bearings with plastigauge. I can only assume that the engine had been rebuilt earlier with the wrong type of babbitt. The plastigauge was intact and there was a groove in the babbitt where the plastigauge had dented it. Around a year or so later, the engine got a bad knock and had to be towed home. When I pulled the pan down, all the babbitt was in the pan.
After this, Schwalm's got the job of building me a HP engine in a '31 block
|
Mr. Bettlesr,
The reason that Plastigauge indented your Babbitt is because you used the Plastiguage dry.
When you do not use the lube, the dry surface will not let the plastigauge slide, or spread out, and so when the Plastigauge has to go some where, so it goes in the Babbitt, instead of spreading out for a true reading.
Never read the Babbitt, always read the crank.
One thousandths per inch should always be used in setting bearing clearance, that is Minimum. The high side should never be more then a one half thousandths more.
If in this case, using a Model "B", a 2 inch crank, when hot, will swell right at .002.
So where is your oil clearance? You have none. So what happens when the bearing has to open its self up. It isn't going to be the crank wearing smaller, it is the crank pushing its self free, and the Babbitt is being moved to struggle, and twist its self loose.
Model T's have a 1- 1/4 inch crank, when broke in, depending how hard, run with 2 to 3 thousandths clearances.
Model A's with a 1- 1/2 rods run about 3 to 3-1/2.