I just acquired a bare block and the front and rear bearings are in very nice shape. However, it looks like someone tried to pry the center bearing out with a screwdriver (long ago).
If I remove the rest of the center bearing and bolted in a crankshaft and camshaft, can I pour new babbitt in just the center bearing and then scrape the center bearing to fit?
Just trying to keep from replacing the other two bearings.
I like your spirit. I would use the crank as a mold(with side pieces) and shim up the crank at journals 1 and 3 to allow for additional babbitt for journal 2. Then I would scrape/machine journal 2 to fit. Seems possible.
You should do them all at the same time. The crankshaft should be checked for cracks and straightness, and if worn it should be ground to round. All 3 bearings should be poured and line bored. The front main would be fitted so that it lines up with the camshaft for correct mesh of the timing gear. The rear main should be cut for proper thrust of the crankshaft so that the timing gears are in line in the front, and at the back and the flywheel is in correct relation to the magneto. It is very important that the center main bearing be in perfect alignment with the other two so that the crankshaft does not bend at the center with each revolution, which leads to metal fatigue and broken crankshaft.
I would advise you to check with local club members to direct you to someone who has experience and equipment to do this work. The rod bearings are something you could try for yourself, but if you do take it to an expert, they can be done at the same time. Later if you should find an engine which all the mains are in good condition but you need to repour the rods, you can do it yourself. Rods can be replaced without removing the entire engine, but with the engine out of the car, it is best to do all major work at the same time to avoid having to pull it again soon thereafter.
That kind of thing has been done successfully. In fact, model T's respond well to some fairly crude repairs done by practical and imaginative people. The problem you would have is to preheat the block and mandrel, in this case the crankshaft, hot enough that the babbit will completely fill the mold and not freeze up too quickly and result in a short pour.
Why not just do it right? You can always get more money, never more time. Eventually you will have to take the time to fix it right, and by then new bearings will be more costly. Your choice. I will say that I am always amazed at some of the things I find when tearing down model T's that were kept alive by old time practitioners of roadside repair.
My understanding is the block only has to be warm and it's more important to peen the babbitt after poring while the babbitt is still somewhat warm and pliable.
Mark, you are correct in a normal pouring scenario. You have to heat the block enough that all moisture is boiled off so as not to boil out explosively when the bearing is poured. What Robert is proposing is far from normal. The crankshaft is larger in diameter than a main bearing pouring mandrel, leaving a very minimal space for the metal being poured. It will chill very quickly if the shaft and block are too cold and not completely fill the mold. Also, in this situation peining the bearing would not be be good because it will not be machined afterwards.
To insure good alignment.....the mains should be line bored. Trying to use a model T crankshaft for checking alignment is asking for trouble. The crankshaft is weak and will easily deflect. With out knowing if all main bearing are in alignment, scraping the center main to fit the crankshaft main dia. could cause the crankshaft to flex more reducing crankshaft life. The more flex the less life.
It would be an Exercise in Futility.
How much wear in the front, and rear mains. They will have to be scraped, along with the center.
As Norm said, the gear clearance is Critical. The chance of hitting .003 thousandths is small.
The babbitt has to be peened, if you don't do it, the crank will, and normally breaking up the babbitt.
That is probably why they pried it up to begin with. Front and rear might not be any better.
If there is oil in the block, it will come out when you heat it, and blow hole the babbitt.
If the crank isn't straight, it will take it out again.