So I'm in the throes of tidying up my garage, and I decided it was time to do something with this Hercules JXB engine, sitting in the engine stand, that has been cluttering up the place for several years. I had bought the engine in Portland, off a military vehicle collector, who said it came out of a US6. I'm pretty sure this is not the case (at least not as original equipment), as the US6 trucks all used the JXD engine, which has more displacement (bigger bore, IIRC). But some of the K-series commercial trucks, pre-war, used the JXB. It has the Studebaker Wheel emblem on the intake manifold.
I aired up the tires on the engine stand, and rolled it out where I could have a good look at things. I noticed the head bolts were loose, so I undid them all, and popped the head off. Mouse nests in the water jacket! But the pistons looked good. In fact, if they are not brand new, they are the next thing to it. No carbon on top, and all are marked for .040 oversize. No ridge in the cylinders at all. I was able to turn it over with a bar in the crankshaft studs, and it turns freely.
The valves were sticking in the guides, so I got out my valve spring compressor, and took out each valve in turn, cleaned the stem and guide, and lapped it into its seat with valve grinding compound. One or two of the valve seats have some fairly heavy pitting, and the exhaust valves are seated right on the inner edge of the 45° surface, so they protrude up into the combustion chamber a fair bit. I think it would be wise to have a machine shop do a proper valve grind on this beast, if I'm going to use it. Anyway, I got all the valves freed up, and lapped enough that it will have some compression on all cylinders.
I rolled it over in the engine stand, and took off the oil pan. It is very dirty inside, mainly because the engine, with the clutch housing off, is open to the elements at the rear, and all kinds of dust found its way in there. The crank and bottoms of the pistons are actually pretty clean, and the pistons look like new on the underside, too.
I removed the rear main bearing cap, and found a shell bearing in apparently good condition, and a journal free of scores or pits. It shows .002" clearance measured with Plasti-gage. I couldn't remove the shell from the cap, so I don't know if it is standard or undersize. The bearing surface appears to be a copper or bronze alloy, but I'm pretty sure it's not bearing backing metal, because the color is 100% uniform. There was one shim between the bearing cap and the block. Anyone know if it was standard practice to use shims on main bearings in those engines? It appears to be a manufactured part, not home-made. If it were removed, main clearance would be too tight, I expect.
I plan on checking the other bearing clearances, and if they are all good, then I think I can assume that this is a rebuild, with practically no time on it. Probably the thing to do would be to carefully tear it down, hone the cylinders to clean up the very slight rust present, and have the machine shop do a proper job on the valves. I could have the crankshaft polished, too. Then order up a gasket set, and reassemble it, to use, at least temporarily in my US6. The current JXD engine in there is VERY tired, and blows a cloud of blue smoke at idle, and really lacks compression. The JXB should readily substitute for it. Would make a little less power, but should run a lot better. Then the JXD could be rebuilt at my leisure.
On the other hand, if there is anyone here who NEEDS a JXB for a K-series truck, I have one. No carb, no distributor, no clutch housing.
I don't plan on spending too much time (or money) on this thing right now, but I will probably Plasti-gage the rest of the bearings. Who knows, it might have been a rebuild that went sour with a bad rod bearing shortly after installation. If the crank is bad, then it's probably worth more as parts.
Funny thing: the heads of the exhaust valves are non-magnetic. Even a very strong magnet won't stick to them. Stainless steel? Or Stellite?
If anyone here can poi