Pratt and Whitney Serial number locations

[MiTasol]

Having worked on a lot of WW2 engines over the last 60 years I no longer trust my memory as much as I used to.

On Bristol and Allison engines the serial of the first engine every major part was fitted to was stamped into the part, eg on the carb mounting flange of the blower case on Bristols. On Allison's they went further and the engine serial is stamped into every crankshaft bearing at the factory and during factory overhaul, though unfortunately not during all overhauls elsewhere.

For the life of me I cannot remember if this is the case on Pratt engines.

Can anyone advise where the engine serial is stamped on R-1830 engines (other than on the data plate on the nose case)?

 

[GregP]

On the Allison parts, there is no good way to punch serial number in. When you "overhaul" main bearings, you have to get them stripped, copper plated. then plated with .002" of Silver on the inside, then .040" of lead on the inside. Once they are done, you have to scrape them to approximate dimensions, fit the Allison go-no go gage, torque it with Plastigage, and then scrape until the required clearance is shown by the plastigage. The clearance desired is 0.0045 inches for nominal and 0.002 inch undersize mains. When I say scrape, it means using an old-style bearing scraper. We made ours by grinding a triangle file. Learning to scrape is not a 1 day process.

In the Allison book (at least for E and F engines), they specify bearing blue instead of plastigage, but you get more accurate results with plastigage, and plastigage is easier to use than bearing blue in my experience. Any numbers on the outside of the old main are usually visible on the "overhauled" bearing in the copper plate. It would be a bit difficult to stamp a new number over the old number and make it look right. I confess to not caring what serial numbers went into an overhauled engine since ALL undamaged bearings not in service condition were going to be refurbished / replated. The important thing is to have proper bearing clearances when torqued for smooth, long engine life.

When I was working with Allisons, the shop generally took 10 - 12 weeks to do an Allison, and all but ONE week was spent disassembling it and preparing / overhauling parts to be ready for reassembly. You have to look at and clean up / overhaul the crankcase including all studs, the bearings, the rods, the pistons, each valve, the rockers, ... everything. We spent half a day on each valve cover to make them smooth and good-looking because EVERYONE who acquires one wants it to be perfect. It takes 6 - 8 weeks to send bearings out and get them back. Once you actually start engine assembly, you can build one in a day and a half. But the previous 9 - 11 weeks are the heart of the engine. We typically balanced V-1710 rods / pistons to within 1 gram or less. Doing it right makes for a smooth-running V-12. Mounting it on a test stand and running in the engine to seat the rings takes longer than actual engine assembly.

The only Bristol parts we ever did were cylinders. People would send Joe Yancey Centaurus cylinders because he can take out the piston ring wear step in the cylinder bore and still have a round cylinder. Almost everyone out there else warps the cylinders before they get the step out. Joe does Centaurus cylinders from all over the world, including for some rather famous fighter operators in Europe.

 

[MiTasol]

Thanks Greg - good info on modern overhauls and the turn around time was not much different from Bristol Herc overhauls in the 60s when spares were relatively plentiful.

Unfortunately it was of no use for this particular project which is trying to identify a specific crash site aircraft powered by a Pratt. The nose case is shattered and the data plate is lost. Other information is contradictory and the engine serial for all possible candidates is known.

The Allison manuals required the engine number be stamped or etched in a variety of locations, including the bearings. Likewise many Herc parts were serialized, tho not the bearings, and I had the doubtful honour of re-serializing several parts in the very early 60's.