Is the 81T a 221 or 239 cubic inch

Nice wright up Jack, on the flathead engine. May I add a couple of things? The 36 engine with the inserts designation was LB, but not all 36 insert engine got the LB mark. The mains on the LB engine are 2.400 (round figure) the 37 and early 38 21 stud used the same crank as the 36 LB. The late 38 24 stud and later engines went to the 2.500 mains. All rod journals from 32 - 41 or 2 had 2in. rod journals. The 59A and later engine have 2/139 rod journals. Walt
 
I picked up an old 46 Ford truck a couple of weeks ago. The weather warmed up this week so I thought I would take the truck apart. I looked at the motor and there was no 59AB on the heads or the bellhousing. I cleaned off one of the heads and it said 81T on it. I am going to pull the motor tomorrow. I'll pull the intake and heads and see what I have. Hopefully a raised intake and round water holes under the heads.
 
81T heads were used on both 221 and 239 inch motors pre-war. The stock 39-40 Mercury engines got the 81T heads to keep compression down to about the same as the Ford 221 car engines, and Ford heavy trucks got the 81T heads on the 221 engines to reduce compression even more so the fleet owners could run the really cheap low octane gasoline.
 
221 engines starting with the LB series in 36 had domed pistons instead of flat top like the earlier babbit engines,
 
Walt Dupont--Me. said:
I think you may be right Bob, I was think about all the 221 engines. Walts
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When I assembled my '42 Merc, I noticed that the bigger 3 3/16 bore was required to install the 2.139 journal rods. Even with the larger bore, they were a close fit. Don't think they'd have dropped down the cylinder with the smaller 221 bore size.

Bob
 
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