OK, I received my truck today, 71 F250 with 400M T18 4spd.
Some of you had comments to my earlier post about its knocking crank - thank you.
Today I changed the oil and put in 3quarts 20W50, and 1 quart Lucas Engine Oil stabilizer - very thick.
When I re-started, everthing was VERY quiet - it wasn't until the oil warmed up that the knock returned, but not even as bad as it had been. The oil that came out was thin and black.
This leads me to suspect that I might be able to change a main bearing and shore it up for a bit. Lucas says you can go as high as 60% of there product in the oil, any comments? - the 80W90 Gear oil on the shelf looks pretty enticing.
The dash oil pressure gauge seems to read, however it varies quite a bit - in odd ways that makes me think it is not right at all. I will put a dial gauge in *** Where is the oil pressure sender now on the 400M????? I cannot see where the wire is going yet, I do know that it is not located above the fuel pump like I would have expected.
True gauge readings will be interesting - I have more reason to believe that changing the mains (or some) will help. The knock is on every revolution, low, and heavy, so I quite expect a main, as opposed to a rod.
Next Question: Can get the pan out with the motor in place??
Thanks

 

Yes the pan will come out with the motor in place ..may have to wiggle it some but it will come out ....

 

the oil sender is behind the intake manifold. there is a plug right next to the fuel pump, so maybe you could put a sender or tube in there and leave the stock one?

good luck!

 

When the bearings get worn the oil pressure will vary considerably with RPM and temperature.

Usually the aftermarket guage sender or tube is tee'd into the block at the OEM oil sender location. If my rememberer is operating properly the sender is upright on the rear of the engine way back behind the carb.