Anyone have an idea on what a 12V Cummins should have for compression? I bought a 96 Ram with a 12V and 560k for my 77 Ford CC swap. Pullled the first 3 nozzles and got 350, 410, and 440 on the first 3 cylinders. I know the 7.3 PS is approx 350 min, figured the 12V should be close.
I plan on checking the rest tomorrow. Had a knock in #3 but with the good oil pressure I am hoping it's a nozzle problem, the knock would almost go away when the #3 line was cracked. Either a fuel problem or wrist pin.
Truck does smoke but not bad and there isn't too much out of the crank tube. Hopefully the smoke is a valve seal. Any help would be appreciated.

 

I used to teach a B-series cummins overhaul class and I went through all of the manuals front to back. I could never find a spec for compression pressure. General rule of thumb is that they should all be within 10-15%. Cummins likes to measure blowby with a manometer on the crankcase breather on the tappet cover on the side of the block to measure ring/cylinder wear. Promlem is that you need either an engine or chassis dyno to accurately do the test. Is that knock constant at all speeds? Was the smoke out the breather at idle. Those things are put together pretty stout, but that is high mileage. Hope it helps.

 

I don't have a manometer, I know how to make one, but the compression tester was available and I am lazy when it comes to fabbing tools.

I ran the test again with a battery charger hooked up and all cyls were above 400 with one near 450. Looks pretty good. Since I'm gutting the Ram ext. cab body off the truck anyhow I plan on tearing into the motor and at least giving it a new set of bearings/rings and sealing it back up. Probbably take a look at the cyl head too.
Can't wait to get this done! 78 Ford CC on a 96 Dodge 3/4T 4x4 with a Cummins and 5sp, Dana 80/60.