Greetings! I just picked up a 1970 220D with a 4spd manual. I was told it had 240D motor dropped in 10 years ago, and a rebuilt tranny 5 years ago. I have the records, but no engine number listing on paper.

I'm hoping to ask a couple questions as I can't decide which direction to go.

The casting on the block says 615.912. Which motor is this?

Second, I put a few miles on it to see what was going on. It has a lot of blowby, and when I pulled the glow plugs #2 had a significant amount of oil on it. Some blue smoke, not too bad. Oil pressure is 15psi at idle, 40 psi at 60mph.

Here's where it gets tricky. Last drive I started to get a loud clanking sound at higher RPM's, not a knock. At idle it sounds fine, but will randomly die and act like it locks up.

I have glow plugs out, can't turn it by hand. Starter will still move it over with no clanking. A trusted mechanic listened to it run, and thinks it's coming from in the bell housing. He advised me to pull the transmission and see what's happening around the flywheel.

I'm gonna crank on it with a stethoscope tomorrow and try and locate the noise.

I can technically check compression but can't check valves as I can't turn it by hand.

Part of me what's to pull the whole combo and go through the whole motor. Or I could drop the trans, look at the flywheel, and see if it unlocks. I could then check valves and perform a leak down test, but can't do compression. I may find that I need to rebuild it, and wasted my time dropping the tranny the hard way.

In the long term I'm going to do the motor anyways. Leaning towards pulling it doing a valve check/leak down on the stand, and compression once it's all back together. I'm not sure of the compression will give me results that I won't see with the leak down.

I've built a few gas motors, confident doing this thing slowly.

I'm also wondering if I'll want to swap to something else instead of rebuilding this motor, once I learn more.

What would you do if you were me?

Thanks