Hey Guys! I'm new here, so if this is in the wrong spot I apologize.

Im looking for advice on an engine that is running rough with cylinder 1 being the culprit.

So my buddy who's a mechanic swapped an '84 300SD OM617A (according to seller has 135k miles) into my '85 G-wagen for me. We replaced the old OM617A that was in the truck since '06. It had some bad piston slap.
Anyways, during the swap we replaced pretty much all the seals and gaskets, including head gasket. We replaced the glow plugs, timing chain tensioner, water pump, thermostat, lift pump, lines, hoses, belts, filters, fluids, ect.
Came time to start her up and it would crank and was on the verge of starting but couldn't get it to start.

My buddy became busy with work and preparing for a baby, so I had the truck taken to a reputable diesel shop in town.

After being there an hour they gave me a call and told me they had it started! running pretty rough though. I guess during our valve adjustment we had them too tight. So they adjusted the valves to be in spec. They also had to mess with the IP and were able to bleed the system better.

Good news: it doesn't have any blow by and is running.

Bad news: it does have some white smoke, so unburnt fuel? And it's still running pretty rough.

So they did some more diagnosing and cylinder 1 is not getting hot and seems to be the problem. They said it seems like a problem with either the intake or exhaust valve, possibly stuck open or closed. They swapped the cyl 1 Injector and that didn't make a difference, they also cracked the lines for cyl 1 and that didn't either.

So they want to do a leak down test to determine which valve is the problem and then go from there, they said they will probably need to remove the head and have it and the valves machined so they seat properly and that should solve the problems.

Any thoughts on the problem? Has anybody ever ran into a similar issue with the valves? Do you think there are any other obvious things that could be causing the rough idle? Do you think cleaning and machining them back into spec will solve the problem?

Thanks guys!

I'm no mechanic and am new to the world of Diesels and OM617's so this whole process has been a learning experience for me. Thanks in advance!