MY HF gage set is fine though I can't speak to the accuracy of the calibration. Like most of us, I don't use it too often but it's nice to have when you need it and you can't beat the price.

I found an adaptor in the kit that fits the glow plug holes and that's how I've done it. While the cal may not be perfect it's plenty good enough to show if there's a bad valve (that will be near zero) or bad rings (I'd expect a reading somewhere around 200PSI or less). From what I can gather, a fresh new engine would show 400PSI or so and the race engine is about 325ish across the board, maybe a tad higher (I'm going off my foggy memory here - actual values are in my build thread). Mutt's engine has at least 225K or so (came from a car with a broken odo) so I'd guess that's pretty typical for a high mileage old Benz.

And don't forget to check the cam. If a lobe is wiped that cylinder either won't fill or won't empty and either way that cylinder won't make power. All it'll cost you is a cam cover gasket which is likely to need freshening up anyhow.

Another thought: If you have access to a bore scope (HF has them for pretty cheap) you can check out a near-zero compression reading by pulling the injector on the bad hole and looking at the valves. Few bore scopes will fit thru the glow plug hole. You probably could see if a corner is missing off the valve w/o pulling the head off. Run that piston down in the bore so there's room for the bore scope - Diesel combustion chambers are pretty small at TDC! Then you can decide whether to pull the head or find a good used engine or......

EDIT: I went back and checked my build thread on BangShift. The compression check showed an average of about 350 with a highest of 360 and a lowest of 320. Not ideal but evidently OK (hey, it pushed me to almost 130 MPH!). The PO checked the back-up engine using his HF gage and the values were similar - both stock, high-mileage engines.

Dan