Hi
I like your idea that the TDC volume is the more important number than the volume of the whole cylinder.
Joseph

Both numbers are equally important. After all, compression is determined by the BDC volume and TDC volume.

I checked my notes from 3 years ago. The differnce is 30 psi, not 60 psi as I stated earlier between the HF glow plug adapter and the inj adapter. See what happens when you go by memory?

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

By "missing the collar" do you mean the heat shield (which is not supplied in the HF kit)?

If it is the heat shield, it was in the engine when I did the compression test and not in the pic I took.

There is no loss of compression in the hose to gauge. The hose can be 100 ft long and it doesn't matter, as long as the schrader valve is at the tip of the adapter. A longer hose will just take longer for the pressure to build and peak.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Hi Funola
I was just considering your argument that the greater volume of the injector adaptor (.78 cubic inch) was accounting for a difference in compression readings.

At TDC the volume of the cylinder is less than 2 cubic inches - so the added .78 cubic inch volume of the adaptor would be a higher (about 39%) percentage.

While with the piston at the bottlom, the volume is of the cylinder is about 36.6 cubic inches - so the added .78 would be a much lower percentage of about 2%

Of course, I could also be having a fuzzy math/logic attack.

Regards,
Joseph

All this is correct, but AGAIN, compression test is for relative numbers, not meeting a particular specification. If you know that the particular setup you're using will result in lower numbers, fudge that in for an overall cylinder condition.