So I have a single cylinder diesel engine. We do not use it to produce power (it is operated by an electric motor) but to measure the pressure at low rpm (100-200). The volumetric compression ratio is around 21.5 and the dynamic CR should be very near to that since the valves open and close near the TDC or BDC. I noticed that the pressure at the end of the compression stroke is much lower than expected, despite accounting for the fact that some air will always leak resulting in lower pressure and found the cause to be bleed/leak from the exhaust valve.
During compression, a significant amount of air is pushed out of the exhaust through the valve and during expansion (power) the piston draws in air from the exhaust valve while the valve is still closed. I need to achieve as much pressure as possible inside the cylinder at the end of compression stroke. So, I was thinking if there is some way to control this air leakage from the exhaust valve. Right now, I am thinking of (1) applying paint or silocone primer to the valve and seat, or (2) applying gasket maker sealants (RTV??), or (3) attaching a thin rubber gasket with a strong adhesive.
I know these are not ideal options, but I would like to generate as much pressure as possible, even if it means some damage to the engine. Any suggestions would be greatly appreciated. Thanks.
PS - Using maths, the max pressure should be around 70 bars (theoretical, lower in reality) but I am getting around 20 bars (EDITED, previously 11 by mistake) at 100 rpm. The pressure increases to 35 bars at around 1200 rpm and does not go any higher.
Edit - I tried lapping the valves and when that did not work, I ordered new cylinder head and new valves. I got slight improvements (11 bars from 7 bars) but this is no way near to what I want. So bottom line, what I need is high pressure at low rpm. Difficult, but let's hope.
Edit - When changing the cylinder head and valves, I changed the head gasket too, and I know the exhaust valve is the main culprit now because you can hear and feel the air being pushed out and sucked through the valve when the valve is closed.