Mobile air compressor

**nicky1** · Dec 26, 2016, 09:45 PM

Hi all,
I recently got a 2 cylinder Lister diesel given to me. It's about a 400 lb engine so it's not an option for a re-power in a GT. It had crossed my mind to run a hi [about 30 cfm] air compressor with it. I have read about some 4 & 6 cylinder gas engines converted to an air compressor. I remember a lot of years ago a tire shop had a Wisconsin v4 that ran on 2 cyls and pumped air on 2.... not a high enough volume like would be needed for sand blasting.
Does anyone have an opinion on converting a 4 or 6 cyl engine to a compressor and power it with this Lister? I think the Lister is about 20 hp. A 4 cyl diesel would be great but a little harder to come by. Just a pipe dream as i'm always needing something blasted.
nicky1

**Frank S** · Dec 27, 2016, 12:32 AM

Congratulations on acquiring the lister
I have a single cylinder Listeroid Diesel 6 HP at 600 RPM 9 HP at 900 RPM that when I was using it, I ran an 8 KW generator with it
Now lets talk engine conversion to air compressors The Schramm brothers pretty much pioneered that technique, I also own a Schramm 300 Pneumatic tractor 4/71 Detroit 152 HP @ 1800 RPM Direct connected to a 4 Cylinder compressor 300 CFM @ 125 PSIG
THe best way to convert an engine into an air compressor would be to loose the conventional head in favor of a head designed specifically to be an air pump this would involve some extensive engineering though do able. Failing that the second way with an overhead cam engine would be to loose everything in the valve train except for the valves plug off all related oil passages replace the valve springs with lighter springs just strong enough to hold the valves closed but weak enough that both the intake and the exhaust valves will be pulled open by the down stroke of the piston This will allow the maximum amount of available air to be drawn in, Next we have to get the air out the only place available for this is the spark plug hole. If at all possible this hole needs to be drilled larger and re tapped on some engines this can be as large as a -10 SAE or roughly that of a 1/2" NPT On others a -8 may be the largest Immediately after the spark plug port there needs to be a poppet check valve that allows the air out but prevents it from returning to the cylinder you will need one of these at each cylinder from there the air should be plumbed into a manifold system, From here it may be a bit tricky because the highly compressed air is going to be very hot and needs cooled before entering the tank if at all possible this can be done in 1 or 2 stages either air to air like in industerial compressors with a coiled finned tubing cooled by a fan or water to air where the tube is passed through a water jacket much like the oil on many automatic transmissions are cooled by passing the fluid through the bottom of a radiator, (NOTE the transmission lines in the bottom of a car radiator are not large enough nor will they hold the high pressures of the air)
Now you have a way to compress your air but you still need an intake this will need to be for both the intake and exhaust ports
Now you engine is probably either set to run at 600 , 900 or possibly 1000 RPM Ir you can develop say 20 HP @ 900 RPM and belt drive the engine from the large flywheels at a 1 to 2 speed up you would yield approximately 127 CFM of free air from a 2 liter engine @ 100% efficiency but due to the restrictive sizeof the spark plug ports about 60% is what is to be expected Higher RPM's will net even lower figures,.This might give you 20 to 30 CFM @100 PSI
The big problem here is the spark plug ports
Good luck
BY the way a slightly larger engine turned at a lower RPM may help but larger pistons and longer strokes will only compound the problem using the smallest 6 cylinder engine possible at a low RPM will be better than a large 4 cylinder engine but the better solution would be to design a proper compressor head or locate a 15 to 20 HP compressor to be powered from your engine

**nicky1** · Feb 10, 2017, 11:19 AM

Thank you Frank S,
I've had double knee replacement and just got to reading my replies. I do thank you for your input and your information. I think I will be using a Wisconsin V4 engine and make solid steel heads, Disable the lifters and use both valves for the intake. I found some check valves that will work for the outlets at Graingers [ part #5x782]. The seats are good for 450 deg F.
I'm just not able to get to work in my shop yet but when I do I will be posting a photo if it all works out.