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Thread: vw diesel air compressor conversion

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    vw diesel air compressor conversion

    im looking at doing a conversion, vw 1.6 diesel into a compressor. I have many. rougly 200 lbs compression. they are so so as diesels now. would it be that simple to pull injectors check valves in their place to a manifold to a tank.
    the fuel pump could be left in place im thinking just recirculate fuel. so timing isn't an issue. same with alternator and water pump. cooling system intact. the exhaust same thing into tank. or is this a pipe dream
    Last edited by volksman; 07-23-2015 at 07:40 PM.

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    jere's Avatar
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    So you want to use the motor as the compressor itself? Not to power a separate compressor? I would use the motor to power a multi horsepower purpose built air compressor head first.

    I know people have turned compressor heads into simple motors so it is feasible. You would have to find a way to get the compressed air from the head, I wouldn't think the manifolds would hold pressure well. And what would you use to power the motor used as a compressor another motor?
    Last edited by jere; 07-24-2015 at 12:15 PM.

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    I think it could be done. It wouldn't be the most efficient method because it would take a lot of energy to rotate the motor.

    Does this motor have overhead valves? If I am thinking this through right, you would need to block off all the holes leading into the cylinder other than the intake and exhaust valves (i.e. sparks plugs or glow plugs). The injectors are on the intake side of the motor and are typically before the intake valve. You probably wouldn't have to do anything with them unless you want to make sure all the air coming into the motor is filtered first. Probably just plug them up. The intake valve would draw uncompressed air into the cylinder. The piston would then compress it and push it out through the exhaust valve. I think the exhaust valve would act as a check valve preventing the compressed air from traveling back into the cylinder. Then you would have to have an adaptor bolted to the exhaust side of the head to connect the head to a hose or tank. For safety, you would need to have some way to shut the system down when the pressure in the tank reaches its desired level. Otherwise you would turn the tank into a bomb. If you are driving the engine with some kind of electric motor, then you would need an electric pressure switch. I am not an expert, but that is how I see it working in my head.

    If we are throwing out ideas, it would be interesting to see if you run the engine normally off a few cylinders and use one for compressing. That way it could power itself.

    I have seen people use AC compressors to fill air tanks. Off road guys leave them attached to their truck and drive them with the engine to fill tires and other things.

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    I got in touch with a freind of mine, cheif engineer on ships. he suggested leave everything as is disconnect the fuel from injectors and put compressor oil in base. the oil will catch fire if blowby is happening, with heat in the air. he figured run the exhaust into a tank. trying it out will prove or disprove. i planned on using pto from a tractor to turn the diesel engine. i want something with enough air volume to sand blast with authority.

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    If you keep the rpms lower and maxium pressure there will be less heat and chances of oil flaring up. There really isn't any "blow" or explosion from the fuel being burned. But carbon could be an issue and maybe oil flare up depending on how hot everything runs at.

    Run of the mill belt driven air compressors use an oil bath to lubricate with automotive engine oil (at least the 4 that I have owned have). The compressor heads get hot to the touch but no fires or explosions in their 40 years or so of use. They all shut off at less than 125psi, so you might want to have a pop off/recirulator/blowoff valve in effect to dump pressure after a similar pressure is reached. It might be hard to keep pressure that low in practice so be cautious

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    Never done one, but thinking about it, I would grind the exhaust lobes off the cam and make the cam run 1 to 1 with the crank then take out the injectors and replace them with one way check valves. That way you have compression on every rotation of the engine instead of every other. A tractor PTO is only 540 rpm so unless you speed it up with a jackshaft you will never get the air you need. But in my world big air compressors are easy to find out of factories.

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    I haven't done the cfm math. the engines new are 23 to 1. interfiernce fit.( the top of the piston is basically into the dish in head). timing is critical or the valves will hit the piston. I see principle behind the 1to 1 in above post. getting a belt tensioned enough not to jump will be the hard part. if I could find an industrial unit that I could turn with the volks diesel that would be ideal. 50 cfm at 70- 100 psi will sand blast well. with a big nozzle for sand . everything is proportional smaller nozzle higher pressure lower cfm. less media used longer time to do work. thei is a flla from Tasmania posted a pic of a diesel he's using as a compressor cant find a word post corresponding to it though

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    Frank S's Avatar
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    Why not cut the head in half and block off the water passages then mount a thick milled out aluminum plate over the other 2.
    and mount commercial air compressor poppet valves like those used on a Quincy air compressor
    route the 2 not used injector lines to the fuel return
    now you would have a self running air compressor that would pump air on every up stroke of the 2 pistons
    I rebuilt a Miller Air-pac 400 amp welding machine that had a 3 cyl air cooled Deutch engine #3 cylinder was done this way it produced 40 CFM @ 120 PSI while welding
    you could add an un-loader valve that would idle the engine down at a set PSI or after a period of time that the pressure stayed at full pressure
    Engines have been converted this way since the days of the model T ford

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    Frank S's Avatar
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    Quote Originally Posted by volksman View Post
    I haven't done the cfm math. the engines new are 23 to 1. interfiernce fit.( the top of the piston is basically into the dish in head). timing is critical or the valves will hit the piston. I see principle behind the 1to 1 in above post. getting a belt tensioned enough not to jump will be the hard part. if I could find an industrial unit that I could turn with the volks diesel that would be ideal. 50 cfm at 70- 100 psi will sand blast well. with a big nozzle for sand . everything is proportional smaller nozzle higher pressure lower cfm. less media used longer time to do work. thei is a flla from Tasmania posted a pic of a diesel he's using as a compressor cant find a word post corresponding to it though
    when it comes to compressors. You obviously want to keep the head cavity to a minimum to reduce the amount of back wash air on the down stroke this is why most commercial air compressors use reed valves, or poppet valves on the larger more expensive compressors with flat head pistons coming very near the head.
    the actual free CFM would be the stroke x the area of the bore times the RPM times the no. of cylinders minus the volume of the head cavity with the piston at TDC.
    If you want to do a very simple conversion without replacing half of the head just remove the injectors, route the lines direct to the return line, and install tubes with a check valve where the injectors were, then weaken the intake valve springs so they will open from vacuum only, on every down stroke plumb in some tubes and check valves to the exhaust ports and run it as a normal 2 cyl diesel engine. this won't be as efficient as fabricating a proper compressor head but it does remove a lot of work.


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