Genius or crazy?

[ftpiercecracker1]

Extreme Air compressor idea.

 

Take a 4.0 and have a custom cam ground such that three of the cylinders no longer have a compression stroke. Only intake and exhaust.

 

Custom make a header to collect compressed air separate from the exhaust.

 

There are some other minor details to work out, but i can't see why this would not work if the cam could be made, which again i can't see why not.

 

Crunching the numbers (2 cubic liters of air per revolution at 1000 rpm converted to cubic feet of air) gives me an air flow of 70cfm at 1000rpm pressure unknown, but i would say 120psi.

 

It would be able to run even the most monstrous sandblaster with ease.

 

What say ye?

[Jeep Driver]

First thing that comes to mind is the valving is wrong.........reed valve which is a one way valve.

 

Also, condensation and oil contamination. 

 

Also, the remaining three cylinders.......the engine half won't run, won't produce enough power if it did run. 

 

Also, inefficient.

 

Also, if it were that easy it would have been done.

 

Also, cost prohibitive. 

 

 

 

 

 

My 60gal compressor runs a small blaster like this just fine- https://www.harborfreight.com/110-lbs-pressurized-abrasive-blaster-69724.html?cid=paid_google|*PLA+-+All+Products+-+Higher+Sales+Items|New+Products+-+(6)+Price+%24100-150|69724&utm_source=google&utm_medium=cpc&mkwid=sJvgeLmmQ|pcrid|278961614564|pkw||pmt||pdv|c|slid||product|69724|&pgrid=59557298587&ptaid=aud-446108146723:pla-296487509509&pcid=1458484684&intent=Higher+Sale&gclid=Cj0KCQjwt5zsBRD8ARIsAJfI4Bg7u6jQVcPHDkQuQ6DmIp8A-Cbm6p8IY2nR10N5kmJ-liq7_kKvGJQaAh7cEALw_wcB

[Jeep Driver]

BTW.......it would be something like a constant 100cfm at 150psi for a large commercial blaster.

 

Dry clean air..........rotary screw compressor is what you want. 

 

 

My little blaster works great for small parts, axle housings, frames............etc.......

 

[Pete M]

well, it's definitely crazy.  maybe genius if you could get it to work.

 

But I'd gotta imagine that it'd be easier to use a gas engine to power an air compressor. 

[DirtyComanche]

Old tech, used to be super common to see that style of compressor running the pneumatic hammers in mines, etc.  Typically they used a V8.  Yeah, there's a little more to it, but basically it was an inexpensive way to make an awful lot of air.

 

I'd waste my time on something else personally.  They didn't stop building them that way because they were awesome.

[schardein]

Reminds me of the book "The Ugly American", where the protagonist helps the local populace by converting old Jeep engines into bicycle driven water pumps to irrigate their crops.

[gogmorgo]

The custom ground cam would probably cost you more than a suitable compressor.

If you want to do it cheap and easy, pop out the exhaust rockers and pushrods for cylinders 4,5, and 6, unplug their injectors, and thread a hose adapter into the respective spark plug holes. You'll need check valves for each of them. You'll only get a squeeze out of each piston every other revolution, and you'll definitely want an air dryer before it sees tools or anything. It'll definitely run like crap.

[mjeff87]

Reminds me of me in my (much) younger days......I took an old B&S lawnmower engine, ground off a cam lobe, threaded an air fitting into the spark plug hole and jimmied up a V-belt pulley to the end of the crank (blade removed).  Ran the belt to an old electric motor, and bolted the whole mess to a piece of 2x10 and plugged it in.  It actually ran, for about a minute, and then self destructed right there on my basement floor. 

 

A teenage boy with nothing better to do and a box of tools and spare parts can be a dangerous thing.  Lucky I didn't kill myself.

[Eagle]

19 hours ago, ftpiercecracker1 said:

Extreme Air compressor idea.

 

Take a 4.0 and have a custom cam ground such that three of the cylinders no longer have a compression stroke. Only intake and exhaust.

 

Custom make a header to collect compressed air separate from the exhaust.

 

 

I'm trying to figure out if this is even possible with a 4-stroke engine.

 

The cam goes around once for each two revolutions of the engine. How can you eliminate the compression stroke? You would have to have one of the valves open on that stroke, which would mean that the corresponding cam lobe would have to be double-sided. Once you do that, you might as well make both the intake and exhaust lobes double sided, which would make the cylinders you're using for compressed air effectively 2-stroke rather than 4-stroke.

[gogmorgo]

Okay, I've been thinking about this all day after posting this morning and I think I've got this figured out. 

 

Check valves for compressed air should not be hard to track down, every truck with air brakes has them on the tanks to stop them blowing off if there's a supply leak. You'll need six of them, three T-fittings, and three pipes (or hose) fittings to adapt to the m14x1.25 spark plug holes. 

The idea is you pull the pushrods for both intake and exhaust on the rear (or front) three cylinders. Fish the lifters out as well. Leave the rockers on, pull them off, doesn't matter much. You've got two check valves on the T off each spark plug hole, sitting opposite so on each downstroke of the piston it pulls in through the intake check valve and on the upstroke pushes out the charge air check valve. You'll have an intake manifold of sorts to pull in filtered air, then an "exhaust" manifold for the compressed air, but it all goes through the spark plug hole.

You'll get better compression if you pull the head and seal off the valves, but I wouldn't go that far until you've got proof of concept. My concern is it won't want to run on three cylinders.

Dropping the front (or rear) half of cylinders pulls out every other normal power stroke. Firing order is 1-5-3-6-2-4 you'll notice that's the front three between the rear three firing. Convenient. Ignoring the engine's valves and using the spark plug hole and check valves means you get a compression stroke for every upward movement of the piston without needing to do anything fancy to the camshaft or exhaust manifold. Using the engine's valves to do that would require a custom double-lobe cam which will not be cheap when you don't even know if the thing's going to work. Doing it that way, not only are you losing 50% of the firing strokes, you're turning them into compression strokes, which doubles the work being done just to keep the engine running. A heavier flywheel will probably help, but again, cost. Not doubling up the compressor strokes and sticking with the four-stroke setup would mean pulling a vacuum on the former power stroke, which I think would harm the engine more than a second compression stroke.

 

Another thing that might work that I just thought of, keep the "exhaust" blowing out the spark plug hole but eliminate the T and intake check valves. Instead use a super weak intake valve spring so the intake valve gets pulled open when the piston pulls a vacuum on the downstroke. I'm not positive that will work however. In theory the cylinder pressure will keep the valve closed, but I think you'll lose a fair amount of pressure before it closes with a weak spring. 

I don't think the exhaust manifold sealing surface will be good to retain compressed air, hence using the spark plug hole. The exhaust manifold is clamped on with bellville washers, which means that yes they hold tension, but it will only hold so much before they lift off, especially with only two per port. Arguably only one, because it's only held on by half of each washer (the other half holds on the intake). You're looking at getting 150(ish) PSI out of the system, but the stock exhaust system isn't going to see anything close to that. Maybe a tenth if it's completely plugged up. The exhaust/intake combo is notorious for having trouble sealing even before you put 150 psi behind it. 

[Jeep Driver]

Go pull your plug wires on 1, 2, and 3.........see if it will run.

 

It won't, and there's your answer. 

 

 

Spend your time and energy making money to buy a good compressor. 

[DirtyComanche]

Ford one.

 

https://forums.vintage-mustang.com/general-discussion-non-vintage-mustang/575181-ford-v8-air-compressor.html

 

Ford V8s were the most common from everything I remember, going back as far as the flathead days.  Before then they often used 2 cylinders of whatever type.

 

Like I said, it's not new, but there's lots of reasons why it isn't popular.

 

If you explore old mines you're likely to stumble across one at some point.  The kit to convert them was cheap, and used engines were cheap, and most mining of old was done on the cheap.

[dasbulliwagen]

We one rented a jackhammer and trailer compressor setup to demo an old school playground. the compressor consisted of a small block Ford v8. The only way i can see it working properly is with a custom crank set up to run half of the engine like a 4 cyl with the one side crank throws spaced properly as a 4 cyl, and the other side with either a custom head or like was said with no exhaust valves opening and the cam lobes for that side setup for 2 stroke operation with check valves on each port. 

[gogmorgo]

I don't happen to have a 4.0 handy because I'm about 400 miles away from home for the next month, but my 2.5L will fire up and idle with spark plug wires unplugged on cylinders 3 and 4. It wouldn't start on only a single cylinder, but that's not totally surprising. It was firing and it did have some inertia, it took it a few seconds to spin down and stop after I let go of the key, makes me think it would likely run with a heavier flywheel... but that's getting a little beyond the scope of the experiment. 

I see no reason a 4.0 wouldn't run on three cylinders. Three cylinder engines exist, and they do meaningful work. They typically have a 120° crank angle, same as a straight six. Generally they use a balance shaft because they don't have balanced reciprocating mass, but the three compressor pistons would help with that. Crankshaft longevity might be a concern because the harmonics of the compressor and not firing half the engine would be different from what the crank was developed for, so a healthy harmonic balancer would be critical. I'm curious why someone might categorically state it wouldn't work without producing any evidence to support their statement, or even any theory to support the hypothesis. 

 

Another "easy" solution would be to find a belt-driven compressor and drive it off the crank pulley, leave the engine as-is, but that also defeats the purpose of this thought experiment. 

 

And one more argument against using the exhaust valve is you'd only want it to pop open when there's more cylinder pressure than compressor tank pressure, which would mean a brief period at TDC. I don't think you'd be able to have a cam lobe profile that would open and close it quickly enough with such a short duration and still be strong enough to tolerate smashing into the lifter, even with a roller lifter. 

[ftpiercecracker1]

This was fun.