Little O/T Eng to Air Compressor Conversion

I saw a picture of a Briggs and Statton one cylinder motor that had been
converted into an air compressor and got to thinking about doing the
same thing to a 36 hp 1200 CC bug engine. The basic change is to remove
the push rods and somehow lock the lifters in place, install two one way
air valves in the head (one for intake and one for out flow) with the
appropriate pluming to a tank. An electric motor is used to drive the
engine wired with an adjustable pressure switch.

Has anyone tried this type of conversion. I know about the conversion
with two cylinders running and the other two acting as an air pump. It's
a little on the expensive side and much more air then I would ever need.
I already have a 30 gallon propane tank and a pressure switch that would
handle the electrical load for a large motor. Graingers has the valves
for a reasonable price. What I need to know is how big of electric motor
would I need and how many rpm's to run it. I'm looking for about 120 PSI
max with around 20 CFM output.

Does this sound like a feasible project? I'm figuring no more then $125
for the valves and wiring and maybe $150 to $200 for a new electric
motor. Less if I can find a used one. Any thoughts on this would be
appreciated.

Contact Dunn-Right Inc at and it might save you a lot of
time trying to get something to work for you for what you want and have alot
more power. Haven't built one yet...... too many projects stacked up, but
if the claims are anywhere near the facts they claim you could get over
50CFM @ 100 psi. Email them and get the same package I've gotten from them.

If you would like I could scan the documents I recieved from them and e-mail
them to you to save time.

Mac



"Wes Pearson" > wrote in message
news
>I saw a picture of a Briggs and Statton one cylinder motor that had been
>converted into an air compressor and got to thinking about doing the same
>thing to a 36 hp 1200 CC bug engine. The basic change is to remove the push
>rods and somehow lock the lifters in place, install two one way air valves
>in the head (one for intake and one for out flow) with the appropriate
>pluming to a tank. An electric motor is used to drive the engine wired with
>an adjustable pressure switch.
>
> Has anyone tried this type of conversion. I know about the conversion with
> two cylinders running and the other two acting as an air pump. It's a
> little on the expensive side and much more air then I would ever need. I
> already have a 30 gallon propane tank and a pressure switch that would
> handle the electrical load for a large motor. Graingers has the valves for
> a reasonable price. What I need to know is how big of electric motor would
> I need and how many rpm's to run it. I'm looking for about 120 PSI max
> with around 20 CFM output.
>
> Does this sound like a feasible project? I'm figuring no more then $125
> for the valves and wiring and maybe $150 to $200 for a new electric motor.
> Less if I can find a used one. Any thoughts on this would be appreciated.

Wes Pearson wrote:
> .... 36 hp 1200 CC bug engine.
>..... The basic change is to remove
> the push rods and somehow lock the lifters in place, install two one
way
> air valves in the head An electric motor is used to drive the
> engine wired with an adjustable pressure switch.
>
> Has anyone tried this type of conversion. I know about the conversion

> with two cylinders running and the other two acting as an air pump.
It's
> a little on the expensive side and much more air then I would ever
need.
> I already have a 30 gallon propane tank and a pressure switch that
would
> handle the electrical load for a large motor. Graingers has the
valves
> for a reasonable price. What I need to know is how big of electric
motor
> would I need and how many rpm's to run it. I'm looking for about 120
PSI
> max with around 20 CFM output.
>
-------------------------------------------------------------

Dear Wes,

This kind of conversion dates back to the days of the Model T. There
was even a commercial unit built on the same principle using a flathead
Ford V8, four cylinders driving, four pumping.

As originally conceived for the VW (ie, two driving, two pumping), you
merely replaced the exhaust valve springs on cylinder's 1 & 3 with
light gauge compression springs and fitted air cleaners to the exhaust
ports. The light guage springs caused the movement of the piston to
lift the exhaust valve off its seat which allowed the chamber to fill.

The front two jugs (position on a VW engine is always relative to the
driver) were used for pumping since the VW draws heat for the intake
manifold from the #2 cylinder, the outlet being positioned at the
TAILPIPE. (One of those pesky little details non-VW mechanics
sometimes overlook :-)

The intake valve and spring were left alone although the rockers were
removed, and for the later engines, the push-rods too. (Early engines
used a single piece cam-follower & push-rod.) This effectively locked
the intake CLOSED. Since they usually pulled the heads to replace the
exhaust valve springs (you don't have to, but some didn't a big enough
compressor or didn't know the rope trick), they took the opportunity to
SOLDER the intake valve to its guide, hopefully in the closed position
:-) ... and to seal the seating surface with Permatex.

To get the compressed air out of the cylinder you simply modified a
pair of spark plugs. That is, you removed the metal holding the
porcelain insulator in place, drove out the porcelain, removed the
copper sealing ring and you're left with a threaded barrel. The
one-way valve was nothing more than a ball-bearing slightly larger than
the chamber-side opening of the spark plug barrel. Because of the
angle at which the spark plugs are mounted in the head, the check-valve
could be assembled without an internal spring, allowing gravity (and
the suction of the inlet-stroke) to keep the ball in position.

A standard male pipe-thread to tubing adapter was then brazed or
hard-soldered into the spark plug barrel. This works because of the
taper on the pipe thread, which is the end of the adapter that goes
into the barrel. The tubing-end of the fitting used annealed copper
tubing to connect the output to the receivier (ie, tank, etc). All
standard parts as used for installing gas-fed appliances (ie, water
heater, kitchen stove, etc.) (You'll need a crow-foot wrench to
tighten the tubing to the adapter, or install a riser to bring the
tubing out from under the engine's cooling tin. Be sure to seal the
opening or the remaining pair of jugs will run too hot.)

A pressure-actuated throttle position was fitted to the mounting flange
of the carburetor, the 'on' stroke adjusted to give about 2500 rpm, at
which the two cylinders could pump about 50cfm at better than 90psi.
Typical applications were sand blasting, powering jack-hammers or
needle-scalers.

Since you had to remove the exhaust pipes from the front jugs to the
muffler, you needed to drive Welch plugs into the holes.

The engine was started with the standard (back then) VW hand-crank
which mated with the nut on the fan pulley.

Some guys made a little hair-pin gismo to center the one-piece push-rod
in its tube so it wouldn't rub but I think most just ignored it; the
compressor didn't cost anything to speak of and most gave several years
of reliable service if the oil was changed now and then. Cam lift for
the early VW was just over a quarter of an inch. Without the rockers &
valve springs to return it to position, once the cam pushes it to the
side it tends to stay there.

Since it ran on gasoline the thing was usually mounted on a trailer or
at least outside the shop.

This was back in the late fifties and early sixties, when
collision-damaged 36hp VW engines were a drug on the market. Nowadays,
if you've got an early 36hp engine, it may have some value to someone
restoring a bug or bus of that era.

As you've no doubt seen from the Dunn-Rite (?sp) ads, this is one lily
that can take a lot of gilding, although their prices are probably fair
if you don't have a shop full of VW engines. But with few exceptions,
the simple conversion methods described above may also be applied to
the later engines.

Later engines dropped the special hand-crank nut on the pulley hub (and
VW stopped including a hand-crank with each Transporter (ie, bus,
etc.)). When they went to the mushroom-type cam-follower ('tappet'
etc.) they also used a separate push-rod. On these later engines most
conversions removed the push-rod and in some cases, the push-rod tube,
sealing the resulting holes in the crankcase and valve gallery with
metal plates gasketed with the stock push-rod tube seals. As
pneumatically-actuated throttle positioners became more expensive, some
guys used a regular air-compressor control unit wired to a solenoid
from a washing machine. It's action was a bit faster than a regular
throttle positioner (which was damped by a dash-pot) so you had to use
a vacuum-advance distributor and reset the timing a bit closer to TDC
to prevent the engine from stumbling. On the up-side, the thing is a
lot easier to start with the hand-crank when the timing was closer to
TDC. (Early VW's used 10 degrees BTDC for static timing.) You can
install the regular 6v or 12v starter on the engine if you wish, either
by buying one of the adapters sold for that purpose or by cutting up a
junked tranny to get the bell housing.

The '36hp' of course is the usual SAE bull**** from those by-gone days.
The DIN rating of the engine was about 25hp and a lot closer to the
truth. Running on just two jugs, at that rpm it was probably cranking
out about 10hp.

This conversion, and others, was fairly common back then, especially
for shops in the country or in older buildings not fitted with
high-capacity electrical systems.

------------------------------------------------------

As for using ALL FOUR cylinders for pumping air, although the swept
volume is only 1192cc (ie, 64mm stroke x 77mm bore) keep in mind that
is for the OTTO CYCLE... two revolutions of the crankshaft. Pumping
every stroke, you're looking at an output of about 70 cubic inches per
revolution at more than 100psi, which sounds like you're going to need
about 20hp to drive the thing.

-R.S.Hoover

On 4 Mar 2005 05:15:56 -0800, scribbled this
interesting note:

>The '36hp' of course is the usual SAE bull**** from those by-gone days.
> The DIN rating of the engine was about 25hp and a lot closer to the
>truth. Running on just two jugs, at that rpm it was probably cranking
>out about 10hp.
>
>As for using ALL FOUR cylinders for pumping air, although the swept
>volume is only 1192cc (ie, 64mm stroke x 77mm bore) keep in mind that
>is for the OTTO CYCLE... two revolutions of the crankshaft. Pumping
>every stroke, you're looking at an output of about 70 cubic inches per
>revolution at more than 100psi, which sounds like you're going to need
>about 20hp to drive the thing.
>
>-R.S.Hoover

So you can run it on two cylinders at about 10hp or spend a boatload
of money on a 20hp electrical motor? Sounds like simple math to me!:~)


--
John Willis
(Remove the Primes before e-mailing me)