Subject: Re: Speaking of air compressors

From: [email-masked] (Jonathan M. Elson)
Date: 5 Jun 1996 06:40:59 GMT

bikerbil ([email-masked]) wrote:

: I have an old 750 Virago motorcycle in real bad shape but runs well
: that I want to turn into an air compressor for my shop. Mainly for
: sand blasting, though it would be nice to have a couple of air tools
: too.

: The engine is a 750 V twin, I was thinking of removing 1 carburetor
: and installing some kinda air filter in its place, and taking the
: shimms out of the exhaust cam so it wont open.And installing a check
: valve in place of the spark plug for the output. Then just running the
: engine off the remaining cylinder.

<snip>
: But how do I figure out what the output would be ? I know that the
: compression is better that 100 psi. But I have no idea if it will put
: out enough cfm to run a sandblaster.. or actually fill the tanks in
: reasonable amount of time.

Well, each cylinder is 375 cc, but it has a large volume trapped above the
piston, so you get some losses from that.  Lets assume you get 300 cc
delivered per stroke. You will still be running the compressor on a
4-stroke cycle, so you lose every other up stroke on the piston.
Lets assume you run this at 3600 RPM (the spark plug hole is pretty small
for the air to escape from, so we should keep the RPMs down).

3600 RPM = 60 strokes/sec / 2 (for 4 stroke) = 30 strokes/sec x 60 sec/min
	= 1800 strokes / min

1800 strokes / min x 300 cc / stroke = 540000 cc/min

540000 cc/min / 1000 cc/L = 540 L/min x .0353 L/ft ^3 = 19 ft ^3/min
					or 19 CFM

Not too bad for one little cylinder.
Now - the bad news.  I'm not an expert on thermodynamics, and especially
the thermodynamics of choked-up air compressors (I'm referring to the
restriction at the spark plug hole).  But air compressors heat air by
(mostly) adiabatic compression.  Some of this heat is transferred to the
cylinder, head, etc.  If the compressor has a choke point at the outlet,
it will run hotter, because the peak cylinder pressure is a lot more than
the storage tank pressure.  This is an air cooled (I think) engine, which
has somewhat of a problem with heat removal anyway.  You may need a large
cooling blower to keep the compressor cylinder from overheating.  I'm
thinking that a large part of the energy output of the engine cylinder
will be dissipated in the compressor cylinder, and only some of that
energy will leave as hot air - some of it will stay there.  But maybe I'm
overestimating this problem.

Good luck with it.
						Jon

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From: [email-masked] (Robert Galloway)
Date: 7 Jun 1996 10:07:29 -0600

>: engine off the remaining cylinder.

I'd remove the original head and make a substitute.  You want no dead space 
i.e. the combustion chamber and any extra volume leading up to your 
valves.  I'd look for a slab of aluminum and probably mill some cooling 
fins into it in the process.  I'd also try to find some replacement 
catridge type ball valves for a commercial compressor to adapt into my 
ersatz head.  If that fails, you could machine your own or try to adapt 
check valves.  Breaths there a machinist with soul so dead he hasn't at 
least ruminated about converting some of the cylinders of a 
multi-cylinder engine for use as a self powered air compressor?  How 
about one bank of a V8?

rhg

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From: [email-masked] (bikerbil)
Date: Sat, 08 Jun 1996 01:46:02 GMT

On 7 Jun 1996 10:07:29 -0600, [email-masked] (Robert Galloway)
wrote:

>fins into it in the process. 

I like this idea better than my origanal. This way if it dosent work
out I can still salvage the engine for some other project. (Grin)

 I'd also try to find some replacement 
>check valves.

What exactly are cartridge type ball valve, I guessing that  the check
valves I have are the same thing,  Small cylinder with a ball and
spring .... The ones I have are only 3/8 inch, from the sound of the
last responce that will be too small. How big should I try to makem 

 Breaths there a machinist with soul so dead he hasn't at 
>multi-cylinder engine for use as a self powered air compressor?  How 

If its true that more is better than the V8 should be just about
right, but a 12 cycl Jaguar would be perfect. hehehe

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From: [email-masked] (CBear81438)
Date: 8 Jun 1996 00:49:14 -0400

>>multi-cylinder engine for use as a self powered air compressor?  How 

Smith compressors make a compressor out of a 429 ford and use one bank
forr running and the other for compression.   They still make these.  They
will run a 120 # Jackhammer all day and never get hot.   There is a co
that used to supply a plan for converting a 429 into a compressor.

Cecil in OK

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From: [email-masked] (Blake Malkamaki)
Date: Sat, 08 Jun 1996 01:36:24 -0400

In article <[email-masked]>, [email-masked] (Robert
Galloway) wrote:

$ >: The engine is a 750 V twin, I was thinking of removing 1 carburetor
$ >: and installing some kinda air filter in its place, and taking the
$ >: shimms out of the exhaust cam so it wont open.And installing a check
$ >: valve in place of the spark plug for the output. Then just running the
$ >: engine off the remaining cylinder.
$ >
$ 
$ I'd remove the original head and make a substitute.  You want no dead space 
$ i.e. the combustion chamber and any extra volume leading up to your 
$ valves.  I'd look for a slab of aluminum and probably mill some cooling 
$ fins into it in the process.  I'd also try to find some replacement 
$ catridge type ball valves for a commercial compressor to adapt into my 
$ ersatz head.  If that fails, you could machine your own or try to adapt 
$ check valves.  Breaths there a machinist with soul so dead he hasn't at 
$ least ruminated about converting some of the cylinders of a 
$ multi-cylinder engine for use as a self powered air compressor?  How 
$ about one bank of a V8?
$ 
$ rhg 
Schramm built many air compressors from 4 cylinders of a Ford flat head
V8.  Not one bank, but two on each side.  They also built them from Model
A 4 cylinders and Domestic hit and miss engines.

Blake
Blake Malkamaki, Little Mountain Ironworks, Concord, Ohio <[email-masked]>
>>Steam engines - Cletrac Crawler Tractors - Maple Syrup - Metal Signs<<
http://www.ncweb.com/users/blake

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From: [email-masked]
Date: Sat, 8 Jun 1996 16:12:13 GMT

:  Breaths there a machinist with soul so dead he hasn't at 
: >least ruminated about converting some of the cylinders of a 
: >multi-cylinder engine for use as a self powered air compressor?  How 
: >about one bank of a V8?

: If its true that more is better than the V8 should be just about
: right, but a 12 cycl Jaguar would be perfect. hehehe
: >
: >rhg 
: >

Its not the number of jugs, its the displacement (or more probably total 
swept volume) I believe the Jag is only a 305cid or so.

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From: Pete Bellas <[email-masked]>
Date: Mon, 10 Jun 1996 20:01:31 GMT

> multi-cylinder engine for use as a self powered air compressor?  How

Actually this is fairly standard. Take a look in the box of any of the 
trailer portable rigs and you will find most likely a small or big 
block v8 with one bank converted to pump air. Dodge 318s seem to be 
particularly popular.

			-Pete-

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From: [email-masked] (Robert Galloway)
Date: 11 Jun 1996 06:02:06 -0600

>swept volume) I believe the Jag is only a 305cid or so.    

I don't think he was thinking about the capacity 8-)

rhg

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From: [email-masked] (Robert Galloway)
Date: 11 Jun 1996 05:53:42 -0600

>last responce that will be too small. How big should I try to makem 
Some of the better compressors have replacement valves that have the ball 
and the seat in a cartidge with holes just above the ball letting the air 
out to the side.  I think I've seen some with a disk instead of a ball on 
this same design.  The cartridge has two "O" rings on it to seal at the 
level of the seat and at the level of the top of the head.  The air 
passage surounds the center part of the cartidge.  One advantage over an 
unmodified checkvalve is that the valve seat is as close as possible to 
the chamber, minimizing dead space.  The top of the cartidge is a big hex 
to drive with a wrench and the threads directly under the hex secure it 
to the head.  Some have a separate cap with threads and no cap or threads 
on the cartridge.

I hope this gives you something to work on.

rhg

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From: [email-masked] (Robert Galloway)
Date: 11 Jun 1996 05:59:54 -0600

>that used to supply a plan for converting a 429 into a compressor.

It seems like such an attractive idea, I'm glad to know that it actually 
works.  A question: Does it matter if the firing order alternates from 
bank to bank?  I looked at the firing order on a number of V8's back in 
the late 50's and found that some alternated banks in the fining 
order and some had sequential cylinders in the same bank firing.  I 
figured the thing would run smoother if every power pulse was 
interspersed with compressor stroke.

rhg

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From: "John R. Johnson" <[email-masked]>
Date: Tue, 11 Jun 1996 10:53:18 -0500

Actually, if you modify the head to allow intake and exhause check valves
and disable the intake and exhause valves in the engine, you will get four
compressor strokes for each two fireing strokes.  It pumps a lot of air!
John