Air compressor

Old 02-13-16, 02:37 PM
Thread Starter
Join Date: Feb 2016
Posts: 2
Upvotes: 0
Received 0 Upvotes on 0 Posts
Air compressor

Hi guys. Was wondering if you think this is possible. There's a 7hp gas Briggs and Stratton motor at a local antique store for $40 and there is also an air compressor on cl for $40. The guy says it has a blown head gasket. Would it be possible to remove the old motor, strip off all the air compressor stuff, and put the 7hp motor on with all the air compressor stuff attached to it? Or is it more work than it's worth? A 7hp air compressor for $80 sounds pretty neat is the only reason I'm considering it. I'm an avid DIYer. Mostly just mechanical stuff and welding.
Old 02-13-16, 03:00 PM
Join Date: Jan 2011
Location: USA
Posts: 4,463
Received 129 Upvotes on 114 Posts
Sounds like a gamble to me.
If it's just a head gasket (which is anyone's guess if that's true) just change the gasket.
Anytime you buy a used 4 stroke engine you buying a pig in a poke.
Is the gas tank rusted inside, carb. will need to be rebuilt, what's the shaft size and rotation, will the old pulley even fit?
Why do you need a gas powered compressor and not electric?
Old 02-13-16, 07:10 PM
Thread Starter
Join Date: Feb 2016
Posts: 2
Upvotes: 0
Received 0 Upvotes on 0 Posts
Don't need a gas powered compressor just thought it might be a fun little project. But you're right, I didn't consider all that you mentioned. The motor isn't in terrible condition but the tank is definitely rusty. Plus I don't even know if the other motor works. It's not seized is all I know haha. Is a head gasket easy to do on an air compressor motor?
Old 02-13-16, 07:23 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,775
Received 4,121 Upvotes on 3,701 Posts
It would make a great DIY project but the one thing that makes it expensive is that when you run an air compressor on a gas engine you need an unloader valve that controls the engine speed and allows the built up pressure to release before the engine re-engages and starts compressing again.
Old 02-14-16, 03:18 AM
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 45,783
Received 871 Upvotes on 762 Posts
How rusty is the tank? Since there is a lot of pressure in the tank I would be concerned about it's integrity!
Old 02-14-16, 06:00 AM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,500
Received 68 Upvotes on 62 Posts
Pete is right about needing more parts than just a gas engine to make a conversion possible.

I did what you are proposing and can briefly describe the details:

You first need to figure out what the rpm of the compressor pump is with the stock motor then select a pulley for the gas engine that would match this speed when the engine is running at full speed.

You will also need two specialized parts.
One is the unloader mechanism.
This will attach to the tank to sense tank pressure.
On it will be a connection for a 1/4" line and an open port.
You will also need a small air cylinder designed for the purpose that attaches to the engine and connects to the throttle linkage.

How it works is when the gas engine turns the compressor to build the receiver tank to 100 psi the unloader valve trips, opening the vent bleeding air from the compressor to atmosphere while also allowing 100 psi air pressure to flow to the 1/4" connection.

The 1/4" connection which is connected to the air cylinder will cause the cylinder to move, making the gas engine go to its idle position.
The open vent on the unloader will bleed air produced while idling.

*You need to be warned.*
This is a potentially deadly project for you and anyone within the blast range of the air receiver tank!
You first need to make sure the tank has a pressure reief that works and can handle the cfm of the compressor.
You also need to make sure the throttle cylinder works and that the bleed on the unloader can handle the cfm at idle.

Mine works fairly well.
I built mine many years ago before the internet made finding parts ezee.
On a US visit I had time to kill while my better half was dress shopping and a Menard's store had bins of compressor parts which included unloader valves and air cylinders!
Sadly, I am sure parts like these are probably not mainstream any more.
Hasibul Haque voted this post useful.

Thread Tools
Search this Thread
Ask a Question
Question Title: