gearbox mounted compressor

[Harlé Sylvain]

Hello

here is a picture of my ford Fat compressor, I restore it , it looks in great condition , but I dont understand how it could work without leaking.
The crankshaft is monted on a copper bearing with no seal ,and the aluminium cover has a hole on the botom.

Is something missing?

Cheers
Sylvain

[Lang]

Sylvian

The bottom part of the compressor is just the drive from the gearbox with a crankshaft, connecting rod and piston (just like a car engine)

The air section all happens on top of the piston, like a car. As the piston goes down it draws air in through a one way valve. As the piston goes up again that valve closes and the air is squeezed out a second one way valve into an air tank or air hose.

The round hole in the bottom of the cover is to drain the oil, it needs a plug.

The big opening in the cover is there because, when the piston goes up and down, the volume of the crankcase changes. If you put your hand over it when it is running you will feel air going in when the piston goes up and blowing out when it goes down. When it is running fast at normal speed this will just be a continuous pulsing. This air vent is what makes most of the "choof-choof-choof" compressor noise.

Lang

Here is a drawing.

[Jacques Reed]

Hello Harle,

Just checking my Ford Parts list and there were two types of compressors made for the CMP trucks.

One was Outboard Marine or Saylor-Beall and the other one was Webster- ( your compressor type).

The Outboard Marine type had 3 screws retaining the cover and yours has 4.
Part No. 19947 located at your open cover hole is listed as "Fitting- Lubricator (Webster)"

It may be the type as used on the clutch throwout bearing on the transmission housing but I am only making a guess. Perhaps someone else can confirm what that lubricator was.

Hope this helps.

Cheers

[Jacques Reed]

Hello Harle,

Further to previous post: I believe your concern is leaking at the shaft where it goes into the bottom of the compressor.

If the shaft and/or bronze bushing are not worn, there should be little or no leakage into the compressor base. The viscosity of the transmission oil would also help to prevent leakage. The problem arises if either the shaft or bushing are worn and then transmission oil will certainly pass.

When manufactured, the clearance between the shaft and bushing would most likely be a precision running fit which allows for smooth rotation with minimum play between the bushing and shaft. If sloppiness between the shaft and bushing exists then it would require the bushing to be replaced and reamed to the correct size for the required fit. Most often it is the bushing that wears due to being the softer material. Ford distributors are a good example of this.

If your compressor has seen a lot of use then new bushings would be the way to go or just monitor for any leakage and then decide if the bushings need replacing.

I had a look at a picture of a Webster type transmission mounted compressor that I once had and it too lacked the fitting at the bottom. Wonder if the parts book is accurate?

Cheers,

[Lang]

I just had a look at my box of pumps. I have about 8 of them Chevrolet and Ford. No two are exactly the same and none of them has a name plate. Some cast iron and some alloy.

The plug in the bottom is just a hole for an oil can. Most have a right angle fitting with a little tin flip lid. The one in question has a spring loaded tin lid but coming straight out.

I think so long as there is about an inch of oil in the bottom all will be well as that is the height of the tin lid oiler. If gearbox oil does come along the shaft it can not fill the pump crankcase as it will just leak out the oiler fitting to maintain the correct level.

Quite apart from that there would not be a CMP in ten thousand that used its air pump sufficiently to wear it out when you consider early air brake trucks had similar compressors running continuously for thousands of hours.

Just an observation in my collection are two pumps mirror image to the CMP ones. This gives the option of fitting a pump with the head forward or back to clear chassis rails etc or on the opposite side of the gear box (does not matter which direction they turn) so a winch or hydraulic/mechanical tipper power take off can go on the other side. I had a Dodge WC53 with a winch take-off one side and a compressor identical to a CMP model on the other.

Lang

[Lang]

blitz pump oiler

Here is the oiler on 3 of my pumps. There are two which have no place for an oiler. I looked in the Chevrolet book and they say no maintenance on the pump because it is lubricated from the gear box. In other words they expect oil to go through the bush into the pump crankcase. If it goes higher than the gearbox oil level it will track back into the gearbox by gravity.

Lang