Reconditioning a Stuart Compressor/Vacuum Pump

[redhouseluv]

I have just started a refurb of this eBay bought Stuart compressor; it has sat under my bench for a while.

- The engine seem to be coated in a thick black slimey gloop which smelled of old engine oil, some vigorous activity with a wire brush and washing up liquid made quite a difference. (before/after pic)

- I then started to dismantle the beast and happened upon some interesting anomalies; see if you can spot odd 'bolt' out from the ones in the picture? 
 
- I took the top a cover off and discovered 2 flat disks; these are apparently the valves, but it looked like they had never had the recessed portion machined to hold the springs in place (see the diagram)?

- I started to machine 2 new valves to spec, when I discovered the valve cover recesses had not been machined to spec  so with minutes to spare before my lathe was loaded onto the back of a truck and put in storage for 4 months, I just managed to machine another set to fit!

I am learning why buying pieces from eBay comes with its own issues compared to machining from scratch.............

[Charles Lamont]

A pristine kit of castings for one of these sold on ebay two days ago for just over £300. I wanted it, but not badly enough.

[redhouseluv]

Yeah, I know, that was me, apologies........................

I have not yet received it and agree, it was a bit too pricey, however when you look at the price of new Stuart castings, they can be rather eye watering too. I had never seen an unmachined set of compressor castings and caught auction fever. I promised my wife I would sell the one I'm fixing up atm in order to fund the castings 

My heart is in machining and building not reconditioning, but with no workshop at the moment, this keeps me occupied and is a welcome distraction from work

[Charles Lamont]

Considering, as you say, the price of new kits and the rarity of the compressor castings, I thought the price you paid was not far out. At least mine was not the penultimate bid, so you can't blame me. Looking forward to the build.

[redhouseluv]

Carried on with the dismantling and clean up operation today; its great to see how one of these is put together before I machine my own. I found 2 gaskets above and below the valve plate, but no mention or indication of these in drawings; I'm guessing these were added to give a good seal.

Weirdly they appear almost metallic in appearance and feel, but maybe that's what they look like after many many years? The crankshaft rotates wonderfully and the pistons have really tight seal against the cylinders.

Oh yeah I love the little extensions to splash the oil about! 

[redhouseluv]

Looks a lot better and found some interesting gunge. I think the engine had been exposed to some damp, but seems to be cleaning up quite nicely after some rust remover, paint stripper and some wire brushing with a Dremel

[redhouseluv]

I've put some steam oil on the bearings, crankshaft, conrod ends and in the cylinders to keep everything moving after the cleanup operation; does anyone have any idea of what oil should be used in one these, I can't find any references or information???

[redhouseluv]

Primer is on ......... and ready for hand painting in the traditional Stuart regalia

[redhouseluv]

The old gaskets were looking tired and the base gasket snapped and crumbled to dust as I removed it; time for some new ones (see pic)

[redhouseluv]

Got busy with the fine emery then the Dremel; not looking too shabby!

[Mike R]

I've put some steam oil on the bearings, crankshaft, conrod ends and in the cylinders to keep everything moving after the cleanup operation; does anyone have any idea of what oil should be used in one these, I can't find any references or information???

I don't know for sure, but as its not running steam, and its acting as a compressor with most of the action of an internal combustion engine - I'd either use regular automotive engine oil (probably one such as 10-W30) or an air compressor oil if it was lying around (usually just a straight weight oil ~ SAE 30).

[redhouseluv]

Thanks Mike

I wondered that too; especiallly as both Stuart Sirius and Sun engines have a similar configuration to this compressor with a wet sump which splashes the oil about. Any Sirius/Sun owners out there gotta any info on what oil they use?

Finished of the valve cover which came up nicely with just the use of a mini wire brush on a Dremel. On the reverse, I cleaned up the new valves I made, ensuring they seat into the valve recesses

[Admiral_dk]

Looks loke a very fine recondition - should be able to work for years to come (if you choose to make it so) 

I'm guessing that anything from SAE 30-60 would do fine here ....

Per     

[MJM460]

Hi Red, it is worth remembering that the actual mechanism has only a minor effect on the lubricant required.  Much more important is the operating conditions of the oil.

Steam engines require steam oil which has high viscosity at ambient conditions so it is still adequate at the steam temperature. Steam oil also has soaps and demulsifying components to avoid becoming a sticky mess with the inevitable water contamination, especially as the steam partly condenses at the low pressure pistons.  None of these properties or conditions are required, or even desirable in an air compressor.

Similarly, a combustion engine oil has additives to cope with the combustion byproducts which tend to blow past the pistons and valve stems to contaminate the oil.

An air compressor on the other hand operates under relatively benign conditions, low temperatures, no condensation ( that happens after compression outside the compressor) and so a moderate viscosity, straight machine oil is used.  The compressors I worked with used a straight VG30 oil from the smallest up to very large machines.

For your model, I would suggest even the ubiquitous 3 in 1 would be fine, or the lower end of the viscosity range others have suggested as your temperatures will be very moderate.

I am enjoying following your build and looking forward to seeing it operating.  It will be a very nice machine to provide a load for your steam engines (which do need steam oil) so they actually do some work as they were intended to do.

MJM460

[redhouseluv]

Thank you all for your advice regarding the type of oil

I have finished the refurb and I think it looks ok especially when you look at the how it came to me.

There are a few pics below and I have also put together a video of the start to finish (I'm kinda bored without my workshop atm ). Sadly, I have to make good on the promise to the wife and sell this one   

BUT I have a full set of castings for this compressor waiting for my attention once I'm back in action in my new workshop ..........

<a href="https://www.youtube.com/watch?v=jIpoDL3zcEw" target="_blank">http://www.youtube.com/watch?v=jIpoDL3zcEw</a>