ABC Mk1A APU

I made my way to furthest East Anglia (I live in Bristol) over the weekend to purchase a New Toy. It is a mid thirties Mk1A ABC auxiliary power unit (APU) originally fitted to Short’s flying boats of various kinds. They lived in the starboard wing root and provided compressed air for starting, pumping to lift petrol into the tanks and a similar pump to shift water out of the bilge and the floats. At the rear was a shunt wound dynamo that provided 300 watts.

They were (are!) amazingly complex bits of kit and therefore I am surprised to find one in absolutely complete and unmolested form after over 75 years.

The trip there and back was uneventful if long & the traffic all moved along quite well and I got home not long after 3.00pm.

Yesterday, I had a look at the engine. The oil on the dipsticks is golden yellow and this and a few other signs leads me to think that this was a service exchange unit removed from the aircraft, serviced and put back on the shelf. The home made blanking plate covers the hole where the water pump used to fit - I do have one & might try & fit it in due course.

The label on the dynamo is so corroded it is hard to read, so I'm not sure if it is an early 12 Volt version or the later 24 Volt. Some early DC3's (for instance) were 12 Volt, so it was more common than one might think.

I first tried a 12 Volt battery (the dynamo is shunt wound and is intended to act as the starter) but it only turned it over very slowly. I ganged two 12's together and applied 24 Volts whereupon it flew round, the oil pressure came up straightaway and the HT lead gave me a belt!

Sploshing a little petrol in the tank led to immediate popping and banging, but the float is stuck I think and whilst it would fire on both sides whilst cranking, it would not sustain repetitive combustion without battery assistance.

It was a very hopeful beginning as I was not looking forward to trying to get at the points!

Photos here

http://community.webshots.com/album/580580470HAxTgI

Hi Kim,

Thats an interesting bit of equipment. good luck with whatever you intend to do, and keep us up to date with progress.

Paul

hi Kim..
looks like that was a bit of a tite squeeze in the car,looks like you have a nice project there...
good luck with it,please keep us posted with how you get on with it,and some pics along the way..
regards,mike...

With the float chamber off and scrubbed with a nail brush and washing up liquid, I dried it out under a lamp bulb. With a small file, I ran over the surface of the poor corroded old thing (Mazak I shouldn’t wonder!) and found a couple of cracks off the lower gallery - probably water in the petrol freezing out - which I've repaired with JB Weld. All three of the jets are mounted on an arm of the float chamber & fit into the choke tube from an angle. I ought to say perhaps that the carb – a very special Solex – has the inner of its two flange mounting bolts buried out of sight in the crankcase/sump joint. To remove it for cleaning would mean – at the least – four or five hours work to get at the nut, plus reassembly time. I’ll pass on that I think …..

I cleaned the plugs but there is something definitely amiss with one of them as the cylinder that runs follows the plug! Therefore, I fitted a couple of other 18mm plugs that I have around and that fixed it.

It has no choke (must have been external somehow) but a prod at the tickler provided the rich mixture it needed to burst into life. The throttle has been disconnected from the governor and a neat little lever on top of the engine connects by rods and levers to the carb. I then sorted out the coolent pipework, filled the radiator and ran it for twenty minutes. I even tried engaging the pumps and compressors. Both pumps and one set of compressors work OK but the other set of compressors may be seized as engaging them stops the engine. It shows 20+ PSI oil pressure at tickover & double that as the revs rise.

It will now start on the pull cord from cold after a few pulls.

I've started to clean it up now and removed the spec plate to do it properly. It had not occurred to me before, but it has an engine number of 28 and its veracity is borne out by the dynamo so/no of 33. This means it was a very early production engine. Mark 1's are rare enough, but I suspect that this is the earliest survivor from 1932, the first year of production.

I could do with a couple of shielded HT leads – I have the correct shielded plugs – I don’t suppose anyone has a couple? They are very short, probably no more than a foot or so long.

My club has a crank up tomorrow evening & I shall take it along to amaze the hit and miss men!

hi there
sounds like you have a good project under way
and is moving along well for you
hope it goes well for you tomorrrow at the crank up
and awaiting future updates on your progress
thanks kev j

Sounds like an interesting engine, some pics would be nice

Stu.

I took the ABC to the crank up on Monday and it ran for about an hour and a half. It stopped occasionally and it is burning a bit of oil.

It got hot all the way through and the water was hot in the top pipe and just warm in the bottom run, so just right. I suspect that it would get hot & bothered on a really warm day and I'll probably fit an electric fan - give the dynamo something to do ;o))

I spent yesterday tidying it up and I I've updated the Webshots album with new photos this afternoon.

http://home-and-garden.webshots.com/album/580580470HAxTgI

I'm writing it up for SEM & it should appear in a couple of months time.

Regards,


Kim

That's certainly something different, a lot bigger then I'd expected. Very nice engine Kim, thanks for sharing with us and looking forward to the write up.

Stu.

Hi Kim,

Nice engine the abc, will be seeing one tomorrow in a museum, was going to bring my T300 and swap it out as they don't really know what it is...

Cheers Steve

Here is the one in the Ulster Folk and Transport Museum.





Dont think they would sell it to me lol

Cheers Steve

The ABC engine in the Ulster Folk and Transport Museum is a circa 1915 500cc exhaust over inlet flat twin. They featured crowded roller big ends and four ball bearing main bearings. The pistons are thin section cast iron and the heads are interchangable, having a bolt on handed exhaust valve seat casting. The cylinder barrels are turned from steel billets.

Sans magneto and exhaust, they weighed just 14lbs. They would run at 8,000 rpm off load and suffer no ill effects.

Thjey were used to drive trench pumps, to inflate the envelopes of derigibles and could drive a 1 KVA generator by Lyons & Wrench. Rarely, they were used to drive aero engine starters and mock up machine gun rigs to give new pilots confidence that they could shoot through a spinning propeller!

There was a 250 version called the "Firefly" which was fitted into a motorcycle frame for testing but it was not proceeded with.

Left over barrels from the Firefly were used on the 125cc single that drive the ABC Scootamota.

Several thousand were made but few survive today.

Regards,

Kim siddorn

Thanks for that info Kim, I'm after something from WW1 next, got enough from WW2.

Cheers Steve