Rare Pistons

[graham-xrfx]

Hi Douglas folk
I have inadvertently walked into a problem. The engine is a Douglas T35, which is the 350cc horizontally opposed twin, also used, (with a different crankcase), on a variant for generators and other static engine needs during WW2. This time, it is the Douglas T35 generator engine, fitted onto a tiny flying death-trap called Le Pou du Ciel. It was neglected, and the bores corroded.

I then found F.W. Thornton pistons supplier, who provide Douglas T35 and Dragonfly pistons, imported from Australia.
--> https://www.fwthornton.co.uk/
.. where one can navigate to the Douglas pistons. I had no idea the "domed" sort were only made for a couple of years.

I went ahead, and had the cylinders re-bored +0.020 inch. Thorntons had a regular delivery to the re-bore folk, Saunders in Cadnam, and offered to send them direct, saving me a long trip. When I first got to see them - oh dear!

Thorntons are happy to take the unused pistons back, and refund me, but now I need to find "something that will work". There are pistons about at 61mm diameter, and a bit of a dome (Honda), but I need one with the 5/8" wrist pin, and a skirt oil control ring to oil the bores. Almost any ideas would be much appreciated.

PS. The picture of the assembled engine was pre-COVID era, before it got neglected. Something like this needs to be turned over every few days, and run up occasionally.

[DJS]

If you are an LDMCC member then the post-war spares scheme has used pistons of the sort that you are seeking.
Contact details are in The New Conrod.

[graham-xrfx]

Many thanks for the pointer to the club. I will have a look

[EW-Ron]

JP Pistons also in Australia list 8:1 pistons for the T35

https://www.norndaautomotive.com.au/images/pdf/PISTONCATALOGUE2016v2.pdf

Having already had the cylinders bored may require some honing out to get the required clearances ?
JPs usually require an extra thou or 2 ?

[graham-xrfx]

If you are an LDMCC member then the post-war spares scheme has used pistons of the sort that you are seeking.
Contact details are in The New Conrod.

Unfortunately, joining the LDMCC club did not go as planned.
I used their web page, followed the "Join the club" tabs, filled out the form, but the "Submit" was totally unresponsive. It defaulted the the "Create a form" application.
I am sure I will get there in the end, but perhaps not via  the WUFOO page -->https://ldmcc.wufoo.com/forms/m1lh20yq14h55e2/

[graham-xrfx]

JP Pistons also in Australia list 8:1 pistons for the T35

https://www.norndaautomotive.com.au/images/pdf/PISTONCATALOGUE2016v2.pdf

Having already had the cylinders bored may require some honing out to get the required clearances ?
JPs usually require an extra thou or 2 ?

Thanks so much for the reply. The PDF is an expansive thing that covers the range of what they do. It will take some careful attention to zero in on the exact correct piston.  I suspect that JP Pistons are the very likely import supplier to F.W. Thornton in the UK.

I would be wanting to source pistons that are made for cylinders that have been bored out and honed to +0.020 inch over the nominal original size. It was a beautiful job, with a cross-hatch pattern ready for break-in.

Regarding the compression ratios. In the picture with the first posting, the original domed piston shown worked at ratio 6-to-1, according to the rebuild manual. The flatter top piston in the picture was for a T35 motorcycle from a later year, using 8-to-1 ratio, (according to the supplier at Thorntons) For this to be so, the shape of the head internals would also have to be different. The flatter head piston, fitted into what I have, could only lower the ratio from an already low 6-to-1. The dome shape in the head pretty much needs to be filled up with a dome on the top of the piston.

For context, I should explain that this T35 Douglas engine was the variant from the motorcycle crankcase, intended for stationary use, and it was fitted to a tiny vintage 1930s aircraft. So, not actually a motorcycle, but so closely related, many parts look identical.

[DJS]

If you are an LDMCC member then the post-war spares scheme has used pistons of the sort that you are seeking.
Contact details are in The New Conrod.

Unfortunately, joining the LDMCC club did not go as planned.
I used their web page, followed the "Join the club" tabs, filled out the form, but the "Submit" was totally unresponsive. It defaulted the the "Create a form" application.
I am sure I will get there in the end, but perhaps not via  the WUFOO page -->https://ldmcc.wufoo.com/forms/m1lh20yq14h55e2/

Hi Graham,

You have a PM.

Regards,

David

[EW-Ron]

Nice cylinder head shot.
What microlight would these have been used with.

The PDF is an expansive thing

Try typing in "Douglas" in the search-on-this-page under 'edit'
This took me straight to the Douglas versions.

I would be wanting to source pistons that are made for cylinders that have been bored out and honed to +0.020 inch

Thats putting the cart before the horse !!
Workshop manuals tell to ALWAYS  have the pistons in hand, and thus to bore to suitable dimensions.

Having said that, why don't you contact JP with a photo of your pistons, and enquire.
They recently supplied me with a pair that weren't even in their catalog, and were most helpful.
It did cost, but even common pistons seem to have skyrocketted in price everywhere lately ??

Since they do all the manufacturing, they could control the diam to the size ye seek ?

[graeme]

JP Pistons will make pistons from their catalogue to any size you'd like. I had 4 pistons made up to suit an Austin 7, and I had each bore taken out just enough to clean them up, so ended up with 4 slightly different diameters. So I gave them the sizes I wanted, and they made the pistons to suit. And yes, for an air-cooled application, you want to stipulate a decent amount of clearance, like 5 or 6 thou.

Cheers, Graeme

[graham-xrfx]

Nice cylinder head shot.
What microlight would these have been used with.

It's a French origin vintage (1930's) flying death-trap called Le Pou du Ciel.  There is a whole lot I could post about it, but maybe not right here among the pistons

I would be wanting to source pistons that are made for cylinders that have been bored out and honed to +0.020 inch

Thats putting the cart before the horse !!
Workshop manuals tell to ALWAYS  have the pistons in hand, and thus to bore to suitable dimensions.
Having said that, why don't you contact JP with a photo of your pistons, and enquire.
They recently supplied me with a pair that weren't even in their catalog, and were most helpful.
It did cost, but even common pistons seem to have skyrocketted in price everywhere lately ??

Since they do all the manufacturing, they could control the diam to the size ye seek ?
[/quote]
Honestly, I really did put the horse first. FW Thornton said they did T35 pistons made by JP Pistons. Size would be 60.8mm +0.020" with the correct 5/8 pin, and they would send them to the re-bore company (Saunders in Cadnam) with their regular delivery, saving me the long journey. Saunders did the lovely job on the re-bore, to fit those pistons, and then I discovered how Thorntons had got it wrong!

You are not wrong about how the prices have soared.
JP Pistons have replied. The piston, they say, looks like a Douglas AE10003, and there is an information sheet (attached)
They have one casting that will make this as a new special piston.
The price for a new special piston is AUD$600.00 per piston assembly (includes rings, pin & circlips) + postage & handling.
[ Translation to GBP is £311.22 each!! ]
That is £622.44 before shipping, and handling, and (I guess, VAT) .
We are up to £746.93 for the pair before shipping!
The GHC heritage centre get my work on the engine for free, but I am pretty sure that that much for a pair of pistons will stall the project. I think it's just too rich for us!

I am a LDMCC member now. If, one day, I get this together, then Douglas enthusiasts are welcome to be my guests at Lasham, and let us start it up, if anyone  can face swinging a propeller!

[EW-Ron]

Gee. Thats about double what they charged me, only a few months back,
I wonder why the difference.  Must be the mountain on the top ?
And I thought that was approaching being expensive ....

What a neat little flying machine.
We are glad you recognize a "death trap" when you see one !!!
Stick to taxiing displays when/if it runs ?

[graham-xrfx]

What a neat little flying machine.
We are glad you recognize a "death trap" when you see one !!!
Stick to taxiing displays when/if it runs ?

That design killed a few people back in the 1930s. The design flaw was recognized very quickly. It was the first time the folk who worked that huge wind tunnel at Farnborough had put full-sized aircraft in. They normally had to use scale models, and they confirmed the problem in a couple of hours.

Even though folk here may not be experts at aeronautical design, it is not hard to see what is "unusual". Do not think of it as a regular "biplane". Just look at the tail, and notice there is no elevator tailplane.  Is it that it has moved forward to become some kind of lower wing? In any event, to go UP, or DOWN, has to be done some other way.

Notice that the entire tail fin is also the rudder. Notice that there are no ailerons on the main wing. Banking for turns is achieved by the secondary effect of the rudder yaw, thankfully at least it is in the correct direction because of the lack of ailerons. For those who don't know, the way an aircraft is persuaded to go around a turn is by the lift force from a banked wing. The rudder is only to correct the adverse yaw that happens.

The trouble was that Henri Mignet was absolutely hopeless at coordinated use of controls in regular airplanes. His design aim was to "simplify" it. Thus, there are NO rudder pedals in that airplane,  LEFT and RIGHT moves are done simply by moving the stick left or right. The cables that would normally work the ailerons are simply connected directly to the big rudder.

Stick back is UP and and stick forward is DOWN (except for the design flaw)!
This is done by tilting the attack angle of the main wing, which is hinged at the front leading edge.

The danger was, whenever there was sufficient speed, and airflow, the air over the rear "wing" had enough lift to tilt the tail up, which made it go faster, which tilted it some more. If one put stick forward, the nose would go down, and speed increased. Then, pull back on the stick, to discover the airflow had increase through the wings gap, so it went DOWN some more instead. Locked in a positive feedback dive, it would meet the ground that way.

They were made safe, but the reputation (in UK at least) was so damaged, hardly anyone would look at them again. There are hundreds being flown all over France, most of them evolved into modern airplanes with full canopy, avionics, more person space, etc. They are slow, extremely easy to fly, very cheap to make and maintain.

The pictures show an original in black-and-white. The two-person variant has turned a "pusher", with the propeller behind the canopy, modern wing sections, offering amazing visibility all around. There is even a version that folds up so it can be stashed in a garage.

[graham-xrfx]

Here I am about to explore the more insane end of what folk might do to fix up an old Douglas engine. Given that we are now up the creek without the proverbial paddle, I have been giving some thought to possible ways forward. The pretty shocking price of replacements, about double what (Ron?) paid for his not so long ago, suggests JP Pistons simply do not want the work to make them, though at least they do have the casting. Arguably, for what I am about to propose, it could cost even more, but my time on these, and the machining facilities, and various folks expertise is free.

David (DJS) has offered a couple of T5 +0.030" pistons that look about right, differing only in the position of the oil control ring arrangement. My original pistons have a series of 8 holes immediately below the second ring slot, and then 12 more holes under a full oil control ring positioned 5mm from the bottom of the piston skirt. They also look like they have been through the wars, and as they are, are not really OK to use on a re-bore build. Thus we get to plan A. I know this will sound a bit extreme, and I am not sure the scheme is even viable, but it goes something like this..

1. Turn them down, removing 0.005" in general, using the correct taper-turn.

2. Dress the ring slots to be correct for the new diameter.

3. Selectively make the "oval, using strips of emery cloth, to relieve the skirts by the correct amount at 90° to the wrist pin axis.

4 Provide it with a new set of rings, gapped to suit the +0.020 bore.

About the only thing left is the question of the oil control ring being different.
(Yes - we can all see that only one piston has what is left of an oil control ring. The other seems to have a collection of any old thin rings that will fit)!
I was thinking to use the same kind of oil ring as fitted into the original skirt, but in the higher position.
There might need to be some kind of shim ring slot adjustment, or, if the oil ring slot is too narrow, then turn it out to fit.

I don't know how low the oil ring has to sweep to reach the point it can fetch oil up from the crankcase, normally through the little holes in the skirt behind the ring, but perhaps adding a little 2-stroke oil to the fuel can be precaution measure.

At least, in messing with these, we start with very little to lose if we mess up in the attempt.
Might there be folk in the forum who have attempted something like this?

Plan B
It seems that it is quite possible to weld on pistons, the better way being TIG. Also, the weld needs to be the right alloy, best found by using metal from old pistons. The notion is to start with a new set of +0.020 pistons, and "add" enough metal to the crown, then turn it into a hemisphere, mill the valve clearances to correspond to where the clearances already are, and then do some hand filing/shaping.

The first picture is of Davis's donor pistons.

The second picture is of my original set after the first (pre COVID era) stripdown, showing the broken first slot rings. They were a little scored, but seemed OK to put back into a standard bore which had been lightly honed to clean up.

The third picture is of a piston for that same rebuild,

The fourth picture is of the corrosion that led to the ring breakage first time around, and the stuck top ring failure this time, motivating the re-bore.

I completely accept that experts in this forum may well tell me this plan is somewhat dodgy, if not completely non-viable. It may be that I end up going where nobody else would, and that is OK. You can all see the ensuing  débâcle posted here!