Hi, what is the approx date of the next New Conrod please?

Hi Ron.

Yes - the firm that supplies pistons to the UK, including Douglas types, is JP Pistons in Adlaide. They even have the patterns and drawings of the (1934?) original. It would be a one-off order. AU$600 (each!) before UK shipping, VAT, Imports taxes etc. I don't think they wanted to do it. It was a non-starter for us.

There are firm in UK that can rework camshafts. I have not explored them. The main need is to fix the one we have.

Going for a cam that would work, and two carbs would give an immediate boost, and that would be interesting and fun. My present ambitions are more prosaic. Just to get it going again, so it can display would be a big deal for me. The interest is about what was it in the little airplane that made it a killer, and the simple fix that makes it safe, but alas, the reputation was ruined, except apparently, to the French. Know also that this one has exhaust pipes without silencers.

I do have another engine, given to me, it having rested in a Scottish basement for 80 years, is in unknown condition. I haven't even looked in it yet. If ever there is to be an audacious modification, then that one would be the candidate.

Today - we cut on piston #2, with fingers crossed!

Goodness !
With a long enough runway, you could circle the Earth ?

In this neck of the woods, there are folks who can re-profile camshafts.
Inc adding more metal, to give more lift.
This might be useful to add more to that 3 bhp, plus adding more rpms.
Light valve springs notwithstanding....

For those who might like to know what it takes to re-manufacture a piston from wrecked, seized up, scrap. The donor was sized to fit a +0.030 inches re-bore over the standard. That left metal to cut it back to fit a +0.020 inch re-bore. A jig to hold it in a 4-jaw chuck.

The taper cut, widest at the bottom of the skirt, up to just above the pin, is only a few thousandths. I chose to cut it by simply advancing the tool in stages about 20 microns each, to cut 135 microns deeper for every 10mm move to the right. It seemed easier than trying to set up the compound slide only 1/3rd of a degree off line.

A fixed up lathe from WW2 era, though still apparently a precision thing. One can machine to within about 25 to 30 microns. The grey metal plate behind the tailstock quill lets you know it has been given a DRO (Digital Read-Out). The Kennedy dial gauge is 0.0005" divisions. It is a bit touchy to use with the cheapo Chinese magnetic holder.



Then the insides of the jig used to hold it all in place.



There remains a very slight mark where the gouges from the piston seizure did not quite cut away clean. The top ring groove is now somewhat bigger than the original after I cut away the mess.

Perhaps of limited interest - I don't know.

Eddie
Thanks for the info about camshafts. I am not about to get into major engine mods of that sort, besides which, an engine running the "other" way would bring about the need for the propeller to be swapped for one that also goes the other way. I just had the passing thought that two carburetors might be better than one.

You would be the Eddie when I refer to "Eddies Method", meaning the suggestion to achieve piston skirt oval shape. I have now salvaged the first piston into something better, to fit a +0.020 rebore.



This job has already taken me way beyond anything I ever imagined. I have had to pick up a whole lot of new skills. There is no opportunity to have a "practise run on any operation. Given the pair of domed +0.030 salvage donor pistons are probably the only ones around, I am not allowed to make even one "oops" mistake. I have to go slow. I keep checking measurements.

It only takes a small force to expand a skirt to "round", but it takes a whole lot more to push a skirt to be 0.008" beyond where it should be, so to make the cut, and then let it relax. Also, now having done it, I think the expansion might not be exactly symmetrical to the axis. Regardless, it is done now. The piston will have to work as it is.

One stumble to consider is that when one "stretches" the skirt across the pin axis, the measure across the thrust axis gets smaller. That means the whole thing won't fit back onto the jig spigot. I had to modify the jig to get it to fit.

When I have "completed salvage of piston #2, we then move on to getting rings, including a special to fit the now wider top slot on piston #1, and we can try and get this machine together. You are right about the feeble valve springs. I can squeeze them down with only my fingers and a rag!

I am not the first to have tried this engine type with a propeller. My friend Julian Aubert, who has constructed and flown replica early aircraft did try one at Dunsfold. It did actually lift off, but then came down again before running out of runway. It takes a special sort of nerve to do this stuff!

Here --> 

Graham, 
             The generator engine has the very limited (3HP) output because it was built to power generators, so was only expected to run at a much slower speed than the motorcycle engine (probably to give the required frequency from the AC generator) - reliability being more important than horsepower. Hence, the camshafts used in the generator engine are much smaller than those in the motorcycle engine. Changing the cam profile to that of the motorcycle engine would probably give a considerable power increase, but that is not an easy modification - the generator engine has the induction on the timing side whereas the motorcycle engine has it on the drive side (so effectively, a cam swap would make the engine run backwards!). Also, due to the fact that the generator engine was only expected to run relatively slowly, it has very weak inlet valve springs, so any increase in power or revs would require more modification of the valve gear. However, having said that, the bottom end of the engine would easily stand the increase in power (there are quite a few motorcycles running on generator cranks without any problems).

  Regards,
                Eddie.

Hi Ron
Thanks for the reply

The original, (poorly chosen) mission for this FT35 is related Le Pou du Ciel vintage aircraft, which was, by all accounts, originally somewhat dangerous, though once the fix was put in, it became safe enough, but not before the reputation was ruined. The example we have has a Douglas FT35 engine fitted.

The original post is at https://www.douglasmotorcycles.net/index.php?topic=5974.msg21936;topicseen#msg21936

The first rebuild was back in 2017, but unfortunately, it was neglected to the point the bores corroded.
There are pictures here .. https://www.douglasmotorcycles.net/index.php?topic=6534.msg24435;topicseen#msg24435
That was before the neglect!

The answer was to give it the +0.020 rebore + valve guides bushing head job. Unfortunately, the piston supplier messed up. We we left with a part restored engine, and no pistons. Since then, I obtained a pair of wrecked +0.030 pistons, which hopefully would contain within the metal for a +0.020 size. Pistons making is difficult!
 https://www.douglasmotorcycles.net/index.php?topic=10083.msg40509;topicseen#msg40509

I have just this afternoon completed the salvage of the worst one. I will post the pictures shortly, both the machining and the result. The attempt was to achieve correct piston ovality (clearance relief at skirt on wrist pin axis), using a suggestion from Eddie (Eddies Method!).

I managed to remove the torn up metal from the top ring slot, and machined it to take a slightly wider ring. The reason the donor engine failed was clear. The top ring was "just any old ring". I ran out of feeler gauge trying to measure the ring side clearance, specified to be 0.001" to 0.002", it was something more than 0.016". Sixteen thousandths is enough to have it rocking about like crazy! The other rings were locked solid in carbon, and the oil return holes were hard blocked.

The generator engine was always 2.8-to 3 HP. Clearly the 350cc engine is capable of more. I think the motorcycles of that range topped out at 17HP. I do not expect the generator engine to get anything like that. Since I do happen to have two carburetors, I did wonder whether trying to use them both would work.Even if the power went to 5HP, or 8HP, that would be OK


     

In the motorcycle world, having twin carbs aided acceleration, but generally didn't boost max bhp much, if at all.
And the jetting for twin carbs was the same as for a single carb - it just takes a breath more (or less) often.
The potential for carby icing with twin carbs would be greatly reduced, however.
Being closer to a source of warmth.

Remind us again, what is this to be used for ?
3 bhp is a miniscule amount, for a 350cc engine.
The revs would have to be curtailed, vastly, to hold it down to that. ?

First thing to say here is, I fall about in various stages of ignorance in even asking this! It may be a very poor idea, and if you know, then do tell.

In my experiences with the Douglas T35 (stationary engine version), it is clear that it was a grossly tuned down version of the Mk1, MK2, MK3. It used a AMAL 174 feeding a truly tiny manifold pipe to a shared pair. At best, it would be good for about 3HP. Of course, in this setup, the whole constant speed governor linkage was removed.

I do know that the T35 MK1, MK2, MK3 used left-hand and right-handed versions of the AMAL274, but here we get to that the engine is not on a motorcycle, but instead, it turns a propeller. I don't have such carburetors, and there were things in the motorcycle engines detail that were different anyway. Things like valve spring length and rate.

Suppose I just put two AMAL 174 carburetors on it (they do fit OK), and perhaps adjusted the jets if need be, and ran them via throttle cables on a common lever. Could such an arrangement actually run? Also, not having to run two cylinders through a shared 1/2" bore pipe, might one hope for a little bit more than 3HP? 

Bump