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Another mystery engine competition

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5 months 3 weeks ago #1241 by archer
Another mystery engine competition was created by archer
A very Happy New Year to all

I came across this old pic in an online archive which got me curious. It didn't have a title. The chassis looks distinctly ABC 12hp /Sports.

But the flat twin engine looks very unusual, some kind of prototype with unique valvegear?



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5 months 3 weeks ago #1242 by Roger
Replied by Roger on topic Another mystery engine competition
Very much an ABC chassis with its unusual cantilever suspension with gearbox set well back. No front brakes so early 1920s design.
I really can't work out how the valves are actuated as they appear to be at the side of the cylinder rather than on top when viewed with the cylinder vertical. The absence of a a pin for a conventional rocker and the substantial fixings for the "push rod" tube indicates a totally different arrangement.
Quite how the valve operated by such an arrangement fit into the combustion chamber is another mystery.

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5 months 3 weeks ago #1243 by Paul
Replied by Paul on topic Another mystery engine competition
Here's my fivebob's worth, about the valve operation...
Those substantial 'pushrod tubes' contain, in fact, rotating shafts: each with a cam at its outboard end. Each cam works a valve, angled down in the direction of the (visible) sparking plug. There must be a pocket 'above' each piston, for the valve heads and 'plug points.
Where do I claim my winner's coconut?

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5 months 3 weeks ago #1244 by Roger
Replied by Roger on topic Another mystery engine competition
Paul,

That was my initial though although it does make the combustion chamber a very odd shape but with a compression ration of around 5:1 that would not be a problem.
The main problem with that solution is working out how to rotate the shaft at the cam end. The camshaft is in the standard position and the tube connection appears to be in line with the camshaft so how does it impart rotation?

Roger

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5 months 3 weeks ago #1245 by Paul
Replied by Paul on topic Another mystery engine competition
Hi Roger,
Let's start afresh.
What would normally be a camshaft, is in this case a camshaft driveshaft.
It does its driving via bevel gears to the inboard end of each camshaft-proper. (These gears could also perform a 1:2 reduction-stage). The hefty 'pushrod tube' surrounds at their inboard ends, carry the inboard camshaft-proper bearings, which resist radial and axial loads. There are similar bearings (except for radial-restraint only) at the camshaft outboard ends.
I liked your compression-ratio rations!

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5 months 3 weeks ago #1246 by Roger
Replied by Roger on topic Another mystery engine competition
Paul,

I now realise that the engine is a totally different design to that of the standard 12hp and the take off tubes to the head are not in line with the camshaft. This means that the rotation on the rocker rod could be by means of a face cam. Dougal Marchant designed the face cam Chater Lea engine for 1924 that used a vertical bevel driven camshaft actuating rockers in the head.

It looks as though there is a Super Sports in the background so this would be a works special with knock off hubs and that would explain the radical valve gear design which would have been experimental.

I hope I've used up my ration of auto-corrections!

Regards,
Roger

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5 months 3 weeks ago #1247 by degraaff
Replied by degraaff on topic Another mystery engine competition
What i see is used car and gearbox with a new engine yet to be connected.

I think there is a normal cam but the rocker is turned 90 degree and the rocker axes are as long as the distance be tween the cam and valve so the rocker is pushing the valve directly.

The coolingvan axs is of center becouse it's also driving the sump oilpump.

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5 months 3 weeks ago - 5 months 3 weeks ago #1249 by degraaff
Replied by degraaff on topic Another mystery engine competition
It looks like there is a name on the front of the engine something like "Pest" or "Prist", could that be a bug.

I also think that the "pushrodtubes" are the rockeraxels them selves so the are the turning part.
Last edit: 5 months 3 weeks ago by degraaff.

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5 months 3 weeks ago #1251 by Andrew Kelsey
Replied by Andrew Kelsey on topic Another mystery engine competition
The chassis, steering and gearbox are ABC.
The engine does appear have name on it -
A real long shot here - could it be Pedersen -of Hursley-Pedersen?
Primarily bicycle makers, they make a single cylinder motorbike but had developed a flat twin engine before they were taken over by Douglas.

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5 months 2 weeks ago #1252 by archer
Replied by archer on topic Another mystery engine competition
The longish cast script ***st** inclines me to think it's not a prototype ABC design. The crankcase and timing cover looks to have been well designed, specifically for the unique cam/valve layout.

Was it put into an ABC chassis just to test the engine? A prototype for another application that may have never gone into production? And where on earth were the valves? My resources don't go beyond the 1920s A-Zs for bikes and cars so there i am at an impasse.

I guess the prize would just be feeling very smug!

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