Oddball engines and prototypes

[Michael Moore]

Cobra, who make some mini MX bikes/engines, have an interesting two-part cylinder. The lower section is shrunk in after all the CNC work on the tops of the transfers is done. This gives them full machining access to the transfers.

cheers,
Michael

[guyhockley]

Cobra, who make some mini MX bikes/engines, have an interesting two-part cylinder. The lower section is shrunk in after all the CNC work on the tops of the transfers is done. This gives them full machining access to the transfers.

cheers,
Michael

I suppose an early version of this would be those 2 stroke cylinders with bolt on transfer port covers.

Then there's the alternative approach.

[Frits Overmars]

Cobra, who make some mini MX bikes/engines, have an interesting two-part cylinder. The lower section is shrunk in after all the CNC work on the tops of the transfers is done. This gives them full machining access to the transfers.

Two-part? Are you saying there is no sleeve? I wonder what the piston ring might think of that.
This reminds me of the two-part Garelli cylinders that Jan Thiel used on the flow bench. One cylinder was turned down on the inside, another one on the outside,
so that together they were a sliding fit; ideal for port and duct experiments.

[guyhockley]

Husa, while looking for something else on my hard drive, I came across these. No idea where they came from, though!

[Michael Moore]

Frits, it appears they shrink the upper and lower sections together and then do the finish bore, plating and final hone. The cylinder is treated as one-piece after assembly and is not to be disassembled. They say "the lower transition line is located such that the piston ring remains above it at all times." They use that only on a UAV engine now, it was too expensive for the production 65cc MX engine.

cheers,
Michael

[guyhockley]

Posted a picture from this article on the ESE thread so I thought I might as well stick the full thing here. Don't think any finished bikes ever actually materialised.
Supposed to be wet sump, recirculating oil, oil seal on big ends, dry top end using carbon pistons...

[190mech]

Appears to be a typical 2 stroke bottom end,with sealed/pressure lubed bearings,,wonder about the small end bearing?Couldnt figure out the cog belt drive on the front of the engine,perhaps a rotary valve and that small pump also??
Wonder how well the top end would hold up with no oiling and that magic carbon piston??

[guyhockley]

Cog belts to twin front-facing disc valves via a shock absorbing mechanism that allows for a certain amount of timing change.
One of the microlight UAV engine manufacturers was offering carbon pistons as a "never sieze" option. I thought it was Hirth but no mention of it on their current website that I could see from a quick look just now

[guyhockley]

ITMA! More Bradshaw.

[guyhockley]

One more Bradshaw bit

[husaberg]

Hello Guy find some stuff on this one i know it has a cross head crankshaft and i thing a stuffing piston.

Here's a real oddball, Excalibur, by Major John Treen. This was proposed as a 'world beater' in the 60s, it was to be funded by sale of raffle tickets, but I guess they didn't manage to sell enough tickets.

In about 1967 I won quite a few books of the raffle tickets, along with a nice Bulova watch, which was presented to me by Freddy Frith, for correctly predicting 1st 2nd and 3rd in the Senior Manx Grand Prix .

I always wondered what happened to Excalibur, and was surprised to find this exhibit at the Sammy Miller museum in England.

https://www.kiwibiker.co.nz/forums/a...3&d=1467075181

There was talk of it in a book I read with hopes of 40-50 hp at some astonishingly high revs in 125 form.
I posted something about it on ESE but no one could add much or had heard of it..
I think he swallowed a whole heap of lottery development funds for his project world beater.........

[guyhockley]

Well I've seen it! I think your link is actually to a picture I took at Sammy Miller's (from Michael Moore's Eurospares site?).
At that point it was stashed above a doorway so hard to get a good look at it and no-one seemed to know anything about it.

[husaberg]

Well I've seen it! I think your link is actually to a picture I took at Sammy Miller's (from Michael Moore's Eurospares site?).
At that point it was stashed above a doorway so hard to get a good look at it and no-one seemed to know anything about it.

Wooley mentioned it in a Classic bike or racer column, but only in passing.
why original understanding was he had a 125 running, but i don't believe the HP claims.
plenty of world beater claims came out of GB at the time, i read something recently where Williams can't even remember riding the KRM350.

[ken seeber]

So, nothing too tangible and it says four (foul, hey Frits?) strokes and not the number of cylinders, probably only relevant to one or two, but it is something of interest:

https://newatlas.com/electromagnetic...-engine/55254/

It might be interesting for 2 strokes in terms of altering the crank rotational timing such that a fixed length exhaust system (ie 99%) might be more useful over a wider rpm band.

[guyhockley]

Wooley mentioned it in a Classic bike or racer column, but only in passing.
why original understanding was he had a 125 running, but i don't believe the HP claims.
plenty of world beater claims came out of GB at the time, i read something recently where Williams can't even remember riding the KRM350.

I've got nothing on it as far as I know (away from home and hard drive at the moment) but I did have a search online in case doing it from the UK brought up something you didn't get.
Different picture on South Bay Riders forum - quite grainy.
Few odd mentions here and there but nothing useful.
Lots of links to the modern Polish version and some to an Australian one.
Somebody on a Formula 1 site said they'd read a proposal for a 32 cylinder car version!

Local bike shop cafe has a pile of books for customers to read, one of them is Peter William's "Designed to Race". I'll have a look next time I'm in.