Chenery Vee-Twin

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Hi Dean,

I have sent you a PM

Keith

[Tim StevensParticipant @timstevens64731]

I'm sure that the cooling effect of the oil, being more effective one side, is a factor. I wonder if another might be the uneven timing of the suck strokes resulting in two different mixture strengths. A look at the plugs after a good run would be revealing – I bet the cooler head has a blacker plug. It could also be that one cylinder ignition is timed later than it should be – a further good reason for overheating.

Cheers, Tim

[JasonBModerator @jasonb]

I had an e-mail from another member who said the same thing Tim , the uneven induction gaps between the two cylinders caused problems when running on a single carb, when changed to two carbs it came to life.

[John HinkleyParticipant @johnhinkley26699]

With my apologies for resurrecting this old thread, but I have just ordered the drawings and construction notes for this kit from Hemingway's, having temporarily run out of ideas for new tooling and reinventing the wheel. It would appear that the promised video never did appear for whatever reason and I am aware that there is another thread on here started by Keith Beaumont, but it has been made disjointed by the removal of posts by another member. I won't pursue that; it's been covered ad nauseam in another recent thread.

My reason for posting is that, reading various reports on getting the motor to run and remain running seems to have thrown up an issue with the induction system. I intend to separate the induction to each cylinder and make a pair of carburettors after the style of the Amal ones. If that has been done before at this scale, I'd be interested to be pointed in that direction.

Also, if anybody else has made the engine, I would likewise be interested to hear their experiences (good or bad).

I might add that I intend using electronic ignition instead of glow plugs and will investigate the possibility of a pressurised lubrication system. On the cards is a 3D model, too, if I can manage to reproduce the castings to an acceptable degree of accuracy.

John

[HopperParticipant @hopper]

Strange, the single carb causing running problems. Almost every V-twin made traditionally used a single carb between the two cylinders, and Harley still uses it today, with a single fuel-injection throttle body feeding two cylinders. It may be a factor of the sharp T shape of this manifold and the long straight piece between the two intake ports giving some kind of weird Heimholtz resonator effect or reversion. V-twin motorcyle manifolds are usually much shorter due to 45 or 60 degree V angle, and they are a flowing curved shape so there is no straight shot from one intake port to the other.

Or it could be the carb is too small to feed two cylinders and gas velocity through it is too high. Usually on v-twin bikes, the carb bore is quite a bit bigger than the size of the manifold/port for each cylinder.

I have never seen the uneven firing intervals on a Harley etc cause one cylinder to run leaner than the other.

But things may well happen differently at model scale. Keep us posted on how your build goes.

[JasonBModerator @jasonb]

Interestingly the GA on Hemmingway's site seems to show two swept piped for the inlet but the one they have photos of is a more abrupt tee shape. It will be interesting to know what the drawings show when you get them John.

Edited By JasonB on 12/11/2022 13:40:35

[John HinkleyParticipant @johnhinkley26699]

I'll let you know, Jason. Kirk says they will be posted out on Monday, so it'll be midweek before I get them. I'll start a new thread when the build starts to run concurrently with the YouTube videos, but that will after I've had a go at the 3D render.

John

[KEITH BEAUMONTParticipant @keithbeaumont45476]

I had no problem with uneven running, once I had increased the compression to work on glow plugs. I did not make the Chenery designed manifold and made a tee shaped one . I tried various carbs trying to get max revs together with a decent slow running, with good transition between, but ended up with the original single one that I had in my bits, not the Chenery design.The trick was to get the size of the inlet correct and I made several before I was satisfied. . I did not have pressure lubrication, just 5cc of oil in the crankcase and drained after each running session.The breather was replaced from its drawn position,as it made a mess over the crankcase, I replaced this with a plain 3mmm pipe in the rear face ,which allows oil fume to pass over the camshaft. If you use sparks you might not be able to do this.

Keith.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

The other modification I made to the design was to make long nuts for the head holding down bolts, As drawn ,you cannot get to them for re-tightening after the valve brackets are put on and making them longer to be above the valve brackets allows re-tightening when engine is hot.

Keith.

[Graham MeekParticipant @grahammeek88282]

The above engine was owned by Dr John Beddard. You will see it has been modified quite a bit from the original design. Most of the modifications can be attributed to me and include cast iron cylinders , re-designed cylinder heads and valve gear.

The engine was originally run using a single carburettor, but it ran very un-evenly. This was put down to the induction periods of the 90 degree lay-out. Converting to a twin carburettor set up made this engine more docile and a joy to run.

Regards

Gray,

[John HinkleyParticipant @johnhinkley26699]

Thanks Graham for your input. Very useful and food for thought. I had in mind a twin downdraught carb with a Weber DCD look to it. Should be an interesting build. It won't be driving a propeller, though, my interests are more in the automotive direction. Maybe a Morgan three-wheeler like vehicle, with a flywheel attached to a modified taper, much like an Austin 7. All the proposed mods will be made inside my computer first to ensure that they are workable.

John

 

Edited By John Hinkley on 12/11/2022 16:06:27

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