Triumph 650 Twin Engine

[gbritnell]

Hi Mike,
While it's always the goal to try and stay true to the prototype when building and engine or anything for that matter sometimes a little discretion is in order. I have found that for model engine work the more complex the carb is the harder it is to machine and to tune. Reducing jet sizes and air bleed orifices becomes a task in miniature machining and not always with the expected outcome.
Over the years I have experimented with many types and styles of carbs only to have settled on the basic air bleed type found on most throttling model airplane engines.
These carbs can be built and machined to look like an Amal, Delorto or Mikuni but still have the basic properties of the air bleed carb.
I'm attaching pictures of the carb I built for my V-twin engine which somewhat resembles a motorcycle type carb. In your case a little design work could outwardly replicate an Amal and you wouldn't have to do all the experimenting and testing to possibly sort out a truly miniature Amal.
The drawing you presented won't work at all, at least not by what I'm seeing.
gbritnell

[mikemill]

George

Thank you for the advice, your carb sounds like just the job, do you have a drawing I could buy, you could PM me?

Mike

[gbritnell]

Hi Mike,
PM sent.
gbritnell

[mikemill]

Progress on the Triumph is a case of two forward one back, after a week of machining the rocker boxes I tried to line up with the head only to realise I had the centre line of the rocker shaft 0.200in out. How did that happen? god only knows or lost the plot when drawing the part, so have to start again.
I consoled myself by making the carburetors, the functional design is by George Britnell who kindly let me have a drawing, the rest is to emulate a Amal carb used by Triumphs.

Mike

[Ye-Ole Steam Dude]

Still following along Mike and cannot wait to see this beauty run.

Thomas

[Vixen]

Hello Mike
Sorry to hear about the rocker box problems. **it happens from time to time. But those two carbs are your compensation, they are looking oh so beautiful.

Mike

[gbritnell]

Hi Mike,
 Beautiful job on the Amals!
gbritnell

[Art K]

Mike,
The twin is looking great. Don't worry you're not the first of us to remake a part.
Art

[mikemill]

Thanks for the encouraging comments. It’s not the first time I have had to remake parts but for some reason this one got to me probably because I drew the part incorrectly.
New ali billet arrived today so will endeavour to get it right this time!!

Mike

[Nick_G]

It’s not the first time I have had to remake parts
Mike

.
I bet my scrap bin is bigger than your scrap bin.! 

Very inspiring build. 

Nick

[mikemill]

I remade the rocker boxes and this time all is well the push rods engage into the rocker arm cups and the valves open! great relive, the beast is starting to look the part.
Regarding gaskets, I found some 0.5mm copper foil on eBay or considering using liquid silicone, I would appreciate some advice on the subject.

Mike

[Vixen]

Hi Mike

Those rocker boxes look good. The whole engine is progressing well.

Regarding the gaskets, both the paper joint gaskets and the copper head gasket, why not try one of the 3D printing companies such as https://www.sculpteo.com/en/ . They advertise a laser cutting service as well as a print service. Send them a drawing file and they provide a quote by return. I have used their 3D printing service but not the laser cutting service. Let us know how you get on.

Nice work

Mike

[mikemill]

Hi Mike

Thanks for the advice re laser cutting and comments, I am more concerned to the efficiency of the head gasket, latest thought is a 0.8mm mineral auto grade material sandwiched between two layers of 0.1mm copper foil. Then hold the gasket between two layers of 4mm acrylic and cut out shape on the CNC mill.

Mike

[Vixen]

Hello Mike

A composite sandwich head gasket sounds like it will have more compliance and should therefore seal better than a solid copper gasket.

Mike

[Vixen]

Hi Mike

Are you going to try to wrap the copper foil from one side to the other to 'seal' the combustion chamber flame from the non-metallic part of the gasket?

Mike