Randall Cox Hoglet V Twin Build

[David CambridgeParticipant @davidcambridge45658]

For my next project I’m planning on having a go at the Randall Cox Hoglet V Twin, with a few modifications.

Rather than a cast iron cylinder, I’m planning on an aluminium cylinder with a cast iron cylinder liner – not for any good reason or particular advantage other than that’s what I fancy doing. I’d also like to learn TIG welding of aluminium, and so as an excuse for something to weld I was planning on using a TIG weld to attach the aluminium cylinder to the engine base block. Bearing in mind that the object of the exercise it to invent an excuse for TIG welding, thus precluding just bolting the two together, does anyone see (skill aside and at least in theory) why I won’t be able to successfully weld the below. The cylinder will fit into the base plate which is 6.35 mm thick and the cylinder at the join will be 3mm thick? Everything is aluminium.

David

[David CambridgeParticipant @davidcambridge45658]

Randall Cox Hoglet V Twin Build

[Jeff DaymanParticipant @jeffdayman43397]

TIG welding aluminum successfully requires a LOT of practice. If you are not experienced with TIG on aluminum suggest you practice every chance you get for 6 months or a year before you try the flange to cylinder joint in your picture.

It will weld a lot easier if both pieces are same thickness of metal.

Be sure to choose a weldable grade of aluminum alloy for the parts – some grades of aluminum are very difficult to weld.

Check with your welder supplier that the TIG machine you buy is rated for the very high current and the correct waveforms/starting profile needed for aluminum welding, also be sure to use the right gas mix for aluminum.

For the cylinder to cool properly you will need a perfect fit between the CI liner and the Al cylinder. Any gaps and heat will not transfer properly. I would not recommend the liner approach for a very small air cooled engine. I have seen some successful ones but the liner in those engines had the aluminum cast directly around the CI liner, with the liner preheated to just below the temp of the melted aluminum.

If you made your cylinder from a piece of Durabar continuous cast iron in one piece you will have a durable cylinder that is one piece with no welding needed, wears very slowly, and transfers heat perfectly, as well as machining beautifully.

JD

[JasonBModerator @jasonb]

I'd be a bit worried about distorting teh cylinder bore. Why don't you weld up a bottom end and screw the two cylinders to that, it could be made more like an enclosed crankcase if you did it that way.

I've seen a couple of the Hoglets done with ali cylinders and iron liners so easy enough to do. I did mine as per the drawings. This is a good build thread of an ali/iron liner one, photos gone from the first couple of pages but OK after that. And a thread with a welded crankcase like my sketch above

 

Edited By JasonB on 29/06/2015 14:37:40

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