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Hey Michael.

Following your current build closely. (And the Demon build) What's the origin of the casting kit/plans ???

Is that a HM50/51 mill your playing with ??? I've got the HM52 H/V with plans to retrofit for CNC.

Regards,

Trevor,
Melbourne, AU.
Hi Trevor

I got the engine kit from a member in the states that was selling some of hi casting kits
Looks like you can still get the kit from here 1945 Thompson Vertical Air Cooled

Yes that is a HM50 retrofitted to cnc

Milling Machine CNC 2).jpegMilling Machine CNC.jpegMilling Machine CNC 3.jpeg
 
Good progress on the kit

It is also possible to make a similar looking engine from scratch which is what I did from a few photos. There is also a bit about the history of the design in the first part of my build for those interested in the origins of this engine

https://modelengineeringwebsite.com/Thompson_four-stroke_1.html
 
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Good machining and photography.

Getting good photography in a shop setting is very difficult for me, as is good machining sometimes.

.
I ALWAYS have good machining ....

.....

.....

.... it's just that sometimes my photography makes it look bad. Really. I'm sure that's what the problem is.

Oh, and bad videography. I assure you that the engine really is turning and sounding great, no matter what you see in my video. Scout's honor!

:)
 
I ALWAYS have good machining ....

.....

.....

.... it's just that sometimes my photography makes it look bad. Really. I'm sure that's what the problem is.

Oh, and bad videography. I assure you that the engine really is turning and sounding great, no matter what you see in my video. Scout's honor!

:)
Michael,
thanks for putting up this build log. It gives me some good ideas on set ups when I start mine.
Mike
 
Worked on the head and got some of the holes drilled and the inlet and exhaust valve guides done
I drilled small pilot holes for the inlet and exhaust valves, the transfers to the four jaw on the lathe
I the drilled and reamed the valve guides, then drilled out for the ports and turned the valve seat

Thompson Engine - 1.jpeg

Thompson Engine - 2.jpegThompson Engine - 3.jpegThompson Engine - 4.jpeg

Back in to the mill and drilled the ports out, having the head screws to a square block made changing setups much easier

Thompson Engine - 5.jpeg
 
Hi Michael how did you decide dimensions for the insulator shape? Having worked with Champion selecting correct heat range plus for engines, I know this can be very difficult and "company secret" in industry...
K2
HI
I don't know anything about the science of spark plugs

I am also in the process of building the Demon V8 and I have made the plugs for that, so I just scaled them up to the size I needed

Michael
 
Aha! I hope they work alright! Longer surfaces from live to earth mean you can run a higher voltage coil. Also means spark gap can be increased. But the cooling, or rather permitting the central electrode and insulator to reach a high enough temperature to stay clean, without burning, is often critical, so short initial runs and lots of checking is what I recommend.A melted electrode tip or overheated insulator can lead to broken bits flying around inside the combustion chamber. Oily plugs are a lesser issue.
But well done on the manufacture of nice looking plugs!
K2
 

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