Thompson Engine

[michael-au]

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

 

[Jasonb]

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

 

[michael-au]

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.

https://modelengineeringwebsite.com/Thompson_four-stroke_1.html

I did see your engine Very well done, looks great

 

[awake]

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!

 

[mnay]

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

 

[michael-au]

I made Fixture to hold the head so all the holes could be drilled, this will allow me to hold the head in a vice and four jaw chuck
The recess in the back is just for better access to the head when drilling reaming for the valves

 

[michael-au]

Started to mack some new spark plugs and a fixture for swaging the parts together

 

[michael-au]

Finished off the fixture for swaging the spark plugs


Plug is just sitting in there has not been swaged yet

 

[michael-au]

Finished off the spark plug

 

[michael-au]

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





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

 

[Steamchick]

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

 

[michael-au]

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

 

[Steamchick]

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

 

[Jojo]

I like your design and insulator shape.
Well done!

 

[michael-au]

Got some more work on the heads done

Cleaned up the matting surface of the head



Inlet and Exhaust ports drilled a tapped


Turned down the stems so the valve rings fit over them






The only thing left to do on the head is drill and tap the spark plug hole

 

[michael-au]

Drilled and then recessed the rope starter to fit on the crankshaft, drill and tapped the end of the crank and surfaced ground a flat for the grub screw

 

[michael-au]

Started on the rocker pivot post, still need to put a slot in the top that the rocker arm fit in

 

[michael-au]

Made the two valves, the plans call of the valves to made out of two big nails that come in the kit
I didn't like that idea so I made the valves out of silver steel and used the small cnc lathe to machine them

 

[michael-au]

These are 3D prints that I use as templates to cut out the head gasket

 

[michael-au]

Jig for holding the rocker arm so I could machine the pivot point flat on both sides and the drill and ream the hole



Counter bored the hole for the socket head bolt that holds the rocker post to the head