Recreating a Stuart Lightweight

[Jasonb]

There is no exhaust shown on the drawings but I had seen a photo of a straight through one that I liked the look of. First job was to make a former to bend the 1/2" OD stainless steel tube around, an old plumbing fitting donated a suitable piece of brass which was free hand turned with a 3/8" bull nose lathe tool offering up the tube towards the end to judge the shape.





Another scrap of bar with half a 1/2" hole down it was used to support the outside of the bend and the pipe bent to about 45degrees which was all that was needed. It was then just a case of cutting the tube and soldering it to a suitable round disk with a couple of holes to take the studs in the cylinder boss and a slot to let the gasses out.






The timing bracket was originally supplied as a grotty pitted casting, I can only think of one person who could get excited about this lump



I thought I could come up with something a bit better so drew it out and sliced of a bit of square 6082 ali



Into the 4-jaw to bore a hole that was a nice fit to the spogot on the front of the crankcase about which it can be rotated to advance and retard the timing.



Then with it mounted on a mandrel and using the rotary table the shape was formed leaving the long arm that holds the insulated contact and the smaller lug for the clamping screw.



With the part flipped over the recess on the other side was milled out leaving the shape at the left which gives greater support to the cam follower.



The cam follower rides in a 5/32" wide slot but this is deeper than my broaches will cut and also goes through two different diamaters so it was planed out on the lathe with a 5/32" toolbit by moving the carrage back and forth putting on a thou or so cut on each pass.



Add a couple of holes and then the clamping lug can be split in two with a slitting saw.



Followed with a bit of file work to round over the lug and a good cleanup and thats another part done.



There are a few other bits to go with it, knurled nut, cam follower, pushrod, insulated washers and spring contact



Then with a couple of screws it can all be assembled



And if you promise not to look at the colour as I don't want to give that away yet here is a short video of how it all works.

[youtube1]https://www.youtube.com/watch?v=0_gXyCs7utI[/youtube1]

J

[Jo]

The timing bracket was originally supplied as a grotty pitted casting, I can only think of one person who could get excited about this lump

  That is one of my much loved castings, years of fondling has gone into getting it to look like that.

Jo

[Jasonb]

A quick repost of the stand construction.

4 off cuts of steel were welded together to form the bottom plate



The 4 sides welded up into a box, they actually taper inwards towards the top dispite what it looks like in the photo



Bottom plate welded to the sides internally to make clean up easier



Cutting the curve to clear the crankcase with a boring head



Fettled & filled ready for paint



Primed, satin black and satin fuel proofed.



J

[Jasonb]

Right, now that we are back upto date it must be time to tackle the carb, on the model this comes as a main aluminium casting together with a lid for the float chamber and top for the oil feed.  Don't look too bad castings on this example, constant stroking has no doubt improved the surface finish



I turned the bottom of the lid first and cut the thread, then parted it off and set aside.



I decided to fabricate the "casting" from brass, as my engine won't be going into a boat or car there is no real need to worry about teh weight. So starting with some 1.5" brass this was reduced to a large pile of swarf leaving a float chamber that was then threaded to take the lid while the change gears were set up from doing the lid.



I was then able to use the float chamber as a means to hold the lid while the top was finished off.



A MDF plug was put into the chamber so it did not crush and then the bottom profile was completed



A disc of brass was bored and threaded 5/8 x 40tpi and then soldered onto a suitably threaded piece of 5/8" bar that had been drilled out to 1/2". This was then shaped into a flange on the rotary table.



The top of the oil inlet and its flange are similarly shaped so first the ali top was turned



Then with it screwed to the brass both pieces were shaped at the same time with full depth cuts.



Another piece of hollowed out 5/8 bar was also needed to form the rest of the vertical inlet tube



An aluminium venturi fits into the vertical tube, the taper was bored from each end using a 3-flute cutter held in teh lateh tool post.





The throttle is a piece of 1/2" aluminium with a curved end, this not only slides across the top of teh vertical tube to adjust teh opening but teh curve also smooths the airflow as it is turned from vertical to horizontal, the other two turned bits are a gland and locknut to set the throttle.



To be continued.................

[Steamer5]

Magic Jason!

Cheers Kerrin

[Jasonb]

The float chamber and vertical pipe are joined by an angled piece of brass which is a bit tricky to machine as it does not run on the same centre line as either of the other parts.

A 1/16" pilot hole was drilled through some 5/16" brass which was then held at the correct angle in an ER32 block, the centre found and the DRO used to give the correct offset for the float chamber and a boring head used to do the cope cut to match the 1.5" float chamber diameter.



To ensure the work did not twist out of line when the other end was cut I used this method to change the grip of the work by tightening the 5C block before loosening the ER block the part stays indexed to the edge of the blocks.



The 5/8" cope cut was then made with a similar sized milling cutter using a few plunge cuts.



Here are all the carb parts prior to soldering, there is also a web cut from 1/8" flat to brace the joint between float/diagonal and vertical parts as well as a small boss for the mixture needle to screw into.



And here they all are soldered together. I passed a bit of studding down through the vertical parts with a nut and washer on top and packing below to hold those parts together, the boss on the bottom of the float chamber sits in another hole and you may just be able to make out a slotted screw holding the needle boss in place - I ctr drilled this prior to soldering so it was easy to locate and drill out later. Block of metal at the bottom and the packers were given a good coat of Tipex correction fluid so they did not get soldered too.



Thats the last construction photo I took but there was some minor machining of the assembled carb and a sight glass for the oil feed added too.

So time for a coat of paint in a nice subtle shade

















J

[Jasonb]

Finally its time for a  or two

[youtube1]https://www.youtube.com/watch?v=gVPlj3Q90xY[/youtube1]

[youtube1]https://www.youtube.com/watch?v=x86Snja-Z00[/youtube1]

The engine was getting quite hot without any water cooling so I did nor run it for much longer. It still needs some tweaking of the carb and finding the sweet spot for the timing but that will have to wait until some cooling is sorted out. Though knowing me I won't run it much more as once I have satisfied myself that an engine runs my interest turns to the next project.

Thanks to all those who have commented during the build.

J

[vcutajar]

Nice one Jason. Love the colour.

Vince

[Admiral_dk]

It runs nicely for an engine that hasn't been adjusted yet 

I like the colour - kind of makes you smile 

[yogi]

Fantastic engine Jason!!! 
Congratulation on the successful project. Very well done!

[b.lindsey]

Beautiful Jason and I very much like the yellow too!!  So what is the next project??

Bill

[Don1966]

One thing I can say Jason, is that you have fabrication work down mate. Just down right gorgeous work........I............like.........


Don

[Gas_mantle]

Great job Jason and thanks for taking the time to show the entire build, it makes interesting reading from the beginning.

I was intrigued by that method of cutting an internal taper using a 3 flute mill in the lathe.

Peter.

[Kim]

Very nice Jason! That's quite an impressive first run!  And the yellow really makes it pop! 
Kim

[Flyboy Jim]

Very nice looking and running engine, Jason.

I bet you could solve the cooling issue if you built a racing boat to install it in. 

Jim