Recreating a Stuart Lightweight

[Jasonb]

In about 1935 Stuart's introduced the "lightweight" petrol engine, a 2-stroke spark ignition engine of 30cc capacity. This was available in both air and water cooled versions, it is the later watercooled engine that forms the subject of this build.



I had bid on a couple of part made engines on e-bay but they went for more than I thought they were worth, I also got to handle an untouched casting set but even that had a few flaws so I thought I may as well make one from scratch, at least you know where you stand with a block of solid metal. As you can see from the above to make the engine live upto its lightweight name Stuarts used "Electron" for some of the castings which was a magnesium alloy but I have opted to use 6082 for these parts. To make fabrication easier I also opted for steel for the cylinder with an inserted iron liner, here are the main bits of metal ready to make a start.



I decided to make a get going on the cylinder so a bit of 2.625" steel that I have had for years was poped in the lathe and a lump parted off - I did hacksaw the last 10mm. On reflection I would rather have bought a known bit of steel as this was not the nicest to machine but as it is going to represent a casting the finish is not critical.



The outside was machined to profile - you can see the poor surface finish.



Next the hole  for the liner was drilled and then bored out 1/16" undersize. You can't easily see it in this photo but a section of the hole was increased in dia to form the waterspace that surrounds the top of the liner.



The embrio cylinder was then parted off leaving an over thickness flange at the bottom and a lump in the chuck which the head can be made from later, though I did just take a skim off the flange clean up the parting cut.





The flange was then drilled for the fixings and shaped to profile which gave me some straight edges that I could reference against for the next stage



But before that an inlet boss was needed so with the vice on the rotary table that was milled out of a steel offcut



Closely followed by the lump that forms the transfer passage



I could now start making holes in the main cylinder starting with the one for the inlet boss



Then the transfer port, I had to file the lower corners square after milling



The water inlet was a simple round threaded boss which was drilled and then finished with a 5/8" milling cutter



The exhaust was again a round boss but being somewhat larger needed the boring head to form the hole



Here are all the bits



And here they are again all silver soldered together, I'll leave them to cool until the next installment.



J

[Jo]

  Looks like the price had gone up by 1935

And my original set of castings so there is something to compare it with

Jo

[Graham G]

 , Nice, i WILL BE WATCHING THIS ONE EVOLVE.
Graham

[b.lindsey]

Nice little engine Jason. What are you using for plans?

Bill

[Dave Otto]

Hi Jason

Pulling up a chair to follow along here; I will be interested to see how you go about fabricating all the different parts for this little guy.
Did you do all the soldering on the cylinder in one heat?

Dave

[tangler]

VERY interested in this build.

 

Cheers,

Rod

[10KPete]

I'm in.

Pete

[Jo]

I am sure JB tried winding me up by telling me of someone else who had picked up a set of lightweight castings 

Jo

[Jasonb]

Bill, I was lucky enough to be lent a set of drawings, very faint but usable. I did have to do quite a bit of redrawing of the main cast components as the drawings only showed dimensions of the machined surfaces of the castings as is usual. Also needed to adjust things to suit the inserted liner and create the water passages as these were cored in on the original. Couple of renderings anf a pdf attached, I left off fillets and minor holes for clarity.

Dave, all done in one heat using our Tenacity 5 flux which is made to stay active during long heats.

Rod, I thought it might interest you

Jo, yes I did identify the castings for someone who was looking to sell them. Told him they were worth far more than they really are as I knew someone else was sniffing about and thought we could stitch him up and split the profit

J

[b.lindsey]

Thanks Jason. I'm along for the ride as well.

Bill

[mnay]

I have seen a couple of these engines on the internet. 
Does anyone know if plans are still available somewhere?
Mike

[Jo]

Hi Mike,

Stuart Turner will sell you a set of plans for a very reasonable price if you contact them

They may even be selling the castings again in the not too distant future 

Jo

[mnay]

Thanks Jo
I did not see it on their list, but I sent off an email to see if they still have them available.
Mike

[mnay]

Jasonb
sorry to interrupt your thread.  I will be anxious to see you progress on this neat little engine.
Mike

[Tennessee Whiskey]

I'm  ,  , and following,  however,  knowing how you work : how does it run? .

Cletus

[tangler]

Hi Mike,

They may even be selling the castings again in the not too distant future 

But will the crankcase be cast in Elektron ? 

Rod

[Jasonb]

Hi Mike,

Stuart Turner will sell you a set of plans for a very reasonable price if you contact them

They may even be selling the castings again in the not too distant future 

Jo

I hope they have redrawn the plans and are not using the feint ones that I had to work from

They also told me they hoped to do the lwt soon but that was about 4 years ago when I asked Maybe this thread will create a bit of a demand and they will get their finger out.

Whatever the materials I can't see it being a cheap kit. With the complex cores in the head, cylinder and slightly easier one in the crankcase there will be a lot of work and possibly higher failure rate. Though I suppose some of the modern setting core mixes should help.

J

[Jo]

Reworking the Lightwieight plans is on my list of things to do next time they are paying me to have a break at work 

Whatever the materials I can't see it being a cheap kit. With the complex cores in the head, cylinder and slightly easier one in the crankcase there will be a lot of work and possibly higher failure rate. Though I suppose some of the modern setting core mixes should help.

Based on the price of my missing IP/LP cylinder for one of my orphans I could see the cylinder being priced around £150. My guess would be around £600 to £800 for the set if they started doing them again 

Jo

[Jasonb]

In that case it won't be a fast seller when all the metal to make one from scratch would be about £40-50 and you get a much more impressive pile of swarf as a bonus

[Jo]

Which is probably why they have not yet reappeared.

In the same vain you could built a triple for about £50 but for some reason people prefer to buy castings  .

Jo

[Jasonb]

Once the cylinder had cooled it was given a 1/2hr pickle to remove the scale and old flux then holding by the top of the cylinder the bore was taken out to final size and the bottom flange machined back to thickness. You can just see the fine brass coloured lines of the solder on the inside which is a good sign that it has flowed right into the joint.




After which it was reversed in the chuck, brought down to final height and a recess cut to take the lip of the liner (no pics)

Then onto the mill and each of the bosses were finished off, this is the exhaust one which had the slot cut to final size and a couple of stud holes drilled & tapped



Then onto the rotary table for final shaping of the flange, followed buy stud holes and cooling slots for the head.








The remaining bit of steel for the head had a spigot turned on it that would fit into the cylinder liner, then holding by this spigot the shape of the head was formed. I drew it out in Alibre and took offsets at 0.025" intervals which gave the basic shape. This was then refined with hand graver and files. The hole for the plug was also tapped M10x1 at this stage.



Then the head was bolted to the mill table and dialed in.



Following which the 4 stud holes and one water passage were drilled and then deeply counterbored.



A few stub ends of steel were then soldered into these counterbores to form the stud and water pipe bosses.



After a bit of a clean up the bosses were machined to height and the holes taken to finished size.



I also cut some slots into the head to match those in the top of the cylinder, these should allow some water cooling of the head.



The last job on the head was to shape the underside of the spigot to match the shape of the top of the piston and use a bit of JBWeld to form some fillets around the bosses to get that cast look.





J

[Kim]

Wow Jason!  That is cool!
Very impressive fabrication to say the least.
And great pictures too!
Kim

[Roger B]

Very nice indeed   

[fumopuc]

Hi Jason, very impressive fabrikation work, as usual. I enjoy to follow and to learn.

[Jasonb]

A 3" dia piece of 6082 was held in the 3-jaw and a start made on the crankcase cover. After facing off it was bored and counterbored for the bronze bearing then the outside diameters were taken to size.



It was then reversed in the chuck, the bolting flange brought down to thickness, a spigot for the timing bracket turned and as much waste as possible removed between the two.



It was then over to the mill to drill the eight stud holes and mill out more material to leave four stiffening webs. After machining these were attacked with the Dremel to get them looking more like castings.



The cankcase started out as a 100mm length of 3" square 6082 and was quickly brought down to size on the vertical bandsaw, who says woodworking bandsaws can't cut metal .



I started by cleaning up some faces on the lathe, cut quite nicely with a dab of kerosene and certainly was not sticky



Then over to the mill equiped with a flycutter do do the rest of the faces.



Back on the lathe and the crankcase was hollowed out, it's not that easy to see but there are several undercuts to give minimal clearance to the crank webs and conrod bigend, you can also just see the hole and counter bore for the bearing.



Finally add a shallow cut for the crancase cover to mate with, yes it is meant to just break the edge of the block.



And a quick test fit of the cover, this needs to be a good close fit as it ensures the two bearings either side of the crank are concentric.



Now with the top of the crankcase facing outwards the hole for the cylinder liner was bored to depth, that little ledge you can see will later have a CSK oil hole drilled down through the bearing the idea being that some of the 2-stroke oil will gather on the ledge and then find its way down into the bearing.



From another angle you can see the shape of the inside of the case better



Finally the back of the engine had as much material removed as possible in a similar way to the cover earlier.



With all the turning done it was over to the mill to make some serious swarf by machining away a lot of the waste to leave the two mounting lugs. I used one of the 2-flute milling cutters from ARC that are designed specifically for alumininm, this is a 12mm cutter and I'm cutting with 35mm of the flute length, 0.020" (0.5mm) depth per pass.

[youtube1]https://youtu.be/AXk2zimLC2c[/youtube1]









That's it for tonight, there is swarf to be cleaned up

[Roger B]

That's indeed a lot of swarf (that's why castings were invented  ) A wood bandsaw should be ok with aluminium, it might struggle with Mould Steel (I know I did  )

[b.lindsey]

That is some beautiful work Jason. Still following alone here 

Bill

[steamer]

I always love watching you fab up stuff Jason.    Sweet!

Dave

[Ridjobradi]

This is an great build to watch for a newbie.  I am seeing how much more tooling, material, and skills that I need to acquire.  All the more reason to start small and acquire a little at a time.

Sent from my SM-T330NU using Tapatalk

[Jasonb]

When the swarf was cleared away I could see that the lump of ali was starting to look more like an engine crankcase







With the part held in the vice mounted ontop of the rotary table the cylinder mounting flange had some shape added to it.



The rotary table was then mounted vertically and the 3-jaw chucks jaws expanded inside the crankcase opening to hold it. I also turned up a plug to fit the bearing hole so that the R/T tailstock could be used for added support then the case was roughed out to shape.



And then another pass to bring it down to final size.



Then using a ball nose cutter some more excess material was removed.





The R/T was then mounted horizontally again and a start made on machining the stiffening webs at the rear of the crankcase



The top half was a bit trickier as there is a rounded bulge that follows the line of the cylinder liner cutout, not easily seen in this shot but better in the second where I have hade a start at blending some of teh machined surfaces with a carbide burr







I was then just a lot of time with the Dremel and files to refine the shapes. Luckily as the stuart castings are quite textured there was not as much work as there would be doing a diecast crankcase that would be left in bare metal. Here it is with some etch primer.







Thats the crankcase out the way for now while I decide on a nice subtle colour to paint it. Next time I'll see what is hiding inside this piece of EN8 Steel.



J

[Roger B]

Could it be a crankshaft? 

[crueby]

Excellent work on some complex shapes!

 

[steamer]

hmmmmmm  much too long for a crank...but right diameter....

Dave

[Jasonb]

Depends which side of that parting cut I use

[deltatango]

and I thought I was making a lot of swarf for Mastiff!!

That crankcase is an object lesson in carving from the solid, wonderful work.

DT

[Jasonb]

The crankshaft was worked on over a period of time as and when other parts were made that are affected by it and also to retain the ctr holes for as long as possible should any slight adjustments have been needed but I will describe its construction all in one go.

Stuarts originally supplied this as a disc that was friction welded to a shaft but I cut mine from solid.

Starting with a length of 2" dia EN8 steel a suitable length was parted off,  well deeply grooved and then finished with a hacksaw. This should be the last time I need to use this method as I have heard a whisper that Santa will be trying to force a Femi 782XL bandsaw down the chimney this year.



The two ends were faced off with the bar held in the 4-jaw. To drill the ctr holes in each end on round stock I find that clamping it to the vertical slide ensures the two holes are in exactly the same vertical plane at each end. The bar is clocked central and a hole drilled then raised up by the required amount and the ctr hole for the crankpin drilled. Then rotate the vertical slide 180degrees on the cross slide and repeat the hole drilling in the other end.



I then removed a bit of waste material from each end to reduce the inbalance as much as possible as the pin was turned starting with a parting tool.



Then cleaning up the inside edge of the webs with a HSS tool that had a small radius on the end to reduce any stress points in the corners





A spacer was then turned up to stop things deforming while the shaft was turned, this was retained with a zip tie and a spot or two of hot melt glue to stop it rattling about.



A short taper was turned on one end to take the ignition cam and a longer one on the other end for the flywheel. Both these two other parts were bored at the same taper setting to make sure they seated well.



An M8 thread was cut for the flywheel retaining nut.



And a slot cut for a woodruff key



An unused bit of my lathe cabinet was put to use for the two counterbalance weights which were machined and filed to shape.



Some matching holes were added to the crank webs with the aid of a long ctr drill and extra long 3mm drill.



The weights were then screwed on with a drop of Loctite 648 on the screws and finally skimmed down to match the dia of the webs.



The final job to keep true to the "lightweight" theam was to drill out the middle of the pin and down into the shafts to get the weight down a bit further.



J

[Nick_G]

.
Cool. 

.................... for a beginner.! 

Nick

[Dave Otto]

Nicely done Jason!


Dave

[fumopuc]

.
Cool. 

.................... for a beginner.! 

Nick

...as Nick said, easy if your are watching only.......

[Jasonb]

The most economic way to make the conrod was to use some 1.5" round 2014 stock rather than square or rectangular.

Two bits were squared up for the rod and cap and then drilled & tapped. As the rod has to be assembled with the crank in situe the bolts need to have their heads towards the little end so a couple of rough recesses were cut so the bolts could be put in position.



With the two parts now now screwed together the big end hole was drilled out and then using the boring head opened up to finished size.



Following which the little end was drilled and reamed for the wrist pin.



Using a milling cutter that had the corners rounded over the two cuts were made to taper the rod.



Using a fly cutter the big end was reduced down to the finished thickness



Then with the little end mounted on an arbor held in a chuck on the rotary table it was rounded over first with a 10mm roughing mill





Then cleaned up with a long series 4mm dia cutter to remove the ribs left by the rougher and also to get a smaller internal radius where the end meets the rod sides.



A 6mm cutter with rounded corners was then used to round off the little end and reduce the tickness of the rod.



No pics of the next bit which was to hold the arbor in the lathe and turn tapers on each end of the now round little end but you can see it in the next shot where I am using a 4mm bull nose cutter to shape the big end.



The sides of teh rod were then tapered blending the cut into the two end cuts.



To reduce the weight of the rod still further tapered rounded flutes were cut with a 7/16" bull nose cutter.



The last milling was to remove the remaining unwanted metal around the bolts.



A final bit of blending with needle files followed by some emery cloth and the conrod can be ticked off the list



J

[yogi]

Beautiful work Jason!    

[Jasonb]

The piston started life as a length of 35mm dia 6082 round bar which had a chucking spigot turned onto one end. Then holding by this spigot it was turned to finished diameter, piston ring grooves cut and the bottom bored out to leave the skirt



Next using the rotary table on the mill the internal cavity was machined out



With the R/T repositioned the wrist pin hole was drilled and reamed



Once the chucking spigot had been parted off the head needed shaping to match the profile of the cylinder head so some co-ordinates where worked out using Alibre, a holding collar bored out from some Corian to avoid damaging the piston and then the profile done in a series of cuts.





The cuts were then blended in with a file before polishing the top of the piston.





The wrist pin is just a length of silver steel (drill rod) hollowed out and fitted with a couple of bronze plugs to stop it scoring the cylinder bore.



And finally a family shot of conrod, piston and pin.

[Dave Otto]

Nice work as usual Jason; the piston and rod assembly turned out great!

Dave

[Gas_mantle]

Looks great Jason, I'm impressed by the way to manage to fabricate complex items.

[Jasonb]

The flywheel started life as a piece of 4" steel bar, held in the 4 jaw the outer face was turned. The smaller dia part that sticks out is what was used to start the engine in the good old days before electric starters, a length of strapping was wound around this and then given a sharp pull, much like a recoil start.



It was then parted off and the other face turned finishing off with a round nosed tool to give a fillet to the internal corner as you would find on a casting.



With a boring bar held upside down and cutting on the far side of the lathe the taper was cut.



Doing it that way allowed me to turn the matching taper on the crankshaft at the same topslide setting



While the crank was in the lathe I also screwcut the M8 thread to take the flywheel retaining nut



To stop the flywheel rotating on the taper it has a keyway for a woodruff key. To cut this I made up a tapered guide bush and then pushed a 1/8" broach through



Then the matching slot for the woodruff key was milled into the crankshaft.



While I was at it the short taper was cut on the other end of the crank for the timing cam (you can just see it on the right) and the taper in the cam cut at the same setting



To complete the cam a very shallow recess is milled part way round the circumferance which is just enough to open and close the ignition contacts.

J

[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

[Roger B]

   Runs well for the first starts    What with Steve Huck's copper block and your yellow we must be moving into a new era of engine colours 

[Rivergypsy]

Looking good, Jason!

[Dave Otto]

Hi Jason

She looks and runs wonderfully! The carb and intake fabrication are also very nice!

No comment on the color though. No really it looks very nice.


Dave

[zeeprogrammer]

Awesome Jason. Stunning. And I do like the color.