Well seeing as David has given us this new topic heading I guess that we should make use of it and as a few people have asked for some more details of my build of the Firefly thats currently being covered in ME here goes.

Before I get going these photos are the way that I have gone about things with what I have, there are many other options for those with more or less equipment, please feel free to ask about other methods if you don't have the tooling.

Drawings can be downloaded from HERE

Crankcase

I had a lump of 2"x4" HE30 that was not used on another project so decided to use this, it was marked out somewhat oversize and one of my woodworking bandsaws made quick work of reducing to size.

The rough sawn block was then held in the milling vice and a flycutter used to cut the four edges to 0.5mm oversize.

The centre was then marked and punched on the end of the embrio crankcase and then clocked true in the 4-jaw using a sprung centre and dti

The majority of the waste was drilled out right through starting with a spot drill then 1/4", 1/2" and 9/16". In hindsight I would suggest drilling 3/4 of the way through only – see later.

A boring bar was then used to open the end out to 28.2mm dia and a little longer than needed.

A depth gauge was then used to check the depth of the 28.2mm hole and the end faced back until finished size was reached. The edge of the hole was then given a slight chamfer to break the edge.

I then set about boring the 16.6mm hole, as you can see this needs quite an overhang on the bar and even at 1/2" dia I was not getting the type of finish that I wanted so opted to flip the work end for end and use a shorter bar from the other end. If doing it again I would clock the work in and drill 9/16 from the front end before boring to 16.6mm as the 28.2 and 16.6 holes do not have to be perfectly concentric this is not an issue.

Here the end has been faced back to get the correct overall length and again the edge of the hole tidied with a small chamfer

Cont'd

Edited By JasonB on 22/01/2021 16:15:02

Bearing

Talking of Bearings I started out with a stick of 3/4" nominal bar and took a light skim along it which gave a dia of 19.6mm, this will be close enough to the required 20mm. The end sawn end was then faced.

The outside was then reduced to to give a good press fit into the crankcase, measure from job. Inside was drilled then bored out to 12mm, check the outside dia again after boring as the bearing may have grown.

The length was then faced back to finished size

And as usual edges broken with the chamfering tool.

Part off a little overlength

Reverse in the chuck and lightly grip while the flange if faced to size and finish with more chamfers.

Cont'd

Thanks Jeff.

The completed bearing was then pressed into the crankcase using a vice, put a washer or similar on the end as the bearing needs to protrude slightly beyong the end of the case, I used part of a ballrace.

The next job was machining the chamfer on the top of the crankcase, start by marking a line 23.45mm from the front face.

Then mount the work in the milling vice at 20deg not the 20.1 that the photo shows, the right one wa sout of focus. The bit of steel flat gives the magnet of teh angle box something to stick to.

Flycut away the waste until the new face meets the previously marked line.

Pick up the junction of the two faces with a centre finder and then crank back 8mm to locate the carb hole.

Form carb hole, I went spotdrill, 1/4" & 3/8" drills followed by 10mm FC-3 cutter. Lock the quill and feed down the head or up with the knee so the tools won't snatch as they break through the bronze at an angle. Then use a CSk to just tidy the edge.

Mark out the two carb retaining screw holes and lightly punch

Back in the mill locate the dot punch mark with a center finder, spot drill, drill 3mm and counterbore with FC-3 cutter, I used 1/4" . Repeate for other side

Con't

Barrel

I cut another piece of the lump that I used for teh crankcase and machined it up on 4 sides to 44×41 to give 0.5mm each face to play with and plenty of length to go in the chuck.

The centre was marked on one end and then dot punched

The piece was then set up in the 4 jaw using a dti to get the centre to run true while also making sure it was square to teh lathe axis

The end was then faced and deeply centre drilled and the tailstock centre brought up for support. A parting tool was then used to establish the top of the mounting flange and underside of the exhause block.

Then the same tool used to cut the top face of the exhaust block

And then most of the material between this cut and the chuck removes, I used a series of plunge cuts and then traversed with the parting tool to remove the last 0.2mm

The tailstock centre was then withdrawn and the flange machined to thickness and , the spigot was machined to fit the cranckcase testing to get the right fit.

And with the dia correct the spigot was trimmed back to 2mm long

With the tailstock back in place the grove and chamfer around the top of teh barrel were machined

Cont'd

With the burrs removed the centre of the surface was located and then the two silencer mounting holes spotted, drilled and counterbored with a 1/4" FC-3 cutter. As they are quite deep holes I drilled half way from this side and then the rest from the silencer mounting face.

The barrel was then set to 45deg using the angle box and with a sharp cutter this time the chamfer machined to a premarked line just like the carb face was done, repeat for the other chamfer

Flip teh part over, machine back to finished width, complete drilling and then mill out the exhaust port. I went as far as I could with a standard length cutter and then changed to a long series one to complete the passage.

The final job was to drill and tap the four head fixing holes, just like the crankcase was done.

And to finish off tonight here are a few quick snapps of teh finished part, save for a bit of final cleaning up.

J

Edited By JasonB on 28/06/2012 20:50:37

Just before starting the next bit I should have said that the UNEF tap required for the glow plug can be obtained from Model Fixings who will also have the socket head screws needed for the engine if you don't have any to hand. Usual disclaimer.

Backplate

A 1" slice of 2 1/2" HE30 was mounted in the 4 jaw as that was on the lathe at the time and faced & turned to the 57mm dia.

The majority of the waste was roughed off and then the part left to cool.

Once cool there was no risk of the spigot contracting so it wa smachined to a push fit in the 28.2mm crankshaft, test the fit in the hole rather than measuring. Notice the fine whispy swarf, how said you can't take half a thou off with carbide tooling.

The spigot can then be faced back to the finished 15.5mm and the edge lightly chamfered.

The larger camfer on the backplate can now be done by swinging teh topslide over to 45deg

With the finished surface protected by paper the flange can be faced back to 5.7mm finished thickness.

Work up through the drill sizes as before to take out some of teh waste from the recess and to allow a decent thickness boring bar to enter.

Bore out to dia and depth and finish with a chamfer to all edges

Hold the work, locate centre and then spot the seven hole positions

Open out to M3 clearance and 4mm as required on the drawings and clean the edges with a CSk if you did not deep spotdrill.

While the holes are all aligned with the mill axis cut the shallow flat on the top of the spigot

Turn the backplate over and CSk tehe four holes, clean the other 3.

Cont'd

Thanks Glenn, they are indeed a nice set of drawings. The 3D pictures should be a great help to any beginners as its often hard to visualise a part in 2D and this is certainly the way forward. I must get myself a decent programme and sit down to learn it, I'm still a pencil & paper man myself.

J

Piston

A lump of 25mm CI bar was put in the lathe, faced off and turned 0.010" overdia and about twice the length needed.

The end was then drilled then followed by boring to finished depth and diameter

The turned length was then sawn off and transfered to the rotary table, centred and the end located.

The wrist pin hole was then done making sure not to break through and allowing for the dia being larger than finish size.

The table was rotated 180deg and the 1.0mm hole put in.

Without removing the work from the chuck the table was mounted horizontally and clocked true to the mill axis, this ensured that the conrod slot is exactly at right angles to the wrist pin hole. I drilled two holes on 5mm ctrs 3/16" then plunged with 5/16" and 7/16" slot drills to remove most of the waste.

It was then just a simple matter of milling to the 12mm finished size

With the milling complete the embrio piston can be parted off a little over length

A simple mandrel was made to hold the piston, the OD is a little less than piston finish size and the short spigot a good fit into the underside of the piston. The piston is place on the end, the pin slipped into the hole and then as the piston is turned the screw pulls it tight to the mandrel.

The piston can then be faced back to length

Then turned and honed until it just starts to enter the liner

I used the same mandrel to lap the piston to the liner but just turned the liner back and forth by hand Not under power. A tiny amount of 1000g is placed onto the piston and the liner slowly fitted to it adding plenty of oil, no more grit until a good fit is achieved.

And here we have the finished liner & piston

Edited By JasonB on 15/07/2012 13:57:55