Pierburg 2E3 choke

[kevtherev]

Here you go
I have this as a spare.
I can post it.

[CJH]

Hmmm - looks like there's more than one design.

[itchyfeet]

There are three 2e3 carbs fitted to the t25
kevs pic is the early carb with a red/brown tube visible
later carbs this tube us black

[kevtherev]

I can get this laser scanned and cast in aluminium at work.
Are they all compatable?

Is the original poster still interested

[itchyfeet]

I can get this laser scanned and cast in aluminium at work.
Are they all compatable?

Is the original poster still interested

my guess is there are two, early and late.
Dunno if they are compatible.
Happy to strip my late carb also to have both made.
even if op no longer needs it sooner or later these will be needed by the worlds wbx lovers.

Probably loads of broken choke flaps out there now because they just are not available.

[kevtherev]

Right, if the op does not want it I'll dig it out and get it scanned.

[itchyfeet]

Can either of you see what that pointy bit on the side does?

I suspect those are both from early 82-85 suffix A carbs which have the red/brown tube on top but please can you check and note what carb?

my pic is from a suffix H carb 85-on there is also a suffix J carb listed for the same 85-on period but not seen one, spec is identical.

I have a spare suffix H carb

[CJH]

The part I photographed is from a suffix H carb, ('7 109' which I think means 9th July 1987), and it has a black top tube. That's my 'donor' carb. I also have a complete 'spare' carb, which is also an H suffix (30th Jan 1986) and has a black top tube. It has the same choke piece, but it's black.

The pointy bit just seems to be an end stop. When the choke flap is vertical, the chamfered edge of the pointy bit rests against the side of the casting. If you look at Kev's photo of the underside of the top plate, to open the choke the rod pulls the lobe with the hole downwards (towards the camera), and the pointy lobe will rotate right until its right hand face touches the right side of the casting.

I can see that the one in Itchy's photo could well do just the same, but I can't see why it has the additional chamfer. If it is also just an end stop, I think they'd be interchangeable, and the shape could be simplified somewhat.

[itchyfeet]

my pointy bits longer than your pointy bit, wonder why if both from a suffix H carb, unless of course one is not origional.

[CJH]

I spoke to my friend at work who has access to the 3D printer, and he says I can have a go. They've got a few different materials, but he wasn't sure what they were. He also said the output can be a bit rough, even on the smoothest setting, and that some finishing might be required. So it may not make a particularly good part, but since it can take an Autocad DWG file as input I thought I'd have a go anyway.

I've drawn up the bit of the model that seems common to both varieties - I'll add the pointy bit later and perhaps print a few of them next week. I simplified the wedge shape between the two ends.

[CJH]

Here it is with the pointy bit added. I figure that even if my 3D printing efforts aren't usable, the Autocad file might be useful to someone with better facilities.

[kevtherev]

Most excellent CJ!

[CJH]

I had an opportunity to print a couple of these choke parts, just to see if the CAD model was ok. The printer was loaded with a material called PLA (poly lactic acid), which is biodegradable and has a low melting point, so not exactly ideal for an engine part! We tried the printer on two settings - one gives a 'quick' print, in about 15 minutes, and the other is the highest quality and takes about an hour.

With hindsight I didn't pay enough attention to the orientation of the part, as the software automatically builds a support structure underneath any overhanging parts, and this is not easy to remove cleanly. Here's the underside.



Here's a comparison with the original part. I need to double check the spindle dimensions, but as a proof of concept it seems to work ok. My plan now is to get a quote for a small run from the folks in our 'additive manufacturing' labs. They have MUCH better equipment and can print in a whole lot of materials - even metal. I'm hoping the price won't be too high, as the CAD model shouldn't need any input from them, and the material quantities are very small.

[CJH]

I spoke to our additive manufacturing people. They're going to do a couple of samples for me using their SLS system (selective laser sintering). No support structure is needed, since the piece is built up surrounded by powder - each layer is formed by fusing (sintering) the powder particles on the top layer of a bed of powder. They recommended nylon 12, but didn't suggest glass reinforced nylon since the main purpose of the glass beads seems to be to make the piece stiffer, which doesn't seem to be a priority for this lightly loaded choke lever.

I was encouraged when they criticised the coarseness of the lithography file I'd sent them! The default settings in Autocad were finer than needed for the process that produced the blue pieces above, but evidently the SLS system is a much finer process, and the coarse triangulation of the curved surfaces would have shown. I found the smoothness settings in Autocad and then set them to maximum smoothness.

I'll see how well they come out (how closely the spigot holes match the drawing, how stiff the piece is etc) and then I'll talk costs with them for a run of about 25.

[kevtherev]

Awesome stuff CJ!