Fuel Resistant Filament

I have been asked whether I could print a float to fit in a Solex downdraught carburetor. Other than the issue of whether I can draw it in CAD, which remains to be seen, is there a filament available which would be fuel resistant. Would it even be feasible to produce a completely airtight/fueltight float, that would float.

Thanks,

Colin

Nylon 66 is probably going to be OK, careful design to facilitate a quality print would ensure it is airtight.

Nylon needs high temperature and some fine tuning, not all off the shelf printers will do nylon but most 'reprap' derived ones will. The filament must be quite dry to ensure good results.

A traditional option is carve from balsa and fuelproof.

Neil

Just a thought, there are carburettor repair kits listed on the internet and for old engines, vehicles or marine applications.

Robert Butler

3D prints are not normally liquid tight though you can paint them, maybe. Might be better to work around a cage to hold a floating thing, like a ping pong ball or fishing float.

The float in my Indian is of rhoacell type material and has been in rhe carb for 8 years now. It was 3d machined and cost me the princely sum of about £30, absolute bargain!!

I have seen a couple of pictures of the float but will hopefully get a look at the car very soon. Carving of balsa or rohacell sounds a possibility.

Colin

Another brand of foam used in car carburetor floats is Nitrophyl. GM used millions of them in the 4 barrel carbs on their mainline 305 V-8's in the late 1970's early 1980's. Never saw one sink, and I remember carving them up to use in small engines and motorbikes where the original brass floats had holes or got bashed. They used to be very inexpensive since they made so many, maybe you can find old stock somewhere.

What about making a soldered brass one like many old carbs used to have?

Potentially a very interesting topic for me and a way of making floats for very obsolete carburetters. However I live in Australia and have not come across the terms rohacell or nitrophyl before. Can anyone tell me what sort of material these are?

I believe that Indian motorcycles always (?) used a float made from cork or balsa wood, covered in some sort of petrol proof lacquer - does anyone know what this lacquer was?

My knowledge and interest of motorcycles only goes to 1939 (with a special interest in New Imperials) but I thought that Amal monoblocs had nylon floats??

Chas

Here's a link to info on Nitrophyl foam.:

https://www.rogerscorp.com/Elastomer%20Components/NITROPHYL

and one for rohacell:

https://www.emkayplastics.co.uk/rohacell/

Edited By Jeff Dayman on 25/02/2021 08:46:42

Colin, further to your original question I have been using polypropylene filament lately as I needed a polymer that can be continually immersed in water but also floats.

It extrudes well if not the best surface finish (you will need a heated bed though).

They do make petrol tanks, I believe, out of polypropylene so it should be fine for a float in a carburettor and not degrade.

I hope this helps

Steve

Certainly have a few ideas now.

The float is (I understand) 2 1/8" diameter, 1 5/8" tall, and with a 1/2" bore through the middle (for the bolt holding the float bowl in place). It has a concave base and a convex top.

Not sure my CAD ability will let me draw this up. I have Alibre Atom.

Colin

I'd suggest starting the CAD work with a revolved protrusion. You sketch a centreline then draw half the cross section. The convex and concave ends should be drawn on this sketch for least complication later. However, if the carb bowl shape allows it I would suggest making the concave end flat, as that will be a far better shape for the eventual 3D print, to be placed on the bed of the printer.

One thought about printing a float in polypropylene - if you print a closed volume solid shape the print will need to have an internal support honeycomb structure (called infill, in the slicer program) to allow printing the top end plate / dish of the float. This would need to be as minimal fill as possible, biggest possible spaces between honeycomb walls to be sure the float would still float.

Second thought about printing a PP float - if the honeycomb structure proved to be too heavy after a float test, you might consider making a two piece float, like a cup and lid, or two shorter cup shaped pieces joined in the middle like traditional drawn brass float parts. The issues with this are the joint will need sealing and must have reliable fastening. a snap fit could be designed in and would give good fastening but would likely not seal well. Glue or sealant could be used but it would need to be gasoline / petrol proof and also virtually no glue will provide a strong permanent bond with PP or PE or nylon parts, as the surface energy is just too low. (now waiting for the armchair experts to say "this glue will sort of work on PP" or "do corona treatment / laser etch before gluing" or other magic solutions - these do not work, in my experience having been tasked with joining PP and PE parts in industry many times. If there was a solution for gluing PP and PE strongly, industry would be using it, believe me.) A rubber o-ring could possibly be designed into the groove of a snap joint but the ring would add weight and the extra plastic of the joint itself would add weight. Heat staking or ultrasonic assembly might work to join and seal the PP parts but it requires special equipment and may not work with 3D printed parts. The layer to layer bond in 3D prints may not stand up to the force of heat staking or the vibration/force of ultrasonic welding These processes do work very well with injection moulded PP or PE or nylon parts though, if the shape of the joint is designed carefully.

All the above considered, I suggest carving the float out of Nitrophyl foam or similar, or making it out of brass shim stock formed and soldered in the traditional way may be better solutions in the home shop to make a float.

If doing one in brass shim stock, 3D printing could be used to make really nice form tools to stamp convex / concave ends. Absolute minimum of solder is needed for the brass float assembly naturally, to keep weight to a minimum.

Just food for thought. Hope the ideas help.

Edited By Jeff Dayman on 25/02/2021 14:51:00