The plastic (pretty sure it's nylon) worm gear in the clutch release of my '68 is pretty badly cracked in a couple of spots as can be seen from these photos:
I haven't been able to find any that are in any better shape, so I don't have much of a choice other than to try and patch this one up. Given that it's probably nylon, my choice of adhesive/fillers is limited. JB Weld looks good but doesn't adhere very well. I've been looking into a product called Surehold Plastic Surgery but I'm a little skeptical about the claims.
Does anyone have any experience doing this sort of fix, or perhaps knowledge of a substitute? I was looking at a NOS part from a K15 Hillbilly, but the width looks larger and it's impossible to tell the dimensions from photos.
I think the only thing that might work would be too use thin cyano that would 'wick' into those cracks.
'Zap' or 'Hotstuff' from model shops are good.
But the part would need to be super-cleaned first... (degreased, hot soapy wash, thoroughly dried).
Using thin cyano, then medium cyano with 'kicker' (accelerator spray) you could build up worn areas and sand them back smooth.
Slightly more off the wall idea.... 3D print the nylon worm part, and bond / pin it onto the old lever part. SLA printed nylon parts are getting pretty durable these days.
joolstacho wrote:Who's gonna write the gocode for this?
No one does that anymore..... any 3D CAD software should be able produce a STEP file which can be submitted into the 3D printer workflow, viola knock out as many parts as you desire
Never said it was an effortless solution, but gluing grease impregnated nylon isn't going to be easy either
I get the 3D print stage, but to initiate it I guess you'd need a 3D scanner to plot the form first? Or CAD to draw it? (Interesting problem to reproduce that spiral 'worm').
I'd model it in CAD, the worm is formed by sweeping a 2D sketch of the desired shape along a spiral path. See the you tube link for an example of modelling a triangular thread form. This would be a little more complicated in that I assume its a multi-start (triple?) spiral. But you'd create 3 planes 120 degrees apart and repeat the process using each plane as the starting reference. You might even be able to do it as a repeating circular pattern. Don't do much CAD work these days, but a 15 minute job for someone competent in the tool they use.
If you can supply dimensions, i'd model it up as I like to keep my hand in occasionally. AS you never know when you might need to call on those skills.
Edit... had a go, just need real dimensions to size it correctly and I can send you file for 3D printing if you want.
joolstacho wrote:I think the only thing that might work would be too use thin cyano that would 'wick' into those cracks.
'Zap' or 'Hotstuff' from model shops are good.
But the part would need to be super-cleaned first... (degreased, hot soapy wash, thoroughly dried).
Using thin cyano, then medium cyano with 'kicker' (accelerator spray) you could build up worn areas and sand them back smooth.
Super cleaning would be very important. I think you would want to go further than a hot soapy wash though. I'd try acetone or MEK if you can get it, or neat alcohol at the very least. Any residual grease will stop the glue sticking.
After all that degreasing though, I would try 2 pack epoxy. It is tougher than cyano, but thicker (more viscous) so you might have to press it into the cracks somehow.
Another thought is to try the polyester resin used to make fibreglass composites. Use the resin and hardner on their own though. I don't know how well it would stick to degreased nylon, not that badly I would have thought, and is tough too.
Agree about the thorough cleaning. You'd just need to to a test before use of acetone as it destroys some plastics.
Epoxy might work, but thin cyano would get right into the deep cracks better. I wouldn't go near polyester resin as its adhesive properties are much inferior to epoxy.
If you are going to try and fill the cracks with adhesive, don't forget to drill a small holes at both ends of each crack. The holes relieve the localised stress and stop the crack growing. Merely filling the crack won't relieve this stress
There's all sorts of glues about nowadays. I've been using some that the double glazers left behind.....they use it on the plastic window frames. The label says "Cyanoacrylate Adhesive - High Viscosity Superglue - SG50THICK"....it's wonderful stuff but I've ran out of things to mend.
No one does that anymore..... any 3D CAD software should be able produce a STEP file which can be submitted into the 3D printer workflow, viola knock out as many parts as you desire 
