custom O rings

[petertha]

This engine design I'm sourcing up calls for some somewhat hard to find metric O-ring sizes. Not so much the section diameters (1mm & 1.5mm) but nominal loop diameters in the 40-60 mm range which don't match common catalog diameters. Basically these act as seals sitting in machined grooves from aluminum nose plate to aluminum crankcase & related components. So not high pressure at all, I guess just a liquid seal (methanol/oil environment).

I was wondering if just buying a few yards of Buna or Viton O ring 'cord' wouldn't be a better way to go & make my own to fit. I have no experience bonding the ends, but kind of looks a lot like CA glue or the semi-flexible,toughened black version. Anyone have any experience with this? Seems like maybe a better way to go?

http://www.theoringstore.com/index....17_119&zenid=8c8f2577419c9a08c40a9dd10f9e594a

 

[Jasonb]

Whats teh exact sizes you need, The bearing supplier I normally use has 1.5mm vitron in almost every 1mm step from 40 to 60mm?

http://simplybearings.co.uk/shop/Products-O-Ring+Seals/c4747_4515/index.html

 

[petertha]

thanks for link Jasonb, here is the shopping list (all mm)

1 x 28 (common, found it)
1 x 58
1 x 59 (think he means 58 within 59 double seal because I see 2mm width groove)
1.5 x 45
1.5 x 64

I'm actually a bit leary by all this, but maybe due to past experience messing with O-rings on some exhaust couplings many moons ago. I remember chasing my tail. Seemed like despite handbook type groove width/depth specs, different combinations of rubber materials, tolerances, durometers, stretch or squish... all made for different degrees of acceptable fits. There will be a fair amount of machining in these parts (at my level), so maybe idealistically thinking machine it only once & conform the ring to suit by splice & glue.

Maybe a smarter approach is just buy some spares if in correct nominal diameters & machine some dummy blanks with groves to validate beforehand.

 

[Jasonb]

If they are 1mm section I cant see a 59mm fitting into a 58mm as the ID of the larger would be 57mm.

That link I posted has the two 1.5mm section rings

For the 1mm you may well be better off with the cord

 

[Scott_M]

Making o rings works very well. Cut on a bias and use a CA.
Here is a link to cord stock and glue http://www.theoringstore.com/index.php?main_page=index&cPath=117

Scott