Thanks for the amazing picture Bill!   I'm as guilty as anyone when it comes to trying to "improve" the design, but sometimes we need an example like this to remind us that Mazda has spent way more time and money getting this right, than all of us combined could ever imagine.   

 

Cheers,

Rusty (going to be hard to run a stock single rotor Mazda though)

Just for reference guys,

 Most fluid o-ring seals fill between 75-85% of the groove WHEN COMPRESSED. That means that the o-ring will be above the groove about 25-30% before assembly. The diameter of the o-ring will USUALLY leave about 30-40% of the width of the groove visible. To my eye this has always looked like too much free space, but like many other engineering items has been established by breaking parts like in the picture. If you live in the USA you can get a phamplet circular from Parker which shows the gland (the o-ring groove) sizes for most standard size o-rings. usually available for free. They have a larger catalog that shows how to calculate the o-ring and groove sizes. This is avalable even from the cheapest sales shops for a few bucks. Highly recomended if you plant to size o-rings. There are signifigant differences between TYPES of groove seals as well; the rotor housings are a static face gland. Parts that move or rotate have different sized grooves and more importantly different surfaces finishes. (roughness or the lack of it!)

 

Bill Jepson

 

Bill,

You stole my thunder, I went out yesterday and bought this machining guide to cutting "O" ring grooves, then set down and worked through some of the dimensions suggested - they came out roughly, that the "O" rings have to be between 70 to 80 % of the groove - very similar to your recommendation above and I, by no means, worked through all the 'Static Application' sizes.

 

Interestingly our cross section range ( .93 to .98) is approximately 80% (or 1: .8).

I know you have provided this info before but often we don't use information provided, until we need it and quite obviously we need it now.

I think someone in the past suggested that silicone can swell up to 20% of it's original size - so that fits well into our calculations.

 

Given my previous numbers that suggests sizes .093 for the inner or even a little less and no more that .1 for the outer  - now given the cross section of the "O" ring varies (+ or _ .05), I think .98 would be the most appropriate size to use.

 

The only other problem is diameter of the "O" ring and Kelly has kindly volunteered to supply a housing to Creavy for physical assessment -Thanks Kelly!!

 

I did suggest to Jeff that more builders were likely to use these "O" rings if they knew exactly what size to use.

 

I'm actually using Cosmo Rotor housings with the grooves in the Rotor Housings for the single rotor, as I'm using 12A endhousings - in the event anyone was confused with my photo.

George ( down under)