I use an Oberon. Funnily enough I was studying pictures of the slaves only yesterday with a view to converting one for another project.
I noticed what they describe as "anti-rotation" grooves in the engine side of the unit.
There's no way that these grooves will stop rotation in our Monsters, with a standard pushrod.
But if the pushrod had a small pin through at 90deg, that engaged in the grooves then it would work.
I changed my thrust bearing as I worried that the pushrod was spinning the slave piston every time it touched it, thus chewing out the seals prematurely, but the pushrod was still just as tight a fit in the bearing as before.
This relies on there being more resistance in the pushrod's tube, than in the bearing, to prevent, or reduce rotation.
Thinking of trying a pin.. (Could be tricky?)
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