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IanR

PRM Gearbox identification.

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Hi folks, our boat has a PRM gearbox and that is about alls we knew about it. Reading the data plate on it and rooting about on tintyweb, it seems that the box is a 302D 1.5

Is this 1.5 perhaps the gearing as I can find reference to ratios of 1 to 1.5, 2, 2.5 and 3. On this plate, as well as the factory embossed details, there is an aftermarket X and an H stamped on the plate. Any ideas what they might signify?

Also, with regard to this box, when we bought the boat, when we were out on a test drive, the seller mentioned that the gearbox was bulletproof and didn't need the revs winding back to tickover before engaging gear, or infact he said going from forwards to backwards either. This seems like an unbelievably harsh way to treat the drive train, are they really that 'bulletproof' !!??? It has to be said we have never subjected it to that treatment and doubt we ever will as it just seems wrong, but is it?

Ian.

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That is how PRM usually describe the gearboxes so 1.5 as a ratio sounds right

What engine, Ian?

I know one of the canal contractors replaces Blackstone gearboxes with PRMs because they can't guarantee the users will drop revs. For them the PRM is suitably bomb proof

Richard

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The engine is a Ruston Hornsby 4VSH, quite a lump. It has way too much power for boating but is great for stopping etc. It was suggested that a change to a smaller prop could be a simple way of using more revs to stop it coking up but perhaps a change in gearing might be an option if the different ratio boxes are interchangeable dimensionally. That said however, we've gotten used to the boat in its current configuration so don't plan on altering it, I was just working aound the gearbox today and realised I didn't have a manual so took the plate details to do a search. Constantly learning!

Ian.

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You'll probably find your engines top speed is something near the idling speed of our BMC 1.8. So, we can only change gear at speeds which you would consider to be too fast with your VSH. The gearbox doesn't mind

Richard

 

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