Author Topic: JP3 and PRM500  (Read 207 times)

Papster

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JP3 and PRM500
« on: October 17, 2022, 03:40:45 PM »
I have a PRM500 gearbox attached to my JP3 in a narrowboat. No problems except that I have not found the sweet spot where the gearbox will go into gear without crunching. I have dropped the revs as low as I dare but even at its best, there is still some crunch, especially for reverse.  I have no tachometer so don’t really know how slow I can get it but I do find there is a spot where it just brings the revs back up a little so slowing it down further risks a stall which is not desirable as I am generally using forward/reverse when approaching immovable objects!

I am interested to hear your opinions.  Hopefully I have just missed something obvious or perhaps crunching goes with the territory!

Cheers

Steve

dieselspanner

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Re: JP3 and PRM500
« Reply #1 on: October 17, 2022, 07:01:34 PM »
Hi Steve

I think your first move should be to contact PRM / Newage for some advice, a 'modern diesel motor will tick over between 500 and 1000 rpm, the 'box should be able to handle that, I've no experience with the PRM 500, but it sounds like the clutch plates are not separating fully, when in neutral.

https://www.prm-newage.com/help-centre-marine

As for the lack of a tacho, less than a tenner on eBay for a cycle computer and then doing this....

https://www.instructables.com/Tachometer-made-from-a-bicycle-speedometer-cycloc/

will let you know exactly what's going on with the revs!

Cheers
Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

Papster

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Re: JP3 and PRM500
« Reply #2 on: October 17, 2022, 09:12:35 PM »
Thanks Steve.

That cycle speedo idea is brilliant.  I will certainly give it a try.  I do have the specs for the PRM and I recently had work done on it so I am confident it is ok.  Trying to match the RPM as a first solution seems to be the best bet. I will order a computer soonest and let you know.


Papster

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Re: JP3 and PRM500
« Reply #3 on: November 01, 2022, 03:10:58 PM »
I fitted the cycle computer today and it worked like a charm (assuming its telling the truth!).  Seems that I am low idling around 275-300rpm, cruising between 375 to 500+.

Also, I have corrected my description from Crunch to Clunk as crunch was a bit misleading. I have found that PRMs do have a reputation for being ‘clunky’ in certain circumstances and I am currently looking into installing a soft-shift valve which purportedly often cures the problem. Expensive though at £4-500.  Beta Marine also offer an accumulator that does the same job - I am currently waiting on a response from them.