We have but a mere 260 Roger, but no crunching
Krystyna & Michael Wooding - tug DRACO
Michael: NABO Webmaster http://www.nabo.org.uk
Michael: CIBC Webmaster http://www.cutweb.org.uk
The CUTPICS site: http://www.cutpics.org.uk
Krystyna: Draco Crafts - http://www.dracocrafts.co.uk
I would be looking for a mechanical explanation like the drive plate
(if it has one), worn bearings, partiall detatched clutch housings
On 5 Sep 2001 05:02:52 -0700, roger....@tinyworld.co.uk (Roger
Crunching gearchange seeps a bit improbable with the standard PRM
design (I don't know the 500).
What's quite common is rattling on tickover, particularly on marinised
vehicle engines where the flywheel isn't heavy enough to damp out the
The cure for that can be to fit a heavier flywheel, or some additional
weight (I've done that successfuly to a couple of 4LK's) ; to increase
the tickover speed (not usually what you want to do) ; or to use a
'softer' drive plate. R&D do some 'asymmetrical', for want of a better
word, drive plates which are supposed to help with this. A rubber or
Metalastik coupling in the prop shaft might also help.
'Proper' marine Gardners had massive flywheels compared with the
vehicle versions, partly to aid hand starting but also to help avoid
Traditional & Modern canal craft repairs
Following up on both Tim and Tony's postings. The salient facts are:-
1. It's all brand new, and the noise has been there from new.
Therefore there is nothing *worn*.
2. There is no bell-housing, the box is mounted on a separate plate to
allow access to the flywheel for generator belt drive, so no *clutch
3. There is the most flexible drive plate in the system that R&D do.
4. There is a metalastik coupling immediately after the output flange.
5. It has had a modified valve block fitted that was designed to stop
6. There is no rattling at low speed whatsoever. My only complaint is
the crunch when engaging gear.
However, knowing how the trolling valve works on this box, I came up
with an idea, which by total coincidence was also suggested by the guy
at Lancing Marine (totally without my prompting) so I am going to have
a go. Will tell you whether it works when I've had a chance to try it.
> 6. There is no rattling at low speed whatsoever. My only complaint is
> the crunch when engaging gear.
......just a thought after Tony's usual excellent advice......
Are you 100% sure that the gearbox is def not even a teeny weeny bit loose
on the housing?
One of the *Un* fleet suffered a similar fault and you could barely feel the
movement between the gearbox and housing.
Neil Arlidge, nb Earnest - Commode D'Or © TNC on Tour.
Follow the travels of Neil and the TNC in hire-boats, Beatty and Earnest at
See nb Earnest being built at http://www.nbearnest.co.uk
See the newsgroups photo call at
>2. There is no bell-housing, the box is mounted on a separate plate to
>allow access to the flywheel for generator belt drive, so no *clutch
I was actually refering to the clutch housings on the counter shafts
in the gearbox, not the engine bell housing or what have you. TMP
boxes were renown for problems in this area (but not PRMs)
>However, knowing how the trolling valve works on this box, I came up
>with an idea, which by total coincidence was also suggested by the guy
>at Lancing Marine (totally without my prompting) so I am going to have
>a go. Will tell you whether it works when I've had a chance to try it.
Please do - this is the way we all learn
Ah no, the gearbox is OK, it's the owner that has a loose screw ;-) In
fact, I even think he is pulling his hair out at the moment (what
little he has left) with some of the "other" problems he's
If that were the case then I would have thought that I would have seen
some signs of fretting where the box is mounted to its support plate.
This is not the case and the paint is uncracked.
No the clutches are not adjustable. They are hydraulically operated
multi-plate clutches that cause the drive to be transmitted from
whichever gear has been selected by the spool valve operation.
No matter how long you wait in neutral the crunch occurs on selecting
gear. Basically I am asking the gears to accelerate an 11 foot prop
shaft coupled to a 22 inch prop from rest to nearly 300 rpm in zero
seconds (approx 400 rpm tickover, 1.5:1 ratio box due to fine pitch 22
x 16 prop, reduces prop walk in reverse), so that's why the gears
protest a little. See my other post though because my modification is
looking very promising indeed, just needs a bit of further refinement.
Me thinks we might be getting back to some type of restriction to the
oil flow, so the clutches engage more slowley. Being wet clutches
there should not be too much of a wear problem due to slip.
>On my new boat with Gardner engine and PRM 500 hydraulic box the
>gearbox makes a rather unpleasant crash/crunch noise as the the box
>goes into forward or reverse..
I caught this thread late due to being away. My boat with a Gardner
4LK and a big PRM also crashes into forward, especially if I'm too
sharp with the Morse. I have tried all sorts of things over three
years with only partial success - the most effective being experiments
with differing the length of the control cable. So if there's a
secret fix, I'd be very glad to know it.