sbillis

Slipping shaft coupling? Check for metel fragments where the prop shaft joins the gearbox, or if you have a python drive of similar where the prop shaft connects to the python drive. Good luck Simon

Thanks to all and yes Brian it is this one. I have to say the replacement as shown is the cheapest I have seen but still an extortionate price. The unit is sealed and does not appear it can be cleaned or maintained without destroying it; unless anyone knows of a fix. Very many thanks Simon

I have a traveller toilet in my boat which has an anti siphon valve at the rear. Water has started to leak from the top of the valve (not the seal to the pan) when the toilet is flushed. I suspect that old age has the better of it but does anyone know of a simple fix or repair to cure the leak which will save me spending sixty quid on a piece of ABS plastic which probably cost pennies to make. Vary many thanks Simon

Let us know how you get on. Simon nb Bulrush

Thanks Tony. What I am proposing is to increase the flywheel mass by approx. 25% of the weight of the outer 50mm of the flywheel. At present I have increased this by around 10% and it has made a significant difference and the engine no longer sounds like a clapped out taxi when it is idling. I still get a clatter at around 1000 to 1500 rpm and I am sure the increase in mass will, as before, reduce the clatter. I understand that Beta fit additional mass to their flywheels "as standard". This allows the engine manufacturer to supply automotive weight flywheels and the extra mass is added at marinisation. I appreciate all this adds additional load on to the crankshaft and bearings but the Perkins M30 (100 series) was developed to power small tractors etc. and so should be capable of carrying the mass of a clutch mechanisms as well as a flywheel. I understand that BMC 1500 engines are sometimes fitted with additional mass on the flywheel. The problems I have are common to a lot of three cylinder engines fitted with mechanical boxes. An engine and set up similar to mine is on the you tube video. Taxi anyone! This is not my boat although the set up is similar; M30 engine and PRM 120 box. https://www.youtube.com/watch?v=9RKc1FcFX7Q Simon nb Bulrush

As I understand it there are several causes of torsional vibration on small marine engines. 1) Low mass of the flywheel 2) Misfiring of the engine 3) Engine mounts not fully supporting the engine. I have sorted the last too as best as I can. This just leaves the first which is to increase the mass of the flywheel. I can also fit a high deflection drive plate but in order to accommodate this I will need to fit a hydraulic gearbox and not a mechanical one hence the PRM 150. With cruising nearly over for the year I hope to start this project soon. Simon nb Bulrush Richard, thanks for your kind words. Just to let you know there area no longer any oil leaks and the engine performed superbly on our trip from Cropredy to Pyrford and back. A great job. Simon

I have a Perkins 3 cylinder M30 engine driving a PRM 120 box and yes it rattles. So much so that in neutral it makes a sound that can best be described as hammering. The problem is the low mass of the flywheel on a 3 cylinder engine. This causes the flywheel to constantly speed up and slow down through the firing cycles and vibrate through through the gearbox. I used to have a Hurth but that rattled. After that box expired I fitted the 120 with a stiff plate and that rattled. I tried a soft plate and that made all sorts of nasty noises when going into gear, hence my calls to PRM and Lancing Marine. I had a inertia plate made up by a local engineer with the aim of increasing the mass of the flywheel. I fitted a medium R and D plate. This has made a big difference and now the rattles and knocking are limited to a narrow rev range. I am currently looking to fit a PRM 150 box and with that a soft plate. I will also increase further the mass of the flywheel by fitting a larger inertia plate. I am mindful that the increase in flywheels mass my put extra strain n the flywheel but as the engine was primarily fitted to machinery and vehicles the flywheel should be able to carry the mass equivalent to a clutch and a bit more The engine though is superb. Always stars first time. SImon nb Bulrush

I was told by both R and D and Lancing Marine that the stiff plate was required. Simon NB Bulrush

I am not sure that PRM recommend a high deflection drive plate with a mechanical box. Simon nb Bulrush

A friend of mine had big problems with significant pitting. He claimed it was his radio which returned through the hull. He caught it just in time and had the hull grit blasted epoxy. Learning his lesson I turn off the power to my radio when I am off the boat just in case. Simon nb Bulrush

I keep a can of cheap hairspray at the back of the boat. As soon as the horseflies are around I give them a quick spray and because the spray is sticky they just fall to the floor. It may not avert the first bite but at least you can get your own back. Simon

The length and drop are not a problem. It is simply that some of the securing bolts will be obscured by the larger gearbox and therefore cannot be fitted. Simon

At present I have a PRM 120 gearbox fitted to my Perkins M30 engine. The gearbox is some twelve years old and may be on its way out. I have started looking at a replacements. I would like to fit a PRM 150 gearbox rather than a mechanical 120 gearbox. The oil cooler is not a problem, however from the drawings I have looked at for the new 150, mounting to the engine may be difficult. The present adaptor plate fitted to the bell housing of the engine is an SAE5. The new 150 gearbox which is larger then the 120 gearbox would appear to cover some of the bolt holes in the adaptor plate which carry the bolts which fit the adaptor plate to the bell housing, particularly the bolt to the right side ( viewed towards the rear of the engine) and the bolts at the bottom of the adaptor plate. Before I go ahead and order a 150 box I need to know how (if at all) this problem can be overcome. If anyone has had any experience of this any help and guidance would be greatly appreciated. Simon

Many thanks to all who responded. I will try the gear selector and then check out the oil levels when I am next at the boat. Simon

I have a PRM 120 mechanical gearbox in my boat. Since it was fitted some twelve years ago when engaging either forward or reverse it has always gone "clunk". Just recently and once warmed up it has failed to go cluck when engaging forward although it still goes in to gear and does not appear to slip. It still goes "clunk" when engaging reverse. If anyone is familiar with these gearboxes can they please advise me if to go silent when engaging gear is a sign of impending failure ? Very many thanks. Simon