PRM 150 oddity

[PCSB]

I'm getting an odd clicking sound when in forward gear and at low / tickover revs from my PRM 150 gearbox. The engine is a canaline 42 fwiw. It does not do this in reverse, i.e. no clicking. At higher engine revs it goes away. Tick over is 850 rpm and it does it up to approx 950/1000 rpm when it goes away. It sounds a bit like the old CV joint on a mini when it is failing. It doesn't happen in neutral irrespective of revs.

 

Oil has been changed at every service interval (50, 250 & 500 hours so far) and currently have 620 hours on the engine. Using 15W 40 mineral oil API CC and it is up to the top mark on the dipstick. The only adjustment I have made in that area was to the morse cable, the nut on the end that locks the socket was loose so I tightened that back, by tightened I mean nipped it up only.

 

The only "event" I can remember is a few weeks back just before Autherly junction on the Shroppie we went over something metal and fairly solid which made a helluva racket. I did check down the weed hatch shortly after and in the engine bay too, but no obvious signs of damage.

 

Other than the odd clicking sound the gearbox works smoothly and goes into and out of gear with ease. At this point I'm not unduly worried but curious if this is normal or fairly normal.

 

Thoughts and suggestions welcome.

TIA

Paul.

[enigmatic]

Is it definitely the gearbox and not the drive plate creating the chatter?

[Tonka]

3 minutes ago, enigmatic said:

Is it definitely the gearbox and not the drive plate creating the chatter?

Wouldn't the drive plate make the same sound when the gearbox was in reverse

[Tony Brooks]

What flexible coupling do you have? Some use a single or a pair of CV joints.

 

Have you used a "listening stick" to try to locate the area of the sound? A large screwdriver, mooring stake, or length of wood between your ear and static parts of the gearbox and flywheel housing.

 

Have you checked the engine mounts and mount bolts/nuts for condition and tightness?

 

3 minutes ago, Tonka said:

Wouldn't the drive plate make the same sound when the gearbox was in reverse

 

I suppose that the thrust on the back gearbox bearing is opposite in reverse and rev for rev be less strong than in ahead, but I agree that it probably would. Anyway, drive plates are often most noisy in neutral.

[magnetman]

edit to remove confusing information. 

 

Also any coupling bolts as they can loosen too. 

I had a boat once with a little Lister engine (quiet one a LPW2) and the engine mounts were bottoming out onto the bearers. That only caused noise in forward gear at certain speeds. 

 

 

Edited July 4, 2023 by magnetman

[Tracy D'arth]

Does the power unit move forwards slightly when in gear and backwards when in reverse? In other words is there no plumbers block bearing on the shaft?

[Eeyore]

30 minutes ago, magnetman said:

Engine mount top nuts is a good thing to check as Tony says. 

Don't think Tony mentioned "top nuts". You would normally check that the lower nut is tightened up against the engine leg.

[Tony Brooks]

29 minutes ago, Eeyore said:

Don't think Tony mentioned "top nuts". You would normally check that the lower nut is tightened up against the engine leg.

 

Yes, and in this case I would be more suspicious of the fixings holding the mounts to the beds.

[PCSB]

3 hours ago, enigmatic said:

Is it definitely the gearbox and not the drive plate creating the chatter?

Not 100% sure but will use a listening stick in the morning as per Tony's advice to confirm.

 

3 hours ago, Tony Brooks said:

What flexible coupling do you have? Some use a single or a pair of CV joints.

 

Have you used a "listening stick" to try to locate the area of the sound? A large screwdriver, mooring stake, or length of wood between your ear and static parts of the gearbox and flywheel housing.

 

Have you checked the engine mounts and mount bolts/nuts for condition and tightness?

 

 

I suppose that the thrust on the back gearbox bearing is opposite in reverse and rev for rev be less strong than in ahead, but I agree that it probably would. Anyway, drive plates are often most noisy in neutral.

Not sure what coupling type is called, when I do the listening tomorrow I'll grab a photo too. I checked the engine mounts to bearers tightness a short while ago, some were not as tight as I'd like so they have been tightened, I will double check them and also the lower nut to mount leg is tight.

3 hours ago, Tracy D'arth said:

Does the power unit move forwards slightly when in gear and backwards when in reverse? In other words is there no plumbers block bearing on the shaft?

If by power unit you mean engine, then I haven't noticed it do so but will double check tomorrow.

2 hours ago, Eeyore said:

Don't think Tony mentioned "top nuts". You would normally check that the lower nut is tightened up against the engine leg.

I'll check that tomorrow.

2 hours ago, Tony Brooks said:

 

Yes, and in this case I would be more suspicious of the fixings holding the mounts to the beds.

I recently tightened these but will double check tomorrow.

 

Thanks all for the advice, much appreciated.

[Tony Brooks]

Don't move the top nuts, tighten the bottom ones up against the underside of the engine foot, otherwise there is a good chance that you will de-align the engine to shaft.

[PCSB]

15 minutes ago, Tony Brooks said:

Don't move the top nuts, tighten the bottom ones up against the underside of the engine foot, otherwise there is a good chance that you will de-align the engine to shaft.

That is my intention, i.e. tighten the bottom ones up to the top if needed. Thanks Tony.

[PCSB]

I've checked the engine mounts best I can. I need to get a bigger spanner to properly check the engine leg nut but using the largest adjustable I had they were tight. I did find a couple of engine mount to engine bearer bolts had worked loose, I have tightened these, again I could do with another 17mm spanner or get sockets back from my daughters.

 

The good news is that I cannot hear the clicking sound with the engine boards up and in fwd gear, the bad is I think I can hear it with the boards down. I am somewhat deaf though to some frequencies, too many rock concerts etc ... I will know more when we set off today.

 

I cannot see any significant movement in the engine when I engage gear either, it rocks a tiny bit but that is what I would have expected to see.

 

I no longer bend as well as I did either!

 

I have, hopefully, attached a photo showing the coupling too. I have checked the alignment best I can using feeler guages, there is a variance of approx 6 thou which I believe is well within tolerances (believe it to be 25 thou).

 

Hopefully it is sorted but will confirm later. In eitehr case many thanks again to all, especially Tony.

 

[Tony Brooks]

PRM gives the maximum coupling misalignment as 0.05mm which is a tad under 0.002". The 0.025" is for the flywheel truth.

 

That coupling does not use a V joint and in my view calling it flexible is pushing the description, there are others that are more flexible (I know it is a very popular coupling).

 

Could the noise be caused by a deck board vibrating at a certain frequency band. try putting an old blanket across the opening and putting the boards down on top of it. If the noise goes away, it probably is board vibration.

[PCSB]

2 hours ago, Tony Brooks said:

PRM gives the maximum coupling misalignment as 0.05mm which is a tad under 0.002". The 0.025" is for the flywheel truth.

 

That coupling does not use a V joint and in my view calling it flexible is pushing the description, there are others that are more flexible (I know it is a very popular coupling).

 

Could the noise be caused by a deck board vibrating at a certain frequency band. try putting an old blanket across the opening and putting the boards down on top of it. If the noise goes away, it probably is board vibration.

I am beginning to think it is more of a rattle too, sounds metallic and hardly noticed anything when we cruised today. Appreciate the help, thanks. 

[ditchcrawler]

I had the bottom plate of the weed hatch cover that resonated against the weed hatch tunnel at a certain rev range. Took me some time to find it.

[Mike55]

Are you sure it's not something around the prop shaft? I once had a tick-tick noise in forwards that turned out to be the remains of a pair of in-ear phones. It was the 3.5mm plug hitting the underside of the boat that  caused the noise.  Being very small  they took ages to find. 

[Jen-in-Wellies]

7 hours ago, Mike55 said:

Are you sure it's not something around the prop shaft? I once had a tick-tick noise in forwards that turned out to be the remains of a pair of in-ear phones. It was the 3.5mm plug hitting the underside of the boat that  caused the noise.  Being very small  they took ages to find. 

Had a similar thing. With the prop stopped, the object hung down towards the canal bed, so was very hard to see through the weed hatch.

[Tony Brooks]

8 hours ago, Mike55 said:

Are you sure it's not something around the prop shaft? I once had a tick-tick noise in forwards that turned out to be the remains of a pair of in-ear phones. It was the 3.5mm plug hitting the underside of the boat that  caused the noise.  Being very small  they took ages to find. 

 

Me as well, as soon as you stop, the plug drops and hides under the shaft.

[blackrose]

Due to the nature of sound which is a spherical pressure wave with a spectrum of frequencies and amplitudes, absorbed by some materials and reflected by others, it can be very difficult to precisely locate the source. When you add in vibration which transfers between materials and objects it makes things even more confusing. The listening stick was a good idea and a basic stethoscope might work, but I'm wondering what made the OP so sure it was their gearbox making the clicking sound in the first place? It seems more likely to be rattling deck boards to me 

Edited July 9, 2023 by blackrose

[Tony Brooks]

2 minutes ago, blackrose said:

Due to the nature of sound which is a spherical pressure wave with a spectrum of frequencies and amplitudes, absorbed by some materials and reflected by others, it can be very difficult to precisely locate the source. When you add in vibration which transfers between materials and objects it makes things even more confusing. The listening stock was a good idea and a basic stethoscope might work, but I'm wondering what made the OP so sure it was their gearbox making the clicking sound in the first place?

 

I strongly suspect it may well be diagnosis by someone with less experience. It only clicks in ahead and at lower revs - hence it has to be a gearbox fault, and that might be a correct diagnosis. But a bit of experience tells some of us that there are other possibilities that need eliminating before staring to take the gearbox off/apart.  I wonder if the main output bearing has chipped a ball or a chunk of track has worn/split away, but that would be a comparatively expensive job, so there is no way I was going to suggest that until all else has been ruled out, and the noise has been localised to the back of the gearbox.

[magnetman]

If the prop has a damaged blade it could cause deck board vibration. 

 

If it is inaudible with the boards off then it seems likely it may be that. 

 

Exhaust silencer mounting is another possibility. This happened on my in mum's nb once when a welded arm supporting the silencer cracked. Very noisy that was.

[PCSB]

16 hours ago, Mike55 said:

Are you sure it's not something around the prop shaft? I once had a tick-tick noise in forwards that turned out to be the remains of a pair of in-ear phones. It was the 3.5mm plug hitting the underside of the boat that  caused the noise.  Being very small  they took ages to find. 

Yep, quite sure ta

6 hours ago, blackrose said:

Due to the nature of sound which is a spherical pressure wave with a spectrum of frequencies and amplitudes, absorbed by some materials and reflected by others, it can be very difficult to precisely locate the source. When you add in vibration which transfers between materials and objects it makes things even more confusing. The listening stick was a good idea and a basic stethoscope might work, but I'm wondering what made the OP so sure it was their gearbox making the clicking sound in the first place? It seems more likely to be rattling deck boards to me 

Not deck boards, only has the one and it isn't the source of the sound. I never said I was "so sure" I just put 2 and 2 together and will be happy if it isn't the box. As you haven't heard the noise I'm not sure how you can be so certain it is rattling deck boards. If it was, and it is a big IF the sound would not be a high pitched, almost metallic click. It would be at a much lower frequency and with a longer tail off. 

 

Unfortunately I need to find either a better listening stick or get a stethascope from somewhere.

 

 

6 hours ago, magnetman said:

If the prop has a damaged blade it could cause deck board vibration. 

 

If it is inaudible with the boards off then it seems likely it may be that. 

 

Exhaust silencer mounting is another possibility. This happened on my in mum's nb once when a welded arm supporting the silencer cracked. Very noisy that was.

I haven't visually inspected the prop but I have felt all around it and there is no obvious damage. Obvioulsy would feel a hairline crack so I gues that could be a possibility.

 

However the noise has significantly reduced since following Tony's advice above so I'd surprised if it was.

 

The exhaust mounts could be a possibility I guess, when I'm next in the engine bay I'll double check them.

On 05/07/2023 at 20:31, ditchcrawler said:

I had the bottom plate of the weed hatch cover that resonated against the weed hatch tunnel at a certain rev range. Took me some time to find it.

Thought I'd responded to this, must be getting old ... Not sure how I would confirm this, perhaps listen to the weed hatch when under way (that will be fun  )

[ditchcrawler]

57 minutes ago, PCSB said:

 

Thought I'd responded to this, must be getting old ... Not sure how I would confirm this, perhaps listen to the weed hatch when under way (that will be fun  )

I found mine by binding some cord tightly round the plate, it stopped the noise for a very short time until the cord parted where it was getting nipped between the edge of the plate and the side of the weed hatch tube. If its a close fit you could use string.

 

Another leg welded between the top cover and the bottom plate fixed it. I t was originally just one length of pipe or box section (cant remember which)

Edited July 9, 2023 by ditchcrawler
Added a bit

[PCSB]

30 minutes ago, ditchcrawler said:

I found mine by binding some cord tightly round the plate, it stopped the noise for a very short time until the cord parted where it was getting nipped between the edge of the plate and the side of the weed hatch tube. If its a close fit you could use string.

 

Another leg welded between the top cover and the bottom plate fixed it. I t was originally just one length of pipe or box section (cant remember which)

Thanks Brian, I'll give it a go