PRM 160 D2 gearbox

[MtB]

This is a noise I've also noticed on other boats in the past, usually in astern, but I've never attached much importance or significance to it. A muffled bell-like clanging or dinging noise, vaguely like someone hitting the fly wheel with a hammer about once per prop revolution. Definitely engine speed-related, and only present at low revs.

 

I noticed our own boat too when we first got it six months ago (it's a Beta Marine BD3 'tug' engine, circa 1990 and PRM 160 D2), but only in astern at tickover. Recently though, I've noticed it getting a bit worse. It used only to happen in astern and opening the throttle even slightly made it vanish. Lately I've had to open the throttle a bit more before it would stop, but still only ever in astern.

 

But now I'm worried. Today I noticed this noise when engaging ahead too. Vanishes when the engine speeds up to 600rpm or higher, but present at low revs now in both ahead and astern. Is this normal or is my gearbox about to dismantle itself spontaneously without warning?

 

The only thing I can think of to check is the oil level, and the gearbox oil level is correct. Engine is slightly over-filled though. Might that be the cause? Seems unlikely to me, but I'm not an expert on marine engines or transmissions.

 

Any advice welcome.

 

Cheers, Mike

[Keeping Up]

I can't imagine it being anything to do with the engine oil level. It sounds to me more like perhaps a worn drive plate - that is the plate which connects the gearbox to the engine. It usually has a rubber coupling between the outer (engine) part and the inner (gearbox) part, and when the rubber wears out or breaks it can give exactly the symptoms you describe.

 

But I'm not an expert, so you may get some reasoned comments later.

[steelaway]

This is a noise I've also noticed on other boats in the past, usually in astern, but I've never attached much importance or significance to it. A muffled bell-like clanging or dinging noise, vaguely like someone hitting the fly wheel with a hammer about once per prop revolution. Definitely engine speed-related, and only present at low revs.

 

I noticed our own boat too when we first got it six months ago (it's a Beta Marine BD3 'tug' engine, circa 1990 and PRM 160 D2), but only in astern at tickover. Recently though, I've noticed it getting a bit worse. It used only to happen in astern and opening the throttle even slightly made it vanish. Lately I've had to open the throttle a bit more before it would stop, but still only ever in astern.

 

But now I'm worried. Today I noticed this noise when engaging ahead too. Vanishes when the engine speeds up to 600rpm or higher, but present at low revs now in both ahead and astern. Is this normal or is my gearbox about to dismantle itself spontaneously without warning?

 

The only thing I can think of to check is the oil level, and the gearbox oil level is correct. Engine is slightly over-filled though. Might that be the cause? Seems unlikely to me, but I'm not an expert on marine engines or transmissions.

 

Any advice welcome.

 

Cheers, Mike

 

 

Hi Mike

I have a feeling that PRM gearbox's will make a noise if it is run to slowly and the fact that it stops when you increase the revs.

Try turning up the engines tick over speed. My modern Barrus engine is set to 900rpm

Alex

[MtB]

Hi Mike

I have a feeling that PRM gearbox's will make a noise if it is run to slowly and the fact that it stops when you increase the revs.

Try turning up the engines tick over speed. My modern Barrus engine is set to 900rpm

Alex

 

 

Thanks for the replies you two.

 

Alex,

 

My MD3 is an old-style slow-revving engine. Ticks over at 400rpm and at 1000rpm we are almost up on the plane! 600rpm is a good crusing speed on the cut. This noise is changing and getting worse, so I doubt it is generic noise made by the PRM box, although I'd like to find out you are right!

 

 

Allan,

 

That intuitively seems a good diagnosis. As the angular velocity of the flywheel varies during a revolution, a broken coupling could clatter at low load, and stop at higher load (i.e. higher speed). Where can I investigate drive plates? What do they look like? Where can I get one, I wonder. I suppose Beta Marine would be a good place to start!

 

Cheers, Mike

Edited May 2, 2009 by mike bryant

[hughc]

R & D do a drive plate with softer than usual inserts which obviates this problem. Regards, HughC.

[casper ghost]

Ring PRM and speak with them, i rang them only the other day on a technical matter and they were very helpful.

[MtB]

Ring PRM and speak with them, i rang them only the other day on a technical matter and they were very helpful.

 

 

Interesting. I did as casper suggested and rang PRM and they confirmed steelaway's suggestion, that the D160 transmission can make a noise like this at low revs. Backlash in the gears I think, although he wasn't explaining very well WHY they make a noise at low revs. He also suggested measuring the gearbox oil pressure as an initial health check for the transmission. Stupidly I forgot to ask what pressure to expect at the 1/8" bsp test tapping. Duh...

 

I also spoke to Beta Marine and the chap there however was of a different opinion. He pointed out that as the noise was initially present in astern only, it couldn't be the drive plate. The engine doesn't know which way the prop is turning so any difference in noise between forward and backwards shows it must be transmission or prop shaft related, not engine. He also thought drive plate failure noise would be present in neutral too.

 

I'm beginning to wonder now if I'm remembering the symptoms right. We've used the boat very little since getting it until now, but since spending a couple of days on the K&A this weekend and getting the chance to do a lot of experimenting, the noise is definitely identical in forward and reverse. If it's backlash in the transmission gears then an extra-spongy drive plate as suggested by hughc might well help. Their website http://www.randdmarine.com/mdamper.asp talks about "gearbox rattle" or "gear hammer" at low engine speeds and that feels to me exactly what we have. I'll follow this up next.

 

Thanks hughc, and everyone else who replied...

Edited May 5, 2009 by mike bryant

[MtB]

Well now I spent an amusing hour this afternoon testing and annoying the neighbours by constantly engaging forward, then reverse, then forward, then....

 

In reverse the clanking noise is ALWAYS present. In forward it happens about 50% of the time. This surely rules out drive plate failure or it would always do it.

 

Using a 3/8" brass rod as a stethoscope suggests the massive prop shaft thrust bearing is the culprit. It's pair of bearings 4" in diameter back-to-back in 6 3/8" square cast iron housings either side of a 3/4" plate welded across the swim plates. Plenty of evidence of the previous owner pumping loads of grease in through the grease nipples, so this may be the answer! Do they wear out? I have 3600 hours showing on the engine timer.

 

I'll try loading them up with more grease tomorrow, but in anticipation, where can I get new 4" x 1½" thrust bearings?

 

Cheers, Mike

[onthecut]

I'll try loading them up with more grease tomorrow, but in anticipation, where can I get new 4" x 1½" thrust bearings?

 

Cheers, Mike

 

Strip it and find the actual bearing numbers and I doubt you will have any trouble at all replacing them. The bearings industry is one of the best at coming up with replacements, even for old or tricky stuff.

 

Mike.

[David Schweizer]

The PRM 160 ( now called the 260) is virtually indestructable. Assuming that the noise is not from the shaft thrust bearing, any noise at low speeds is almost certainly either in incompatible drive plate or a drive plate that is beginning to break up.

 

I have a PRM 160 in my boat, it is 28 years old, and has done over 20,000 hours. When I had the engine re-built three years ago, The gearbox (or so I thought) was making a clanking sound at low revs, which was worse in reverse, so I asked the engineer to re-con the gearbox at the same time.

 

When he removed the drive plate it literally fell apart, nevertheless he stripped and cleaned the box as requested, He reported that there was no wear in the box at all, so he replaced the oil seals and re built the box.

 

Now here is the interesting bit. Only a few weeks after the rebuild, the gearbox started to make an even worse clanking sound, The same engineer came out to the boat, fitted a different drive plate with a flexible centre, and three years on all is well.

 

When I spoke to PRM about the box, the Technician did state that matching gearboxes and engines with the correct drive plate can be a black art, the engineer who re-built my engine confirmed this. To demonstrate this, the second drive plate fitted to my engine had been removed after about thirty hours from an identical engine/gearcbox setup as on my boat, because it was causing an awful noise.

Edited May 5, 2009 by David Schweizer

[RobinJ]

Well now I spent an amusing hour this afternoon testing and annoying the neighbours by constantly engaging forward, then reverse, then forward, then....

 

In reverse the clanking noise is ALWAYS present. In forward it happens about 50% of the time. This surely rules out drive plate failure or it would always do it.

 

Using a 3/8" brass rod as a stethoscope suggests the massive prop shaft thrust bearing is the culprit. It's pair of bearings 4" in diameter back-to-back in 6 3/8" square cast iron housings either side of a 3/4" plate welded across the swim plates. Plenty of evidence of the previous owner pumping loads of grease in through the grease nipples, so this may be the answer! Do they wear out? I have 3600 hours showing on the engine timer.

 

I'll try loading them up with more grease tomorrow, but in anticipation, where can I get new 4" x 1½" thrust bearings?

I was going to mention a problem that arose on a refit, with a clanging noise which did vary, but was worse in forward, turned out to be the flywheel catching on the bell housing as the gearbox mountings had moved.

However the suggestion I was going to make may still help.

Can you easily disconect the coupling from gearbox to propshaft? Doing this would mean noise in forward, reverse and neutral problem with engine, noise only in gear, problem in gearbox, otherwise problem with shaft!

[David Schweizer]

I was going to mention a problem that arose on a refit, with a clanging noise which did vary, but was worse in forward, turned out to be the flywheel catching on the bell housing as the gearbox mountings had moved.

However the suggestion I was going to make may still help.

Can you easily disconect the coupling from gearbox to propshaft? Doing this would mean noise in forward, reverse and neutral problem with engine, noise only in gear, problem in gearbox, otherwise problem with shaft!

I suppose it is worth a try, but I doubt whether any gearbox noise would be heard with the drive train disconnected, as it will not be under any load. Normally the gears inside a box move silently and easily when disconnected from the drive.

[MtB]

I suppose it is worth a try, but I doubt whether any gearbox noise would be heard with the drive train disconnected, as it will not be under any load. Normally the gears inside a box move silently and easily when disconnected from the drive.

 

 

I thought along the same lines then like you, concluded that half an hour removing four M12 bolts with NyLock nuts to disconnect the propshaft would lead to no load = no noise and another half an hour putting it all back together again, all for no benefit.

 

Anyway, I spent an hour assessing it further with a marine engineer today. He couldn't decide where the noise was coming from either. His input was worthwhile though as he demonstrated that the noise disappeared if he gripped the rotating prop shaft with his hand just after the gearbox. (Risky I thought!) Gripping the prop shaft adds torque resistance but only engine-side of the grip point. The fact that his shaft-gripping eliminates the noise shows the the problem must be engine-side of his gripping point. This therefore eliminates the rear thrust bearings on the propeller shaft at the stern end as the source of the noise. It MUST therefore be backlash in the transmission or a knackered drive plate.

 

There is an access panel in the bell housing transmission adaptor plate with four small bolts keeping it in place. Removing this exposes the flywheel. If it was a knackered drive plate I'd have expected an increase in noise level with the plate OFF. Noise didn't change at all, not even the slightest change when removing the inspection panel. We conclude it must be backlash in the transmission causing the clanking noise therefore. Maybe an ultra-spongy drive plate will fix it after all, even if the current drive plate is sound. I'm inclined to give it a try as they are only about ninety quid.

 

By the way RobinJ, it's very UNlikely to be the flywheel catching as the noise disappears whenever neutral is selected.... or are you saying your flywheel noise disappeared in neutral too?

 

Cheers, Mike

[RobinJ]

I thought along the same lines then like you, concluded that half an hour removing four M12 bolts with NyLock nuts to disconnect the propshaft would lead to no load = no noise and another half an hour putting it all back together again, all for no benefit.

 

Anyway, I spent an hour assessing it further with a marine engineer today. He couldn't decide where the noise was coming from either. His input was worthwhile though as he demonstrated that the noise disappeared if he gripped the rotating prop shaft with his hand just after the gearbox. (Risky I thought!)

Well thats an alternative way!

By the way RobinJ, it's very UNlikely to be the flywheel catching as the noise disappears whenever neutral is selected.... or are you saying your flywheel noise disappeared in neutral too?

To be honest it was a bit erratic, usually worse in forward, but clanged whenever the high spots met, worse in gear becuase the gearbox was moving slightly (resolved by shamfering the flywheeel and fitting larger bolts).

 

I am a little surprised with a 160 making clanging noises, even after ten years, what is the oil like?

It could be a bearing, damage or wear on one of the gears, or a loose clutch plate?

There should be a plate on top that can be removed to look at the clutch plates, it might not be easy to measure the thickness in situ, but if the friction surfaces are worn badly you should be able to see it.

[Serendipity]

A muffled bell-like clanging or dinging noise, vaguely like someone hitting the fly wheel with a hammer about once per prop revolution. Definitely engine speed-related, and only present at low revs.

 

Precisely what mine has done since my ownership three years ago (500 hours or so). I would add that in my case:-

 

1) If engaging gear slowly, it is prefaced with a bit of 'clatter', and then as you further increase revs the noise you describe appears until you move out of the tickover/fast tickover range.

 

2) When started from cold, and particularly in winter, a hundred revs or so more than fast tickover are required to make it go away. After twenty minutes running it's only noticeable at slow tickover again.

 

I live with it, but would obviously be very interested to know what you come up with.

 

Julian

[David Schweizer]

Precisely what mine has done since my ownership three years ago (500 hours or so). I would add that in my case:-

 

1) If engaging gear slowly, it is prefaced with a bit of 'clatter', and then as you further increase revs the noise you describe appears until you move out of the tickover/fast tickover range.

 

2) When started from cold, and particularly in winter, a hundred revs or so more than fast tickover are required to make it go away. After twenty minutes running it's only noticeable at slow tickover again.

 

I live with it, but would obviously be very interested to know what you come up with.

 

Julian

You have just described the classic symptoms of a drive plate that is beginning to disintegrate. I had excactly the same symptoms and put up with them for about a year, but when the plate was removed, the centre fell out! it was no longer connected to the friction disc.

 

I would suggest that you get it changed fairly soon. It only takes a good engineer a couple of hours at the most to change the plate, and the plates are around £100, so the whole job should cost well under £200.

[Serendipity]

You have just described the classic symptoms of a drive plate that is beginning to disintegrate. I had excactly the same symptoms and put up with them for about a year, but when the plate was removed, the centre fell out! it was no longer connected to the friction disc.

 

I would suggest that you get it changed fairly soon. It only takes a good engineer a couple of hours at the most to change the plate, and the plates are around £100, so the whole job should cost well under £200.

 

Given your experience with the wrong plate David, I think I'd rather leave well alone for now. Do you recall what plate worked for you in the end, and what effect do you suppose the temperature has on it?

 

Cheers

 

Julian<p>

[Canal Shop Man]

. . . . .I think I'd rather leave well alone for now. . . . . .

I would concur with all those who reckon it is the drive plate wearing out.

 

Leaving it well alone will mean that it will disintegrate when you are out cruising - how inconvenient (and expensive?) could this be?

[Speedwell]

Many years ago I had clattering noise at low revs from a Newage PRM gearbox. I turned out to be a broken circlip(s) used to hold the gears in position on the shaft. The absence of circlip(s) allowed a gear to fly back and forth on the shaft. Only cost a few pence to fix.

Arthur

[David Schweizer]

Given your experience with the wrong plate David, I think I'd rather leave well alone for now. Do you recall what plate worked for you in the end, and what effect do you suppose the temperature has on it?

 

Cheers

 

Julian<p>

I cannot remember the exact description, but basicly it had a flexible centre.

 

You say that the box has made the noise since you had the boat. If it was new when you bought it, you should have had it seen to straight away as it would probably be a mis matched plate, but if the boat was S/H when you aquired it. it may just be falling apart, Drive plates do not last for ever.

[Semitrad]

Wish I had taken more notice when our drive plate was changed, having made the noises you describe. As far as I can remember it looked like a circular flat plate about flywheel size and bolted to it. Imagine a giant ten pence coin with the inside removed and a giant five pence coin inserted in the same plane and connected to the 10P coin by rubber couplings, the drive being taken from the centre of the 5P coin. There are protruding spigots on both so that if the rubber fails the 10p cannot just rotate freely outside the 5P but makes a racket!

[Serendipity]

I cannot remember the exact description, but basicly it had a flexible centre.

 

You say that the box has made the noise since you had the boat. If it was new when you bought it, you should have had it seen to straight away as it would probably be a mis matched plate, but if the boat was S/H when you aquired it. it may just be falling apart, Drive plates do not last for ever.

 

Noo the boat is '91, and 500 hours on makes me wonder whether 'tis the plate, especially as the prop shaft (lazily) rotates in neutral. So why would gently putting it in gear result in extra noise from the plate when it's already (inadvertantly) turning the prop, and why (as I mentioned earlier), different noise profile when cold. I wonder whether it's more gearbox centric as Arthur has suggested.

[Keeping Up]

Picture of a load of different drive plates hanging up at Midland Chandlers

 

[MtB]

You have just described the classic symptoms of a drive plate that is beginning to disintegrate. I had excactly the same symptoms and put up with them for about a year, but when the plate was removed, the centre fell out! it was no longer connected to the friction disc.

 

I would suggest that you get it changed fairly soon. It only takes a good engineer a couple of hours at the most to change the plate, and the plates are around £100, so the whole job should cost well under £200.

 

 

Just to tidy up this thread...

 

I decided in the end to have the transmission removed and drive plate replaced if only to rule out the drive plate as the cause of the noise. I used an engineer highly recommended by Beta Marine (Steve Lacey from Gloucester - now recommended by me too!) to do the work and he brought with him a new drive plate specified by and collected from Beta Marine.

 

The old drive plate was found to be in perfect condition on removal but very stiff/low compliance - very inappropriate for our engine in Steve's opinion. The new drive plate was WAY softer, and after reassembly and running the engine on the mooring it was clear the noise had reduced substantially. It was still slightly present with the engine running at it's very slowest, but raising the tickover up to 400 rpm on the tachometer (from about 370) completely cleared it.

 

Taking the boat out the following weekend showed the new drive plate is a dramatic improvement. The only way of knowing the prop is spinning now is to look over the back of the boat at the wash, whereas before the it was clear by listening to the transmission clanking away. Brilliant!

 

The boat is a delight to steer now with engine noise unexpectedly reduced substantially throughtout the whole rev range, so an excellent result. The only downside is the clatter from the injector pump is now the dominant engine noise!

 

Cheers, Mike