Clanging sound when in gear at low revs

[Mikexx]

This is  BMC 1500 and a PRM gearbox. I assume it's all original, late 1980s.

 

This has only just started. Quiet in neutral but noisy when in gear at low revs. Quiet again with modest power. Everything performs as one might expect.

 

I'm assuming this is a drive plate issue? I would be grateful for a steer?

[enigmatic]

does sound a lot like drive plate.

my engine mounts only rattled at low revs (but were pretty bad in neutral too). I guess there are some bolts etc that might need a specific RPM range and load to rattle.

 

I guess the people who know more about gearboxes than me might want to know the model of gearbox (or more generally whether it's hydraulic or mechanical) to make any suggestions on that front

 

[john.k]

Doesnt really matter ,if the drive plate is loose /broken ,take out the gearbox and fix the problem

[Tony Brooks]

7 hours ago, enigmatic said:

does sound a lot like drive plate.

my engine mounts only rattled at low revs (but were pretty bad in neutral too). I guess there are some bolts etc that might need a specific RPM range and load to rattle.

 

I guess the people who know more about gearboxes than me might want to know the model of gearbox (or more generally whether it's hydraulic or mechanical) to make any suggestions on that front

 

 

I agree, but check all the nuts and bolts on the mount first, just in case, easier than taking gearboxes off.

[Mikexx]

Today the clanging noise has disappeared but the gearbox is still noisy.

 

All visible bolts and mounts seemed ok.

 

I include a 1 minute or so video of the engine on tick over to start with with forward initially engaged and then disengaging etc.

https://drive.google.com/file/d/1RWgbDWMImfKn19E1L0N8rUghyH4mBCgi/view?usp=sharing

 

What is notable if that the noise only occurs when the gearbox is engaged in either forward or reverse. Since the output shaft to prop rotates quietly in neutral this only leaves the gearbox.

 

 

[Tracy D'arth]

38 minutes ago, Mikexx said:

Today the clanging noise has disappeared but the gearbox is still noisy.

 

All visible bolts and mounts seemed ok.

 

I include a 1 minute or so video of the engine on tick over to start with with forward initially engaged and then disengaging etc.

https://drive.google.com/file/d/1RWgbDWMImfKn19E1L0N8rUghyH4mBCgi/view?usp=sharing

 

What is notable if that the noise only occurs when the gearbox is engaged in either forward or reverse. Since the output shaft to prop rotates quietly in neutral this only leaves the gearbox.

 

 

Or a bunch of wire/rope on the prop...................

 

The video won't run for me but it looks like a PRM 160/260/280 gearbox in there with an Aquadrive/Python coupling. I would be amazed if it was the gearbox, they are very solid and regarded usually as bomb proof.

 

Have you tried a listening stick to narrow down the source of the noise?

Edited July 20, 2023 by Tracy D'arth

[Tony Brooks]

30 minutes ago, Tracy D'arth said:

Or a bunch of wire/rope on the prop...................

 

The video won't run for me but it looks like a PRM 160/260/280 gearbox in there with an Aquadrive/Python coupling. I would be amazed if it was the gearbox, they are very solid and regarded usually as bomb proof.

 

Have you tried a listening stick to narrow down the source of the noise?

 

I was about to reply in a similar manner. I suppose the shaft could have bent somehow or the prop has lost a large chunk of blade or is badly bent.

[Mikexx]

2 hours ago, Tracy D'arth said:

Or a bunch of wire/rope on the prop...................

 

The video won't run for me but it looks like a PRM 160/260/280 gearbox in there with an Aquadrive/Python coupling. I would be amazed if it was the gearbox, they are very solid and regarded usually as bomb proof.

 

Have you tried a listening stick to narrow down the source of the noise?

 

The shaft still spins in neutral without the accompany noise, so I dismissed the possibility of any issues with the prop, prop bearing or the coupling. Yes the gearbox is a PRM 160. My next job is to determine the state of the oil in the gearbox. The dipstick bolt head has been chewed and I need to take an 18mm 6 sided socket to undo it.

 

I'm still concerned over the drive plate, even though the more serious clanging noise has gone for now.

 

Many thanks for the replies.

[Tony Brooks]

1 hour ago, Mikexx said:

 

The shaft still spins in neutral without the accompany noise, so I dismissed the possibility of any issues with the prop, prop bearing or the coupling. Yes the gearbox is a PRM 160. My next job is to determine the state of the oil in the gearbox. The dipstick bolt head has been chewed and I need to take an 18mm 6 sided socket to undo it.

 

I'm still concerned over the drive plate, even though the more serious clanging noise has gone for now.

 

Many thanks for the replies.

 

The faster the shaft spins, the greater the forces developed by any out of balance rotating items, so if we ignore the fact that the shaft spins slowly in neutral, which seems a bit odd for a PRM, it is not surprising you don't get noises/vibrations in neutral.

[cuthound]

18 hours ago, Mikexx said:

Today the clanging noise has disappeared but the gearbox is still noisy.

 

All visible bolts and mounts seemed ok.

 

I include a 1 minute or so video of the engine on tick over to start with with forward initially engaged and then disengaging etc.

https://drive.google.com/file/d/1RWgbDWMImfKn19E1L0N8rUghyH4mBCgi/view?usp=sharing

 

What is notable if that the noise only occurs when the gearbox is engaged in either forward or reverse. Since the output shaft to prop rotates quietly in neutral this only leaves the gearbox.

 

 

 

Some years ago we had a really load clanging noise when we engaged gear on our first shareboat.

 

It turned out to be a Sea Searcher magnet which had attached itself to the bottom of the boat and its attached rope had wrapped itself around the prop.

 

 

[Mikexx]

2 hours ago, cuthound said:

Some years ago we had a really load clanging noise when we engaged gear on our first shareboat.

 

It turned out to be a Sea Searcher magnet which had attached itself to the bottom of the boat and its attached rope had wrapped itself around the prop.

 

Fingers crossed it's something similar. I've come to the conclusion to leave all well alone. The noise gave did give me that sinking feeling!

 

In the mean time I checked the gearbox oil, and it is immaculately clean. Possibly slightly overfilled, depending on how you read the stick.

 

Many thanks for all the replies.

[Tracy D'arth]

4 minutes ago, Mikexx said:

 

 

In the mean time I checked the gearbox oil, and it is immaculately clean. Possibly slightly overfilled, depending on how you read the stick.

 

Read full at top mark on the stick when screwed in, read full at bottom mark when just dropped in.

[Mikexx]

23 hours ago, Tracy D'arth said:

Read full at top mark on the stick when screwed in, read full at bottom mark when just dropped in.

 

Thanks, so it's overfull by a mark. I would imagine it's not critical.

[Tracy D'arth]

15 minutes ago, Mikexx said:

 

Thanks, so it's overfull by a mark. I would imagine it's not critical.

worry not.