Gearbox Clunking

[WiseOwl]

Hi all,

 

We have a Isuzu 33hp Narrowboat engine (IM4LB33) with a mechanical PRM120 gearbox - also a Python drive.

 

As we engage into forward or reverse gear there is quite a loud clunk! Everything works ok just concerned with the sound. 

 

Has anyone else experienced this or have this engine/gearbox?

[Boater Sam]

Has it always done this? Is the boat new to you? Have you checked for loose drive coupling bolts etc?

Is there lots of backlash in the drive shaft or Python?

Have you checked the prop?

 

PRM120 is a mechanical box with cone clutches, if the tickover of the engine is too high it will engage with a snatch.

[WiseOwl]

On 01/11/2018 at 21:16, Boater Sam said:

Has it always done this? Is the boat new to you? Have you checked for loose drive coupling bolts etc?

Is there lots of backlash in the drive shaft or Python?

Have you checked the prop?

 

PRM120 is a mechanical box with cone clutches, if the tickover of the engine is too high it will engage with a snatch.

 

On 01/11/2018 at 21:16, Boater Sam said:

Has it always done this? Is the boat new to you? Have you checked for loose drive coupling bolts etc?

Is there lots of backlash in the drive shaft or Python?

Have you checked the prop?

 

PRM120 is a mechanical box with cone clutches, if the tickover of the engine is too high it will engage with a snatch.

It’s a new boat to us so I cannot say, I have not checked for either of those but I can have a look when next at the boat. The prop is fine, it’s just had the prop nut tightened and split pin re-drilled.

 

I would say tickover is about 900 maybe this is too high? Thanks for your response

[dor]

I had this with a Technodrive TMC60, a similar mechanical box.  After my second one sounded as though it was going to jump through the deck boards I fitted a PRM150.  A relatively simple swap and it ha made a world of difference, still engaging almost silently 2,000 hours later.

Even Vetus have given up on the TMC60 and now fit the PRM box as standard.

[GrahamSop]

Does the gear engage before the engine revs start increasing?

We have the same engine/gearbox, and when we first got the boat the cable from the control lever wasn't properly adjusted so the engine was already revving up before the gear engaged. This made a pretty nasty clunk, and sometimes we couldn't engage gear at all.

It's an easy fix to adjust the gear cable so the selector lever on the gearbox is fully turned before the engine starts revving.

Although as others have said there is always a little bit of a clunk with these gearboxes. If it's getting louder then something is wrong.