Rumbling at tick over

[Davo_Willow]

I get a rumble/rattle at tick over when in gear. Goes away as soon as I apply a little throttle. Not happening in neutral. What should I be checking first?

 

Thanks!

Engine is  Beta 38. Otherwise very smooth.

 

Edited September 30, 2020 by Davo_Willow

[Tony Brooks]

Engine mounts for tightness both the big nuts and the bolts holding the feet to the bed. Then any thrust bearings on the shaft and finally the gearbox bearings but with just two posts are you a new boater. Shaft drives often do rumble at idle in gear.

[WotEver]

5 minutes ago, Tony Brooks said:

Engine mounts for tightness both the big nuts and the bolts holding the feet to the bed. Then any thrust bearings on the shaft and finally the gearbox bearings but with just two posts are you a new boater. Shaft drives often do rumble at idle in gear.

OP has made 109 posts, Tony

 

And been a member here for 11 years...

[Davo_Willow]

Thanks Guys. Been boating for a few years but currently out cruising and more in tune with engine note and sounds. I was just looking for some confirmation about where to start looking.

 

IIRC engine mounts should be tightened from below to make sure the prop shaft stays in alignment?

 

[Cas446]

Rattle in gear at tick over, goes when throttle applied, quiet in neutral. I thought that was a classic for worn thrust plate Tony? Although perhaps the more basic checks first. If it is, increase idle speed slightly and it will go away - for a bit. Do you have a mechanical PRM gearbox on that beta 38, about 10 years old?

Edited September 30, 2020 by Cas446

[Davo_Willow]

Is the thrust plate the nylon ring in the shaft coupling? Yes PRM about 12 years old I think. I will tighten everything I can see and get to. Otherwise will need an engineer to take a look..

 

 

Cheers!

 

Tick over is 800rpm rattle stops at around 1000 which feels too fast for tick over speed.

 

[Tony Brooks]

45 minutes ago, WotEver said:

OP has made 109 posts, Tony

 

And been a member here for 11 years...

Sorry, Must have looked at the top days score.

 

In that case it is unlikely to be normal shaft rumble unless he has got something on the prop.

[Cas446]

No it isn't. Do as Tony suggests at first and eliminate the easy wins. I don't  want to send you in the wrong direction, but I had this on same engine mechanical PRM, 2008. The default thrust plate fitted is the rock hard 'commercial' version and it rattled as you describe. I fitted a softer one and the rattling went away. Can't remember the details, but easy to identify the correct one from the catalogue once off. Relatively easy change if you are mechanically minded and don't mind grazing your knuckles. But check the obvious stuff first, including moving everything in the engine bay that can be moved. 

Edited September 30, 2020 by Cas446

[Tony Brooks]

1 hour ago, Davo_Willow said:

Is the thrust plate the nylon ring in the shaft coupling? Yes PRM about 12 years old I think. I will tighten everything I can see and get to. Otherwise will need an engineer to take a look..

 

 

Cheers!

 

Tick over is 800rpm rattle stops at around 1000 which feels too fast for tick over speed.

 

No that is just supposed to be the flexible part. If you cant see anything on the shaft between the coupling and gland you don't have a thrust bearing (actually you do, but it part of the gearbox.

 

I now suspect its a gearbox bearing but would make sure it has engine oil in it and is upto to level and the allows things to develop.

 

Edited to add - That is engine oil in the gearbox just in case its got ATF in it.

Edited September 30, 2020 by Tony Brooks

[Davo_Willow]

Got it. Thanks Tony!

 

[Davo_Willow]

Thanks again. I just found this thread https://www.canalworld.net/forums/index.php?/topic/29501-beta-38-what-are-your-operating-speeds/ which fits my symptoms pretty well. I think I will try upping the tension on the Morse throttle to run between 900 and 1000 when shifted into gear and leave idle at 800. Seems as if this within recommended range for the Beta 38.

Cheers!