Cummins 6BT5.9-M

[Desolation Dan]

I am in the process of purchasing a Monk 36 trawler. It has a single Cummins 5.9 engine. The surveyor says the propellor shaft prop nuts need replacing. I need to know if they are left hand or right hand threads in order to purchase them before the haul-out. Can any of you bright owners on this forum tell me the answer? Much appreciated.

 

[Comodave]

Welcome aboard. They are probably right hand thread. But on my boat there is one right hand and one left hand. Put a block of wood between the prop blade and the hull and give it a try. If not, then try the other way. When you put the new ones on, the half nut goes on first and then the full height nut goes on last. But first use the full height nut to seat the prop, then remove the full height nut and put the half height nut on then the full height nut. Good luck.

 

[Desolation Dan]

Thx! i guess I have a 50/50 chance of getting the right nuts, but you have increased my odds I think. At least I only have one shaft to deal with.

 

[firehoser75]

Dan,
I think they are right hand thread. Maybe buy both, you probably can return the unused ones??? If not, not that big of an expense (comparatively speaking).

 

[High Wire]

Welcome aboard!
I will post your questions on the Monk Owners site. We have a 1984 with a Perkins. Left hand prop but right hand nuts. Btw what year Monk?

 

[Comodave]

Thx! i guess I have a 50/50 chance of getting the right nuts, but you have increased my odds I think. At least I only have one shaft to deal with.

No problem, I hate it when I get the wrong nuts...

 

[kapnd]

Don’t block the prop on the blade, it can and will bend if you push hard, or hammer on the wrench.
Block the propeller at the base of the blade, right next to the hub.
Chances are very good that it’s a right hander, and that it will be fine once it’s cleaned up.
Want some interesting reading on the subject?
Google “little nut vs big nut”, or look it up on sbmar.com

 

[Ski in NC]

What does surveyor say is wrong with the nuts? If badly corroded there may be more issues with the boat. If just beat up from pipe wrenches, the nuts still can be usable.

Usually there is a bit of shaft thread extending beyond the last nut, you can determine thread direction by looking at the threads. A large majority are RH.

I don't usually block a prop to take off shaft nuts. Rather use the inertia of the prop. Put wrench on nut and hit wrench with a big hammer. Hard to swing well underwater though.