Shaft and tight nuts.

[Bobbybass]

I was realigning my engine/ prop shaft and loosened the 4 studs that hold the centreflex to the gearbox (PRM160)

When I did them back up again...with no effort at all...I started to strip one of the studs out of the aluminium casting !

Now..I could ask why one end of the centreflex has 8 serious 3/4 head steel nuts...and the other end is held by 4 flimsy studs tapped into aluminium..but I wont !!

I now have to remove the centreflex and get the stud helicoiled....but my problem is that one..just one of the s*****g 3/4 nut won't shift.

How do you lock the propellor shaft so that it wont rotate when you heave on the nut ?

I have tried jamming things down around the centreflex..but it's going to need serious force to loosen this last nut.

 

I thought about opening the weed hatch and jamming the prop..but this seems a bit desperate.

Is there a simple tequnique ?

 

Bob

[ChrisPy]

nothing like an ambiguous thread title to stir some interest ................

Edited September 28, 2010 by ChrisPy

[n.b.Goldie]

I was realigning my engine/ prop shaft and loosened the 4 studs that hold the centreflex to the gearbox (PRM160)

When I did them back up again...with no effort at all...I started to strip one of the studs out of the aluminium casting !

Now..I could ask why one end of the centreflex has 8 serious 3/4 head steel nuts...and the other end is held by 4 flimsy studs tapped into aluminium..but I wont !!

I now have to remove the centreflex and get the stud helicoiled....but my problem is that one..just one of the s*****g 3/4 nut won't shift.

How do you lock the propellor shaft so that it wont rotate when you heave on the nut ?

I have tried jamming things down around the centreflex..but it's going to need serious force to loosen this last nut.

 

I thought about opening the weed hatch and jamming the prop..but this seems a bit desperate.

Is there a simple tequnique ?

 

Bob

 

I think that the '8 serious 3/4 head steel nuts' might need doing up again to alleviate the stress on the remaining stubborn one. I am not sure they are nuts but might be bolts, I think that they hold in a sort of conical assembly that grips the shaft, so to speak.

Is this what you have?

 

To prevent it from rotating whilst you are trying to undo the nut/bolt perhaps put a spanner on one of the other nut/bolts to lever against.

 

Hope the above gives you some food for thought, I am no expert and would recommend talking to Tony Brooks (forum member) ftom TB Training (other expert forum members are available).

 

All the best

Ditchdabbler

[RLWP]

<snip>

I thought about opening the weed hatch and jamming the prop..but this seems a bit desperate.

Is there a simple tequnique ?

 

Bob

 

I have managed this in the past with a boarding plank down the weedhatch to stop the prop turning. It does depend on the weedhatch, prop and plank of course

 

 

Richard

Edited September 28, 2010 by RLWP

[Tim Doran]

I have managed this in the past with a boarding plank down the weedhatch to stop the prop turning. It does depend on the weedhatch, prop and plank of course

 

 

Richard

 

I was going to suggest holding the prop. I like your idea much more.

[FadeToScarlet]

On the wide end of the Centreflex, there are four protruding bits that stick up.

 

When jiggering around with my prop shaft, I was able to use a mooring pin passed between that protrusion, and the narrower part which attaches onto the prop shaft, and when braced against the engine bearer, that prevented the centreflex from turning. If you look at the picture ditchdabbler posted, you can see the protrusion sticking out.

 

 

Now..I could ask why one end of the centreflex has 8 serious 3/4 head steel nuts...and the other end is held by 4 flimsy studs tapped into aluminium..but I wont !!

 

I think it's because the serious steel nuts hold a lot of force in tension, because they force the cones inside the coupling together and cause it to grip onto the shaft.

 

At the other end, the coupling is rigidly bolted onto the spider, and so the studding takes less force.

[Bobbybass]

I think that the '8 serious 3/4 head steel nuts' might need doing up again to alleviate the stress on the remaining stubborn one. I am not sure they are nuts but might be bolts, I think that they hold in a sort of conical assembly that grips the shaft, so to speak.

Is this what you have?

 

To prevent it from rotating whilst you are trying to undo the nut/bolt perhaps put a spanner on one of the other nut/bolts to lever against.

 

Hope the above gives you some food for thought, I am no expert and would recommend talking to Tony Brooks (forum member) ftom TB Training (other expert forum members are available).

 

All the best

Ditchdabbler

 

Hi...

Yes...silly me..I meant the 8 steel bolts...not nuts.

 

Mine is like the one in the picture.....but I do not have a bearing like the black one you have. My stern tube follows the centreflex and that is bolted to a cross member.

 

The 4 studs that you can see on the right hand side are like mine. I bolted them up and one just started to get longer....and was in danger of hitting the gearbox housing. I hardly had them done up tightly at all so I am reluctant to use them in any way to 'lock' the shaft...as they seem so bloody fragile.

 

Maybe..you are right about the 8 heavy duty bolts..maybe I need to put some back to take the strain from the stuck one ?

I know that when you have them all undone...you then insert some back into the second set of holes in the left hand flange and do them up tight...which forces the joint apart with a bang....so I'm 'told'

I may try the weedhatch route..that sounds like my best bet.

 

Thanks for all your comments.

 

Bob

[Boatgypsy]

Hi...

Yes...silly me..I meant the 8 steel bolts...not nuts.

 

Mine is like the one in the picture.....but I do not have a bearing like the black one you have. My stern tube follows the centreflex and that is bolted to a cross member.

 

The 4 studs that you can see on the right hand side are like mine. I bolted them up and one just started to get longer....and was in danger of hitting the gearbox housing. I hardly had them done up tightly at all so I am reluctant to use them in any way to 'lock' the shaft...as they seem so bloody fragile.

 

Maybe..you are right about the 8 heavy duty bolts..maybe I need to put some back to take the strain from the stuck one ?

I know that when you have them all undone...you then insert some back into the second set of holes in the left hand flange and do them up tight...which forces the joint apart with a bang....so I'm 'told'

I may try the weedhatch route..that sounds like my best bet.

 

Thanks for all your comments.

 

 

Bob

 

Big pair of Stilsons to hold the shaft while you loosen or tighten the nuts.

[Timleech]

Big pair of Stilsons to hold the shaft while you loosen or tighten the nuts.

 

Careful, you'll wake Mr Evo

 

 

Tim

[Evo]

Well, you see, you might take the pee, annd yes a pair of stillsons is appropiate in this situation - namely to grip a shaft. Trouble is I couldn't do it to my prop shaft myself. I'd have to be desperate to put all those horible teeth marks in my shiny propshaft.

 

I go with the guy who said put the other bolts back in and jam a tyre lever or something similar in those to undo the sticky one.

 

I have a very similar setup and had to M10 helicoil all of the threads in my alum/rubber hub. I have experience here..you gotta listen folks.

Edited September 29, 2010 by Evo

[ditchcrawler]

Big pair of Stilsons to hold the shaft while you loosen or tighten the nuts.

With or without a length of scaffold pipe?

[RLWP]

Well, you see, you might take the pee, annd yes a pair of stillsons is appropiate in this situation - namely to grip a shaft. Trouble is I couldn't do it to my prop shaft myself. I'd have to be desperate to put all those horible teeth marks in my shiny propshaft.

 

I go with the guy who said put the other bolts back in and jam a tyre lever or something similar in those to undo the sticky one.

 

I have a very similar setup and had to M12 helicoil all of the threads in my alum/rubber hub. I have experience here..you gotta listen folks.

 

On the shaft? You heathen!! Put it on the prop nut.

 

Richard

 

[Evo]

go away you..

[Timleech]

Well, you see, you might take the pee, annd yes a pair of stillsons is appropiate in this situation - namely to grip a shaft.

 

Granted you said you couldn't bring yourself to do it, but there are much better reasons for not doing it, than there are for using stillsons on the nut.

Stillsons on a big nut like that on the prop do no real harm, a few teeth marks are neither here nor there in the real world of a nut which suffers all sorts of abuse from debris when in use.

On the shaft, teeth marks can be a real problem if it has to be withdrawn. Most nb shafts have to come out sternwards, so everything in front of the gland has to pass through gland and bearing. Many times when shaft is taken out new bearing and packing will be fitted, but not always and especially not the bearings around the gland.

 

real world vs theory.

 

Tim

[PaulD]

On the wide end of the Centreflex, there are four protruding bits that stick up.

 

When jiggering around with my prop shaft, I was able to use a mooring pin passed between that protrusion, and the narrower part which attaches onto the prop shaft, and when braced against the engine bearer, that prevented the centreflex from turning. If you look at the picture ditchdabbler posted, you can see the protrusion sticking out.

 

 

 

I think it's because the serious steel nuts hold a lot of force in tension, because they force the cones inside the coupling together and cause it to grip onto the shaft.

 

At the other end, the coupling is rigidly bolted onto the spider, and so the studding takes less force.

 

I watched this thread with interest because my installation with Centaflex CF-M-160 and PRM 150 had always concerned me.

 

The M10 studs and nyloc nuts that come with the Centa kit seemed perilously close to the PRM oil pump casing. Is this normal? I imagine one loose stud would have a serious imact on your bank balance. I changed them for M10 x 25mm 10.9 hex screws and some locktite when I checked the alignment last week and it looks / feels 100% better.

 

Went with the torque wrench already set at 45Nm per the manual but no room for anything other than a small ring spanner. Easy to see how you can strip the threads.

 

Like FadetoScarlet also managed to lock the coupling with a square section steel bar between the lugs on the prop side of the coupling and the hull. Watch your fingers because it can slip out.

 

Paul