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Gearbox drive coupling

wirren

By wirren
in Boat Equipment

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Bobbybass Experienced

Bobbybass

Posted
Posted

I have one...

In my 'opinion'..they have a big weak spot....

I say this due to having to pay out for a second one in only 2 years..

On the left it grips the prop shaft with a cone and hefty bolts.

On the right it has 4 studs that are tapped only about 18mm into the aluminium casting.

I had to check engine realignment last year as a support had come loose...and while doing up one of the nuts on a stud...it started to pull the stud from the casting.

I hadn't used much pressure well lower on the torque wrench than I had been told....although...nobody seems to have an 'official' figure for this ??

I was near Oxford boats...and they said this is a common fault. I phoned other yards..and they said they helicoil these often...but ii tends to fail.

I have now had to pay for a complete new centreflex...and the engineer...telling me that he has repaired many of these...removed the studs and used long..cut down bolts in their place.

I think the unit is great when in use..but take care with these studs.

 

Bob

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Bobbybass Experienced

Bobbybass

Posted
Posted (edited)

CF-M-127 TA = 45Nm for the M10 studs.

 

Paul

Really...?

That's even worse...I thought it was 35Nm and had the wrench set to that.

Even more reason for care..

The engineer at Barton Turns said...ordinary spanner...hardly any force...just beyond finger tight..

and lots of Locktight.

 

Bob

Edited by Bobbybass
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PaulD Proficient

PaulDDonate to Canal World

Posted
Posted

Really...?

That's even worse...I thought it was 35Nm and had the wrench set to that.

Even more reason for care..

The engineer at Barton Turns said...ordinary spanner...hardly any force...just beyond finger tight..

and lots of Locktight.

 

Bob

 

I got the 45Nm from the Centa CF Marine-03-05 catalogue / data sheet. It does seeem very high for an M10 aluminium thread.

 

Lucky I couldn't get my torque wrench in the gap between the PRM box and coupling - I also used an ordinary spanner and some locktite.

 

Paul

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Bobbybass Experienced

Bobbybass

Posted
Posted (edited)

Thanks Bob & Paul, I know you have to take care with aluminium , it's a different ball game to steel.

Just out of interest Is it possible to loosen the prop shaft without disconnecting the gearbox studs ?

Mark.

The large bolts on the left end are very heavy...3/4 inch heads ...and I think..8 of them..

They force a cone that grips the shaft. I had trouble getting the last 2 out...and so did the engineer...he had to cut them off..hence a new coupling.

If you do get them out you then reinsert a couple into seperate threaded holes that are alongside the normal ones. As you put pressure on..it forces the cone and it finally comes apart..usually with a loud bang !!

Best not to tackle these on a casual basis.

 

bob

 

I got the 45Nm from the Centa CF Marine-03-05 catalogue / data sheet. It does seeem very high for an M10 aluminium thread.

 

Lucky I couldn't get my torque wrench in the gap between the PRM box and coupling - I also used an ordinary spanner and some locktite.

 

Paul

The stud came out at less than 35Nm...its all a bit flimsy...as the stud sticks out by the same amount that is threaded into the aluminium..any sideways forces in use are amplified... in my case with a PRM160...the stud only clears the gearbox by a few millimneters..so not good if it starts to unwind..

Best do what my engineer did..replace them with bolts. This gives you much more clearance if they start to come undone.

He also added a large 'safety ring' to the cone nuts which helps if they come loose. This is Centreflex equipment..but I didn't have one on my original unit.

Edited by Bobbybass
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PaulD Proficient

PaulDDonate to Canal World

Posted
Posted

The stud came out at less than 35Nm...its all a bit flimsy...as the stud sticks out by the same amount that is threaded into the aluminium..any sideways forces in use are amplified... in my case with a PRM160...the stud only clears the gearbox by a few millimneters..so not good if it starts to unwind..

Best do what my engineer did..replace them with bolts. This gives you much more clearance if they start to come undone.

He also added a large 'safety ring' to the cone nuts which helps if they come loose. This is Centreflex equipment..but I didn't have one on my original unit.

 

I also replaced the studs with bolts to improve clearance. Not completely happy with that as it increases the chance of galling the threads in the coupling bore when tightening. Studs are better but the whole arrangement is awkward - most people need to split the coupling here to check alignment.

 

What did we do before locktite?

 

Paul

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  • 4 weeks later...
Capt Ahab Proficient

Capt Ahab

Posted
Posted

I have one...

In my 'opinion'..they have a big weak spot....

I say this due to having to pay out for a second one in only 2 years..

On the left it grips the prop shaft with a cone and hefty bolts.

On the right it has 4 studs that are tapped only about 18mm into the aluminium casting.

I had to check engine realignment last year as a support had come loose...and while doing up one of the nuts on a stud...it started to pull the stud from the casting.

I hadn't used much pressure well lower on the torque wrench than I had been told....although...nobody seems to have an 'official' figure for this ??

I was near Oxford boats...and they said this is a common fault. I phoned other yards..and they said they helicoil these often...but ii tends to fail.

I have now had to pay for a complete new centreflex...and the engineer...telling me that he has repaired many of these...removed the studs and used long..cut down bolts in their place.

I think the unit is great when in use..but take care with these studs.

 

I had the same trouble and ended up using cut down M10 bolts with one pinned through. So far he fix has held OK. The BCN Challenge will really test it!

 

I recorded the fix here:

http://captainahabswaterytales.blogspot.com/2010/12/centerflex-fix.html

 

 

Bob

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