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The previous owner of my boat has at some point put on engine mounts thwt are too small for the engine. The original mounts should be 140mm bolt to bolt but he has used 110mm. In doing so the engine has been moved back. So I'm going to replace mounts as there soft anyway. My question is will I need to cut prop shaft when moving engine forward again? I'm assuming he just moved it back when he replaced mounts. I know engine will need realigning which I'm going to get a professional to do but I'd rather replace mounts myself to keep costs down 

Cheers

John 

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2 minutes ago, Pirateringo said:

The previous owner of my boat has at some point put on engine mounts thwt are too small for the engine. The original mounts should be 140mm bolt to bolt but he has used 110mm. In doing so the engine has been moved back. So I'm going to replace mounts as there soft anyway. My question is will I need to cut prop shaft when moving engine forward again? I'm assuming he just moved it back when he replaced mounts. I know engine will need realigning which I'm going to get a professional to do but I'd rather replace mounts myself to keep costs down 

Cheers

John 

The physical size of the base of the mountings is not important and some are soft by design, putting a firmer type on could result in a considerable amount of vibration being transmitted through the hull.

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12 minutes ago, Pirateringo said:

The previous owner of my boat has at some point put on engine mounts thwt are too small for the engine. The original mounts should be 140mm bolt to bolt but he has used 110mm. In doing so the engine has been moved back. So I'm going to replace mounts as there soft anyway. My question is will I need to cut prop shaft when moving engine forward again? I'm assuming he just moved it back when he replaced mounts. I know engine will need realigning which I'm going to get a professional to do but I'd rather replace mounts myself to keep costs down 

Cheers

John 

Why would you need to cut the shaft when moving the engine forward?  Maybe when the engine was moved back the shaft was left as it was. Have a look down the weed hatch and see what length of shaft you have sticking out.

 

Pearley beat me to it.

Edited by Flyboy
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1 minute ago, Pirateringo said:

Yep just felt plenty of space there, so next question as I'm new to this ? can I move it back easily, can I do it with boat in water? 

Maybe, but if the replaced mounts were to low then its possible there is a big ridge warn in the shaft where it goes through the stern gland. How did you decide what size mounts it should have and what problems are the smaller ones causing.

 

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I'm just going on what I have read on the web. My engine is a 42hp isuzu. All the mounts I've found for it are 140mm bolt to bolt but the current ones are 110mm The boat shakes excessively with engine running but then 2 of the mounts have become like putty so it could be that. Unless there areounts suitable for my engine at 110mm? 

Engine doesn't look to low as it enters stern gland

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The hardness does not tell you much unless it is accompanied by the size of the rubber part of the mount. 

Most engine mounts are specified by the weight they will bear.  Ideally you would check the loads on each of the engine and gearbox feet and buy mounts accordingly. For simplicity take the weight of the engine and the gearbox, add together and divide by 4 ( if there are 4 mounts).  Then buy mounts where this load is a bit less than the maximum allowed.

N

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1 minute ago, BEngo said:

The hardness does not tell you much unless it is accompanied by the size of the rubber part of the mount. 

Most engine mounts are specified by the weight they will bear.  Ideally you would check the loads on each of the engine and gearbox feet and buy mounts accordingly. For simplicity take the weight of the engine and the gearbox, add together and divide by 4 ( if there are 4 mounts).  Then buy mounts where this load is a bit less than the maximum allowed.

N

OK, so if I do that then the dimensions whether there 140mm or 100mm shouldn't matter? 

If I did decide to move engine back whqt would that entail. Does the prop shaft just slide through stern gland? Or will I need to undo the fittings? 

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Size does not matter?

Nor does the fastening bolt spacing, The verical threaded stud on which the engine fits should be close to the same size as the hole in the engine foot. If not washers will be needed.

The prop shaft should just slide in the stern bearing.  You may need to loosen the stuffing box bolts and should regrease and readjust after moving anyway.   You may have real trouble if the shaft had been worn badly in  its original position.   If you have a no grease stern tube seal this will need to be re-fitted to suit the new shaft position. I think, but I don't know these well. 

If you have a separate thrust block the shaft is normally securedin the bearing by collars and grub screws.  These will need to be loosened to allow the shaft to move.

Don't forget to leave a decent gap between the front edge of the propeller and the back end of the swim, or crap may get trapped and vibration is likely.

N

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47 minutes ago, BEngo said:

Size does not matter?

Nor does the fastening bolt spacing, The verical threaded stud on which the engine fits should be close to the same size as the hole in the engine foot. If not washers will be needed.

The prop shaft should just slide in the stern bearing.  You may need to loosen the stuffing box bolts and should regrease and readjust after moving anyway.   You may have real trouble if the shaft had been worn badly in  its original position.   If you have a no grease stern tube seal this will need to be re-fitted to suit the new shaft position. I think, but I don't know these well. 

If you have a separate thrust block the shaft is normally securedin the bearing by collars and grub screws.  These will need to be loosened to allow the shaft to move.

Don't forget to leave a decent gap between the front edge of the propeller and the back end of the swim, or crap may get trapped and vibration is likely.

N

I wonder if someone had moved the engine back as a band aid repair due to wear on the shaft, it's hard to think of a sensible reason to do this?

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2 hours ago, BEngo said:

Size does not matter?

Nor does the fastening bolt spacing, The verical threaded stud on which the engine fits should be close to the same size as the hole in the engine foot. If not washers will be needed.

The prop shaft should just slide in the stern bearing.  You may need to loosen the stuffing box bolts and should regrease and readjust after moving anyway.   You may have real trouble if the shaft had been worn badly in  its original position.   If you have a no grease stern tube seal this will need to be re-fitted to suit the new shaft position. I think, but I don't know these well. 

If you have a separate thrust block the shaft is normally securedin the bearing by collars and grub screws.  These will need to be loosened to allow the shaft to move.

Don't forget to leave a decent gap between the front edge of the propeller and the back end of the swim, or crap may get trapped and vibration is likely.

N

Yeah, the hole is m16 I've decided I'm going to replace the mounts with the correct 140mm mounts. I'm assuming I can undo the coupling, hoist the engine up using a chain lift. Cut 20mm off end of tube and then replace engine and tube. Please telle if this is fantasy? Oh and it is no grease stern tube. I'm going to get a professional in to realign 

On another note, how do I know if my coupling is flexible or not? I'm thinking if it's not when I do all this I might as well fit one. But no idea which one I have 

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42 minutes ago, Pirateringo said:

Yeah, the hole is m16 I've decided I'm going to replace the mounts with the correct 140mm mounts. I'm assuming I can undo the coupling, hoist the engine up using a chain lift. Cut 20mm off end of tube and then replace engine and tube. Please telle if this is fantasy? Oh and it is no grease stern tube. I'm going to get a professional in to realign 

On another note, how do I know if my coupling is flexible or not? I'm thinking if it's not when I do all this I might as well fit one. But no idea which one I have 

I would suggest with your level of knowledge you leave well alone and if you want it changed get the chap who is going to do the alignment to do it, If you start cutting bits of and cant identify the coupling it could end in tears.

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Thanks for the pix.  I can see no problem with what you propose. Cutting 20 mm off the shaft with a hacksaw will be hard work  but an angle grinder will scatter sparks all over ths engine space, so make sure they don't go anywhere you don't  want them, and take the batteries off charge well in advance if that is the way you choose.

 

Get it lined up before you reconnect the shaft-to-gearbox coupling.

 

N

 

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3 hours ago, Pirateringo said:

Cut 20mm off end of tube and then replace engine and tube.

I don’t get this. If you’re moving the engine 20mm forwards and simultaneously cutting 20mm off the drive shaft won’t the shaft then be 40mm short?

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6 minutes ago, WotEver said:

I don’t get this. If you’re moving the engine 20mm forwards and simultaneously cutting 20mm off the drive shaft won’t the shaft then be 40mm short?

I'm reading it that when the OP says 'forward' he means towards the stern (actually backwards) it is the only way his posts make sense.

 

It would help to use the correct boat terminology.

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1 minute ago, Alan de Enfield said:

I'm reading it that when the OP says 'forward' he means towards the stern (actually backwards)...

Oh... so if he says “on the right” should we assume it’s actually on the port side?

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2 minutes ago, WotEver said:

Oh... so if he says “on the right” should we assume it’s actually on the port side?

 

 

9 hours ago, Pirateringo said:

The previous owner of my boat has at some point put on engine mounts thwt are too small for the engine. The original mounts should be 140mm bolt to bolt but he has used 110mm. In doing so the engine has been moved back.

Unless the propeller is at the front of the boat the picture shows the engine was moved towards the bow 'forward' (you can see the old mount holes), so he intends to put new mounts on and move it towards the stern where it originally was.

 

 

DSC_0222.JPG

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