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Tips for engine alignment with cutlass bearing


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Hi,

I know this is a fairly well-covered topic on here, but I'm after tips in aligning my engine better. It's an Isuzu 35, with a solid coupling between the flange of my PRM120 gearbox to the propshaft, and the shaft goes through a Vetus cutlass bearing stern gland.

With a dial gauge and turning the shaft by hand I have around 0.4-0.5mm radial misalignment. The whole engine moves in a small ellipse when in gear, and starts to vibrate quite badly above 1000rpm.

I've read lots about doing the alignment:

http://www.canaline-engines.co.uk/wp-content/uploads/2017/06/Canaline-Operators-Handbook-CE-Version-3870T.pdf

https://www.yachtsurvey.com/Alignment2.htm

 

But with a cutlass bearing, when you disconnect the prop shaft it just sags down, so you can't align the engine to it. When connecting the two flanges together, they seem to fit very nicely with no obvious angular mismatch. I admit I haven't actually checked this with feeler gauges, but I don't see the point if the propshaft is free to flop around anyway?

I've tried one thing by keeping the propshaft connected, and making small adjustments to the engine mounts, re checking the eccentricity, re-adjust, and so on. After an hour I had improved it slightly to about 0.3mm, but surely it can be better? 

I've also heard the propshaft can be supported in place when disconnected with a bit of wood with a V notch, or similar. But in this case how do you know the shaft is in the correct place? What do you have other than 'feeling' when it's in the centre of the cutlass bearing, and how to you know it's sitting at the right angle?

 

Any tips greatly appreciated!

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Checking the coupling with feelers gauges gets the engine and prop shaft in line, as the cutlass bearing end of the shaft can't 'flop about'.

How old are the engine mounts?  They could have lost their stiffness.

I have Beta38, PRM120, R&D coupling, cutlass bearing. My vibrations and noise improved tremendously when I had the prop reconditioned by Crowthers. Not cheap but worth every penny. My shaft was worn, and I also replaced it and the bearing, along with the engine mounts, but it was the prop that made the difference. 

 

Richard 

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3 hours ago, GrahamSop said:

I've also heard the propshaft can be supported in place when disconnected with a bit of wood with a V notch, or similar. But in this case how do you know the shaft is in the correct place? What do you have other than 'feeling' when it's in the centre of the cutlass bearing, and how to you know it's sitting at the right angle?

 

Any tips greatly appreciated!

 

The way I have done it is to move the shaft vertically and horizontally and estimate the centre position and the hold the shaft while someone else puts the wood in place.

 

Unless you have a flexible stern gland like the Vetus etc ( you do) the shaft should not drop to an appreciable degree because its supported by the gland the plain bearing behind it. If it does the it suggest a worn shaft and/or worn plain bearings. If you do have a flexible gland  you could set your piece of wood by looking at the rubber section and getting it as near straight as possible.

 

I have just checked a PRM manual and it gives the maximum misalignment of 0.05mm. I think this is   angular  so get those feeler gauges out. There should be as close to  zero radial misalignment as possible.

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5 hours ago, GrahamSop said:

Hi,

I know this is a fairly well-covered topic on here, but I'm after tips in aligning my engine better. It's an Isuzu 35, with a solid coupling between the flange of my PRM120 gearbox to the propshaft, and the shaft goes through a Vetus cutlass bearing stern gland.

With a dial gauge and turning the shaft by hand I have around 0.4-0.5mm radial misalignment. The whole engine moves in a small ellipse when in gear, and starts to vibrate quite badly above 1000rpm.

I've read lots about doing the alignment:

http://www.canaline-engines.co.uk/wp-content/uploads/2017/06/Canaline-Operators-Handbook-CE-Version-3870T.pdf

https://www.yachtsurvey.com/Alignment2.htm

 

But with a cutlass bearing, when you disconnect the prop shaft it just sags down, so you can't align the engine to it. When connecting the two flanges together, they seem to fit very nicely with no obvious angular mismatch. I admit I haven't actually checked this with feeler gauges, but I don't see the point if the propshaft is free to flop around anyway?

I've tried one thing by keeping the propshaft connected, and making small adjustments to the engine mounts, re checking the eccentricity, re-adjust, and so on. After an hour I had improved it slightly to about 0.3mm, but surely it can be better? 

I've also heard the propshaft can be supported in place when disconnected with a bit of wood with a V notch, or similar. But in this case how do you know the shaft is in the correct place? What do you have other than 'feeling' when it's in the centre of the cutlass bearing, and how to you know it's sitting at the right angle?

 

Any tips greatly appreciated!

Maybe I'm reading this or interpreting it wrong but if you can't disconnect the prop shaft how do you check the radial alignment? 

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2 hours ago, Neil2 said:

Maybe I'm reading this or interpreting it wrong but if you can't disconnect the prop shaft how do you check the radial alignment? 

I suppose you use a DTI and look for the amount the engine moves under the influence of the out of alignment but it would be far easier to split the coupling. I think the OP has used a DTI. At least with a solid coupling he has no need to use a dummy in place of a flexible to align the two half couplings

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17 hours ago, Neil2 said:

Maybe I'm reading this or interpreting it wrong but if you can't disconnect the prop shaft how do you check the radial alignment? 

I can disconnect the propshaft. But even without disconnecting it, as Tony says you can put a dial indicator with the base fixed to the hull and the needle on the propshaft.  Turning it by hand will still show if the propshaft is oscillating in an ellipse or not.

I initially attached the indicator base to the engine block and registered no misalignment...only to realise this was because the whole engine was moving ? 

(although this is a nice check to see if the shaft is bent or not)

Edited by GrahamSop
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On 23/07/2019 at 14:45, Tony Brooks said:

 

The way I have done it is to move the shaft vertically and horizontally and estimate the centre position and the hold the shaft while someone else puts the wood in place.

 

Unless you have a flexible stern gland like the Vetus etc ( you do) the shaft should not drop to an appreciable degree because its supported by the gland the plain bearing behind it. If it does the it suggest a worn shaft and/or worn plain bearings. If you do have a flexible gland  you could set your piece of wood by looking at the rubber section and getting it as near straight as possible.

 

I have just checked a PRM manual and it gives the maximum misalignment of 0.05mm. I think this is   angular  so get those feeler gauges out. There should be as close to  zero radial misalignment as possible.

Thanks Tony, 

Yesterday I spent a few hours trying to get the alignment as perfect as possible using feeler gauges between the two flanges (gearbox flange and my split half-coupling on the propshaft).

Unfortunately after bolting everything back up it is only very slightly improved, and the shaft still moves about 0.3mm when it is turned.

 

However, I think I discovered a bigger problem:

After aligning as best as I could, I mounted the base of the dial indicator to the engine itself, not the hull.

First I measured the radial displacement of gearbox flange. this was zero. Then the flange on the half-coupling, this was also fine, <0.05mm.

Then I measured the propshaft to have a significant displacement. The further I measured from the coupling, the bigger the displacement. So it seems my propshaft is clamped at a slight angle in the half-coupling, or it is bent. I think this is the main cause of my vibrations and it explains why I can't align the engine better.

 

I am pretty reluctant to loosen the half coupling as I think it'll be the start of other problems like not getting it tight enough again, or making the alignment even worse!

I could possibly fit a flexible coupling between the flanges but I feel it's really covering over the problem rather than sorting it out.

 

What are your thoughts?

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If you have no run out on the gearbox flange with the propshaft disconnected it would appear to me that when the shaft is connected to the gearbox you get run out either the shaft is bent or the coupling on the shaft is not running true with the shaft. This can be checked by measuring the gap around the two faces of the coupling when they are pushed together. If it is not running true it will try and bend the shaft when tightened and cause vibration as will a bent shaft or a damaged propeller. You could fit an R and D flexible coupling if you have room which may give it a bit more fredoom and take some of the load off the gearbox bearings. I think prm recommend that you do this.  It should not cause any problems to take the half couping off and examine it - maybe the keyway/key has been damaged a bit it if you hit something. I had a boat with very long shafts on cutlass bearings and when you disconnected them they sagged by about 1/2 inch so the only way to align them was on the faces of the coupling. Hope this helps

M

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33 minutes ago, GrahamSop said:

Thanks Tony, 

Yesterday I spent a few hours trying to get the alignment as perfect as possible using feeler gauges between the two flanges (gearbox flange and my split half-coupling on the propshaft).

Unfortunately after bolting everything back up it is only very slightly improved, and the shaft still moves about 0.3mm when it is turned.

 

However, I think I discovered a bigger problem:

After aligning as best as I could, I mounted the base of the dial indicator to the engine itself, not the hull.

First I measured the radial displacement of gearbox flange. this was zero. Then the flange on the half-coupling, this was also fine, <0.05mm.

Then I measured the propshaft to have a significant displacement. The further I measured from the coupling, the bigger the displacement. So it seems my propshaft is clamped at a slight angle in the half-coupling, or it is bent. I think this is the main cause of my vibrations and it explains why I can't align the engine better.

 

I am pretty reluctant to loosen the half coupling as I think it'll be the start of other problems like not getting it tight enough again, or making the alignment even worse!

I could possibly fit a flexible coupling between the flanges but I feel it's really covering over the problem rather than sorting it out.

 

What are your thoughts?

That depends on exactly how the half coupling is secured on the shaft. On the hire fleet we used a standard prop shaft taper with key secured by nut in a deep recess in the half coupling.  In that scenario I would suspect poor machining on the shaft and doubt removing the half coupling would do any good. If its a shrunk on coupling then you stand as much chance of  slightly bending it a s getting it off. But you talk about not getting it tight enough so suspect it is one with clamp bolts through the coupling on either side of the shaft. If so I doubt you will do any harm in loosening the bolts and seeing it it will come off without too much effort but if it involves a key then you only have one way of reassembling it so may not be able to do much. If you do not have a large torque wrench a socket on a half inch square breaker/knuckle bar plus a tube extension will probably get the bolts tight enough.

I would comment that some of the stainless steel shafting we bought in to may shafts fro the hire fleet was not exactly true when we got it. If the shaft is bent then messing with the coupling will do no good at all. This was true even if the shafting came strapped to wood. I think it would be a good idea to set the shaft in the V block we talked about earlier, secured a well as you can and put the DTI on the disconnected shaft just behind the coupling. That would give you a good idea if its a coupling or shaft problem.

 

I suspect in the end if you want it better than you have it now the cheapest way might be a decent flexible coupling.

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16 hours ago, Mike Adams said:

If you have no run out on the gearbox flange with the propshaft disconnected it would appear to me that when the shaft is connected to the gearbox you get run out either the shaft is bent or the coupling on the shaft is not running true with the shaft. This can be checked by measuring the gap around the two faces of the coupling when they are pushed together. If it is not running true it will try and bend the shaft when tightened and cause vibration as will a bent shaft or a damaged propeller. You could fit an R and D flexible coupling if you have room which may give it a bit more fredoom and take some of the load off the gearbox bearings. I think prm recommend that you do this.  It should not cause any problems to take the half couping off and examine it - maybe the keyway/key has been damaged a bit it if you hit something. I had a boat with very long shafts on cutlass bearings and when you disconnected them they sagged by about 1/2 inch so the only way to align them was on the faces of the coupling. Hope this helps

M

Thanks Mike, glad to have a second person suggesting either the shaft is bent or the coupling is not running true.

 

16 hours ago, Tony Brooks said:

That depends on exactly how the half coupling is secured on the shaft. On the hire fleet we used a standard prop shaft taper with key secured by nut in a deep recess in the half coupling.  In that scenario I would suspect poor machining on the shaft and doubt removing the half coupling would do any good. If its a shrunk on coupling then you stand as much chance of  slightly bending it a s getting it off. But you talk about not getting it tight enough so suspect it is one with clamp bolts through the coupling on either side of the shaft. If so I doubt you will do any harm in loosening the bolts and seeing it it will come off without too much effort but if it involves a key then you only have one way of reassembling it so may not be able to do much. If you do not have a large torque wrench a socket on a half inch square breaker/knuckle bar plus a tube extension will probably get the bolts tight enough.

I would comment that some of the stainless steel shafting we bought in to may shafts fro the hire fleet was not exactly true when we got it. If the shaft is bent then messing with the coupling will do no good at all. This was true even if the shafting came strapped to wood. I think it would be a good idea to set the shaft in the V block we talked about earlier, secured a well as you can and put the DTI on the disconnected shaft just behind the coupling. That would give you a good idea if its a coupling or shaft problem.

 

I suspect in the end if you want it better than you have it now the cheapest way might be a decent flexible coupling.

Thanks Tony, it is a split half coupling with the clamp bolts either side of the shaft. I will have a look more closely, I am not sure if it has a key or not. I don't have a torque wrench but I do have large socket set with breaker bars etc. I'll try again putting the shaft in the V block and try to determine if it is the shaft that is bent or the coupling.

 

Regardless, I think I will get a flexible coupling for now, as I'd be happier taking some of the vibrations out of the gearbox flange. It seems a sensible addition to have in the drivechain anyway. I have plenty of room between rudder and prop to push back the 3cm or so to get the flexi coupling in. But is it a bad idea to have this length of shaft sticking out the other end of my cutlass bearing, between the end of the bearing and the prop? I have no plans to take the boat out of the water until next year, so shortening the shaft/getting a shorter one is not going to happen at the moment.

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17 minutes ago, GrahamSop said:

Thanks Mike, glad to have a second person suggesting either the shaft is bent or the coupling is not running true.

 

Thanks Tony, it is a split half coupling with the clamp bolts either side of the shaft. I will have a look more closely, I am not sure if it has a key or not. I don't have a torque wrench but I do have large socket set with breaker bars etc. I'll try again putting the shaft in the V block and try to determine if it is the shaft that is bent or the coupling.

 

Regardless, I think I will get a flexible coupling for now, as I'd be happier taking some of the vibrations out of the gearbox flange. It seems a sensible addition to have in the drivechain anyway. I have plenty of room between rudder and prop to push back the 3cm or so to get the flexi coupling in. But is it a bad idea to have this length of shaft sticking out the other end of my cutlass bearing, between the end of the bearing and the prop? I have no plans to take the boat out of the water until next year, so shortening the shaft/getting a shorter one is not going to happen at the moment.

Have you considered fitting an Aquadrive or Pythondrive?  No more alignment problems and includes a thrust block to take the thrust off the engine/gearbox, and no problems with sagging engine mounts either.

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I have had one experience of a clamp on split coupling being out of true due to having been fitted with all the bolts on one side tightened before any on the other side. Maybe this is a red herring but I would try slackening all and tightening opposed ones.

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2 minutes ago, Flyboy said:

Have you considered fitting an Aquadrive or Pythondrive?  No more alignment problems and includes a thrust block to take the thrust off the engine/gearbox, and no problems with sagging engine mounts either.

In an ideal world that would be nice. But this would definitely need a shorter propshaft and the boat out of the water. Maybe one day. There are plenty of boats without a thrust block, and my mounts are in pretty good condition so I think for now I'll make do with how it is.

3 minutes ago, Boater Sam said:

I have had one experience of a clamp on split coupling being out of true due to having been fitted with all the bolts on one side tightened before any on the other side. Maybe this is a red herring but I would try slackening all and tightening opposed ones.

Interesting suggestion, I might try loosening and re-tightening to check this, thanks!

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1 minute ago, Flyboy said:

Have you considered fitting an Aquadrive or Pythondrive?  No more alignment problems and includes a thrust block to take the thrust off the engine/gearbox, and no problems with sagging engine mounts either.

I hope he won't mind me saying this, but member "DOR" did exactly this on his Vetus sterngear setup. A fine job it is too.

My Vetus set up  had an R&D nylon type flexible coupling (not very flexible in reality.) It was been fine for 10+years (I no longer have a Vetus stern gland and much prefer the Radice unit now fitted.) Vetus have changed their stance slightly over the years as to whether a flexible should, or shouldn't be included in this setup. They told me that "they would expect to see a flexible coupling>"

6 minutes ago, Boater Sam said:

I have had one experience of a clamp on split coupling being out of true due to having been fitted with all the bolts on one side tightened before any on the other side. Maybe this is a red herring but I would try slackening all and tightening opposed ones.

I think that is a good point. When I refitted ours I did the bolts as if it where perhaps a cylinder head, taking them up to half torque working diagonally opposites and then full torque.

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Hi all,

Over the weekend I installed an R&D type flexible coupling, and to do it I had to remove the split half-coupling from my propshaft anyway, in order to get the old bolts off it.

After installing the new R&D flex and reclamping the half-coupling onto the shaft, doing the pinch bolts alternately, I'm happy to say my alignment is now much better ?

I think the reclamping of the half-coupling was what made the biggest difference, as now there is <0.05mm movement on the shaft, but there is also barely any angular misalignment, judging from the red bolt system on the R&D coupling with feeler gauges. But I'm happy to have the flexi coupling installed now as well - all runs much more smoothly and no engine oscillating around in the mounts any more.

Thanks for all the helpful replies!

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1 hour ago, GrahamSop said:

Hi all,

Over the weekend I installed an R&D type flexible coupling, and to do it I had to remove the split half-coupling from my propshaft anyway, in order to get the old bolts off it.

After installing the new R&D flex and reclamping the half-coupling onto the shaft, doing the pinch bolts alternately, I'm happy to say my alignment is now much better ?

I think the reclamping of the half-coupling was what made the biggest difference, as now there is <0.05mm movement on the shaft, but there is also barely any angular misalignment, judging from the red bolt system on the R&D coupling with feeler gauges. But I'm happy to have the flexi coupling installed now as well - all runs much more smoothly and no engine oscillating around in the mounts any more.

Thanks for all the helpful replies!

Great result :)

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