Shaft alignment.

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burgundyben

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So once I get the half coupling engaged in its register ring, how close should I be aiming to get the shaft alignment?

Using feeler gauges around the circumference.

Fairly bendy wooden boat.
Rubber mounted engines.
6ft long 1.25" shaft with only 1 P bracket.

I have an opinion, just wondered what others think.
 
IMHO I reckon if more than 0.003" can be measured between the 'tight' side and the slack, it can cause rotational stiffness n the form of a tight spot. That is why I put flexible couplings in, but still try and work to 003". Now if the whole lot was completely accessible, hmmmm, in that case it would not be a boat!
 
Floating Preferably said:
IMHO I reckon if more than 0.003" can be measured between the 'tight' side and the slack, it can cause rotational stiffness n the form of a tight spot. That is why I put flexible couplings in, but still try and work to 003". Now if the whole lot was completely accessible, hmmmm, in that case it would not be a boat!
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I think its easier on mine than yours. You are the oracle of such things, afterall, I've had mine a mere 12 years.

I'll leave it for now and double check afloat.
 
burgundyben said:
That's not an answer, engineers work to numbers.

Been suggested to me 1 thou for each inch of hub diameter which would be 5 thou.
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I would go for 5 thou ashore then re-check afloat again to 5 thou. Any closer and you will simply spend hours and hours at it, get bored and then give up with the alignment out one way or the other possibly more than you started with.
 
As already stated "dead on" but the reality is that near on impossible.

Now on Little Ship I spent hours getting to couple of thousands of an inch, then I fitted an R&D coupling which they say can absorb up to 10 thousands.(if memory serves me right) Little Ship is wood and as they all do can flex.

Get it as close as you can and fit the R&D coupling and you won't have any problems.

Tom.
 
LittleShip said:
As already stated "dead on" but the reality is that near on impossible.

Now on Little Ship I spent hours getting to couple of thousands of an inch, then I fitted an R&D coupling which they say can absorb up to 10 thousands.(if memory serves me right) Little Ship is wood and as they all do can flex.

Get it as close as you can and fit the R&D coupling and you won't have any problems.

Tom.
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Exactly my point, its a wooden boat, a fairly bendy one at that, with 1.25" shafts over 6ft long bolted to rebbuer mounted engines.
 
Not wishing to piss on your chips Ben,

first question, are the shafts true, even before you start,shafts of your and my boats vintage,(40/50 year old) the possibility of the the shafts being within 3 thou throw before you start is very unlikely. just sayin'
 
epervier said:
Not wishing to piss on your chips Ben,

first question, are the shafts true, even before you start,shafts of your and my boats vintage,(40/50 year old) the possibility of the the shafts being within 3 thou throw before you start is very unlikely. just sayin'
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That's a valid point.

Just to follow up on this thread, I got the half couplings within 5 thou ashore, one thing led to another and before I knew it I'd done 100 miles.

The port engine stalled a couple of times and on inspection the shaft was a little tight, I had a half arsed go at it saturday but ran out of time, I lifted the front mounts by 2 turns. It was improved.

Tonight I had another go, took paper and pen, drew a circle, used the feeler gauges in a go/no go fashion and wrote down the numbers, I decided the top was a huge 0.019" further apart than the bottom! Side to side spot on. A further 10 flats of the nuts, so a 1 2/3 turns, and I have it within 0.0015". We'll see how she runs.

Maybe she wasn't comfy in the cradle, maybe something's on the move, it is an old wooden boat afterall.

Port idle is a little on the low side at 550/600 or so, if there is still a bit of stallyishness I'll up the idle a little.
 
Only 0.0015" afloat Ben, that sounds pretty darn good. With the bolts tight, is the shaft giving the same resistance when you turn it 360 degrees slowly by hand, or does it still have a tightish spot? All the thrust is taken on the gearbox, so whilst rubber mounts cut noise 'if' they distort more than a gnats that may not help underway, but there is no way we could measure it. Somewhere I had a data sheet that showed on my old set up with original non turbo Fords developing only 105HP the thrust was almost 1000lbs on each shaft, so double it for 200HP. So damn near a ton pushing on each engine. That means every single bolt on each mounting needs to be 100% tight. As you found out you dont need much movement to cause problems. After this episode I am going to regularly check the shaft tightness by hand. Let us know how it goes?
 
Floating Preferably said:
Only 0.0015" afloat Ben, that sounds pretty darn good. With the bolts tight, is the shaft giving the same resistance when you turn it 360 degrees slowly by hand, or does it still have a tightish spot? All the thrust is taken on the gearbox, so whilst rubber mounts cut noise 'if' they distort more than a gnats that may not help underway, but there is no way we could measure it. Somewhere I had a data sheet that showed on my old set up with original non turbo Fords developing only 105HP the thrust was almost 1000lbs on each shaft, so double it for 200HP. So damn near a ton pushing on each engine. That means every single bolt on each mounting needs to be 100% tight. As you found out you dont need much movement to cause problems. After this episode I am going to regularly check the shaft tightness by hand. Let us know how it goes?
Click to expand...

No tight spots, free to turn by hand, I previously thought that when feeling the shaft was tight on our boats you have to consider that you'r doing it upside down at arms length and what may feel tight isn't really very tight at all, but having got this as close as I have I'll retract that.

Our boats are wood and bendy, the shafts long and skinny, in a rubber bearing one end and bolted to rubber feet the other, I think underway its all over the place. As you say the thrust load must move stuff about.
 
In reading this subject it's not clear if during the alignment process the shaft has an intermediate bearing or not! If not are you using a means to hold the shaft central during mount adjustment! Without, how do you measure the central misalignment introduced at the stuffing box and to a degree the 'P' bracket bearing! Agreed a coarse adjustment issue mainly, but just as important overall.

Ideally and I can see your aim is precision (which given the other variables outside your control is not easy) it's worth remembering that to adjust one corner will also require a proportional adjustment elsewhere due to the fact that the centres relationship between each mount and the gearbox could be in the order of 2:1.

e.g. consider a perfect set up which is a tort piano wire between the outboard face of the 'P' bracket and a point to replicate the front end of the crankshaft. Hence to raise for example the front of the engine not only alters the gearbox 1/2 coupling but also the shaft 1/2 coupling with respect to the true drive line. Any adjustment can impact considerably on this fundamental requirement. That's after you consider the effect of shaft droop and then whirl introduced by the inclusion of a flexible couplings!

Not an easy one to crack given the crude methods provided by standard mounting studs and engine bracket slots, and the fact that shaft suppliers can have difficulty in obtaining true original shaft for machining !
 
Surfacesub said:
In reading this subject it not clear if during the alignment process the shaft has an intermediate bearing or not! If not are you using a means to hold the shaft central during mount adjustment! Without, how do you measure the central misalignment introduced at the stuffing box and to a degree the 'P' bracket bearing! Agreed a coarse adjustment issue mainly, but just as important overall.

Ideally and I can see your aim is precision (which given the other variables outside your control is not easy) it's worth remembering that to adjust one corner will also require a proportional adjustment elsewhere due to the fact that the centres relationship between each mount and the gearbox could be in the order of 2:1.

e.g. consider a perfect set up which is a tort piano wire between the outboard face of the 'P' bracket and a point to replicate the front end of the crankshaft. Hence to raise for example the front of the engine not only alters the gearbox 1/2 coupling but also the shaft 1/2 coupling with respect to the true drive line. Any adjustment can impact considerably on this fundamental requirement. That's after you consider the effect of shaft droop and then whirl introduced by the inclusion of a flexible couplings!

Not an easy one to crack given the crude methods provided by standard mounting studs and engine bracket slots, and the fact that shaft suppliers can have difficulty in obtaining true original shaft for machining !
Click to expand...

All valid comments.

There is no intermediate bearing, just the P bracket, the location at the fwd end is by engaging a register ring on the half coupling into its recess in the gearbox flange.

Stern gland is floating (sorry!) on rubber hose mount.
 
Shaft alignment

Surfacesub said:
In reading this subject it's not clear if during the alignment process the shaft has an intermediate bearing or not! If not are you using a means to hold the shaft central during mount adjustment! Without, how do you measure the central misalignment introduced at the stuffing box and to a degree the 'P' bracket bearing! Agreed a coarse adjustment issue mainly, but just as important overall.

Ideally and I can see your aim is precision (which given the other variables outside your control is not easy) it's worth remembering that to adjust one corner will also require a proportional adjustment elsewhere due to the fact that the centres relationship between each mount and the gearbox could be in the order of 2:1.

e.g. consider a perfect set up which is a tort piano wire between the outboard face of the 'P' bracket and a point to replicate the front end of the crankshaft. Hence to raise for example the front of the engine not only alters the gearbox 1/2 coupling but also the shaft 1/2 coupling with respect to the true drive line. Any adjustment can impact considerably on this fundamental requirement. That's after you consider the effect of shaft droop and then whirl introduced by the inclusion of a flexible couplings!

Not an easy one to crack given the crude methods provided by standard mounting studs and engine bracket slots, and the fact that shaft suppliers can have difficulty in obtaining true original shaft for machining !
Click to expand...

Yes, good suggestions, and appreciated. We have decent engineering companies who can confirm, or not, how true shafts are if we are in any doubt. The lateral adjustment is relatively easy if the front seal support rubber tube is all loosened off, as the shaft will lay at its lowest point and on the centre line. The real work is getting the up/down line correct, and as you correctly point out both front and back adjustments have to be co-ordinated. It would be easy if all at eye level on a bench, but grovelling around with arms at full stretch is not too much of a laugh. It is easy to stop too early, saying, 'stuff it that is near enough', but maybe Ben has nailed it this time!
 
burgundyben said:
All valid comments.

There is no intermediate bearing, just the P bracket, the location at the fwd end is by engaging a register ring on the half coupling into its recess in the gearbox flange.

Stern gland is floating (sorry!) on rubber hose mount.
Click to expand...


No flexible coupling I trust!
 
I had a mysterious problem, the shaft ran out of true, I established this by running it slowly with a long lever against it. In the end it was the female register of the gearbox coupling 10 thou out. PRM said that was within normal parameters. Took it to an engineer who fitted an insert and made it right.
 
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