Engine Alignment Question

[Fish 0]

I'm attempting to check the alignment of my engine with the prop shaft.

 

I am using a dial indicator - I have this crazy idea that accurate measurement will make the job easier.

 

The gearbox output flange appears to have substantially more play in it than the tolerance I was aiming for in the first place.

How much play would you expect in a gearbox output flange?

 

The gearbox is about 35 years old, the whole set up has had periods of bad vibration, so it is likely the bearings etc are a bit flogged.

 

I was hoping to get the alignment to within 0.125 mm, but currently seem to have a much greater margin of error on my measuring, i.e. the output flange has play in it.

 

Note, I suspect the current problem is with the propeller or shaft (most likely just barnacles on the propeller), but I wanted to start from the top and work through checking everything was correct with the alignment, including basic engine alignment (we use and R&D flexible coupling), both flanges are square on their shafts, the vertical alignment is correct, and if I can, see if there is any obvious bend in my shaft, before I have another go at the propeller.

 

We replaced the engine mounts a while ago and haven't re-checked the alignment after the initial install (which made a massive difference). We also replaced the cutless bearing, and I want to exclude any serious issues that would flog that out, like a bent shaft or completely unacceptable engine alignment. The current vibration feels like it is coming from the back of the boat.

[Fish 0]

The old cutlass bearing was flogged out. The new one seems fine at the moment (minimal play if any). The reason I'm interested in that is we didn't think the old one lasted as good as it should have. Having re-done the engine mounts, drive damper plate and getting the alignment fairly reasonable, we are getting vibration from the back of the boat now. I suspect the prop, but want to rule out a bent shaft (or anything else, like the P bracket, which would really make my day).

 

I don't really want a gearbox shaft bearing problem...

Haven't noticed an oil leak, movement is about 0.3 - 0.4 mm fore and aft. I haven't measured the sideways movement, its not 'sloppy', but I am planning on investigating with a bit more focus on that rather than just the alignment.

 

Our gb weighs about 50 kg, need to pull the engine out to get at it... we did that to change the drive damper plate. The whole set up weighs 280 kg, for a 37 Hp donk. Apparently modern engines are lighter...

[wheels 543]

Whenever you have a vibration, you need to check the Prop first before anything else. It could be anything from a bit of rubbish, some fishing line, some fouling, to a chunk out of a blade, or the most common and often overlooked, is cavitation. Cavitation can be caused by either leading or trailing edge being damaged or as many make the mistake, they sharpen the blades edges thinking that gives a better slice through the water. Then there is the possibility that prop has hit something and a blade is bent ever so slightly.
A shaft does not easily bend. So unless you have had an oopsy, then I doubt it will be bent.
Realigning the engine when you have replaced the mounts is essential.
Don't worry about fore and aft movement on the box shaft. That is normal. The closer you can get the alignment between engine and box the better, but that is more for improving the wear of the flex coupling. The flex coupling takes out the misalignment, but the greater the miss, the greater the wear.
P bearing alignment won't cause vibration issues, but can cause wear of cutlass.

[Fish 0]

Yes Lateral, understand checking a shaft in-situ is unreliable, its more that I invested in a dial indicator for the alignment so thought I'd see if any other rotating parts were out of whack.

 

Thanks Wheels, your comments are pushing me towards something I kind of know is the issue but was putting off dealing with. We've got a kiwiprop, so any fouling (especially barnacles) can cause issues. On top of that, I've been mucking around with blade size and pitch. I went to a larger blade (18.5") which was really good and could run with a reduced pitch, but decided I was getting cavitation with the hull (classic high pitch pinging, just like in a water pump dead-heading). I changed back to an older set of 17" blades, but I'm not convinced they are perfect (we took them off for a reason). The high pitch pinging did go away (which was the purpose of the exercise), but there is still plenty of rattle and noise from the back of the boat. I'll have to buy some new blades, prop-speed them, dry out and fit them.

 

As we hadn't re-checked the alignment after the initial install of the new engine mounts I thought I'd do that and work through the system to make sure everything is in good order before changing the prop again. I thought I'd go for the most accurate method possible with the dial indicator, but it looks like a feeler gauge over the flexi-coupling bolt head is just as reliable for the tolerances we are talking about.

Live and learn.

[John B 106]

Kiwiprop, each blade has its own pitch adjustment screw. Apart from running the thing in gear and observing the shaft for wobble via the poor man's dial gauge, screwdriver, it'd be worth double triple checking the pitch is even for each blade.

[Steve Pope 243]

Are Kiwiprops prone to vibration?

Seems checking the pitch is equal would require a jig setup?

Not really, just count the no. of threads exposed and you should be correct. As they are so light in comparison to a Bronze prop the only reason to vibrate would be mis-adjustment or tooooo many barnacles attached.

[Island Time 1,230]

Measure the distance by the back of the pitch screw, between the blade and the pitch screw stop. If it's the same on all blades, you're good.

[Island Time 1,230]

I've had issues trying to get engine alignment sorted out on several boats before. It's one of the few jobs I won't do. Seems to me that the shaft can sag under its own weight, and be out of alignment when disconnected from the gearbox. If the cutlass bearing isn't perfect, then it can be a bit of an issue.

So, what's the exact proceedure meant to be? Do you use wedges to put it in the centre of the shaft tube? How do you be sure the shaft is absolutely straight before offering it up to the gearbox, and using the feeler blades.

[Fish 0]

Measure the distance by the back of the pitch screw, between the blade and the pitch screw stop. If it's the same on all blades, you're good.

Yes this one (I read it in the manual, but don't tell anyone I gave up and read the manual...)

[Island Time 1,230]

Yes this one (I read it in the manual, but don't tell anyone I gave up and read the manual...)

Yep, that is the last phase, but it does not work if the shaft isnt straight to start with......

So, How do you ensure that the shaft is perfectly aligned first? Given that many shafts are supported only at the cutlass bearing, then at the gearbox...

[Fish 0]

I've had issues trying to get engine alignment sorted out on several boats before. It's one of the few jobs I won't do. 

That's a shame IT, if I got fed up with this job, I was going to give you a call 

 

Barnacles and fouling are the most likely offenders, followed closely by the fact I've got an old set of blades on at the moment They aren't perfect. We have three sets of blades, we keep the old ones for 'spares'. 

[Fish 0]

Yep, that is the last phase, but it does not work if the shaft isnt straight to start with......

So, How do you ensure that the shaft is perfectly aligned first? Given that many shafts are supported only at the cutlass bearing, then at the gearbox...

The difference between the dynamic and static position of the shaft is something I've chosen not to consider yet. I'm currently working on establishing the accuracy of my measuring...

I believe our cutlass bearing is in good order (its new and had low hours). We have a stuffing box, then the gearbox obviously. I know it is very difficult to see if the shaft is bent in-situ, but as wheels says, that is low on the list of likelihood.

 

My basic plan is to check for 'gross' misalignment with the engine, see if there is any gross issues with the shaft, and then tackle the prop (again). This is mainly as we haven't checked the engine alignment since installing the new engine mounts. I understand the rubber can settle a little bit. They are good cushy-float mounts (not cheap).

 

All of this is on the understanding that we use a flexible shaft coupling, and that should handle all but gross misalignment.

There is the practical element that I can check the engine alignment on the water, but have to either dry out or haul out to do the prop. We have no need to haul out for annual maintenance (copper coat), but we are getting up to the point where we should dry out and give the copper coat a scrub, which is when I can suss the prop.

[Island Time 1,230]

Yep, this is why I wont do it as a paid job. A stuffing box should not support the shaft - its on a rubber sleeve on most systems anyway. So, the shaft drops at the engine end under only its own weight.

I've done what I think are very small tolerance adjustments before to static shafts, that are no good at all underway. This is something I've been meaning to investigate properly, to get consistent good results. In my experience simply measuring at the GB is insufficient. Also, even at idle, the engine will move position on its mounts.

A flexible coupling with a thrust plate makes a good deal on sense to me... 

[Fish 0]

Hay IT, when you were doing engine alignment, how did you measure it?

 

My father (who has done it previously) leaves the shaft coupling in place and puts a feeler gauge between one bolt head and the flange, does this at 4 points around.

 

I wanted to check that the shafts are flanges are square on the shafts, and the vertical offset, as well as the alignment.

My first method was to use a key steel between the flanges. The closest we can get the flanges together is 44mm (otherwise I'd just bring them together and put a feeler gauge in them). I got a 22mm key steel and cut it in half. Only one flange has a raise lip in it (to centre it in the opposite flange). I ground out an indent in one key steel. This promptly warped it... I've been filing it back with wet and dry on a flat surface, but it is a real hassle holding the two key steels secure, in what is a very small space, while trying to measure the gaps...

 

So I got a dial indicator. The stand is not ideal, and I can set it up to measure some aspects, but not all of them. This is mainly due to space limitations and the axis of the stand. Basically I could do with a more expensive stand, but things are starting to get silly now.

 

I'm starting to think the feeler gauge on the bolt head is actually the best method, but it doesn't assess the squarness of the flanges or the vertical offset.

[Fish 0]

A flexible coupling with a thrust plate makes a good deal on sense to me... 

Oh, yes I priced one of those... never going to happen.

We don't have space either. The only way I could create space is install a new, modern and much smaller engine. But that would end up with a full re-design and re-build of the engine bed etc, and combined with a thrust bearing, would match the current value of the boat...

[John B 106]

Alignment which is not badly out  is not going to cause vibration, its  bent shaft , prop issue as above ,or the shaft anode( if you have one ) flying around, or grossly eroded out of balance.

 As to getting it right  I think what Matt suggests  is right . Its what I do. You  assist the shaft position by blocking it ( if you think its flexing down over its length) and  adjust the motor mounts to that. In the water.

Actually if you ever observe a motor under power its amazing just how much it moves , mostly forward as the prop leans on it  but  also against the torque of the rotation too.

As an aside  I eyeballed through the shaft log of a Twilight on the hard a few years ago . Very clearly the engine  was out of alignment  in a major way . I'd estimate at about 50 mm.

 When I talked to a Townson guy after that he laughed, that was common . Des being Des he kept weight down by running  a very long  , light shaft and they tended to whip. So by running the engine out of alignment they pre loaded the shaft  and ran it that way , no whip.

[Island Time 1,230]

How come the flanges wont come together? I'm missing something in this picture..

 

What I've done is bring the flanges together until they touch at one point, then adjust the mounts, then check again. Going around and around until a gap of 4 thou or less is achieved.

 

I've just spoken with a boat builder friend. Here is the correct proceedure. HAS to be done out of the water.

Loosen the stuffing box and slide it forwards.

ensure the shaft is in the centre of the tube, support it with wedges/spacers. 

Put dish detergent on the shaft at the cutless bearing and at the stern tube outer end bearing (if fitted - it should be!)

Now slide the shaft up and offer it to the gearbox flange. 

Measure the gap, max 4 thou

Adjust engine mounts as required to get the flanges to click together, and gap less than 4 thou

Bolt up, refit stuffing box (remove wedges of course!), launch and test.

 

Shafts with no bearing in the stern tube can sometimes suffer from shaft whip, which no amount of balancing will fix...

 

My mistake previously was not using the wedges at the stuffing box.

[Fish 0]

How come the flanges wont come together? I'm missing something in this picture..

The prop shaft length is designed to allow for the flexi coupling. The prop is mounted snug to the P bracket, so we can't pull the shaft up to the GB flange. The flexi coupling is about 44mm deep.

 

Tell me more about this bearing in the stuffing box? I've questioned that before. As far as we know there isn't a bearing there, if there is, we've never changed it and its probably stuffed. We have a conventional stuffing box, with flax or hemp stuffing, and grease (and a whole lot of dead wood). I have to pump it every time we've been out, otherwise it weeps and starts filling the bilge (assume that is normal). I've got a grease gun permanently mounted with an extra long hose (so I can reach the damn thing).

 

We had the shaft out 8 to 10 years ago (maybe more) and had it checked for straightness by an engineering outfit. It was fine then. It's 1 1/4 inch, so not a skinny bendy one like on the Townson. We do tighten and re-pack the stuffing box when required.

 

I've never thought of the anode causing an issue. We change it regularly, but it does erode fairly quickly. Its right by the P bracket. I would have looked to the kiwiprop before the anode.

[John B 106]

Its interesting that the boatbuilder says to do all that out of the water, all the advice I've had and worked to over the last few decades is that boats change shape in the water and you must align in. Obviously you do your best out of the water but fine tuning gets done in.

 Shaft anodes can also become loose and rattle,shake around and  carve things up. I daresay you'll know if thats the case

[Fish 0]

Fish, I am surprised your prop is hard against p bracket.

Its not hard up, there is a bit of a gap, just not enough to pull the shaft up to get the flanges face to face. 

I'll measure the gap and see how close I can get it. I think I can get it to about 20-25mm. Flexi coupling is 44 mm.