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Engine Alignment Question


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#1 Fish

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Posted 15 May 2018 - 10:58 AM

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.


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#2 lateral

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Posted 15 May 2018 - 01:50 PM

No expert, but if you have got play (side to side) in your output shaft you have got shaft bearing problems in you gb. Should be 5/8 of FA.

Surprised the oil seal ain't letting oil out.

What sort of play have you in your cutlass?

 

Last year I machined the output shaft a smidge as it wasnt going to seal on the newy..

Just to next size down seal. Good as gold.

 

I did break a quarterbirth bunk lid hoisting the gb out tho.

Did it in the water with a bit of contorsionary.


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#3 Fish

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Posted 15 May 2018 - 02:03 PM

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...


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#4 lateral

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Posted 15 May 2018 - 02:21 PM

I think ruling out a bent shaft would be a bit hit and miss to set up insitu. 

I  have to pull the motor forward to get the prop shaft out & set up on a lathe/dial g or straight edge it on a table.

 

The fore & aft play you would have to check your manual, but doesn't seem like a cause of off axis

vibration.

Should really cleanup your prop first.

 

Need an expert. Too many variables.


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#5 wheels

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Posted 15 May 2018 - 05:44 PM

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.


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#6 Fish

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Posted 15 May 2018 - 07:52 PM

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.


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#7 John B

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Posted 15 May 2018 - 09:24 PM

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.
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#8 lateral

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Posted 16 May 2018 - 08:18 AM

Are Kiwiprops prone to vibration?

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


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#9 Steve Pope

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Posted 16 May 2018 - 08:45 AM

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.


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#10 Island Time

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Posted 16 May 2018 - 08:54 AM

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.
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There is nothing, absolutely nothing, half so much worth doing, as simply messing about in boats





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