Engine/shaft alignment

[Manny]

Last time I ran my diesel I noticed the stuffing box seemed to run warmer than usual (even with 3 - 4 drops per minute), so today I decided to check the alignment of the engine and prop shaft. It was off ever so slightly and I went ahead and tried to tweak it. Using a feeler gauge around the flanges, the least amount of misalignment I could get was .025. My question is, Is that still to far out of alignment?
One other thing I was wondering, should the prop shaft rotate fairly easily, or is some resistance expected due to the stuffing box and cutlass bearing? I can turn mine by hand but I am surprised at the amount of force required.

Thanks,

Manny

 

[Stu Jackson]

.025 is very good - usually .03 is fine

and resistance by hand is to be expected, with the transmission in neutral. What engine and transmission do you have?

 

[Maine Sail]

Stu & Manny it's..

Actually .003 not .030. The general rule is .001 for every inch of coupling diameter. I just aligned a Sailnetter's Pearson 303 last week and we were able to get it to .002.

Even Globe the makers of the Drive Saver recommend an alignment of .003 before installation of the Drive Saver.


Here's the exact wording form the installation manual of my Westerbeke:

"The alignment between the propeller
shaft half-coupling and the transmisson half-coupling can
contain an error no greater than .001 in per inch of
the coupling diameter. For example, if your propeller shaft
half-coupling is 3” (76mm) in diameter, the maximum error
that can be allowed in the alignment is .003 in (.076mm)."


There is a HUGE difference between .030 and .003!! Here's a photo..

 

[Ross]

A flexible Drivesaver coupling also helps.

I wouldn't install an engine on flexible mounts without one.

 

[Ross]

One millimeter equals

.0394 inches. A .308 rifle bullet is 7.62 mm.

 

[Mike B]

Now do Manny's specs

That's nice to know Ross but I don't think Manny wants to shoot his coupling
How about you save my brain and do a conversion on Manny's numbers we can trust?

 

[Ross]

I think Maine sail lost a decimal point somewhere

in his numbers. if you measure with a feeler gauge use one that is thick enough to not flex and pull the shaft and coupling to the transmission and check the gap at four points around. Then rotate the shaft a half turn and check again this will show if the shaft is bent. It should be posible to coax the engine around to get perfect alignment. If you are out by .030" you can see that. It is almost the thickness of a dime. It is 10 sheets of paper.

 

[Warren Milberg]

Manny: I have a year old

cutlass bearing and packing gland on my H28.5. I've adjusted the gland so that it doesn't drip at all when the shaft is not turning. It may drip one or two drops per minute when it is turning. Yet I can turn the shaft by hand at the coupler with relative ease -- which I know is a relative term. I'm not sure how much force you must apply to be able to turn your shaft, but it should not be "that hard to do." Clearly, if your shaft is either bent or out of alignment, that would make the force needed greater. But it would seem to me that you may be able to feel it if bent as that would create uneven friction when you try to turn it by hand. Good luck with this...

 

[Bob S]

.025mm

.025mm = .00098 inches close to .001
1mm = .03937 inches

 

[MoonSailer]

Supporting the Shaft

I have a dripless seal and my shaft saggs when uncoupled. How should you support the shaft??? I ask this as when I aligned my shaft it looked great. But with a snorkle I discovered that underwater the shaft wasn't centered in the hull exit hole. Maybe use a coat hanger or car jack to center the shaft in the hole??? I raised the engine some so that the shaft is not rubbing but how to align the coupling and support the shaft??

 

[Stu Jackson]

So much for MY engineering skills

Time to back to my Table -- of Conversions!

Thanks for sorting that out, guys.

 

[Deadhead]

FWIT

Does this make sense?

Reported play in Manny's shaft coupler = 0.025 mm.
Maine Sail's recommended shaft play = 0.003"

First:

25.4 mm = 1"
x mm = 0.001"

So: x = 0.0254 mm

Therefore: 0.001" = 0.025 mm

Also:

25.4 mm = 1"
x mm = 0.003"

So: x = 0.0762 mm (100 times less than Ross' rifle bore)

Manny's shaft alignment would seem to be about right if he used a .025mm feeler gauge.

 

[Maine Sail]

Yup..

I missed the mm part and because my feelers are only labeled in inches I incorrectly thought that's what he meant..

If he got it to .025mm and his coupling is 3 or 4 inches it's better than spec. If he actually meant inches then it's out...

 

[Don12364]

Thrust

We take great pains to achieve 'perfect alignment' between gearbox and shaft.
Our engine is on flexible mountings so when the engine is in gear the propshaft is pushing (or pulling) the engine with the thrust necessary to propel the hull through the water.
A calculation with 'Propcalc' on my H376 shows that this thrust can be as much as 907lbs.
What price the alignment now? The engine mounts will not have a chance of maintaining the alignment to .004" and the chances of a 40" long 1" diameter shaft staying in column are slight.
The design is crazy to bolt it all up rigidly because any misalignment then has to be taken up in the constant flexing of the propshaft and the yielding of the anti vibration engine mountings. Yet still boat builders persist.
Before AV mounts the only way was to bolt everything up solid and hope nothing moved but things are different now.
My solution was to install a flexible coupling which also made things much quieter and made space to fit a rope cutter in front of the prop.
A better solution is a proper cardan shaft but few take the trouble to do this.

 

[Maine Sail]

Donalex

Can you guide me to the Prop Calc web site I have a few scenarios I'd like to run? The only one I can seem to find is for aircraft..

 

[Mike B]

Barnacles

Unfortunately you can have your alignment "spot on" but once the barnacles set up shop on your running gear you'll get vibrations. Just something to be aware of; if you've done alignment to smooth things out and it still doesn't seem right it's time to clean the prop and shaft.

 

[Manny]

Thanks guys

Stu - it's a Renualt RC8d, the transmission is also a Renault as far as i'm aware.
Maine Sail - the engine and transmission have plenty of "issues" ;D My feeler gauge set is in mm due to all the cars I have owned have been Japanese or German so just about all my tools are metric. I have a heck of a time converting Newton Meters to Foot Pounds on my torque wrench! I don't know the exact diameter of the coupling but it is small, maybe about three inches.
Ross & Mike- the 308 idea may be useful to put the Renault diesel out of it's misery ;D
Moonsailor - my shaft also sags when uncoupled (that just sounds wrong!! ) After rebuilding the transmission I ended up aligning to that sag. It seems the stuffing box offers very little support
Donalex - whats a Cardan shaft?
Warren - I tried to find a comparison of how much force it takes to turn the shaft, the only thing I could compare it to are the candles in a glass jar with a glass lid that has a clear plastic or rubber seal on the lid. My wife has a bunch around the house. If you try and turn the lid, it takes about the same amount of force. It rotates 360 degrees requiring an equal amount of force.

Thanks again!

Manny

 

[Mike B]

Shaft sag

Manny, there are drugs that can take care of that shaft sag you're experiencing. Just remember that you don't want you shaft to be sagless for more than 4 hours
Mike

 

[RichH]

Suggestions and comments.....

Manny

Simply align your engine as close as possible using feeler gauges. Try to be as precise as possible so that when you are using the feeler gages (doesnt matter WHAT value/thickness of gage you use) the feeler gage is retracted from the coupling, etc. joint ***with the same approximate amount of hand force***; .... this will insure that the face to face alignment of the coupler is within .001 - .002 inches. All you are doing is adjusting so that the 'faces' of the coupler are **parallel** when you assemble it back together. Dont make this a mathematical nightmare of endless calculations .... just choose 'any' feeler gage, insert it between the coupler faces, move the coupler faces together WITH the gage between, make sure that it withdraws with the ***same force*** at 4-6 places around the circumference .... USE THE FORCE, Luke!

If the prop and shaft is unbent and the blades are clean there will be no induced side forces that will make the shaft 'whip' when rotating under load. Thrust is 'axial' along the shaft and can be totally ignored if the shaft is 'beefy enough' (the shaft would have been already 'knocking and banging' if there already was a 'whip problem') ..... this all assumes that the OEM design engineer did a good job; so, there is no need to 'contemplate someone else's navel'.

If you suspect the very remote possibility that the propshaft has been bent, after you closely align and assemble the faces/coupler, etc., simply use a dial-indicator gage somewhere near the 'mid-span' of the shaft, rotate it and measure the 'run-out'. If you dont have a dial indicator, just put 'something close' to the shaft so that there is the 'teeniest' gap between the shaft and the 'something', put a strong light underneath all and simply visualize how much actual run-out there is when you turn the shaft. If 'significant' then measure the run-out by turning the shaft in ~90° increments, etc. while using feeler gages between the shaft and the 'something'.

Keep it simple; use the force, Luke.

 

[Rick Sylvester]

RichH, I read these sites

(this one and CSBB) for entertainment and to learn. That was one of the most useful and coherent posts I've read in a while. I love your posts. Thanks.

I've aligned my share of shafts and when I do I can never find my dang feeler gauges so I always end up using a hack saw blade. I've always done it the way you describe because it just always seemed to work out okay. Your post made it all make sense.

You da bomb.