Engine vibration Part 3

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rays

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A brief summary for new readers!
Attempting to solve vibration which dogged us all last season.
So far: Prop been reground (was out of balence) now declared perfect. Prop shaft tested. Perfect. Cutless bearing checked. Fine.
Yesterday re-installed prop shaft with solid bush in shaft tube and attempted alignment. Boat not straight in cradle as evidenced by locker doors/cabin sole binding. Agreed with engineer to get roughly right and do final adjustment once afloat. Here's my question: with a volvo flexable seal which allows the shaft to droop under gravity, how do you work out the correct alignment on the gearbox coupling? Lifting the shaft slightly by hand allows it to be bolted up. But this proves nothing. How do you proceed?? This is doing my head in (as my children say!)
 
good question, i had the same thing with my aquadrive (early type), in the end i got an old coupling that slid on the shaft in place of the flexible coupling and aligned. then put the aquadrive coupling back.


steve
 
If the shaft is drooping this suggests there is no bearing support for some distance? this may be the source of any vibration. More support = less vibration.

The point to remember is that as soon as you put the engine in gear all the alignment work goes out of the window as the engine moves and tilts under thrust and as a result of boat movement.

Better or longer bearings reduce the ammount of shaft movement but in some designs you are pretty much stuck with the shaft/bearing arrangement you have from new.

After all this work I hope it is better.
 
We always advise chocking the shaft to check bearing and carrier alignment before these are epoxied in place. If you can spin them in the carrier and on the shaft the carrier and bearings are aligned which is a key part of the whole job.
 
The Volvo seal is a very substantial lump of solid rubber and shouldn't let the shaft droop by much, if at all. Can you support the shaft so that the Volvo seal looks straight, then match the gearbox to it?
 
You seem to have done an awful lot but not addressed the original problem.

You told us that the shaft was straight as tested in a lathe....You told us the shaft appeared bent when installed..you told us you percieived run out when you straight shaft was rotated.

We told you that this indicated misalignment. It is not good enough to offer the shaft flange up to the engine and just cos the bolts line up to tighten it all up and head off on the briny. You have to ensure also that the prop shaft and the engine crankshaft are both in line with each other. The information you gave us suggested this was not the case as you appeared to be bendng the prop shaft by tightening the coupling bolts.

You need to offer the shaft flange to the engine coupling. with the shaft flange close to the coupling try depressing it as far as it will go....lifting it as far as it with go ...move to the left as far as it will go and move to the right as far as it will go.

The shaft coupling should move approximately the same amount out of alignment in all four directions to indicate that when connected the shaft is in the middle of the Hole! If the engine is definitely higher or lower than achieves this then correct on all four mounts. Once satisfied the engine is at right height then check the relationship of the two flanges by loosly connecting them and with a feeler gauge check that you get the same feel of friction all the way around the mating surfaces when trying to slide the feeler between them.

You can also try just using the thinnest feeler to measure for a gap when the two couplings are justt touching however on small flanges the first method is adequate and saves the inexperienced from mashing up small feelers.

If you find the coupling faces are not parallel then you adjust the engine angle to rectify. If there is more clearance at the top then the front of the engine needs to rise and if there is more clearance at the bottom then the front of the engine has to drop. The same goes for clearance on the sides where the front of the engine has to be moved in the direction where the max clearance is felt.

Once you are happy you have the same feel all around the mating faces DO TIGHTEN UP and go to the pub ,you should do a second test which will confirm there are no machining defects of the coupling face . Move the shaft coupling half away from the engine,turn the shaft 180 degrees and reconnect the coupling flanges losely just nipping the feeler. Now test again with the feelers. The feel again should be the same all around the mating surfaces. If it isn t then the face of the shaft coupling is out of true and if this is mesurable should be rectified in a lathe. I suspect this may be your problem as this is a test often not bothered with as everyone expects a perfect world and perfect couplings!!!!!

Sorry to repeat my self but I am telling you to suck the same eggs as I did in your previous post

I am sure your problem is nothing to do with out of balance propellers etc but due to the engine not lying in line with the propshaft which would give this bowing effect you talk about.
Running the engine in this state means you are creating unnecessary wear in the cutless and cyclic loads on the coupling bolts which is likely to cause premature failure.

When the engine and shaft are in line then you will not detect this run out of the shaft and the whisky glasses wont slide of the cockpit table.
 
You mention a solid bush in the tube. Is this permanent and supporting the shaft? If so then you need not worry about the shaft, only getting the engine lined up. You will not get significant "droop" from the Volvo seal even if you have no fixed bearing in the tube. It is a very substantial rubber bearing and most of it acts in much the same way as a cutless bearing.

If I were doing this job I would align on shore - I think the amount of flexibility of engine beds in relation to the hull on a boat like yours is negligible, and then fine tune when it is in the water. Installing a flexible coupling like a Bullflex is a further refinement and essential if you have indeed put a fixed bearing in the tube. Otherwise you have a flexibly mounted engine and a rigid shaft.

Hope I have not confused you - just that your mention of a bush in the tube adds a new dimension!
 
Tranona,

We used the solid bush to check the alignment before substitueting the Volvo seal. The alignment was close and we adjusted the engine mounts to get closer still. When I said that the Volvo seal allowed the shaft to "droop" this was only by 2-3mm. However, I presume that I need a tolerance approaching this?
 
Bilgediver,

Thanks for your very clear advice. This is exactly what we shall try and do.
The buggering around so far has been to exclude the posibility of the prop and/or shaft being the problem before we launch and then have to crane her out again at vast expense. Also, the prop had a visible ding in one blade.
 
If I understand correctly, one your concerns is ensuring the shaft is correctly aligned with the p bracket shaft bearing, and knowing how much to lift it up at the coupling end to achieve this once the boat is back in the water.

Although, as it turned out for me any hull flexing changing the alignment was negligable, I was similarly concerned as you are and therefore did the following;

With my boat ashore, I made up a removable block (with locating lugs of polyester filler) to support the shaft in the correct place to maintain free running in the bearing. I have subsequently been able to put the block in position, uncouple the shaft, adjust the engine alignment and know the shaft is where it should be in relation to the p bracket bearing.
 
Hello Ray
Commercial Vibration process equipment is my Business but much I have found applies to boats.
I have just picked up your thread and do not see some of the obvious points to check first before spending lots of money for engine vibration problems as you may well be up a gum tree!
Vibration transmits and normaly amplifies in distance, Water is one of the greatest amplifiers and transmitters of vibration.
Visual Vibration (where you may see or hear it) may not be the cause of the vibration.
I do not see on posts (maybe on earlier) but I would start with the engine mounts.
A) Are they all tightly secure?
B) Are they all level?
C) Have you checked that the rubber isolation mountings are in good condition?
D) Have you checked all 'interfaces', ie is any part of the engine other than normal rubber hoses/cables coming in hard contact with the engine bay when the engine is running?
Your problems may lie elsewhere and you appear to be concentrating on the shaft alignment which is also a possibility but my point is do not think this is the obvious answer!
If I can help ask.
Mike
 
Thanks for clarifying the use of the bush. If you lined it up with the bush in place and the shaft turned freely then it should be OK when you bolt it up again. Don't forget to burp the seal when you go back in the water!
 
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