Problems with new engine! aaahhhh, views sought

[noswellplease]

I had a new engine fitted recently which is 10 hp more than the original of 15 hp but so far has been disappointing both in terms of speed and overall noise. The main gripe is that at high revs (e.g above 2,000 rpm) the noise from the general drive shaft area is excessive and I fear not all is as it should be. I'm thinking of getting a second opinion from a marine engineer as I'm not convinced the shaft is lined up properly or as good as it could be. I've had a bolt from the stern tube drop out I'm told from vibration and the boat took water so things just aint good enough. Is it black majic getting this business right or whats the problem anyone know? /forums/images/graemlins/mad.gif

 

[richardabeattie]

A few facts wou;d help! Type of engine for example. Method of mounting. Type of coupling.

 

[Genie]

Re: Problems with new engine! aaahhhh, views sought

Sounds like excessive vibration from not being balanced properly - might also account for power being down as well.
I think I would tell the engineer who fitted it to re-examine it, and if still no better to have it independently assessed.
Either way, if bolts are dropping out, that's not good!
Sorry to hear of your woe - hope it gets sorted pronto for you.

 

[Pye_End]

Speed -

To improve performance you either have to have a more powerful prop, or a faster running prop. Have either of these things changed?

 

[noswellplease]

The engine is a Beta 25hp replacing old Volvo Penta. Mounting, using same engine bed with flexible mounts.
Coupling to drive shaft is again with flexible coupling. Hope that help but no expert on engines.

 

[noswellplease]

Have new prop fitted which should give plenty of push through the water as its 3 bladed.

 

[ccscott49]

Sounds to me to be out of alignment, get it checked pronto. It might be an idea to check the prop has been balanced properly as well, but alignment first. The engine should not be on too flexible mounts!

 

[noswellplease]

Sorry what do you mean by too flexible mounts!.....is it that the amount of adjustment should be down to a minimum?

 

[fireball]

Flexible mounts or springs .... the flexible mounts should dampen any vibration but not allow the engine to wobble out of line too much .... springs would be the ideal flexible mount if you didn't need to line it up... bolted directly to the engine beds would be ideal for lining up, but play havoc with too much vibration through the whole boat.

 

[ccscott49]

No, sorry, but even a "flexible" shaft coupling is mainly for vibration, not to take out any misalignment, the engine should not be on flexible car type mountings, but if beta supplied the mounts, they will be the right ones.
I've fitted a few.
The "flex" coupling, is it a white disc of plastic? which the flange bolts go through, one side only and the other bolts from the shaft coupling, the other way, one side only?
This is the normal way, but the shaft has to be aligned very well, but the fitter should know this.
Check that first, then check the tightness of the engine mounts, before slipping and inspecting the shaft (for straightness), cutlass bearing and prop.

 

[fireball]

Just as a quick question - why do we not seem to use UJs on propshafts? there must be a reason ... ??

 

[stevebirch2002]

Check you have a Right hand Prop for the Beta. The Volvo would of used a Left-hand Prop. Is the installer a professional Marine Engineer?

 

[noswellplease]

Yes beta supplied the mounts but from the manual I think the hight should be kept to a minimum. The flex coupling is a white plastic disc just as you described. Not sure but how does one check the balance of the prop? I think it best for peace of mind not to mind safety to get a second opinion from someone I trust in this this business that the coupling is as they say "spot on" Thanks for your assustance on the problem, much appreciated.

 

[Stemar]

[ QUOTE ]
Just as a quick question - why do we not seem to use UJs on propshafts? there must be a reason ... ??

[/ QUOTE ]I think the main reason is that they're no good at in-line thrust. On the vast majority of set-ups, the thrust from the prop goes through the engine mounts. The aquadrive uses a thrust bearing mounted to the hull to handle the power, and UJs to line everything up. It's a great bit of kit, but more than a little pricey.

 

[Pye_End]

The BZ482 manual gives a min and max height for the mounts. Presume the same in yours.

 

[Searush]

Speed is mainly limited by the waterline of your hull. Excess drive will just make her squat against the bow wave. Max speed should be reached at about, or just before max power.

In a nutshell, if she isn't reaching max speed, or is over revving, you are under propped. If she flies along at low revs & can't reach the revs that give max torque, you are overpropped.

Finally, speed can also be limited by poor setting of the throttle cables - my boat would only do 3kts when I bought it. Readjustment got it to 6.5kts hull speed.

 

[boatmike]

UJs do not compensate for misalignment. Sometimes UJs are used in pairs to transmit power from one centreline to another but even then the output shaft should be strictly parallel to the engine crankshaft in a vertical and horizontal direction to achieve constant radial velocity. Thats why front wheel drive cars have constant velocity joints not universal joints....

 

[boatmike]

Aquadrives are constant velocity joints not UJ's.

 

[boatmike]

If your engine was fitted out of the water it will almost certainly need re-aligning now the boat is afloat. Either way it is clearly not right. Get the guy who installed it to put it right!

 

[Mudhook]

A couple of details...

1. The Aquadrive does not have, as far as I know, a thrust bearing. It is simply a pair of CV joints. I have one and it works brilliantly.

2. UJs give undulating rotational speed and won't handly poor alignment. This give rise to vibration.

Regards, Mudhook.