Vibration when put into reverse

E

Ehoyles

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I was training a boat owner on a 41 foot, 1990 Silverton with 3208 Cats. There was a bad vibration from the Stbd engine when placed in revers. It seemed to smooth out as RPM was brought up from idle. No vibration when in forward.
Any ideas as to what might be the problem?
 
It had just come off an out of the water survey 1 week before with no problems found in the running gear. Struts, wheel, bearing reported to be ok. On sea trial it was not reported as any vibration.
 
Low speed V Drive rattle? Does it have Walter V Drives?

Bob
 
It occurs for the same reasons in straight drives as well. Idle too low for the load. Aggravated by irregular turbulent flow over the blades from cupped aft edges in reverse, especially when shifting into reverse with vessel retaining forward momentum. It's not necessarily the problem on Capt. Ed's trainee's boat, but it's usually the 1st thing to consider with idle noise that disappears with slightly higher rpm.
 
someone should watch that engine and shaft when it is happening to see if the motor mounts are OK.
 
Probably excessive clearance on strut bearing.
Did you see when it was checked? I don't trust "mechanics".
 
Vibration or rhythmic knocking at clutch astern that goes away as the speed is brought up? And it only does it on one side?
 
In talking with a surveyor, he suggested the oil pump in the transmission could not have sufficient pressure. Oil levels are ok.
 
A semi-balanced rudder if it's loose in it mount will do that. The rudder will flutter.
 
quote:
Originally posted by JimPend

A semi-balanced rudder if it's loose in it mount will do that. The rudder will flutter.

Click to expand...


Will pass this one on, thanks
 
The first inboard I had did that, I tighted the packing nut and it stopped. Most rudders are semi-balanced so it's a real possibility.
 
open up the engine room hatch and look at the motor when this is happening. put your hand on the motor and see if the motor is shaking more than the other thru the gear changes. look at the tachs and see if both engines are spinning at the same speed thru reverse and forward shifts. a very low RPM when the gear is engaged will make the engine run very rough. if the engine is idleing just below rated idle and its cold any drop in RPM's will make it run very rough. a photo tach will answer this question.

its also worth the trouble to put on a mask and hop over the side and visually verify that there is nothing fouling the gear on that side.

almost forgot the most important thing to look for, check for a broken motor mount. you'll be able to see it when the engine is under load. check in both directions.
 
quote:
Originally posted by vic33004

its also worth the trouble to put on a mask and hop over the side and visually verify that there is nothing fouling the gear on that side.

Click to expand...


With the engines off, keys out of the ign's etc etc etc. And also make sure someone is watching you while your diving.
 
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