I have a 1986 Mercruiser 190 3.7L 224 CI engine and an Alpha one Stern drive. I am experiencing a loud knocking/rattling when the boat is under load. Now for some background history.... This year had the boat in the water, everything ran just fine and dandy. I was taking in water so the next day I looked at the bellows and there was a nice large chunk of the universal bellows missing. Took the boat out of service and proceeded to change all the bellows and gimbal bearing. The drive shaft on the drive was pretty rusted so I had it replaced by a marine mechanic along with a seal since there was gear lube all over in the bellows. Put it all back together, installed the drive and made an adjustment to the shift cable according to the manual.
With fresh gear lube in the drive, I started her up in the driveway and put it in both forward and reverse. All sounded just fine.
Brought the boat to the dock. Puttered out and slowly and began to increase the throttle. Before I even got up on plane a loud knocking sound occured. I backed off and slowly did the same. Again a loud knocking noise. Stopped and puttered back to dock. Attached the muff once out of the water and I can hear the noise, only slightly at idle now. No noise when slowly increasing the throttle through the whole range. Can only duplicate the noise (to some degree) by whacking the throttle when out of the water. Took a mechanics stethoscope during idle and listened to both bottom end, upper end, rear...etc..All sounds just fine EXCEPT the transom plate on the rear of the boat. This is the only place I hear slight knocking at idle. Have not had the opportunity to have another person whack the trottle while I listen with the stethoscope.
Now before I picked up the stethoscope, I removed the stern drive and ran the motor (with cooling water) to try to isolate if it was due to the drive or the motor. The noise WAS STILL THERE. Again only noticable when whacking the throttle. I had re-installed the drive for ease of supplying cooling water and began listening with the stethoscope as mentioned above.
So here I am, Boat was just fine running as it should first day of the season, find torn bellows, replace them and gimbal bearing and universal on the drive, reinstall and now a loud knocking coming from the motor when under load.
I should mention that I did purchace a alignment tool and was able to insert it fully to the back of the coupler. Although the markings on the top of the tool indicated that the front of the motor is high, but the front motor mount is crancked all the way down. I was able to easily insert the drive shaft into the coupler.
The motor was rebuilt and has only approx. 70 hrs. on it. It was pulled last time due to a spun bearing. Don?t recall if it was a main or a rod bearing.
So what do you think?.............
With fresh gear lube in the drive, I started her up in the driveway and put it in both forward and reverse. All sounded just fine.
Brought the boat to the dock. Puttered out and slowly and began to increase the throttle. Before I even got up on plane a loud knocking sound occured. I backed off and slowly did the same. Again a loud knocking noise. Stopped and puttered back to dock. Attached the muff once out of the water and I can hear the noise, only slightly at idle now. No noise when slowly increasing the throttle through the whole range. Can only duplicate the noise (to some degree) by whacking the throttle when out of the water. Took a mechanics stethoscope during idle and listened to both bottom end, upper end, rear...etc..All sounds just fine EXCEPT the transom plate on the rear of the boat. This is the only place I hear slight knocking at idle. Have not had the opportunity to have another person whack the trottle while I listen with the stethoscope.
Now before I picked up the stethoscope, I removed the stern drive and ran the motor (with cooling water) to try to isolate if it was due to the drive or the motor. The noise WAS STILL THERE. Again only noticable when whacking the throttle. I had re-installed the drive for ease of supplying cooling water and began listening with the stethoscope as mentioned above.
So here I am, Boat was just fine running as it should first day of the season, find torn bellows, replace them and gimbal bearing and universal on the drive, reinstall and now a loud knocking coming from the motor when under load.
I should mention that I did purchace a alignment tool and was able to insert it fully to the back of the coupler. Although the markings on the top of the tool indicated that the front of the motor is high, but the front motor mount is crancked all the way down. I was able to easily insert the drive shaft into the coupler.
The motor was rebuilt and has only approx. 70 hrs. on it. It was pulled last time due to a spun bearing. Don?t recall if it was a main or a rod bearing.
So what do you think?.............