knocking sound from lower unit that came then disappeared?

[dave buckner]

i have '74 mercruiser 165hp i/o i have had for one month. boat seems to be well cared for and it has performed flawlessly until today. all at once a knocking sound appeared from the lower unit(motor sonds fine). as rpms increase, knocking increased.(propeller shows no signs of contact with ground) i was worried something was going to snap, so i nursed boat home at idle. when i got close to ramp it seemed sound was gone , i increased rpms and boat planed out, etc with no noise. problem seemed to disappear. whats going on?? does this sound like gimbal bearing? i intend to recheck lower unit oil tomorrow, but it was at proper level with no water in it when i bought boat. any input would be appreciated. THANKS, DAVE

 

[sea wolf]

Re: knocking sound from lower unit that came then disappeared?

start the engine & turn the wheel left to right. if u hear knocking noise it's probably u joints. you'll have to pull the drive to check/replace em. if u do pull drive u might as well change em out anyway. while u got it off check gimbal bearing.

 

[dave buckner]

Re: knocking sound from lower unit that came then disappeared?

i tested motor in driveway and got no strange noises anywhere in the steering range. there seems to be no problem. if u-joints are going bad is it something that will make more racket , or break all at once? im wondering if lower unit check can wait till end of season or if im about to have catastrophic failure? thanks again, dave

 

[SS MAYFLOAT]

Re: knocking sound from lower unit that came then disappeared?

Did you notice this when you shut off your engine while still in gear? If so that is normal. It is the prop spinning on the output shaft that has stopped turning when the engine was turned off. Hopefully this is the noise that you heard. Good Luck.

 

[dave buckner]

Re: knocking sound from lower unit that came then disappeared?

ss mayfloat, no this was not an intermittant sound between gear changes. it was continous in either forward or reverse for 30 minutes at least, but then disappeared. it was a knocking sound from the lower unit that varied with rpms. i really thought something in the lower unit was going to bread, but noise went away i hasnt happened again...yet. im confused as hell. i definately need a manual. if anyone has feedback on where to get a good deal it would be appreciated. thanks, dave

 

[kdmiller8251]

Re: knocking sound from lower unit that came then disappeared?

Have you check the fluid levels in the lower unit???<br /><br />Could be a problem there?<br /><br />Tallman

 

[searay srv180]

Re: knocking sound from lower unit that came then disappeared?

i have a 74 searay with a merc I/O 165hp. as luck would have it I just had the same experience today. but the noise would not go away. I have checked it over and the only thing i have found so far is that the pivot pins on each side of the gimbal housing are quite loose. when i shake the stern drive sideways or up and down it makes the same kind of noise. i have a full manual and intend on checking further into it. lets keep in touch.<br /><br />best of luck to both of us!!!

 

[dave buckner]

Re: knocking sound from lower unit that came then disappeared?

thanks for all the input everybody! <br /> tallman8251:when i bought boat i greased all zerk fittings and added around 10 oz of gear oil to the lower unit. 5 trips later, after the noise , i checked and added about 2oz to lower unit. <br /> <br /> searay srv180: how are you doing? i tried moving the lower unit around and i got no strange sounds. i am waiting for a manual i have ordered. ill either recieve manual by this weekend , or ill probibly go to lake on saturday and see what happens! let me know how your doing. good luck