mercruiser preaplha lower unit knocking

[syuhas85]

Hello, I have 76 sea ray srv195 it has a mercruiser v8 188/888 (5.0L) I just changed the water impeller and outdrive fluid this June she ran like a beauty cruises at 4500 Rpms @ 46 mph I love it anyhow went fishing today was out about a mile ran fine when I started it up to come back in and put in forward the lower unit started knocking u can feel it and deffiantly hear it... Didn't sound like it was doing it in neutral but hooked it up to the muffs in the drive way and you can hear it knocking in neautral its coming from my lower unit any ideas....tryed the shift cable that didn't do anything still knocks in neutr..al and forward... But not really in reverse u cNt really hear it... I have no idea what it would be there's nothing really down there but the water impller unit and she's not over heating

 

[NHGuy]

Re: mercruiser preaplha lower unit knocking

Pull the drive and check for bad u-joints. Is the sound less when the drive is tilted slightly above the absolute bottom stop? That's where the joints are straightest.

While the drive is off also check the gimbal bearing & coupler.

 

[syuhas85]

Re: mercruiser preaplha lower unit knocking

I'll take it off today and no the knock does not change if you lower or pick up the prop...

 

[syuhas85]

Re: mercruiser preaplha lower unit knocking

Ok took the outdrive off the gimble u can feel the bearing move but its not shot spins nicely no play...took the 4 bolts off the top no gears are mashed all look nice and clean...the u joints are real limp as in u can move it around with Ur pinky the driveshaft just flops around like a dead fish unlike new u joints that have some resistence that's the only thing I can guess that's bad any suggestions?? Wired part there was water in my drive bellow even though the bellows look brand new nice and rubbery no cracks the gear lube in were the gimble gear and the u joints all look terd brown.....either the grease is that color or it changed that color from the water being in there......

 

[Bondo]

Re: mercruiser preaplha lower unit knocking

Ayuh,... Find where the water is coming from, 'n fix it....

Then replace yer U-joints....
I imagine after you take 'em apart, you'll see the roughness on the crosses...

 

[ziggy]

Re: mercruiser preaplha lower unit knocking

agreed^^^^^

+ from what i understand. if ya've had water intrusion into the bellows area, the gimble brg. will also be short lived. ya might wanna replace it also. + ya need to pressure test the drive. water intrusion into the bellows area is bum deal. the water also can get into the drive lub via the ft. seal of the drive. this seal is such that it keeps gear lub in. but it's not designed to keep water out. when water gets in this way it also rusts the drive gear seal surface. this eats up the seal. then ya need to replace the seal along with the drive gear ujoint yoke.

 

[syuhas85]

Re: mercruiser preaplha lower unit knocking

OK here's the deal Im guessing the Leaking is coming from the gasket around the outdrive were the 6 bolts go so will try that but now the knock drained the oil and there was metal flake in it.... So I took the upper apart the drive gears were chewing at the casing so im guessing the bearings are gone the gears look great so hard compared to the case that it didnt even harm them my question is there a website I can find a rebuild kit for the bearings for a mercruiser 888 for the upper go any website i can find a rebuild kit from??

 

[oothomas47]

Re: mercruiser preaplha lower unit knocking

Hello, I have 76 sea ray srv195 it has a mercruiser v8 188/888 (5.0L) I just changed the water impeller and outdrive fluid this June she ran like a beauty cruises at 4500 Rpms @ 46 mph I love it anyhow went fishing today was out about a mile ran fine when I started it up to come back in and put in forward the lower unit started knocking u can feel it and deffiantly hear it... Didn't sound like it was doing it in neutral but hooked it up to the muffs in the drive way and you can hear it knocking in neautral its coming from my lower unit any ideas....tryed the shift cable that didn't do anything still knocks in neutr..al and forward... But not really in reverse u cNt really hear it... I have no idea what it would be there's nothing really down there but the water impller unit and she's not over heating

it's probably a ujoint or gimbal brgor make sure you are in complete neutral. you could try turning the drive side to side while running to confirm it is the gimbal brg or u-joints

 

[syuhas85]

Re: mercruiser preaplha lower unit knocking

it's probably a ujoint or gimbal brgor make sure you are in complete neutral. you could try turning the drive side to side while running to confirm it is the gimbal brg or u-joints

Its non of the above honestly "NO-ONE" has a clue whats knocking..... I took the upper unit completely apart and took it to a Service Marina had a mechanic look at it He said Everything looks good = (bearings,races,gears, shims, u-joints etc...), nothings bad but the upper out-drive Case is chewed around were the gears go.........Weird part is there is no slack and they have plenty of space before they gears even come close to chewing the out drive case... The only thing they could come up with was a piece of metal some how got in there and spun around the gears and chewed the case up... They said Clean it out with parts cleaner and get a new gasket kit and cheap oil put it back together start it on the muffs if it doesn't make noise, then let it run for 10mins and then drain the cheap oil and put Premium blend out-drive oil back in (basically getting rid of the rest of the crap in the out-drive). So far I've taken it to 2 different shops and my work and no one can figure out whats up haha what a pain...
now there's another thing I did just attach the upper today put it all back together and put a new gasket kit on it and started it for couple of seconds with out the lower unit on it theres no knock, soooooo I guess ill be trying to figure out how to get the lower unit apart.... below is a pic of the gears of the upper where i said they were chewing at the case.. View attachment 107518

 

[Maxum88]

Re: mercruiser preaplha lower unit knocking

Mine's doing the same thing!!! I have a 3.0L Mercruiser w/ a PreAlpha Outdrive. Had a wakeboarder behind the boat when all of a sudden I heard a terrible knocking. We idled back to the boat, when we got it back & on muffs, it sounded like it was coming from the top cover of the upper unit, like something was hitting it. We loosened it & ran it and it sounded better with the cover lifted a bit. Still not sure what's going on. Found the gears in the upper unit a little chewed up with metal shavings in the oil
This weekend I'm starting with new U-Joints and fresh oil. Any other suggestions I'm open to!

 

[eldplanko]

Re: mercruiser preaplha lower unit knocking

mercruiser v8 188/888 ... cruises at 4500 Rpms @ 46 mph

I've got the same engine, 4500 rpm seems a bit high... i the max spec in the service manual is 3800-4200 at WOT.

 

[syuhas85]

Re: mercruiser preaplha lower unit knocking

I've got the same engine, 4500 rpm seems a bit high... i the max spec in the service manual is 3800-4200 at WOT.

Once I get this knocking taken care of I'll goto a bigger pitch prop. I have a 14.25 x 19p On now ill try a 21p to get the rpms down maybe I'm over reving everything...

 

[Pikey23]

Re: mercruiser preaplha lower unit knocking

I would be interested in what you find. My drive is doing the same thing. Just replaced u-joints and no change

 

[oothomas47]

Re: mercruiser preaplha lower unit knocking

check your drive fluid surely the yoke seal is bad along with the yoke