Clunking Noise from back of Engine

[jr88fan]

I have had the boat out about 6 times and yesterday I picked up a strange clunking noise at low RPMs. The noise is coming from the rear of the engine. It does not do this in neutral or reverse. The noise appears to go away at higher RPMs. 1987 Chaparral 198 Xl, 305, Alpha drive. Thanks!

 

[Oshkosh1]

Re: Clunking Noise from back of Engine

When were your U-Joints last inspected/greased?

 

[markheck1]

Re: Clunking Noise from back of Engine

That would be my guess too...BTW....where in Western Pa?

 

[spdracr39]

Re: Clunking Noise from back of Engine

Yep u-joints and or gimbal

 

[jr88fan]

Re: Clunking Noise from back of Engine

I have no idea on the u joints as I just bought the boat two weeks ago. I am also a newbie to owning a boat at all.

I drained the outdrive this morning and there was only about 1/2 quart of fluid that drained out after removing the vent plug and letting it drain for about 30 minutes. I ran my magnet through the fluid and there were no metal shavings so I am guessing that is good! I greased every fitting I could find but I realize those are for the pivot points for steering and trim.

I read another post that low fluid levels in the outdrive could possibly produce a noise at the rear of the engine. Any value in that opinion?

I purchased a SELOC Mercruiser Stern Drive manual right after IO bought the boat and according to that I have to remove the outdrive to even get to the u joints. This is not really something I want to tackle right now!

I live in New Castle, PA and the only lake I have been to is Shenango. Like I said I am a newbie! Thanks for all the feedback!

 

[jr88fan]

Re: Clunking Noise from back of Engine

After changing the outdrive lube and filling it all the way the noise is gone while running in teh driveway with the muffs! I am hoping that is good so off to the lake I guess!

 

[markheck1]

Re: Clunking Noise from back of Engine

Hope that was it!

Ahhh, Shenango, never been there yet, I hear it's nice

 

[ktbarrentine]

Re: Clunking Noise from back of Engine

I purchased a SELOC Mercruiser Stern Drive manual right after IO bought the boat and according to that I have to remove the outdrive to even get to the u joints. This is not really something I want to tackle right now!

Aww...it's too bad you had to waste good money on that SELOC manual (I guess you can use it protect your knees when kneeling on in the garage floor), when the best manuals you can ask for are available on this forum....for free!!! Just sayin'.....

 

[Don S]

Re: Clunking Noise from back of Engine

If the knocking went away by doing nothing more than filling the drive with gear lube, I will be watching for further drive problems.

 

[benninj]

Re: Clunking Noise from back of Engine

FWIW

Drive Unit possibly , check it against yours, if it's not the exact on for your drive check out their other manuals and find the right one.
http://boatinfo.no/lib/mercruiser/manuals/mercruiser6.html#/0

Engine
http://boatinfo.no/lib/mercruiser/manuals/mercruiser9.html#/2

Joe

 

[jr88fan]

Re: Clunking Noise from back of Engine

Thanks for all the info and especially the manuals. I also wanted to provide an update after yesterdays excursion to the lake.

So before I start I just want to clarify that I do know (I think I know) the difference between a clunk and the noise you might get from a fan belt. I also know the fan belt is in the front of the engine (that part I do know LOL).

So i get to the lake and launch the boat. Get the people in the boat and head out for some cruising and tubing. Halfway across the lake I lose power steering so I am thinking what now. Open the engine compartment and I see one fan belt pretty much shredded. I'm thinking that is for the power steering so I head over to the marina to see if they sell any fan belts or maybe I have to go to the parts store. In the mean time I decide to look around for anything obvious I am missing because I know most older vehicles have more than one belt.

I find the second belt down in the bilge and it looks almost new except for the piece from the other belt that is wrapped around it and probably what knocked it off. I check the good belt and it's the power steering belt so I put it back on and all is good. I have a spare battery in the engine compartment and I know I still need to replace the belt for the alternator but that's not pressing at the moment.

So the big question is could the piece of belt wrapped around another belt somehow create what appeared to be a clunk? I had a 67 Camaro with a harmonic balancer issue that made the engine make a bunch of strange noises. Replace the harmonic balancer with the correct one for a 327 instead of a 350 and all was good.

I never heard the clunk again all day and I was listening very carefully every time I put the boat in gear! I truly do appreciate this forum and all teh great people that help out us rookies (well maybe minor leaguers is more appropriate!).

Any good online sites to buy belts? I will be carrying a spare in my tool box!