propeler shaft knock...Help...Merc 165 I/O

sladers

Cadet
Joined
Mar 1, 2008
Messages
7
Hello iboats!

I'm new to boating and especially boat maintenance...and I need help. I'm sorry I don't know all of the technical terminology, but I'm working on it.

Well, I have a knocking sound coming from (I think) the lower gear housing. I fired her up for the coming spring and the engine sounds fine, but when I put it in gear I heard a knocking sound. So I cut the engine, put it in neutral and lowered the drive to full down position. The sound is very noticeable when I spin the prop by hand. It makes a small knock about every 6th of a turn. 6 knocks for every full revolution. It's pretty loud when the engines turning it. This can't be normal. Can anyone make any suggestions on what it might be? Do you think it'll make it though the summer?

Thanks!
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: propeler shaft knock...Help...Merc 165 I/O

You probably need to get the shift cable adjusted, sounds like the shift dogs are hitting.
One other thing NEVER run the engine with the drive up. You may have damaged the ujoints and your noise just sounds like it's from the lower unit.
Pull the drive and check.
 

sladers

Cadet
Joined
Mar 1, 2008
Messages
7
Re: propeler shaft knock...Help...Merc 165 I/O

Thanks Don S,

Would it be hard to adjust the shift cable myself? Any tips would be great. Also, when I ran it, the drive was up about 7 inches to keep it off the ground. Would this still hurt the ujoints?
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: propeler shaft knock...Help...Merc 165 I/O

To adjust it properly, you are going to need an OEM service manual. The hard truth is, they don't just fall out of adjustment. The lower shift cable (between engine and outdrive) is probably old, corroded, binding, and not even usable. That cable is a problem that happens to all Mercruisers sooner or later.

Regarding your drive tilt. Keep the rpm below 1200 rpm when trimmed up that high, and you should be fine. Putting the bow of the boat all the way down while on the trailer, will usually give you a little more down trim on the drive.
 

starsnstripers

Lieutenant
Joined
Nov 30, 2007
Messages
1,330
Re: propeler shaft knock...Help...Merc 165 I/O

Welcome to Iboats Sladers I'm no pro but i'm a 165 l6 250cid fan/owner. What year is your boat? is it a V6 or straight 6?
 

sladers

Cadet
Joined
Mar 1, 2008
Messages
7
Re: propeler shaft knock...Help...Merc 165 I/O

Thanks for the tips Don S. I'm going to look at the Shift plate and cable next weekend. I hope that's the problem. I guess it could be worse.

Hey Starsnstripers. It's a 1985 165hp straight 6 Galaxie 18.5ft tri-hull. Just tuned her up...perrrs like a kitten.
 

ziggy

Admiral
Joined
Jun 30, 2004
Messages
7,473
Re: propeler shaft knock...Help...Merc 165 I/O

something seems amiss. you have an 1985, L6? looks like 81 was the last year for useing an L6...... ya may want to confirm what your working on prior to doing any repairs......
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__________________
nice table dons.... thanks
 

sladers

Cadet
Joined
Mar 1, 2008
Messages
7
Re: propeler shaft knock...Help...Merc 165 I/O

oops... Thanks Ziggy. Your right, its an 1981. I checked it this morning. I'm glad I didn't order any parts last night.
 
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