1984 mercruiser 140 making loud knocking

Mtl-Diesel

Petty Officer 3rd Class
Joined
Mar 15, 2019
Messages
91
Hey folks! New to the forum. Learned so much already!

Here's my problem: 1984 Baja Islander 180 with a mercruiser 140 Alpha I

Was out on Friday after several other outings this summer when all of a sudden, the engine changed sound and then a very loud knocking could be heard. I shut her down immediately to open up the cowling to inspect. Oil was good, nothing visible. Turned her over to see and even during the cranking, the knocking was present. Managed to flag a fellow boater down for a tow to the nearest dock.

I have done ALL of the necessary maintenance including changing over to a Petronix system replacing the old points. Boat was running like a top all summer until Friday. She idles beautifully, accelerates strong, cruises without batting an eye. We were having a great summer! Have had the boat 3 years now and was a gem when I bought it. No rot. A little attention to the seating and a good wet sand and polish and she looks like a....well 10 year old boat and not a 35 year old boat! ;-)

I tested the compression and have a strong 125psi on all four. Took the valve cover off expecting to see a bent/broken rod and it looks brand new under. Everything appears to be normal. Rods spin just slightly but none appear bent. Certainly not enough to cause the knocking I am getting. I'm at a loss here and hoping y'all can give me some direction.

Thanks in advance!!
 

Mtl-Diesel

Petty Officer 3rd Class
Joined
Mar 15, 2019
Messages
91
So after some more testing...I found the issue. See the pics below.

Do I now look for a rebuild kit or replace the lower end?
 

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Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,310
Ayuh,...... Welcome Aboard,..... I'm guessin' a new SEI drive will be cheaper than havin' yer mercruiser rebuilt,.....

Outdrive rebuilds are not really a Diy thing, to many special tools needed,......
 

Mtl-Diesel

Petty Officer 3rd Class
Joined
Mar 15, 2019
Messages
91
Ayuh,...... Welcome Aboard,..... I'm guessin' a new SEI drive will be cheaper than havin' yer mercruiser rebuilt,.....

Outdrive rebuilds are not really a Diy thing, to many special tools needed,......

What if I can find an upper unit used? Would it be a big job and huge risk to take? Also, do I need to stay with 1.94 ratio or could I use a 1.84 with a different prop?
 

Grub54891

Admiral
Joined
Jun 17, 2012
Messages
6,305
Just get an sei complete drive. If you just get the upper, I'm not sure they will warranty it. You will be on the water quicker than trying to find used parts that may need some other work. Besides, the shavings from the upper are now in the lower.
The upper blows out when the gear oil gets a tad low, you had a leak someplace that caused the issue
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
Just get an sei complete drive. If you just get the upper, I'm not sure they will warranty it. You will be on the water quicker than trying to find used parts that may need some other work. Besides, the shavings from the upper are now in the lower.
The upper blows out when the gear oil gets a tad low, you had a leak someplace that caused the issue

↑↑↑↑↑ All the advice given above is spot on. You are best advised to replace the entire outdrive with an SEI unit. You can get a good deal on iBoats as a forum member, if I am not mistaken.

Rick
 

Mtl-Diesel

Petty Officer 3rd Class
Joined
Mar 15, 2019
Messages
91
How do I determine my ratio? I was thinking it was 1.94 20/24 but now I'm not sure. Online chart is confusing me.
 

nola mike

Vice Admiral
Joined
Apr 22, 2009
Messages
5,712
At some point the drives were 1.94 and switched to 1.98 iirc. 1.94 will work fine.
 
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