96 force 120 overhaul

[Chrisried]

Found out I had low compression on two cylinders. Had shop go ahead and pull head to inspect. They found water in two cylinders and said that one was starting to score, he wasn't sure where the water came from and an overhaul will be 4000.

I am wanting to only overhaul the affected cylinders if possible. I have already looked and found piston and rings for 75ea and a gasket set for 100. So I'm think I can get this done for 500 depending on cost of machine work.

I'm more looking for pointers on the best way of going about this. I'm mechanically inclined but have never been inside an outboard. I'm thinking the water issue will either be remedied by replacing gasket when I pull the powerhead or with a new head gasket.

 

[Jiggz]

First you need to find out where the water is coming from. If it is just from a blown head gasket, then the job should be a lot easier and cheaper. Now if the removed head gasket is intact and has no indication of causing water leak from the water jackets, then it could be the exhaust gasket causing water intrusion.

Next you need to evaluate the scoring, scratches or gouging in the affected cylinders. If it only need light honing, you can do the job yourself. And yes, you can actually finished it for around $500 for two piston sets and gaskets.

Search the forum on how to remove and install pistons without splitting the engine block.

 

[Chrisried]

I had a mechanic take a look at it, he pulled the head and said he wasn't sure where the water came from said it could be head gasket or exhaust gasket.

 

[jerryjerry05]

Take it to the machine shop FIRST.
They can give you an idea on if the cyl. needs to be bored or just honed?
​Usually??? (maybe) water in adjoining cyl is usually the head gasket.

​The job isn't hard.
You just need a manual, u-tube and help from this site.

 

[Jiggz]

I had a mechanic take a look at it, he pulled the head and said he wasn't sure where the water came from said it could be head gasket or exhaust gasket.

With water intrusion, it is really not that hard to tell if it is due to a torn or worn head gasket. Of course, there are a few exceptions but usually, a good mechanic can tell if it is coming off from the head water jackets. For the exhaust it is a little different but not that hard either except for the actual removal of the exhaust plates and gasket. If you can take a pic of the removed head gasket and post it can be easily diagnosed by experts from this forum.

 

[Chrisried]

Will pick up the boat tonight and will try to get pictures. I found a good video on YouTube of a complete tear down of a same year motor and it doesn't look too terribly difficult. Thanks for the replys.

 

[jerryjerry05]

Top cyl. or bottom?

 

[Chrisried]

Nat sure which cylinder yet. Weather turned nasty yesrerday so I will pick it up today.

 

[Chrisried]

 

[Chrisried]

 

[Chrisried]

 

[Chrisried]

 

[Chrisried]

I talked with the mechanic when I was picking the boat up today. He said that it was not leaking from the head gasket and thought it was the exhaust plate gasket leaking. He also said that the pistons were loose and it probably needs new bearings. I took the head back off when I got home and checked the first cylinder but didnt feel any score marks. and shook the pistons and they each moved 1/16 to 1/8 side to side.

 

[jerryjerry05]

"pistons loose" ??
​Did he explain what he meant when he said that?
​1/16-1/8" is a LOT of play.

​Measure the cylinder and post the measurements.
The pistons look like they're the standard ones for a 96/120

3.309/3.308 to 3.305/3.304 piston size.
3.3750 to3.762 is the cyl.bore size.

See if they match.

 

[Chrisried]

The piston are loose can grab them and move them pretty easily. I didn't measure how far they moved, just guessed, but it felt like they were plenty loose. On the sheet he said cylinder wear was pretty bad. Top cylinder starting to score. And had water in cylinders. How do you know you have water in cylinders besides obviously finding water when opening it up.

 

[Jiggz]

I do not think the mechanic actually saw fluid water instead it's most likely moisture and presumed there is water intrusion. From the look of the piston head, there seems no steam cleaning on the piston which is the best indication of water intrusion assuming the engine is still running.

Your next move is to dismount the pistons from the cylinders. This can be done by dismounting the carbs and intake adapters. Using a 1/4"-12pt socket with an extension you remove the bearing caps one at a time from the intake manifold access. Make sure you have something to catch the roller bearings as they fall and make sure you stuff the gap on the engine cowling to prevent them from falling into the lower part of the cowling which makes it impossible to recover them.

Take pics of the pistons, rings, bearings and also the wrist pins and post. From here you should be able to tell if the problem is just worn out rings or cylinders, by doing measurements.

 

[jerryjerry05]

Water in the cyl??:: the plug will have water droplets and possibly be clean, possible the motor would have a miss as it runs.

​Had a gasket go bad(yours looks good) the compression was at 145 all 3 cyl. but had a dead miss and the plug looked like it had poop on it.

 

[Chrisried]

Never has had a miss just idle issues since I've had it. Have had bad weather all week hopefully tomorrow I will be able to pull piston and borrow a mic and snap gauge from work so I can get the cylinder dimensions Monday.

 

[Chrisried]

 

[Chrisried]

Pulled top piston out and attempted to take some measurements and came up with 3.378 for the cylinder, not sure how accurate my measurements were. I inspected the cylinder pretty well and didn't find any noticeable scores When taking out the reeds I found two with corner chips and one broken. How many boysen reeds do I need to replace both reed blocks? I think the broken reeds might have been the cause of my idle issues. Right now I'm contemplating honing the top cylinder and installing new rings, replacing reeds, head gasket, and hoping for the best.