Need advice from experienced people.

[BraveSoul]

So I was using the boat I just purchased , it’s an older invader. 2.5L 120/153 CI serial number 0C661190 when I lost power after an hour.. brought it back to dock and found water in #1 cylinder. I started to tear it down thinking it was a head gasket. Discovered a rust spot on cylinder head and a very fine crack, so assuming this is where water was entering. The head from what it looks like was damaged by a foreign object maybe a piece of the piston as the piston has a small chip on one edge and again a very fine crack to about the center of piston head.

My question I guess would be is this repairable by welding the head and replacing the one piston? Used blocks and heads are NOT cheap , I’m not hesitant to do the work as I enjoy spinning wrenches but don’t want to have to do all the pistons just one and don’t want to pay a shop to rework anything. I’m on a super tight budget. The head I can get a friend who is an amazing welder to work on but considering where the crack is would it even be Feasible?

 

[BraveSoul]

 

[Scott06]

So I was using the boat I just purchased , it’s an older invader. 2.5L 120/153 CI serial number 0C661190 when I lost power after an hour.. brought it back to dock and found water in #1 cylinder. I started to tear it down thinking it was a head gasket. Discovered a rust spot on cylinder head and a very fine crack, so assuming this is where water was entering. The head from what it looks like was damaged by a foreign object maybe a piece of the piston as the piston has a small chip on one edge and again a very fine crack to about the center of piston head.

My question I guess would be is this repairable by welding the head and replacing the one piston? Used blocks and heads are NOT cheap , I’m not hesitant to do the work as I enjoy spinning wrenches but don’t want to have to do all the pistons just one and don’t want to pay a shop to rework anything. I’m on a super tight budget. The head I can get a friend who is an amazing welder to work on but considering where the crack is would it even be Feasible?

I suspect you had detonation which destroyed the piston. head is not weldable. Cheapest option find a junk boat sitting in someones yard with a 2.5 or 3.0 and swap it over Vs half azz rebuild.

 

[BraveSoul]

I suspect you had detonation which destroyed the piston. head is not weldable. Cheapest option find a junk boat sitting in someones yard with a 2.5 or 3.0 and swap it over Vs half azz rebuild.

What Do you think was the cause of the detonation could I have been revving it to high?

Also I read all over the Internet that you can get these things repaired by welding them or pinning?

 

[Scott06]

What Do you think was the cause of the detonation could I have been revving it to high?

Also I read all over the Internet that you can get these things repaired by welding them or pinning?

Lean mixture clogged carb passages Or incorrect ignition timing. Detonation will literally beat the pistons to death. That may be the pitting you see. Take the piston out see what skirt looks like

What did the plugs look like ? Mat have over heated also

 

[BraveSoul]

Lean mixture clogged carb passages Or incorrect ignition timing. Detonation will literally beat the pistons to death. That may be the pitting you see. Take the piston out see what skirt looks like

What did the plugs look like ? Mat have over heated also

Plug looked normal just really clean from the water intrusion.

 

[BraveSoul]

Lean mixture clogged carb passages Or incorrect ignition timing. Detonation will literally beat the pistons to death. That may be the pitting you see. Take the piston out see what skirt looks like

What did the plugs look like ? Mat have over heated also

Also what will I look for when pulling the piston to check the skirt? Thanks

 

[kenny nunez]

The crack in the head probably caused the piston to crack since water does not compress. The head is probably very thin in that area and there may not be enough material left to heat weld. The only weld that may hold is a “cold weld” or ”lace weld” which is how cast iron can be repaired with a series of overlapping threaded plugs. A new piston should not be very expensive and you could even re use the rings if you can r&r them carefully if they are not broken. I think they are 283 rings.

 

[Scott06]

Also what will I look for when pulling the piston to check the skirt? Thanks

What kenny said - just looking for why the piston broke and what condition the bore is in.

He mentions lock n stich and other types of cast iron repair which is the right way to do it, just likely exceeds cost of used head.

Was this a salt water boat ?

 

[BraveSoul]

Thanks all for your insight, I managed to swap out a piston , along with new rings and bearing on it. Ran ok after rebuild but then I changed plugs , wires, coil and had to do timing. Now it runs without a hiccup . So far I have an hour of use. Feeling more and more confident each run.

I’m no expert on the is old style distributor ignition, and I kinda just winged the timing so it ran . I’m wondering if timing will affect my top rpm and speed. Boat is doing 25mph , it’s the 120hp 2.5L mercruiser on a 17foot 1991 invader fibreglass bow rider. Does this speed seem right or am I missing out due to maybe the timing ?

 

[Scott06]

Thanks all for your insight, I managed to swap out a piston , along with new rings and bearing on it. Ran ok after rebuild but then I changed plugs , wires, coil and had to do timing. Now it runs without a hiccup . So far I have an hour of use. Feeling more and more confident each run.

I’m no expert on the is old style distributor ignition, and I kinda just winged the timing so it ran . I’m wondering if timing will affect my top rpm and speed. Boat is doing 25mph , it’s the 120hp 2.5L mercruiser on a 17foot 1991 invader fibreglass bow rider. Does this speed seem right or am I missing out due to maybe the timing ?

Would think that boat would if properly proper do low to upper 30’s if it was running right . Did u do a compression test after what serial number we can tell I what the ignition timing is supposed to be

 

[BraveSoul]

Would think that boat would if properly proper do low to upper 30’s if it was running right . Did u do a compression test after what serial number we can tell I what the ignition timing is supposed to be

OC661190 is the serial number, did not compression test , but I don’t see blow by in valve cover or any smoke out the exhaust.

 

[tpenfield]

Folks aren't going to recommend to take short cuts. Since you will be tearing the engine down, you may as well do things right.

 

[BraveSoul]

Folks aren't going to recommend to take short cuts. Since you will be tearing the engine down, you may as well do things right.

OK but I just want to know if the timing would affect TopSpeed thanks.

 

[Rick Stephens]

Thanks all for your insight, I managed to swap out a piston , along with new rings and bearing on it. Ran ok after rebuild but then I changed plugs , wires, coil and had to do timing. Now it runs without a hiccup . So far I have an hour of use. Feeling more and more confident each run.

I’m no expert on the is old style distributor ignition, and I kinda just winged the timing so it ran . I’m wondering if timing will affect my top rpm and speed. Boat is doing 25mph , it’s the 120hp 2.5L mercruiser on a 17foot 1991 invader fibreglass bow rider. Does this speed seem right or am I missing out due to maybe the timing ?

What did you do with the head crack?

 

[nola mike]

OK but I just want to know if the timing would affect TopSpeed thanks.

Yes, and it will also put you on a path to replacing your engine. Your blowby compression test also means nothing...

Folks aren't going to recommend to take short cuts. Since you will be tearing the engine down, you may as well do things right.

Nice a avatar!

 

[Scott06]

OK but I just want to know if the timing would affect TopSpeed thanks.

It can set the timing to factory specs , if your total advance is low you wont make full power thus limiting top speed. Too much timing can lead to detonation that can destroy the engine

 

[BraveSoul]

It can set the timing to factory specs , if your total advance is low you wont make full power thus limiting top speed. Too much timing can lead to detonation that can destroy the engine

Thanks if only I knew what factory setting was in how to do it LOL do you by chance have a link I could follow

 

[Scott06]

Thanks if only I knew what factory setting was in how to do it LOL do you by chance have a link I could follow

Best bet is find a factory service manual for your engine. There is a link in the stickies of how to tune up your points ignition (assuming it is points)- but link is broken can PM a mod to see if you can get the correct link . Usually the timing is on the valve cover sticker or flame arrestor cover - this is not a half bad video on a similar OMC 3.0 (same base gm engine as Merc 2.5/3.0)

 

[BraveSoul]

Best bet is find a factory service manual for your engine. There is a link in the stickies of how to tune up your points ignition (assuming it is points)- but link is broken can PM a mod to see if you can get the correct link . Usually the timing is on the valve cover sticker or flame arrestor cover - this is not a half bad video on a similar OMC 3.0 (same base gm engine as Merc 2.5/3.0)

Thanks very much I will check this out