1997 Mercury 150XL - compression.

[Kismiras]

1997 Mercury 150XL - one piston totally shot. 120 psi on all other 5 pistons. Am I SOL or is it worth the time and money?

 

[Faztbullet]

Anything can be repaired but got to find out why it went down so there isnt a repeat.

 

[Kismiras]

Anything can be repaired but got to find out why it went down so there isnt a repeat.

Understood - I’m a bit new to outboards - but very mechanically inclined. It’s just seems off that only 1 piston is shot - I mean shot. It’s loose in the cylinder walls and piston is crumbling at the top - so don’t know if the rest of the internals have damage due to metal most likely went into the port(s).

 

[QBhoy]

She’s going to need at least one new unit…usually more required is likely too…unless you’ve been lucky. I’d be inspecting other pistons too..to make sure…but most crucially other than the obvious damage unit..is to know if the crankshaft and bearings are ok. Often after a top end failure…you can get damage occurring to there, as a result.

 

[Kismiras]

She’s going to need at least one new unit…usually more required is likely too…unless you’ve been lucky. I’d be inspecting other pistons too..to make sure…but most crucially other than the obvious damage unit..is to know if the crankshaft and bearings are ok. Often after a top end failure…you can get damage occurring to there, as a result.

Thanks QBhoy. I figured if rebuild this one - it will be a full rebuild.

 

[Kismiras]

Thanks QBhoy. I figured if rebuild this one - it will be a full rebuild.

I’ll update and a couple more nights of sleeping on it.

 

[QBhoy]

Thanks QBhoy. I figured if rebuild this one - it will be a full rebuild.

Good call. Can I ask what you think causes the issue ?

 

[Kismiras]

Good call. Can I ask what you think causes the issue ?

I have no clue - bought the boat 2 Fridays ago and this is what I got. I didn’t do a compression test - but the rig was not expensive at all. And I know it was a project - just didn’t expect the motor rebuild to be part of the project.

 

[QBhoy]

If it helps…you can thank your lucky stars that it’s not a big v6 yam 2 stroke. Recently learned the eye watering cost for parts to rebuild one of them. Even doing the job at home and after a trade discount. Just crazy money. Over £2k for parts here in UK…with the discount.
With your particular engine…I’d suggest looking for the cause of the failure for sure. Most likely of them all..is a oil injection failure (if it’s the 2 stroke I’m imagining and the same as my old 1998 v6 150). Just famous for failure when the oil injection is still in use.
Other than that and being lucky with just the one unit failing…look for signs of heat being the cause. This being the case…you may find more work is required…if gaskets and or heads/sealing faces have been melted or warped. Additionally, could and can cause failure or cracking of the cooling chambers or exhaust assembly up top…with lack of water traversed

 

[havoc_squad]

I have no clue - bought the boat 2 Fridays ago and this is what I got. I didn’t do a compression test - but the rig was not expensive at all. And I know it was a project - just didn’t expect the motor rebuild to be part of the project.

Do not throw away anything damaged or attempt to clean up the cylinder until a complete evaluation of the cause of the piston failure has occurred.

Post pictures of the damaged piston and damaged cylinder when powerhead is disassembled. People will also want to see pictures of the connecting rods, crankshaft, and connecting rod bearings that fit on the crankshaft.

Could be a number of possibilities of what caused it. Lack of lubrication, overheat complications, lean fuel mixture causing detonation, excessive timing, broken piston rings, etc.

 

[racerone]

Need to check that cylinder sleeve for cracks.

 

[Faztbullet]

If its #1,#3 or #6 it a advance/idle stablizer failure..common problem

 

[Kismiras]

If its #1,#3 or #6 it a advance/idle stablizer failure..common problem

Thanks all. It’s the top left cylinder……. Looking at the engine from the back (port side).

 

[Kismiras]

Here are a few pics. I haven’t gone past this point…….yet.

 

[Kismiras]

Here are a few pics. I haven’t gone past this point…….yet.

The rest of the motor looks pretty good.

 

[havoc_squad]

That piston crown around the edges looks more like heat damage around it than piston & ring material compacted.

Unless there is some other factors identified in fully disassembling the motor, that looks like pre-ignition/detonation damage by the amount of cratering on top of the piston crown. It looks like that damage has been going on for quite some time as well.

What do the piston crowns look on the other cylinders? Need to show them as well.

 

[Faztbullet]

Odd it has foil tape on switchbox and the clear potting leads me to believe it may be a chinesem switch box. Yank powerhead,strip it down, get a factory manual,bore all six, replace switchboxes,impeller and t-stat and reassemble

 

[Kismiras]

If its #1,#3 or #6 it a advance/idle stablizer failure..common problem

Faztbullet - what is this error you are referring to?? How can I avoid it?

 

[Faztbullet]

Take stabilizer off and float test it

 

[racerone]

If you put in a bucket of muddy water it might disappear. -------------That is what you need to do , make it disappear.