2006 90EXLPTO no compression on #1

[interalian]

Neighbor has a 2006 90EXLPTO with no compression on the top cylinder. What's the typical failure mode on these and are they a bear to fix? From a quick look these don't have a removable head, so the pistons poke in from the crankcase side. (I'm an OMC handy with zero Merc skills).

 

[QBhoy]

If you are at an actual figure of “0” psi....I’d maybe suggest one of two things.
Its unlikely a complete failure and probably a broken or sticking ring
or
you have a serious issue and a hole in the piston. These are really the only two slightly common answers. Either way taking the head off will tell all. Not as big a job as you think.
The other slight chance is that the head has gone, but I’d say you’d notice that maybe.

If you arent keen to look yourself, worth throwing a load of 2 stroke down it overnight and see what happens before taking it to bits.

 

[interalian]

I'm just going by what my neighbor said about compression. I only looked at the motor for a few seconds, and not in the best light. Once I have a better look I'll be back with more questions. He was the one that said there's no cylinder head...

 

[Texasmark]

Manual says that anything less than 120 cranking compression, plugs out, throttle wide open could be cause for concern.
"0" PSIG, especially on #1 (easy to get a good reading) is especially of concern.
Yes there is a water jacket cover but no separate head.....been that way since day one.
Peering through the spark plug hole with a fiber optic probe (about a hundred bucks on ebay or less) gives you a peek inside.
More of a problem would be to remove the exhaust water jacket plates where you can see the rings through the exhaust holes in addition to the piston top.
If engine is gummed up, rings may be stuck and allowing compression to leak down. Doing a "decarb" may fix it.....google the word for instructions or go to the archives herein.

 

[interalian]

Thanks for that. I've got tons of 2-smoke experience but only on OMC - most recently a 90-140hp conversion on my old tinnie (link in sig). I did some McGyvering on a 90HP Force a while back with great success too. Winter projects around my area start about now as hard water is only a month away and our local lake (irrigation reservoir) gets drained in 3 weeks.

 

[QBhoy]

Hi
not that it matters too much, but you probably need to take the head off as mentioned.
You usually don’t need to hold the throttle open on a 2 stroke on a compression test.

 

[racerone]

There is no cylinder head on this motor.----Take the exhaust cover off to look at pistons / rings.-----Sounds expensive.

 

[BrettNC]

At 0 compression, you'll need to take apart to fix or trash it. Easy motors to rebuild. Will need to find a machine shop that can bore a blind hole block like yours. No other way around this one.

 

[Texasmark]

Hi
not that it matters too much, but you probably need to take the head off as mentioned.
You usually don’t need to hold the throttle open on a 2 stroke on a compression test.

I can direct you to the section and page in the manual that says to advance the throttle when testing. Common sense says that if you want to pack the cylinder with air to compress, you need to get it in there somehow.........

The head is cast into the block on these Mercury engines; have been since the beginning of time. The cover on the rear of the block is water jacket only.

 

[racerone]

No need to open the throttle plates on this motor.-----Intake AND exhaust ports are wide open before compression starts !

 

[QBhoy]

I can direct you to the section and page in the manual that says to advance the throttle when testing. Common sense says that if you want to pack the cylinder with air to compress, you need to get it in there somehow.........

The head is cast into the block on these Mercury engines; have been since the beginning of time. The cover on the rear of the block is water jacket only.

Hi

eh...it’s a 2 stroke. No need to open throttle at all. Are you familiar with the way a 2 stroke breathes ??