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View Full Version : Merc 15hp water in bores, how?



Salad Fingers
15-08-2011, 11:59 AM
Hey guys, got a bit of a drama with my merc 15hp.
Last two trips out it has seized up approx 24hrs after use/flushing, no good at all, taking the plugs out and looking at them it is clear there is water getting into the bores of BOTH cylinders now, first time was just the top one i think.
Both times have managed to unsieze the motor with some motor oil down the bores and work it slowly back and forth, quickly blow out then some WOT runs. :o

poor motor has had a hard life since i've had it so i'm certainly not blaming the motor here, but what should i be looking at first? how the the water flow through the exhaust housing? any other likely areas? base gasket?

Fed
15-08-2011, 12:38 PM
Check your baffle plate.
Don't break the screws, if they feel too tight hit the screw heads with some heat.

Jarrah Jack
15-08-2011, 12:51 PM
When it happened to me it was the head gasket. Does the merc have a seperate head or is it a one piece cylinder and head unit?

cormorant
15-08-2011, 12:52 PM
Check compression for a start. That will confirm if it is the head gasket.

Water jacket over the exhaust port. Especially if it only happens when the motor is on muffs. When on the water the waterpump stops pumping water when the motor stops so there is no pressure to "flood "the port. Same with a leaking head gasket . Exhaust lower down corroded may cause the same results.

How are you determining that it is water ?

What model merc is it - lot of different models over the years- have a look here and you will see the parts diagram and see the possible spots where water can get to the bores. Areas where gaskets are used to blank off cast water passages around inlet manifold reed block are also a possibility

Parts diagrams http://www.crowleymarine.com/parts.cfm

Salad Fingers
15-08-2011, 01:10 PM
is a 2005 15m (USA model), head and cyl block one piece, no head gasket.
FED, when you say baffle plate which piece are you refering to? im looking at the service manual but cannot see anything labeled as such?
Cormorant, definitely water in there, rust on the spark plug electrodes plus light rust on the bore plus siezed motor after each run, either on muffs or water.

Fed
15-08-2011, 01:18 PM
Click on comorant's link, select mercury 2005 15HP then the 1st model on the list.
Then cylinder block & covers... Part #18 + gaskets #17 & #19.

Salad Fingers
15-08-2011, 01:20 PM
got it. cheers not sure how i missed that.

Fed
15-08-2011, 01:23 PM
Don't run it until it's fixed, get it fixed as quickly as possible & get some miles up on it.

Salad Fingers
15-08-2011, 01:27 PM
yeh nah not going to run it again, sprayed the bores with oil again now and turned it over once or tiwice.
might start taking that plate off today and see what i can see, probably a good time to get all the sand and crud out of there anyway

Salad Fingers
16-08-2011, 08:54 PM
pulled the baffle plate off today ...
what a PITA getting that off was, most of the bolts were pretty howyagoin', a bit rusty and crap.
anyway, nothing really stood out as being the cause for this water in the bores one part of the gasket looked a bit average but it was at the bottom of the plate so would be very suprised if the water got from there to the top cylinder?

So i'm going to clean up these surfaces and put that back together.
any other suggestions as to where to check for water ingress? what is on the other side of the motor are there any water galleries behind that plate?

Fed
17-08-2011, 09:04 AM
Thoroughly check that baffle plate for the tiniest of corrosion pin holes SF.

Noelm
17-08-2011, 09:20 AM
make sure you get some oil into the crankcase, or the bearings will be shagged, the bore is the least of your worries.

finga
17-08-2011, 09:28 AM
Thoroughly check that baffle plate for the tiniest of corrosion pin holes SF.
metho is good for finding pinholes if the plate is dish shaped.
Just pour a bit on the top and hopefully it won't come out the bottom.

A gasket looking even a tiniest bit howdy doody will let water in and it's amasing just where it gets sucked or blown into.

I'd be having a gander under part number 32 too.
http://www.crowleymarine.com/mercury-outboard/parts/11401_90.cfm

Salad Fingers
17-08-2011, 03:51 PM
Fed - I had a pretty good look at it but once i've got all the old gasket off I will have another look...
Noelm - crankcase appears fine from what I can tell, only water appears to be in the upper cyl area.
Finga - I already have that (#32) top plate off, there is nothing in there for the water to leak into it is all sealed, that was my first guess too until I actually took it off.

does anyone know if there is anyting under the 'intake cover' that holds water that might leak in there?

thanks for the replies so far fellas keep it coming! :)

cormorant
17-08-2011, 04:04 PM
You have only got one well 2 left - base gasket and if the inlet / reed block gasket if it is used to blank off holes . Bar a casting , corrosion failure not too many places left. . Was the compression and leak down test ok? Too modern for my knowledge so can't help but there would be photos on the net somewhere or even in the $5 ebay manuals on disc to show those other gasket surfaces.

Fed
17-08-2011, 05:36 PM
I suppose you could have a pinhole in the top cylinder dome.
I don't think you could get water from the lower crankshaft seal to the top cylinder.
As far as I know there's no water near the intake ports.
Can you see any water marks at all near the exhaust ports?

BM
17-08-2011, 07:59 PM
I think you should strip the powerhead down mate. The transfer port cover wont really reveal much as there is no water gallery in there. It will just show you the intake tract and you will see the piston.

Unless water has tracked up through a balance line betwen the bottom and top of the crankcase or through the exhaust the next logical explanation that I can think of is the water has come through your fuel. Check the carby bowls or if thats a single carb engine with water in one cylinder only then that rules out the carby.

In any case, if the salt water has passed through your crankcase then your bearings and bearing surfaces are quite possibly damaged. There are no outboard crankshaft repairers in Australia anymore that I know of.

So strip it right down and see exactly what you have is the safest and best option. It won't take long to do. It's only a baby engine.

Cheers

Salad Fingers
20-08-2011, 09:41 PM
striping it right down sounds like a royal pain in the ass - I think i'll buy a new motor before I resort to that.
ah well anyway motor is all back together, baffle plate and top cover are back on. Took it for a spin and it runs great as always, although it did before I pulled it down before aswell...
See if it's siezed up tomorrow morning and plugs are rusty I guess?

BM
20-08-2011, 10:53 PM
Its only a baby engine mate! Fairly quick to pull down.

Even if it does sound ok I would be worried that it will toss a rod due to crank damage.

Cheers

Fed
21-08-2011, 08:20 AM
Hopefully you inadvertently fixed it SF.
I've been down this track years ago & finished up with a bent rod, as BM says they are pretty easy to work on.

Salad Fingers
21-08-2011, 10:12 AM
Fingers crossed Fed, Just went outside and it wasn't siezed at all. perhaps it was that dodgy bit of gasket on the lower part of the baffle plate? strange that the water made its way into both cyls tho...?
Happy days so far anyway, will give it another good run today and then leave it for a week and see what is going on.
If it's fooked those Parsun's are looking mighty attractive! ;)

this is just my second boat that only gets used for crabbing probably a handful of times a year, so spending a great deal of time fixing it doesn't appeal to me, my big boat keeps me poor and busy enough.

Fed
21-08-2011, 10:42 AM
When you think about the downstroke of a 2 stroke the ports are sort of gasping & wheezing at the same time, unlike a 4 stroke with valves.

I'd deadset go and run a tank of E10 through it in an effort to scavenge any moisture out of the crankcase, I don't know if it would help or not but it sure wouldn't harm it.

Salad Fingers
24-08-2011, 08:29 PM
thanks for the tip fed, I actually ran a bit of metho in the tank (i guess same as using E10) through it and ran it on a super rich mixture of oil for its first outing.
All good, hasn't siezed up again, i'm prepared to call it as being all fixed.
Cannot believe it was the baffle plate gasket, it really did not look that bad at all. I have replaced alot of gaskets in my time in an automotive context and this one really looked like it wouldnt have even been leaking - but there ya go!

anyway, im sure the motor now has a shortend lifespan in terms of its bore and bearings/rods, but we'll see :)