Steaming Cylinder- Where's water?!

[Korbs67]

Hi All,
I keep burning up #1 on 3cyl 60HP, '89. SN: B396723.

My other threads have more detail but I'll keep it quick for this question.

I'm working with a very experience merc mechanic on this side for my project. Given that, I truly appreciate the additional perspective I get form this forum. We both happen to be stumped on this one but have some hunches.

Motor is timed perfect, carbs, water pump, fuel pump and plugs, and all iginition is perfect. New gaskets no visible exterior leaks at all, anywhere. Manifolds and plates are all in excellent condition and lay flat and appear to be true.

A milky frothy mixture of churned oil, gas and water is being produced by cyl 1. at idle. at speed P1 eventually steam cleans itself and burns up. We unplug the spark plug and chug on into the docks.

I took the water cover off and inspected for cracks..I assume its the only areas where water can enter the piston chamber.
I see no evidence of a crack. I lightly wire wheeled where I could but cant get any deeper, it happens to be fairly clean and I see no signs of fracture. No crack in the block from by looking at the water cover view and exhuast manifold view. I have had this motor apart 3 times got up close and personal with the rest of the block and never noticed any unusual cracks, splits, etc. This is why I puzzled.

IF, there were a leak from the exhaust manifold covers (you know how they are back to back?), can water get sucked back into the piston kind of like a backdraft of sorts. Also, if I'm steam cleaning the top of that piston would is originate on the intake or exhaust side of the high-dome piston?

Attached are a couple pics.. disregard the used gasket you see. all gaskets, torques sequence, surfaces, etc were prepared well.

THANKS!!!

Ken

 

[CharlieB]

Re: Steaming Cylinder- Where's water?!

Suspect the cyl liner to block is leaking and allowing water to be sucked into cyl.

The block needs to be pressure tested.

P.I.T.A. but it will show the problem.

Has this motor had an over-heat just prior to loosing the first piston? That could be the root cause of your continuing problem.

 

[Korbs67]

Re: Steaming Cylinder- Where's water?!

Yes it did have an overheat. I was a new boat owner and wish I knew then what i know now. I just replaced the impeller and the old one was basically non-existent. Water flows, no blockage, steady hard telltale stream. I'm 25;1 on my mixture. All cylinders spec fine, honed, all rings replaced, compression test 150 across the board. idles pefect. the spark plug hole on #1 cakes up with aluminum and prevent spark to cylinder..so yes there is detonation occuring after roughly 5-15 minutes of test running on lake.

Can i pressure test this thing on my own? What is the basic methodology behind doing a pressure test? I imagine buttoning it up and pressurizing hole #1 and spraying around motor with soapy water?? Dont want to blow out fuel diaphram if pressure goes back that far or diaphram can handle the psi.

Thanks if you want to elaborate a bit on the pressure testing..I've done everything else so I dont mind giving anything a try to eliminate the block from the equation.

Ken

 

[oldman570]

Re: Steaming Cylinder- Where's water?!

Pressure test, leak down test will tell if the block is cracked. it should hold presure and not leak down very much if rings are good. make sure the rings are above the exhaust an intake ports in the block inorder to get a good test.
Oldman570

 

[Korbs67]

Re: Steaming Cylinder- Where's water?!

Thanks oldman570. A couple questions. Is this a localized test of cyl 1 through the spark plug hole? What PSI am I shooting for? Say there is a leak it must be in the water jacket then becuase I'm on this side of the piston head?? On my model the water jacket covers the piston heads and can be removed exposing all three cyl and plug holes.

How do I differentiate between bad rings or boring in hole 1 vs. cracked cylinder or water jacket liner?

THANKS!
Ken

 

[Faztbullet]

Re: Steaming Cylinder- Where's water?!

cracked cylinder or water jacket liner?

The only way to test for above is to pressure test block.... leak down will not show you this.

Can i pressure test this thing on my own?

yes...

What is the basic methodology behind doing a pressure test?

Take the empty block and install a block off plate on bottom of block, install exhaust plate and water jacket. Add 80psi to block and use soapy solution to spray areas or submerge it in a tank after pressurizing. Merc years ago offered this plate in their special tool section just for inlines.

the spark plug hole on #1 cakes up with aluminum and prevents spark to cylinder.

This is timing problem from a switchbox/trigger failing. If its throwing off aluminum from piston "eyebrow" to plug the timing is off on that cylinder due to switchbox bia's circuit is advanced on that cylinder, trigger is double firing or timing pointer is incorrect. Is this happening before it starts to suck water????

 

[oldman570]

Re: Steaming Cylinder- Where's water?!

Yes the pressure test is only on the cyclender that is giving trouble. I test at 50 lbs. pressure and the pressure should not drop very quickly. You will need leakdown gauge and a fitting that will screw into the spark plug hole inorder to test or a small compresser with a regulater that can be set for the pressure needed. The piston, rings, and block should hold the pressure for a period of time before it starts to bleed down. test works the same as pressure testing a radierator on a car only atmore pressure. Spraying the cyclender exterier walls with soapy water or kids bubble toy soap will show any air leak.
Oldman570

 

[oldman570]

Re: Steaming Cylinder- Where's water?!

Right on Fastbullet. thanks for the help in explaining the test.
Oldman570

 

[Faztbullet]

Re: Steaming Cylinder- Where's water?!

The piston, rings, and block should hold the pressure for a period of time before it starts to bleed down

I disagree as 2 stroke outboard will not hold a steady pressure and will have about a 4-10% leak down due to ring gap at rings., You will hear it leak past the rings as you apply air pressure , it will be hard to check exhaust side as this is where most of it escapes....plus it waste of time to do on a damaged cylinder.

 

[Korbs67]

Re: Steaming Cylinder- Where's water?!

Let me first say. Thank you for the forum response.Wow.
I sure hope its a trigger or switchbox issue. Let me explain more. Per another post reagrding other matter on same motor (which were resolved). I tested all iginition with a Mercury DVA. The Stator, trigger, coils and recitifer all were in perfect shape in terms of requred voltages.


P1 was brand new.Top Dead Center was determined by Merc Mechanic. After finding zero a static timing of cyl 1 was perfromed at -2 (20-21degrees). On the muffs all systems were go. We went to the river timeWOT and final adjust carbs. Carbs were spraying perfect and WOT timing was fine tuned.

I'd love to simply buy a new trigger. I have an extra coil i can install for cyl1, if that wil help. To answer the above question by Faztbullet, this is happening on the water. After first rebuild, I got about 1.5 hours of run time then cyl 1 shut down. Rebuild two is when I did all my timing adjustments as stated above(i figured I learned my lesson by being to eager to test in water. I excercized patience and did the proper tining becfause I was advised I had an advanced timing issue or carburation issue. It took 10-15 minuted of on the water running before the mechanic unplugged cyl 1 and we chugged into the docks. Despite the mild detonation the piston is not trashed and if i can resolve my issues and throw another new piston at the project.

Can DVA indicate a healthy ignition system and there still be double fires by trigger or bad bias circuit in switchbox?? Because for the life of me I have inspected the exterior of this motor and cant blatently see any water leaks, or cracks. I have inspected the water intake areas of the exhaust manifold and water jackets (the "bulbs" you can see when its off) and do not see any cracks.

If i can pressurize cyl 1 to spray some bubbles maybe that will identify i leak in water jacket area which would great b/c its so accessible...the whole uper half of the piston/cyl is cast in that section.

Thanks again!

Ken

 

[CharlieB]

Re: Steaming Cylinder- Where's water?!

Pressurizing the cyl will NOT put pressure on the cyl liner at the ports. The water jacket encircles the liner down to the level of the ports, there is no way that a piston/rings will hold pressure low enough in the cyl for an accurate test. The block must be pressurized thru the water passages.

If the motor is still together and running, a simple test for double firing of a cyl is to use an inductive tach, compare readings between cyls. If one cyl reads twice the others it would be an obvious sign something is amiss. I used to prove the old Force boxes bad this way.