Yam C55 water in cylinders

[cocoglass]

Morning guys. I need an expert in the older C55 (1995) two stroke two cylinder engines. Mine has water getting in both cylinders. There is enough water to shake it out of the spark plugs after running. Here is what I have done so far: Removed head, sent to machine shop for surfacing and trueness check, no problems found. Had same shop check block deck for trueness, no problems found. Removed powerhead, replaced base gasket and side cover gasket. No cracks, very clean in all aspects of the water passages and around cylinder jackets. There was no sign of water intrusion on the head gasket. Re-assembled engine, ran on a hose directly connected to the water tube, and same thing, water on both plugs.
So, I have a cracked block, right? Is there any known problems with these blocks, like where they crack as to allow water into both cylinders? The only odd thing I noticed was that the anode that is mounted between the cylinders was loose. That anode, how does it physically mount? The head is back on, so I can't see. If the boss down in between the cyls where the screw attaches the anode, if that boss is cracked, will it leak into the intake area around the crank on both cylinders, and then get water in the cyls thru the intake path / ports?

I told ya that I needed an expert!!!

[boats.net]

Either have a hole corroded through head or block, check head closly for holes into water jacket.

[99yam40]

Might check under the exhaust plate cover, being water cooled that would be a place I would be looking if you cannot find anything on head ,gaskets, and cylinders

[cocoglass]

Thanks so much for the responses. It is a real puzzle, this one. I have checked all that I can check without splitting the block and looking for some sort of crack that allows water back into the intake area of the crankcase. That is about all I can come up with, and I know....it is a real stretch. Bottom line, water in BOTH cylinders, #2 is worse that #1, sealing surfaces of head gasket are square, straight, no cracks behind side plate, side plate gasket surface square and straight, powerhead pulled and base gasket replaced. No apparent problems there. Another key clue is that I am running it on a hose directly attached to the water pipe. Therefore, no water can be entering the lower crank seal, as someone else had suggested. I have followed the water path as it enters the powerhead and is distributed throughout the block. It is a very simple water flow path. The only real "gotcha" is you can't really see down in between the cyls at the depth of the water jacket. I have heard that water can leak in behind the sleeves and enter the cyls thru the ports, but I see no way for water to get behind the sleeves; they look very firm and secure in the block. Tearing my hair out here.....

Anyone here know the geometry of the sleeves on this motor? By that I mean the shape of the outside of the sleeve. Is it a stepped sleeve, does it have any hollow areas between the block and sleeve, or is it just a plain straight sleeve that has full side contact with the block aluminum?

[TownsendsFJR1300]

I can't answer your question re the jackets but maybe some other things to check...

If the power head if still off (or the lower unit still removed), pull the spark plugs. Don't run the engine, and put water pressure to the water pipe directly. If the head is on, look (preferably with a scope) into the combustion chamber and see if its coming in on the "top end".

If not, pull the carbs / reed valve body and see if any water is entering from the "lower end".


BTW, was the engine used in salt water and if so, flushed religiously or ?

1995 C55ELRT Yamaha Outboard INTAKE Diagram and Parts

[cocoglass]

Thanks Scott. I thought about some sort of pressurized testing, but I don't have the tooling to make up the required plates and sealing fixtures that would be needed. If the head is off, water will just gush out from between the cyls (jacket area) unless I block the top of the cylinder deck with a plexiglass plate and new head gasket. I would love to do that, since I could clearly see where water was coming from, but I just don't have a way to make that up, with any kind of accuracy. I kinda think that I might have some pinholes down in the jacket, and the water is leaking thru to behind the sleeves, and then coming in the intake while running. I am going to pull the powerhead, turn it so that the open cylinders are facing skyward, plug all the water "exits" that I can find with tooling clay, hopefully getting them all, and then fill the water jacket area with mineral spirits. If it leaks down, it should leak into the crankcase area if my idea about it coming from behind the sleeves is right. And the sorry part of all this is that if it is leaking like that, the block is junk anyway.

[TownsendsFJR1300]

I think you may be onto something...

As you stated (and I did but with water), if you have an air compressor use AIR!!

If can hook up to the intake water line and pressurize it to say 20 PSI. Then, if the heads off, spray with say WD40 (soapy water if necessary but spray down with something to prevent rust) around the cylinder ports (where the jackets would meet the block), and the block itself too. Yes the air will bleed off into the water jackets but you'll be watching/spraying area's where water (now air) SHOULDN'T BE for any bubbles.

If no luck there, remove the entire reed assemblies, pressurize again, spray and look for bubbles from the bottom end.

The motors been in service for almost twenty years without leaking, if it was a casting issue, I'd think the problem would have surfaced years ago.

With water getting into BOTH cylinders, I'd be looking real hard at the aluminum block between the cylinders...

Has the engine been run mostly in salt water or fresh water??


Also, you didn't reply to super close examination of the head itself. With a water jacket running thru the head, its very possible, espesically if run in salt water, for the head to corrode and allow leakage. You may not see it unless the both sides of the head are cleaned spotless, with a wire brush, etc.

All it takes is a pin hole, with the pressure of the water pump pumping, the cylinders are full of water...


Good luck

[cocoglass]

Yes it is an old salty. Will examine the head very carefully. What are the odds of two pinholes in the head? Two would be required for a water in both cyls problem. Also, with pinholes maybe compression would be affected? I figured 110 was OK. Whatever it is, it is common to both cylinders. I theeenk eettt eezz junko.

[TownsendsFJR1300]

Many years ago my nieghbor gave me a Mercury (65HP maybe). The head on that model was cast to the block(pistons came out from below). Same issue as yours (but just one cylinder, 3 cylinder engine).

I pulled the coolant head cover off and found a nice large hole inbetween the combustion chamber and the water jacket loaded with salt (he rarely flushed it, salt water use). After I got done digging the corrosion away and got to clean aliminum, I had to make a plug of aluminum (widest end was approx a quarter, 1/8" at the combustion chamber).

Brought it to an aluminum welder, welded in my plug, worked great! Bought another hull, put the motor on it and sold it!

I'd put money on a corroded head, with time and salt, it just finally broke thru to the combustion chamber.

A leak down test with the piston at TDC (head on) to see how long it holds compression (bet it won't be long) will confirm either the above or bad piston rings (but rings wouldn't have anything to do with water intrusion).

With the coolant cover off(head cover), I'd spray some water atop the head while pressured up at TDC, bet you see bubbles of air coming out...