Merc xs with water in #3/4 cause?

[63g3]

Hi,
I'm not new to 6 inlnes but here is something I have not seen and am wondering if the more experienced have and what your comments are.
I run 1500XS on a Shooting Star, runs great at 6300rpm at about 80 plus, it has a SSM lower, I have a water pressure gauge on it too.
Two days ago, flat water so, I could run WOT for a few minutes on every pass, I slow to U-turn and go again. On the 5th pass or so motor lost RPM and then went ugly just stumbling to a halt and stalling out. I got it home, took compression readings, #3 down to 80 psi, all others at 120 to 125 , plug on #3 had creamy grey stuff on it. Pulled the trasfer port covers off revealing creamy white in crankase/ crank/rod area on #3 some on #4. Rings looked great, pistons look great, rings spring back when probed as in Merc rebuild manual.
I suspect the exhaust cover that goes over the waterjacket at the exhaust ports started leaking spraying water into cyls through exhaust port? I have not got that far in teardown, need to pull the P-head to get there. I did spray everything down with WD-40 to displace what looked like water filler oil residue. Any thoughts?
Also, I am speculating that the compresison is down on #3 due to the sudden on rush of water quenching the hot rings, maybe they lost tension? Or could a rod bend reducing the compession? Motor was re-started ran like crap but NO mechanical noises.
Any thoughts?, anyone had similar experience with water intrusion?
Thanks, just trying to feel better about the extent of repair ahead of me and to make sure I get any added secret repair tips. I picked up an NOS exhaust plate in anticipation that this is culprit so I'll have a flat one to go on at repair time. I figure I'm in for a re-ring that's not a big deal, nI have ring sets. I was worried about piston/cyl being junked but it does not appear to be. Weird about the drop in compression though where rings/pistons and bore all look good at least what I can see through the intake ports.
Any info thoughts, or stories of similar experiences appreciated.
Oh I'm building up a 1500 inline for a Vector so any tips on any part of assembly or prep would be appreciated. I do have the Merc tools to do the assembly but I knwo there are always tips that don't appera in stock manuals.
Randy

[Bruster]

Randy,

The powerhead needs to come off. I think when you pull the exhaust cover off you will see what is going on. If not split the case and let us know what you see. I don't think you have any real major damage. You may see some ring sticking on the exhaust side. Good luck!

But, Sometimesm nothing ever goes just as you plan....

http://forums.screamandfly.com/forums/showthread.php?t=196188

[Jeff_G]

Probably your exhaust plates. You may have to replace that piston. Water steam cleans and robs lubrication so scuffing results, not uncommon. Do a search here on S&F I did a long post on fixing the exhaust covers leaking.
While you have it down check your reed cages, look at the ridges inside the cages, there should be no "mushrooming" of the ridges.
Drop the timing to 19* bump the main jets to .084's.

[ChrisCarsonMarine]

If you unbolt the lower cowling pan from its front and rear supports it will move over enough to remove the exhaust plates,oops,also remove the lower shroud[4 phillips screws]most likely the exhaust port cover leaking.In rare cases ive seen cracks on the dome of the cyl,by the spark plug hole,usually after a bad overheat,causing compression loss and water intrusion,chris

[63g3]

Thanks GUYS!!! I have a few standard Merc pistons and ring sets if needed, the motor was all three ring pistons and that's what I have on the shelf. I've run the motor for a few years but have never been inside, do not know complete history of motor. I bought it from second owner who never used the boat/motor much, first owner was Merc mechanic for decades.
My concern is that original owner might have bored this out at one point, can you get .015 over ring sets if that is what I need? I doubt this is the case, I'll certainly find out, just trying to anticipate issues. Power head comes off this week.
As a last resort I have one NOS .015 piston and ring set but don't know if it's high dome or low dome, I don't know how to tell to compare to what's in motor, any help here? It's a stock Merc part not aftermarket. P/N is:768-7438A2 if that helps. I guess I have the same concern even if it's standard bore just to make sure if a new piston goes in, it matches what's there.
Thank-you all and thanks S&F!
CHRIS...I have 4 more inline 1500 blocks that need honing to re-ring, one or two holes might need a bore. When the time comes this winter, I'll send em' down, I think you said you have the blind bottoming bore and hone setup to do these.

[LightNBug]

My experience is that if you were getting that much water on #3 you would also be seeing signs of water on #5. If you are not seeing water on #5, then I would suspect a broken reed on #3 that probably damaged the piston when it went through.

[Bruster]

You can measure the piston domes with the backside of a set of calipers. There is about .100" between the high and low so it will be apparent.
O.S. rings shouldn't be an issue. If you need blocks bored there are some guys with the sunnen power hone that can diamond hone (no boring) and plateau finish the bores like the new motors. I was talking to a guy in Kentucky or Tennesee who had his machine set to do blind holes on the inlines.


Thanks GUYS!!! I have a few standard Merc pistons and ring sets if needed, the motor was all three ring pistons and that's what I have on the shelf. I've run the motor for a few years but have never been inside, do not know complete history of motor. I bought it from second owner who never used the boat/motor much, first owner was Merc mechanic for decades.
My concern is that original owner might have bored this out at one point, can you get .015 over ring sets if that is what I need? I doubt this is the case, I'll certainly find out, just trying to anticipate issues. Power head comes off this week.
As a last resort I have one NOS .015 piston and ring set but don't know if it's high dome or low dome, I don't know how to tell to compare to what's in motor, any help here? It's a stock Merc part not aftermarket. P/N is:768-7438A2 if that helps. I guess I have the same concern even if it's standard bore just to make sure if a new piston goes in, it matches what's there.
Thank-you all and thanks S&F!
CHRIS...I have 4 more inline 1500 blocks that need honing to re-ring, one or two holes might need a bore. When the time comes this winter, I'll send em' down, I think you said you have the blind bottoming bore and hone setup to do these.

[63g3]

Hi everyone who answered my post. Just to follow up here is what I found: I pulled the powerhad and got it apart. #3 piston piston scoring on exhaust side from steam cleaning the oil off when gasket leaked. ...Good call JeffG! This hole will need a new piston but walls, bore ad ports look fine..... whew! #1 which was 5 lbs low compared to others had a very slight scuff, top of block probably got low water level when gasket started leaking and top cyl got a touch hot. Piston will clean up fine. So looks like a piston, a full ring set a new exhaust cover and a hone will fix. I noticed when I removed the exhaust plate that the bolts came right out....so someone along the way must have had this off and when they reinstalled they did not use the Merc epoxy or the HD Loctite...no wonder it failed. That will not happen when I'm done doing it right.
What grit hone? I have a Snap on, for stones 280 is the fine one and 500 is extra fine. I would normally just touch the walls with the 280, and be done, 500 seems to fine anyone on that question?
Thanks,
Randy

[ChrisCarsonMarine]

Randy,When your ready i can do whatever you want to your motors,and i have pistons in oversize in stock,also make a very nice reed set for them,chris

[Bruster]

Mine were the same way, loose, fortunately no water was leaking in, just a little exhaust and goo seeping out. I think all the hot/cold cycles and 30+ years just take the toll on the old gaskets. The cover bolts need to be tightened to 250 in/lbs with Mercury gaskets, no aftermarket here. Pull the cylinder head cover off and re-gasket this too. Careful with the 1/4" bolts, you'll probably break a few off. I replaced all of my bolts with new cadium plated bolts, just to be sure.




I noticed when I removed the exhaust plate that the bolts came right out....so someone along the way must have had this off and when they reinstalled they did not use the Merc epoxy or the HD Loctite...no wonder it failed. That will not happen when I'm done doing it right.

Thanks,
Randy

[Jeff_G]

Do a search I detailed a fix for the exhaust plates a couple of times.
No offense to Chris but I would not recommend changing reeds. The reeds on the inlines rarely, very rarely go bad. I run them around 7000rpm in my inline all day. Due to the hassle of replacing them, and plastic reeds will need replacing, and no benefit to them, is why I would recommend staying with the OEM reeds.
Randy, carefully measure your bores. If they are in tolerances remove any aluminum transfer with muratic acid. Clean and hone (deglaze) with a brush hone, 220 grit is fine.

[ChrisCarsonMarine]

Time to close up for the evening,will discuss the non-beneficial reeds another time,g-nite,chris