[manuelmercury]

bought the boat from a non profit organization with no info other than it had sat for the last four years.got it home and would not kick over. after some troubleshooting replaced the ignition switch and started up after awhile. replaced water pump(impellar was toasted as was upper part of water pump). started her back up and sounded rough.took her to the lake and had hard time starting her up when she finaly started i put it in gear and it died out this went on a few times then finaly got it to move. went about 30 yards and she died and would not start back up.got her home put muffs back on and she started. did a compression check and all had 120 except lower right (5?) which was 5psi. removed the head and piston was melted inward. rings looked to be intac. cylinder has no scoring or scratches although cross hatchings are not visible in that cylinder. also that cylinder was dry. no fuel/oil going into it.my next move is to remove carbs and clean them and put new gaskets on and replace piston in #5 and all piston rings. is there anything else that i missed or should be looking into or am i on the right track? by the way ive never worked on a boat before but i do have the seloc manual and have worked on cars.also will the carb problem and a bad piston cause it not to run in the water?

[emckelvy]

A "dead hole" will definitely make it run poorly in the water!!

Most likely #5 had been running lean for quite a while and probably burnt up from detonation.

What I'd recommend is servicing ALL the carbs while the motor is down for repairs. Then you know this isn't going to happen again. Also check all the fuel lines for rot/restrictions. Rebuild the fuel pump(s), you can get a diaphragm/gasket kit cheap enough.

There are a few problem areas which would be good to address while it's apart; if you're replacing rings in all cylinders, you'll be replacing both head gaskets. That's a Good Thing as it's not uncommon to see head gasket problems crop up on older motors. Even if you don't open the motor up that far, be sure to do both heads.

Take the heads to an automotive machine shop and have them surfaced/trued up. You can even do this yourself by using sandpaper on a metal surfacing plate or piece of glass.

Another problem area lies with the exhaust manifold. The gaskets dry up and then they leak water into the engine. Not good for running either! New gaskets will ensure you don't have any problems with the motor down the road. Inspect the inner exhaust baffle for cracks, perforations, and warpage. This sealing area is (besides the heads) just about the most critical.

Be sure you replace the wristpin and conn rod big-end roller bearings when you renew that piston. Note you may be able to find a very servicable piston/rod assy on eBay, it's worth a look anyway.

When renewing the dead cylinder, if the conn rod has body-fit bolts with nuts, you can re-use the rod bolts. Degrease and put a drop of Red Loctite on the nutted area of the threads.

If the conn rod bolts thread directly into the rod, without nuts, you MUST renew the bolts as they are "stretch" or Torque-to-Yield bolts and cannot be reused. If you do they are virtually guaranteed to break.

Be sure to torque the conn rod bolts, head bolts, and exhaust manifold bolts to specs. You'll need to pick up a manual to help with this. These torques are extremely critical and can cause you to lose an engine if not done correctly.

When you're in there, check the upper and lower crank bearings for roughness, inspect the crankshaft and rods for pitting/wear/etc. Renew the upper and lower crank seals.

You'll also want to time/synchronize the motor to specs, this'll ensure you don't destroy it from detonation caused by too much spark advance.

One last thought, I can't recall if the 175 had chrome bores, but if it does, don't use any kind of hone or 'glaze-buster' on it.

If they're just steel liners, it's OK to use one of the "dingleball" type of deglazers to 'rough up' the bores so they'll seat-in new piston rings. Only run the glaze-buster enough to get a good cross-hatch, and no more.

The V6 actually isn't that bad of a motor to work on, it's just a bit on the heavy side. Don't try lifting it off the motor by yourself, get a strong friend, an engine hoist, or eat a bunch of Wheaties before you start. I did it in my younger days but no more, that's fer sur!

Oh, and this site is a great place to look up parts/diagrams for your motor:

http://www.mercruiserparts.com/Selec...asp?class_id=2

HTH & Happy Wrenching...........ed

[manuelmercury]

ed thanks alot for the insight. i will definetly look through the whole power head for any other wear and tear.i planned on cleaning up all carbs.and yes the port side gaskets are leaking on the head and thermostat so those will definatly get replaced. and no these cylinders are not chromed lined.well id appriciate all other comments and help. i will keep all up to date as i progress!

[achris]

My first tip would be to lose the solec and buy a Merc genuine manual... You're need it for a re-build.

Chris.......

[manuelmercury]

took the carbs off today, they looked pretty clean.all holes seemed to be clear not gummed up or anything. soaking them in carb cleaner anyway.float looked discolored a little but looked pretty good. gonna replace anyways.ill keep you all up to date.

[manuelmercury]

after 7 months im getting back into fixing the boat.today i pulled the power head off i noticed the lower end cap had alot of black soot on it, is this normal?

[manuelmercury]

anybody?anything?

[manuelmercury]

opened her up and found that when the piston melted the skirt shattered and pushed two holes through the block and cover.

[manuelmercury]

decided to weld it with alumi-pro welding/brazing rods.i have nothing to loose. i ordered $250 worth of parts when i took off the cylinder head and saw that the piston melted but cylnder and evrything else looked good.wasnt until i took the engine apart more that i saw the hole and crack. tried a trial test with the alumi-pro welding two pieces of aluminum bar together and hammered the heck out of it while in a vise and couldnt break it apart until i used a small sledge hammer.will post before and after pictures and let everyone know how it goes.place your bets. note one hole is at the bottom of piston cylinder next to rod hole/passage about the size of a nickle square in shape. one crack is in the crankcase cover horseshoe shape and another crack in the the bottom of another piston cylinder horseshoe shape as well.