25hp Merc Cylinder Rework

[dkondelik]

1985 Mercury 25hp 2 cylinder outboard.<br />Dropped a cylinder last Saturday. Compression; TOP-90psi, BOTTM-135.<br />I think I know which end of the screw driver to hold BUT, new to boat motors<br /><br />Question. Before I undertake the repair, want to know what I?m in for. Do I need to pull powerhead to remove jugs? <br />I have heard the phrase ?Split the Case?. Does this apply to 2cyl 25 horse ?85 Merc?<br /><br />Any advise or tips?

 

[S.T. Marine]

Re: 25hp Merc Cylinder Rework

You have to pull the power head. After that you have to split the block in half to take the crank and pistons out. I myself am only 18 and I own my own outboard business. It is rather simple once you get into it. Feel free to e mail me at stmarine@hotmail.com

 

[dmessy]

Re: 25hp Merc Cylinder Rework

b4 pulling powerhead,<br />1)Try decarbing your engine using spray(follow instructions on can)you may just have carbon buildup causing stuck rings. If compression rises to >120#, great, you'er in luck. If not...<br />2)Remove head itself(can be done without pulling powerhead ) Inspect suspect cylinder and piston for scoring.If cylinder is scored be assured you have broken or ceased a ring. You are then in for a pwerhead pull and rebuild. If it isn't excessively scored...<br />3)Piston rings can be checked for brakage or stuck by removing exhaust plate and pushing on rings with a small screwdriver when piston is at the level of the exhaust opening. If they rebound when pushing, all is good, move on..<br />3)If the above checks out, you've blown a head gasket. Check the head for warpage,rectify if needed, replace gaskets and retorque AS SPECIFIED,both head and exhaust plates.<br />I hope this helps and good luck.

 

[dkondelik]

Re: 25hp Merc Cylinder Rework

Photon Dispencer?<br /><br />Thanx<br />Will first try de-carbon. Any suggestions for cleaning agent?<br /><br />Assuming FAILure, any tips or tricks in pulling head? Or, is it an obvious/logical sequence?

 

[dkondelik]

Re: 25hp Merc Cylinder Rework

^

 

[steelespike]

Re: 25hp Merc Cylinder Rework

Klon, Start with a manual.

 

[dkondelik]

Re: 25hp Merc Cylinder Rework

Manual?<br />Published knowledge?<br />There's 'n i-de-ear<br /><br />Sounds Like a plan.<br /><br />Thanx Spike & others

 

[dmessy]

Re: 25hp Merc Cylinder Rework

Rad. Tech.---<br />Most any marine dealer or place like NAPA should have a good decarbonizer. I used some stuff by Yamaha will good results. Follow thier directions. <br />Basically, heat up your motor, go to fast idle and spray the stuff into the carb. throat(s), then shut it off, pull the plugs and douse the cylinders, let it sit for a couple of hours, then start er up. The smoke will roll! <br />Run at > 1/2 throttle for a while, then either clean or replace the plugs. Re check your compression, warm, with throttle open and both plugs out and grounded (with wires on). Good Luck