Rings change

ferscha

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Feb 1, 2002
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Hi<br />I have a OMC Saildrive in my saliboat, similar to Johnson 35, but inboard<br />The compression is off: 55 and 60.<br />Its a good idea only change the rings?, or need reboring, and change pistons? How i know if changing only the rings the compression will be good?<br /><br /><br />Thanks to all and good winds!
 

JB

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Mar 25, 2001
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45,907
Re: Rings change

Howdy, FER. Your engine may simply be choked with carbon. Carbon build-up will make the rings stick. Then compression goes down.<br /><br />You can dismantle the engine and clean the carbon from the pistons and rings, or, if you are lucky, you can clean it out without tearing the engine down. Ask your boat/engine shop for a decarbonizing spray and follow directions exactly. It might require several treatments, so recheck your compression after each treatment.<br /><br />Good luck.<br /><br />Red sky at night. . .<br />JB :)
 

ferscha

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Re: Rings change

I already removed the cylinder head, and there a lot of oiled carbon at pistons tops and cylinder head. Wich type or brand of decarbonizing spray you recomend?.<br />I can move the pistons laterally, and it moves at least one milimeter, it is normal?<br />The year motor is 1979. I need to dismantle all the crankcase to clean? if the reponse is yes...it is advisable to change rings?<br />Why carbon make low compression?<br />Sorry for a lot of question!<br /><br />Thanks!
 

petryshyn

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Re: Rings change

Hi FER:<br /><br />>Whats the history on the engine? <br />>Was it running before?<br />>Did it knock?<br />>Low power?<br />>Is this a new engine to you?<br />>Why did you do a compression test?<br />>Was this just routine maintenance?<br />>Did you try a different compression gauge?<br /><br /><br />
carbon.gif
<br /><br /><br /> If it were my engine, I'd spray alot of decarbonizer (any kind from your nearest marine shop) on the pistons and let it sit as per instructions. I'd apply it when the piston is near the top, so some will leak by the rings, hopefully freeing them up. Bolt the head back on and try it again. You may get a few more years out of her, or you may not.....What have you got to lose other than the price of a gasket.<br /><br />Just my humble opinion... :)
 

ferscha

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Re: Rings change

I have the motor for 2 years. It was in good conditions. The unique service that it had was the rotor of the water pump. It run well, but spark plugs common wet and oiled. Last summer , dead the water pump, and had an overheating. The alarm did not work. But I believe that i detect it enough (?) fast: by the sound, and the smell...<br />After changing the water pump, the motor works, but a cylinder not always start, run after 1-2 minutes and sparkplugs was covered with wet ash , oil, carbon... , more every day.<br />Spending 4 spark by weekend. Finally cylinder 1, does not start.<br />After this, came the compression test , and the removal of the head of the cylinder, its gasket, gasoline pump check , etc<br />I believe that I am going to put the head, new gasket, and to prove with some decarb product. Thanks for the aid!
 

petryshyn

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Re: Rings change

You may have damaged the engine when it overheated. The rings could have lost their tension. You could also have scored the cylinder walls, causing compression leakage as well. It all makes sense now, and doesn't look good...but I guess it won't hurt to try.<br /><br />Good luck!! :(
 

G DANE

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Nov 24, 2001
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2,476
Re: Rings change

Hi Fer<br /><br />The lateral play is normal, both on saildrives and older Johnson/Evinrude ourboards of that kind. Last time i had a head off one i noticed same play, but compression was beyond 110 when assembled. <br /><br />Try the decarb Scematic suggest. Saildrives dont often have many hours - and lots of slowrunning which builds up carbon.
 

G DANE

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Re: Rings change

See the other thread of OMC/Johnson/Evinrude saildrives on this side.<br /><br />Good luck
 

harrison20002

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Re: Rings change

Hi FER, It sounds like Schematis' solution is right on. The man knows his stuff.<br /><br />One thing about your problem bothers me. You said that you could move the pistons. Is that back and forth or up and down? If it's back and forth go with Schematic. If it's up and down, this indicates bad bearings, in this instance I would go completely through it.<br /><br />One other thing is don't forget to make your compression check with the engine warm, 55 & 60 seems awfully low. I think I might go with new rings. What ever you decide, goodluck. Hal
 

ferscha

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Re: Rings change

The compression (55-60) is in cold engine.<br />The piston movement is like schematic scheme: Up and down with the motor in his site (90deg of the scheme).<br />I call to OMC dealer. He has OMC engine Tuner at 18U$S (?¡?). I will buy one can and one head gasket, one sealing, and make a prayer!!<br />Thanks to all.
 

ferscha

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Feb 1, 2002
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Re: Rings change

I cleaned the cover, the pistons, new gasket(sierra), closed everything... and Started, in one cylinder(#2), after 2 min, other cylinder(#1).<br />With the warm motor, I applied OMC TUNER, and I left all the night it. On the following day, I felt best compression (not gauge test), but..., cylinder #1, did not walk.<br />In total depression, I decided to check sparks, and I discovered that cyl#1 did not have spark! As the fault had been intermittent (but always in cil#1), I checked cables for brokens=none. Ignition coils, thinked. Then I interchanged the coils (2x1, 1x2), and cylinder #1 follows without spark = coils of ignición=ok.<br />The question is: it can be another thing that the Black Box? If cylinder 2 has good spark, indicates that charge coil, sensor coil, capacitor and kill wire and ignition timing are ok?<br />I do not have mercotronic nor another Black Box to prove.<br />They have some suggestion before buying powerbox (U$S 149)? <br />Thanks to all.<br /> :confused:
 

ferscha

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Re: Rings change

OH! I FORGETED TO TELL:<br />Sometimes the motor dont shut off.<br />AND<br />The RPM meter, shows always (in two years works well ONLY 10 minutes) bads RPM, aprox. one half of reality.<br /><br /> :eek:
 

petryshyn

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Re: Rings change

Fer<br />sorry man, I can't be of much help without a schematic. If you have only 1 charge coil, and sensor coil, and you have spark on one cylinder, it is possible that a grounded sensor or charge coil will do this. Disconnect them from the pack and see if either have continuity to ground. If they don't, I'd suspect bad pack. Be sure pack is getting good ground. Retorque the ground for the pack.<br />As far as the engine kill goes, trace kill wire to pack. Try grounding at pack. If this doesn't kill engine, replace pack. <br /><br />The tach can read half because:<br />>tach is set on wrong pulse type<br />>rectifier has partially failed (do a diode check)<br />>tach has bad feed or grounds<br />>bad tach<br /><br />hope this helps..... :)
 

ferscha

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Feb 1, 2002
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Re: Rings change

Hi, tanks for the help!<br /><br />I check, charge and sensor coils, and there are OK. The kill wire have good ground when key-off, and not whith key-on=I will change the power box.<br /><br /><br />Very thanks again!<br /><br /> :)
 

petryshyn

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Re: Rings change

I'm going to be honest with you......I have never seen a sail drive!! What a funny lookin device!! Someone else will have to help with parts location, or, you'll have to get a manual.... I'm sure someone will pitch in.<br /><br />Good luck! :rolleyes:
 

ferscha

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Feb 1, 2002
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Re: Rings change

I changed the power box, and the motor run OK!!!!!!!!<br />The compression is 90-100, after gasket change and decarb.<br /><br />Very thanks to all this forum, special to SCHEMATIC.<br /><br />bye!<br /><br /> :) :) :) :cool:
 

petryshyn

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Re: Rings change

You're welcome Fer, But its J.B. who deserves the credit...he trouble shot it for you!<br /><br />Hopefully you'll get a few more years out of that puppy!!<br /><br />good luck! :)
 
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