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 Catalina/Capri 25/250 Sailor's Forums
 General Sailing Forum
 motor / compression question		  New Topic  Topic Locked
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Dan86
Navigator

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130 Posts
Initially Posted - 02/14/2005 :  19:40:06  Show Profile
Just got the diagnosis from the mechanic working on tuning my 1986, 9.9 johnson motor. He tells me that one cylinder has 90 compression and the other has 70, and that I will have a failure immenent. He says it could last a few days, or a long long time with the little use I give it. What is the forum's concensus on this issue, chuck it or keep it or no problem at all. Thanks as always.
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ClamBeach
Master Marine Consultant

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3072 Posts
Response Posted - 02/14/2005 :  20:29:18  Show Profile
In my experience... low compression usually doesn't result in catastrophic failure in a 2 stroke... they'll just progressively have less power, start harder, run rougher, produce more smoke, foul plugs etc.

A couple thoughts.

What's your sailing venue like? If your motor conks out can you get into trouble real fast? (Heavy currents, a bar to cross, rocky shorelines, ship traffic?) If so, I'd really think new motor.

Is this a freshwater motor? If so, you may stand a chance with a rebuild. For a saltwater motor, kiss it goodbye, you've got your 20 years out of it...
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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts
Response Posted - 02/15/2005 :  08:18:35  Show Profile
70 psi compression on a 4-stroke car engine is so low that the motor will barely run, if it starts at all, and is probably pouring out a big cloud of oil smoke. I'm not sure if 70 would be considered "catastrophically" low on a 2-stroke. I'd guess that the rings in that low cylinder are worn to a nub. The engine is certainly polluting a lot more than it did when new. Did you get an estimate on having the mechanic replace the rings? This assumes than the cylinder bore isn't worn beyond maximum diameter tolerance, which would require a re-bore, and new pistons as well as rings, which would probably cost more than the engine's worth. Plus there's the question of whether or not you can even still get over-size pistons and rings for a 19 year old outboard.
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atgep
Master Marine Consultant

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1009 Posts
Response Posted - 02/15/2005 :  08:44:19  Show Profile
How does the motor run? If it has enough power and runs smooth, don't worry. I am sure there are plenty of people who never check the compression. Running a little more oil in the mixture "may" help with the ring sealing.

I would run it for about an hour at cruise and check the temperature of the cylinder head. If was cool enough, I would run it till it dies.

Then.....Plop down $2000 for a new one.


Tom.
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JimB517
Past Commodore

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USA
3285 Posts
Response Posted - 02/15/2005 :  09:47:59  Show Profile  Visit JimB517's Homepage
ring job on a 2 stroke is easy. Get a bid. Have him clean all water passages, change impeller and lower end oil, re-ring both pistons, change head gasket, plus tune up. Over $1000? I'll bet it is. Still cheaper than a new motor.
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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts
Response Posted - 02/15/2005 :  10:45:03  Show Profile
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by JimB517</i>
<br />ring job on a 2 stroke is easy. Get a bid. Have him clean all water passages, change impeller and lower end oil, re-ring both pistons, change head gasket, plus tune up. Over $1000? I'll bet it is. Still cheaper than a new motor.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Yeah, it's cheaper than a new motor, but throwing $1,000.00 into a 20 year old outboard that's worth only a few hundred is like putting a brand new engine in an 86' Escort beater...it would run great, but it's still a 20 year old Escort.

I'd be inclined to chip in the extra $1,000.00 and come out twenty years ahead.
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JimB517
Past Commodore

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USA
3285 Posts
Response Posted - 02/15/2005 :  12:10:49  Show Profile  Visit JimB517's Homepage
agreed. I thought the conclusion would be self evident.
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.