compression info needed

Discussion in 'Boats and Motors' started by ezbite, Apr 2, 2008.

  1. ezbite

    ezbite the Susan Lucci of OGF

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    put the old compression tester on the 150 merc today and they all came to about 92/93 except for #2 which came to 85. i thought the seloc manual i have would have the specs in it, it doesn't. can some one tell me what i should be getting or maybe have a link or website? thanks.
     
  2. NUM1FIRE

    NUM1FIRE FIREFIGHTER/1ST RESPONDER


  3. ezbite

    ezbite the Susan Lucci of OGF

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    thanks, i found several replys, some say its low, but most say as long as all cylinders are within 15% of each other its ok. 15% seems like a large margin to me, but there the experts. id still like some more input from anyone.
     
  4. KaGee

    KaGee Monkeywrench Staff Member

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    15% would be the the high number. Usually it's around 10%.
    Did you warm the motor up prior to the test?
    Proper compression test should be done on a warm motor.
     
  5. ezbite

    ezbite the Susan Lucci of OGF

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    i let it run for over 10 minutes with the muffs on, nice and hot when i tested her.:p
     
  6. Workdog

    Workdog "One More Time"

    A Merc service manual would state the recommended range (and that would probably be in the 120-130 range), but it doesn't matter nearly as much as being within 10%. It would be a rare occasion that all six holes are bad. By my calc you are within 9%, so you should be good to go. Doing the compression test on a warm engine is correct, and, with the throttle wide open and all plugs removed. It is possible your guage reads low, thereby giving you low compression readings. If you are still concerned, you might try a leakdown test.

    Workdog
     
  7. donkey

    donkey Permanent Part Time

    If it is a 2 stroke have you ever Decarbed the pistons and rings.I have brought back several 2 stroke outboards to respectable compression levels by decarbing the engines.There are several products available in spray can form that work really well.One ic OMC engine tuner or Valvetech decarb another Is made by Merc and I believe it ic called Ring Free.
    The piston rings coke up on 2 strokes rather quickly and need this treatment at least annually.Once the ring cokes up to where it is locked in place it WILL score your cylinder wall and cause permanent damage.All 2 srokes should be decarbed at least annually.You can go to this link and they will describe how to do it.

    http://continuouswave.com/ubb/Forum3/HTML/007656.html
     
  8. ezbite

    ezbite the Susan Lucci of OGF

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    i did the decarb last year the week before hawgfest with seafoam. i did troll with this motor a bit after that. when i did this last compression test i didnt have the throttle open. im going to get another gauge, decarb again and redo the test with the throttle WIDE open:)
     
  9. LakeRaider

    LakeRaider EEEEEK!

    Need to know what year the motor is. And if its a 2.0,2.4 or 2.5 litre. Assuming is an older 2.0 litre the comp should be 116-118 lbs dry across the board. Compression guage really won,t tell you much. Best way to see if there is a problem or a problem going to happen is to do a leakdown test on all six. 4% is ok. If you troll alot keep the mota trimmed up so the exhaust circuit is out of the water. The upper two small holes on the top of your mid section is the upper exhaust circuit. At idle this is where the exhaust is expelled. When you open the throttle is mostley bypasses this small exhaust outlet and goes out the prop. These motors run better on NGK spark plugs also. Change spark plugs often. The motor should have a very crisp idle when running correctley. ONE MORE TIP, get rid of the oil injection. When the plastic gear fails in the mota it will cook your motor in seconds. We mix Merc synthetic or Klotz. L77JC4 Champions are a good plug also but don,t last as long as the NGK,s. If you troll alot stay at 50-1. If you like to make long runs at wot we mix 32-1. Carbon guard a few times a year. One other thing to check is the powerhead gasket. While the engine is running with the cowl off, look at the base of your motor and see if there is water or exhaust seeping out. If you see bubbles the exhaust can fill up under the cowl and go thru the carbs and fowl the spark plugs faster. Lots of tricks for the Mercs! :)
    Raider
     
  10. ezbite

    ezbite the Susan Lucci of OGF

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    its a 1995 carberated, solid state ign. i have no idea how many liters. motor is in top shape(one of the reasons i took the boat) no leaks or corrosion anywhere. everything looks brand new. even the wires, no green or white powery crap anywhere. sounds like it has a small miss somewhere. i put new plug wires, plugs and fuel pump diaphram on it last year. i got new plugs yesterday(NGK-BU8H), but im waiting till i get the decarb done before installing them. i checked the coils but im not really sure what im looking for. all 6 showed between 12 and 14 volts. any thoughts on the miss? whats the leak down test? i assume pressurize the cylinder and let sit and see if it leaks down??lol. please explain. are you talking about pre mixing my oil and gas? its a 52 gallon tank, wouldn't that be tought to get exact?
     
  11. LakeRaider

    LakeRaider EEEEEK!

    The small miss is probably a crossfire between the cylinders, due to a slightley fowled sparkplug or a small amount of fuel puddling in the carborator. Check to make sure none of the small lines on the carbs are cracked or pinched. To premix your fuel you need to diconnect the oil injection and install the correct blockoff-spacer kit where your oil injection pump is at on the motor. I can explain that in detail if you decide to do that.
    Costs about $30. If you mix your own fuel its simple. Start with a fresh tank of gas. Then read the chart for how many ounces of oil to gallons of fuel. Then next time you fill up simply read how many gallons of gas you added, then add the proper amount of oil to the fuel tank. Very simple and most oil bottles have the ounces guage on the side of the bottle. A real leakdown compression test guage has two guages on it. One is in lbs and the other is in %. I,ll post a pic of mine sometime. Your motor could be a 2.4 or a 2.5 litre. Only difference really is a 2.5 has the rods behind the liner and a slighly different exhaust can.. Has a little more low end torque. I prefer a 2.4 myself because you can disconnect the rev limiter. The 2.5 has an ECM that you have to reprogram. Sounds like you have a great motor. Maintained properly it will last approx. 1500 hrs with the oil injection. Mix your own fuel and they will last around 2000 hrs. between rebuilds. Actually you can turn up the oil flow on the oil injection unit if you wish. I think 100-1 at an idle is a little bit too lean on the oil. Just my opinion. Raider