Top speed with 18hp Evinrude on 14′ aluminum

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This topic contains 105 replies, has 22 voices, and was last updated by Avatar stephenspann27 2 years, 6 months ago.

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    stephenspann27

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    #50921
    quote Chris_P:

    Obviously those pistons were junk!

    In the bore, are my eyes playing trick, or are there gouges out of them? Bottom of 4th pic. OR is that just heavy pitting?

    No chunks missing,this is a fairly deep groove, but the rest of the scoring is light.

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    stephenspann27

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    #50922

    You can see the rust rings the wristpin circlips lift in the bore, this was a salt water motor with a lot of damage, the head gasket was also leaking. This block is most likely junk. I had to build up with JB weld and file flat the midsection surface that the powerhead bolts to because so much material was missing. I probably picked one of the worst 18hp motors out there.

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    stephenspann27

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    #50927

    Just for fun I checked the ring gap on the old motor:

    Piston 1

    ring 1 = .022

    ring 2= larger than .035

    ring 3 = larger than .035

    Piston 2

    ring 1 = .023

    ring 2 = .018

    ring 3 = .012

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    wannabe-outboard-guy

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    #50929

    Stephen….stop trying to talk yourself into a myth. The pistons , rings and bores are bad. Sugar coat it any way you want but the advise you have received here is from guys that have been there and done that hundreds of times. Frank, Chris and Fleetwin would not steer you wrong. When a motor is worn out… well… It’s worn out.

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    stephenspann27

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    #50931

    Thanks wannabe, keep in mind the pics I posted are of my old powerhead. It does sound like my current powerhead could be bad as well, knowing the totally toasted one made 90 PSI, my "good" powerhead that made 100 PSI might be in bad shape as well.

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    stephenspann27

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    #50932

    I found the ebay ad for the powerhead I have, the seller said it had 125psi top and bottom.

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    jerry-ahrens
    US Member - 1 Year
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    #50937

    You really have to watch the compression gauge closely, to see how fast they pump up while cranking. I had an 18 a little older than yours that had near 95 psi, but the pistons were scored from overheating. Its a good idea to pull the intake port covers and have a look before purchasing. These old engines would run so good for so long, that folks wouldn’t bother with impeller maintenance! Then one good over heat would spell the end for an otherwise good engine.

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    stephenspann27

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    #50938
    quote Jerry Ahrens:

    You really have to watch the compression gauge closely, to see how fast they pump up while cranking. I had an 18 a little older than yours that had near 95 psi, but the pistons were scored from overheating. Its a good idea to pull the intake port covers and have a look before purchasing. These old engines would run so good for so long, that folks wouldn’t bother with impeller maintenance! Then one good over heat would spell the end for an otherwise good engine.

    When pulling the rope, if the rings/bore are good, should it only take about one pull to build max PSI?

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    stephenspann27

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    #50940

    I found this on iboats, plan to try it:
    "wot drop to idle and it wants to die points towards a loss in crankcase pressure…try this sequence, wot, quick drop to idle, quick snap to 1/2 throttle….if the engine won’t recover and dies this points towards leaking or loss of crankcase pressure in 2 strokes < this assumes the ignition and fuel delivery are ruled out >…causes?…crank seals, crankcase halves seam leaking, worn piston to cylinder tolerances, loss somewhere else."

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    wannabe-outboard-guy

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    #50954

    One other thing to think about Stephen. Just because it makes compression when doing the compression test, whats not being measured is "blow by". As was stated earlier in this thread, a leak down test will most likely reveal that it is not holding that cylinder pressure for the complete combustion stroke. That is where the significant power loss comes from. The pressure is leaking past the rings.

    Also, be very careful when buying powerheads from Ebay. They show you a compression gauge pegged at say 120lbs. and state the power head "has great compression". Last winter I had a 66 FD 20 with 120 on top cylinder, 60 on the bottom. If i put about a teaspoon of 2 stroke oil in that bottom cylinder I could get it to read 95psi. on the gauge. You see where I’m going with this? Buyer beware.

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    stephenspann27

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    #50955
    quote wannabe outboard guy:

    One other thing to think about Stephen. Just because it makes compression when doing the compression test, whats not being measured is “blow by”. As was stated earlier in this thread, a leak down test will most likely reveal that it is not holding that cylinder pressure for the complete combustion stroke. That is where the significant power loss comes from. The pressure is leaking past the rings.

    Point taken, I think I’ll buy a leakdown guage and do the test.

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    wannabe-outboard-guy

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    #50956

    re read my last post, as I have edited it.

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    outbdnut2
    US Member - 2 Years
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    #50979

    I had a cheapie compression gauge a few years back that had the check valve at the far end of the rubber hose (the cylinder end), so unless you were measuring a big cylinder, like in a big car engine, the volume of space in the hose between the checkvalve and the gauge offset the readings down significantly. Be sure you don’t have that problem. I tossed that one out.

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    immulmen

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    #50988
    quote outbdnut2:

    I had a cheapie compression gauge a few years back that had the check valve at the far end of the rubber hose (the cylinder end), so unless you were measuring a big cylinder, like in a big car engine, the volume of space in the hose between the checkvalve and the gauge offset the readings down significantly. Be sure you don’t have that problem. I tossed that one out.

    My "Snap-on" gauge is like that,,,,I don’t think I am going to toss it!

    fisherman6
    fisherman6
    US Member - 2 Years
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    #50993

    My compression gauge has a hose about 12" long. I don’t find it errors to the low side if you continue to crank until the needle stops. For a rope start outboard I find it usually takes about 4 brisk pulls of the rope. I usually give 5 just for good measure.
    -Ben

    OldJohnnyRude on YouTube

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