?????? Question Johnson QD-16

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  • Buccaneer
    Buccaneer

    US Member - 1 Year
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    Topics: 894
    #176024

    Sounds like it’s time to try a different compression gauge!

    Prepare to be boarded!

    tinkerman
    tinkerman

    US Member - 1 Year
    Replies: 105
    Topics: 18
    #176029

    Ok so I see my mistake on the reed valves, as their behind the carburetor. How would you know that they are sealing correctly? There was a lot of oil or really thick gas back behind the carb. On the compression gauge IDK I checked it on the QD-16 after it had ran a bit and it went from 50 up to 60. I know it’s a cheaper one but the one I saw at nappa wasn’t much different just a shorter hose but they wanted $80 for it. I’m a plumber by trade and we build our own test rigs for different systems we install and hardly ever is the gauge flat out bad. Like I say this engine , you can tell by the pull rope compression is weak. My question I guess is weak compression ALWAYS worn rings-piston or bore? Are there other common worn components to be on the look out for? 2- strokes are new to me. I’ve rebuilt chevy v-8’s and a Kohler k-241 mower engine which purrs like a cat. I just need pointers on where to start with these weak compression engines. Someone on here said the QD-16 at 60 was real low, so I’ve kinda quit on it cuz it’s running like crap and I feel like I’m spinning my wheels trying to get it to propel a boat and run consistent with the compression at 60. On the scot Atwater I’m gonna see if I can get the compression up BEFORE I do anything else.

    Happy is a place we visit from time to time, content is a place where we can spend our life

    bobw
    bobw

    US Member - 1 Year
    Replies: 672
    Topics: 28
    #176030

    A bad head gasket could allow compression to leak between cylinders resulting in low readings. From the picture, it looks like your head gasket is OK but hard to tell from just a picture. Stuck rings will also result in low readings. Take a small screwdriver and push on the rings through the exhaust ports and see if the rings have some “spring” to them. If the rings are not stuck they should push in slightly then spring back when you release pressure on them. Again, hard to tell from just the pictures but your pistons and cylinders all look OK except the one piston ring visible in the picture, that ring looks like it might be partially stuck in its land (in the portion visible through the top exhaust port).

    Edit – yes, in your first pic it is normal for carbon to have built up in the exhaust area especially with the older oils used back in those days. That can easily be cleaned up.

    Bob

    1954 Johnson CD-11
    1956 Johnson RD-18
    1958 Johnson QD-19
    1959 Johnson QD-20

    • This reply was modified 5 months, 4 weeks ago by bobwbobw.
    • This reply was modified 5 months, 4 weeks ago by bobwbobw.
    tinkerman
    tinkerman

    US Member - 1 Year
    Replies: 105
    Topics: 18
    #176049

    Thanks for the info bob. I’ll check the rings. I really enjoy the thought of bringing one of these 70 year old engines back to life but just not having any luck as of yet. Maybe I just need to paint em to look new and be happy with that.

    Happy is a place we visit from time to time, content is a place where we can spend our life

    tinkerman
    tinkerman

    US Member - 1 Year
    Replies: 105
    Topics: 18
    #176052

    Each ring was springy on both sides (intake and exhaust) not a lot of push,but some. Would anybody happen to know the bore size and tolerance for it to be considered within spec? I’m thinking if the cylinder is really close then I can put new rings in and maybe it won’t be like new but have enough compression to run smooth once again for a little occasional use (after carb rebuild, check coils, clean or replace points and condenser and go thru lower unit.

    Happy is a place we visit from time to time, content is a place where we can spend our life

    Tubs
    Tubs

    US Member - 1 Year
    Replies: 2463
    Topics: 148
    #176113

    tinkerman
    tinkerman

    US Member - 1 Year
    Replies: 105
    Topics: 18
    #176115

    I have jumped around on this forum like a squirrel on crack but to clarify, I’ve kind of given up on the Johnson QD-16 at present as it DOES have noticeable scores in the cylinder walls that would seem to make it impossible to obtain good compression. I did manage to get the water pump working and it DID start but wouldn’t idle and smoked to high heaven (bun your eyes and throats smoke) after it ran a bit the compression went from 50 up to 60 but still really low from my understanding. So as I say I set this one to the side for now. The one I’m working on now is a 497 Scott Atwater . Compression felt really weak when I pull the pull rope. Checked compression and it was less than 40. Cylinder walls look great, no scratches. So I was looking for other suggestions for causes of low compression. I noticed the underneath of cowling was oily, sticky, greasy so I got to thinking maybe the crankshaft seal could be causing low compression. Even though underneath cowling is sticky oily, the engine is really clean. You wouldn’t look at it and say wow that’s a worn out piece of junk. As I’ve said I have 8 non running engines and EVERY ONE that I’ve check d compression on shows 50# or lower. (I have a 30 hp mariner on my boat that runs great and it shows 85 psi per cylinder so I’m thinking my gauge is ok. Are there any other “fixable” causes of low compression. I really do appreciate yalls patience and willingness to help

    Happy is a place we visit from time to time, content is a place where we can spend our life

    Mumbles
    Mumbles

    Canada Member - 2 Years
    Replies: 4212
    Topics: 425
    #176121

    I got to thinking maybe the crankshaft seal could be causing low compression.

    The condition of the crankshaft seal will minimally, if at all, affect the cylinder compression in a two stroke motor. It’s there to maintain the pressure/vacuum cycles in the crankcase itself. The sealing capabilities of the rings to cylinder wall and the condition of the head gasket are the major players in determining cylinder compression.

    tinkerman
    tinkerman

    US Member - 1 Year
    Replies: 105
    Topics: 18
    #176126

    Ok that’s the answer I was looking for. Not the one I wanted but it gives me something to go on. I understand what tubs was saying with the re ring theory. Never anywhere in any manual for any motor do they recommend installing new rings without checking the bore to see if it’s in spec or if it’s egged so bad that you need to bore it and install oversize pistons. I KNOW this is the correct procedure …..BUT we are talking about a 70 year old engine and parts are scarce to nonexistent for internals so for the sake of getting an old low compression engine up and running for a while longer, would it be acceptable to hone the cylinder (can this be done without removing the pistons?) install new rings and see what happens? Or do you just say ok compression is too low so I have a 70 year old conversation piece? yall have been doing this a lot longer than me so I’m open to suggestions. I’ve been tinkering with painting and cleaning it while I’m debating what it will take to make it run, so it’s gonna look like it rolled off the showroom floor regardless.

    Happy is a place we visit from time to time, content is a place where we can spend our life

    Tubs
    Tubs

    US Member - 1 Year
    Replies: 2463
    Topics: 148
    #176127

    .

    • This reply was modified 5 months, 3 weeks ago by TubsTubs.
    bobw
    bobw

    US Member - 1 Year
    Replies: 672
    Topics: 28
    #176128

    If you are planning on installing new rings, you’ll have to break the case open and pull the pistons anyway. If it were my motor, I’d pull it apart and check the bores for being round or out-of-round. If bores are within spec, then hone them, install new rings and crankshaft seals, then re-assemble. But even before that, as Tubs suggested, I’d run the motor for awhile and see if it’s just stuck rings causing the low compression. Running for awhile with modern oil and maybe some OMC Engine Tuner might clean up the rings and improve compression.

    Bob

    1954 Johnson CD-11
    1956 Johnson RD-18
    1958 Johnson QD-19
    1959 Johnson QD-20

    • This reply was modified 5 months, 3 weeks ago by bobwbobw.
    tinkerman
    tinkerman

    US Member - 1 Year
    Replies: 105
    Topics: 18
    #176140

    Thanks for the input. On this Scott Atwater, the crank rope jammed up before I began disassembling so I didn’t attempt to start it. Since,it’s,partially torn apart I think I’ll check the bore. hone and re ring if possible. maybe I’ll get one running before too long. If it wasn’t challenging it probably wouldn’t be near as much fun

    Happy is a place we visit from time to time, content is a place where we can spend our life

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    garry-in-tampa

    Lifetime Member
    Replies: 3251
    Topics: 30
    #176160

    I don’t know what that flap of metal is in the second picture, but it is not a reed valve. I don’t have the Johnson book digitized (I’m EVINRUDE special interest group leader) This is for Evinrude’s equivalent . . . Most parts are interchanegable












    tinkerman
    tinkerman

    US Member - 1 Year
    Replies: 105
    Topics: 18
    #176214

    No sir that is the picture of a Scott Atwater model 497 and it is actually a sleeve for the intake port behind the inspection plate. I was gonna see about getting rings and maybe honing the cylinder and putting new rings in and maybe help the compression a little BUT, guess what NLA there are virtually NO parts available for this engine anywhere on line. I did find and order a gasket kit so I can completely reassemble everything but not actually fix anything. No carb kit available heck can’t find a decal set for it. Pistons and rings out of the question. My paint job is pretty much complete and I’m really proud of it. But I guess I’ll put it all back together and decorate my shop with it. Next up I have a early 50’s 5 hp sea bee or a late 40’s evinrude I can tinker with. The next motor I buy I will check compression first and have something to build upon. I’ll post some pics of the Scott Atwater when I get it reassembled. May go ahead and clean the carb and fix the pull rope and see if it’ll start

    Happy is a place we visit from time to time, content is a place where we can spend our life

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    garry-in-tampa

    Lifetime Member
    Replies: 3251
    Topics: 30
    #176218

    Sorry – I thought it was a QD-16 Johnson . . .

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