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Psyching myself up for the top end - any veteran eyes up to read borescope pictures?

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    Psyching myself up for the top end - any veteran eyes up to read borescope pictures?

    1981 Suzuki GS 650 G, just under 30,000 miles (see signature).

    Long story short, I'm pretty sure I'm leaking quite a bit of oil out of the base and head gasket after my last valve adjustment. Note that I'm pretty sure - I've been fooled by sneaky cover leaks before, so I've tried to make very sure - I was like 95% sure this morning, but now after some more poking around, I think the PO's subpar gasket job on the clutch side could possible be to blame?

    Let's assume it is actually coming out of the base (and maybe the head). I'm not sure if I previously misidentified oil burning on start-up as caused by valve stems and this is the real cause, or if both were an issue. In any case, if I am leaking oil from the head gasket, it probably indicates the ring situation isn't so good, and I should fix that when I'm in there.

    I got my hands on a borescope camera and took some pictures inside the cylinders. As expected, I saw evidence of burning oil in cylinder 1 (where the majority of the leak seems to be coming from). Unexpectedly, I also saw it in cylinder 4; in both cylinders, it almost looks like it's coming from the intake valves rather than around the rings?

    I have an idea of what I'm looking for, but I am not experienced in this at all, so in the next few posts, I'm going to put the pictures I took with commentary as to what I think I see. I hope you can tell me if I'm right or point out anything I'm missing.

    The plan
    Here's what I know I have to do inside the top end:
    - Replace the base gasket
    - Replace the o-rings on the engine studs (and something else that's slipping my mind)
    - Replace the head gasket.
    - New hardware and a lot of antiseize wherever possible

    Here's what I think I also need to do:
    - Drill-hone all four cylinders (or are 2 and 3 good?)
    - Clean all four piston heads and grooves (or are cylinders 2 and 3 good?)
    - New rings on all four cylinders (or are cylinders 2 and 3 good?)
    - Probably put new (viton?) valve stem seals in all eight valves.

    Here's some things I'm not sure if I should do:
    - Relap the valves?
    - New pistons? I've got a set of the cruznimage repops on the way (if the de minimis changes don't screw me out of them).
    - New piston pins? See above?

    Anything I'm missing? Anything I need
    Last edited by seinwave; 08-26-2025, 10:45 PM.
    1980 GS450S - The Dearly Departed
    1981 GS650G - 4,338 miles since June 2024 - 28,282 total

    #2
    Cylinder 1 - the major suspect.
    I see a lot of burnt oil (the shiny stuff on the bottom lip and piston head, right?)


    a LOT of burnt oil - but it seems there's a little bit on the piston head (from the rings) and a lot under the intake valve (bottom of these sets of image) - or is it the other way around, and the valve leaks on the head while the rings lean around the edge?


    ​I also think I see some ridging (damage around the radial direction) and possibly scoring (damage up and down the cylinder) in this image (right hand side). It's hard to tell because the crosshatch lines catch the light differently at slightly different angles - but there seem to be a lot more lines going straight around the cylinder here than on other cylinders.


    Cylinder 2 - looking good enough, I think
    Cylinders 2 and 3 have cylinder walls that look a lot like this. This seems to be pretty clear cross-hatching to me, which is a good sign.​ EDIT: now I'm seeing a horizontal line in this image...



    However, you can still see there's some burnt oil. Old rings, or about what you'd expect from a 44 year old engine?


    Cylinder 3 - even cleaner
    Cylinder 3 has the same pattern as in 2 on the walls. It also has a significantly cleaner piston head - don't believe I saw any evidence of burning oil in there.


    Cylinder 4 - kinda nasty
    Cylinder 4 also has some burnt oil - not as much as 1, but a little more than 2. This picture also appears to show a vertical score to me.


    The cylinder walls are suspect in places. Here's one place I think I see a vertical line and maybe some ridging.​


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    Last edited by seinwave; 08-26-2025, 10:39 PM.
    1980 GS450S - The Dearly Departed
    1981 GS650G - 4,338 miles since June 2024 - 28,282 total

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