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81 Suzuki GS650G - oil pressure light flickering on hard stop - marginal pressure?

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    81 Suzuki GS650G - oil pressure light flickering on hard stop - marginal pressure?

    Hi all. Took my newly resurrected bike out for the first long-ish (~100 mi round trip) since I dealt with the ignition issues.

    On two occasions I saw, as I braked semi-hard to a stop, the oil pressure light flicker on, off, on again, and then off again inside the blink of an eye. I say "semi-hard" because this wasn't an emergency stop or anything. Both times were when coming to a stop - I braked hard into a couple corners but didn't see the light come on in those cases, though I was mostly watching the road.

    The oil light turns off as soon as the engine starts coughing to life - though not the moment I hit the starter, which may have been when it usually turned off in the past? I can't quite remember. It switches back on again not instantly but certainly quickly after I turn the engine off.

    Does this indicate a serious issue with oil flow inside the engine? It makes sense the oil should slosh from back to front under hard starting, but the oil pressure switch is relatively low and pretty far forward on the engine and I feel like it should remain pressurized in that case.

    I have a couple very slow oil leaks (secondary drain and the filter plate) but the oil level is just barely below the F mark on the sightglass when the engine is cold. The sightglass refills within a minute or two after I turn the engine off.

    As part of the ignition replacement I also replaced and remounted the green wire leading from the pressure switch behind the timing cover to the green wire in the harness that handles the switch. I tightened down both the switch mount and the new switch wire->harness wire connection and tested both, so I doubt that's the issue. I also don't think an intermittent or weak connection there would cause this issue only on braking - I'd expect it under heavy revs or acceleration too.
    1980 GS450S - The Dearly Departed
    1981 GS650G

    #2
    First 2 quick things, check oil level on center stand and level place. Then check oil pressure wire connection on top center of eng under carbs. Wire connector slides onto sending unit brass pin.
    1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

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      #3
      rphillips, as he stated, the oil pressure sensor on the 650 is behind the timing cover. On my 750, it's at the bottom of the oil filter cover. On some other models, like you say, it's on top of the engine case, below the carbs.
      Rich
      1982 GS 750TZ
      2015 Triumph Tiger 1200

      BikeCliff's / Charging System Sorted / Posting Pics
      Destroy-Rebuild 750T/ Destroy-Rebuild part deux

      Comment


        #4
        Aw shoot, I thought I read GS850... Sorry
        1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

        Comment


          #5
          I had an oil light issue with my 850 when I got it.
          Under engine braking or at idle if I leaned the bike over to the right, the light would come on.
          Never under acceleration or leaning left at idle.
          Turned out the clutch basket was loose and with the helical drive gears the clutch basket was being pushed out of engagement with the oil pump drive when engine braking and gravity was doing it at idle.
          97 R1100R
          Previous
          80 GS850G, 79 Z400B, 85 R100RT, 80 Z650D, 76 CB200

          Comment


            #6
            I hope this is just a loose wire…..grounding out at times
            my oil light goes out during cranking normally. No issues during turning ,braking, etc
            after a run, with bike on center stand, it takes a about ten minutes for 15-40 oil to reappear in sight glass …I keep it to full mark.
            there is an oil “regulator” mounted in pan just after the pump…hopefully this ain’t your problem
            1981 gs650L

            "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

            Comment


              #7
              Originally posted by seinwave View Post
              ...I also replaced and remounted the green wire leading from the pressure switch behind the timing cover to the green wire in the harness that handles the switch.
              Is that when the problem started?
              1982 GS1100E V&H "SS" exhaust, APE pods, 1150 oil cooler, 140 speedo, 99.3 rear wheel HP, black engine, '83 red

              2016 XL883L sigpic Two-tone blue and white. Almost 42 hp! Status: destroyed, now owned by the insurance company. The hole in my memory starts an hour before the accident and ends 24 hours after.

              Comment


                #8
                Originally posted by rphillips View Post
                First 2 quick things, check oil level on center stand and level place.
                Originally posted by tom203 View Post
                I hope this is just a loose wire…..grounding out at times
                my oil light goes out during cranking normally. No issues during turning ,braking, etc
                after a run, with bike on center stand, it takes a about ten minutes for 15-40 oil to reappear in sight glass …I keep it to full mark.
                there is an oil “regulator” mounted in pan just after the pump…hopefully this ain’t your problem
                I park the bike on the center stand when I check the oil. I might be wrong about how long it takes to refill; there's definitely *some* oil visible about a minute after stopping, but it takes longer to refill. I'll time it just to get some baseline measurements.

                If I have to crank the starter for longer than a single stab, the light *does* go out. I just seem to remember it going out immediately, rather than after a tiny period of time.

                The oil regulator doesn't seem too hard to access - any tests to eliminate it?

                Originally posted by Brendan W View Post
                I had an oil light issue with my 850 when I got it.
                Under engine braking or at idle if I leaned the bike over to the right, the light would come on.
                Never under acceleration or leaning left at idle.
                Turned out the clutch basket was loose and with the helical drive gears the clutch basket was being pushed out of engagement with the oil pump drive when engine braking and gravity was doing it at idle.
                Hmmm, I've been meaning to check on the clutch but that sounds a little different than my issues. Haven't seen it at idle at all, nor tilted or leaned.

                Originally posted by Rob S. View Post

                Is that when the problem started?
                Not exactly? It didn't happen *before* that, but it's not happening consistently afterwards either. I did a ton of braking on the trip, some of it pretty hard, and only those two times (which weren't the absolute hardest) did I notice the oil light flicker. I've taken it on a couple shorter trips where I had occasion to brake and I didn't notice it then either.

                I'm going to see if I can't find out any consistent causes with some more riding in the next few days.
                Last edited by seinwave; 09-25-2024, 11:35 PM.
                1980 GS450S - The Dearly Departed
                1981 GS650G

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