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

seinwave

Forum Apprentice
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.
 
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.
 
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.
 
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.
 
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
 
First 2 quick things, check oil level on center stand and level place.

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?

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.

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.
 
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For my legions of fans who are no doubt waiting with bated breath for an update: 1100 miles later and this never happened again. The oil light turns off with the starter now. No sign of any damage whatsoever and I've been through a filter and oil change since.
 
Finally, I can stop worrying! Best to avoid oil regulator testing unless you’re overly ambitious.
 
For my legions of fans who are no doubt waiting with bated breath for an update: 1100 miles later and this never happened again. The oil light turns off with the starter now. No sign of any damage whatsoever and I've been through a filter and oil change since.

Interesting. When I put my 650e back together, my oil pressure light would not go out.
I figured since it is a single wire switch, the metal portion needed to make contact with the engine block for the lamp to go out. Sitting without use for 30 years could have deposited a thin layer of dried up oil, or out in the open for a year could have possibly oxidized the metal and not allowed it to make solid contact.
I pulled it back out and cleaned it along with a light scrub with scotchbright and verified continuity. Reinstalled and no more problems. Sounds like you may have had a similar problem.
 
As i remeber the manual states start and let run a minute then shut off and wait 2 minutes. At the 2 minute mark is when you "top off" the oil. Regrdless of how much has trickled back after shut down you check level at the 2 minute mark. As long as its not over the F line it good.
 
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