Topic: My oil light came on today....

[Scott S]

 My '71 CB500 has about 18K miles on it. The P.O. had the transmission rebuilt and rings/valve job done....about 28 years ago. He put a little over 1,000 miles on the bike and parked it because of a cracked triple tree.

 I resurrected the bike last year and have a little under 2K miles on it since then, so let's call it 3K miles since the top end and trans has been done. Other than a few oil leaks (minor and some misting from around the head gasket), the bike runs like a top. It doesn't smoke, doesn't knock and uses less than half a quart of oil between changes (most of which I attribute to the leaks).

 I use Castrol 20W50 motorcycle oil. I've driven it in heavy traffic in South Carolina in the Summer. I've done the ton on the highway with it.

 The only time I've ever seen the oil light come on is when I first turn on the key. Usually, 2-3 kicks and it goes out.

 
 About 60 miles into our trip today, we pulled into a gas station and, after the RPM's dropped to down around idle, the oil light came on. I put the bike on the centerstand and waited a couple of minutes, then checked the oil. It was a little low, so I bought some cheap, gas station oil and topped it off.
 Fired up the bike and within a second, the light went out. :Cool, that musta been it!", I thought.

 Drove about 20 miles down the road and stopped for a photo opportunity. As I pulled to the shoulder, the light came on again. If I revved the engine past 2200-2500 RPM's, it would go out.

 Finished our trip and pulled into the gas station to top off the fuel tank. The oil light once again came on after the RPM's dropped. Left the station and the light stayed on for the last 4.5 miles to my house. Checked the oil at home and it hadn't used a drop since I topped it off.

 My thoughts:

 A) Sending unit. This would be the simplest and cheapest fix. Especially since there's never been ANY indications of an oil pressure problem in the past.

 B) Oil pump. The bike does have ~18K miles on it and, as far as I know, the pump's never been touched. This would be the 2nd easiest fix.

 C) Bottom end issue. Since the bike does NOT smoke, even under hard acceleration, I assume the top end is OK. However, if there was something out of whack on the bottom end, I would expect a knock or poor running or something. The bike is smooth as silk and runs just fine. It's a pleasure to ride. No unusual noises, grinding, nothing in the oil or filter on oil changes, etc. (So far, anyway)

 I'm thinking about trying to pick up a sending unit this week and see if that's it. If not, what next?

 

[shizzomynizzo]

My 550 had the same issue. I just replaced the sensor and it went away.

I first installed a oil pressure gauge (bought a fuel pressure gauge from summit and used it as a oil presure) and tapped the oil galley plug on the motor.

It had plenty of pressure. If you do a search, you will see it is very common. They get gunk on them and give bad data.

[Scott S]

 I was hoping that's all it was. I've seen various threads about them going bad.

 Where did you get your switch? I have a local Honda dealer that can order it, but is there an alternative to genuine Honda, maybe?

[shizzomynizzo]

I want to say I got one for a honda prelude from autozone or something like that.

Do a search to be sure though...some car units set the light off at the wrong pressure.

[Roach Carver]

I think the MC sender comes on at 3 lbs and the car one comes on at 5?? this is from memory so you should check for yourself......

[Scott S]

 I found one using the Honda part number for the CB500. Autozone can have it from their hub store by 10:00 a.m. tomorrow and it was only $16, tax included. I'll give that a shot.

 Here's the thread that helped me, so no one else has to search for it: http://forums.sohc4.net/index.php?topic=75212.0

[Scott S]

 Oh, and a note on my "oil usage".....

 I've had a few hot-rodded VW's over the years (still have a 190HP '63 Beetle). When running a sump, full-flow, etc., it was common to run the oil level between the two marks on the dipstick; what would appear to be 1/2 a qt. low.
 Last oil change on the CB500, I left the oil level 1/2 way up the dipstick, as is/was habit for me. I also screwed the dipstick all the way in to check the oil level.

 Today, when topping it off at the gas station, I checked it both ways; screwed all in and just dipping it in. I must admit, I've probably been riding around with it ~1/2 a qt. low. In reality, it's only leaked  or used a teaspoon or two since the last oil change. It is now topped off to the top of the line and didn't use any oil on the last half of our trip.
 I had checked  the oil level two days ago and, had I done it correctly, it hadn't REALLY used any oil today when we first stopped.

 All of this leads me to believe that it's the switch (wishful thinking, anyway).

[Scott S]

 Yep...the pressure switch cured it. And even though they could get the genuine part # for only $16, the kind gentleman at Autozone cross referenced it and found the same item for only $6.99!

 Duralast PS123 cross references for the Honda part #, FYI.

[donpark1086]

Use a very slender eyedropper to swish solvent into the switch to clear debris, and she'll probably come back to life.  Done this many times.  The switch is a dead flow zone for debris to collect.

[TIM TINGEY, age 55]

I'd recommend you get rid of the oil pressure switch. They have always had a tendency to leak. Either plug the outlet with a pipe thread cap or run an oil pressure switch from there to where youi can see it. Most importantly check your pressure at the pump first thing. Around 20-30 cold at idle and upwards to 60-80lbs at speed with healthy rods and main bearings. If you don't already Know it, oil pressure is developed in the rod and main bearings. Pressure can drop to 30 to 60 in high mileage motors.. Typically 500-550's won't ever lght the oil pressure beyond start up unless oil level is extremely low(1 1/2 qts. to 2.0 qts) and during rapid decells and the oil gets flung to front of the motor or during a wheely with the mentioned  level.  The oil pick up is centralized so the level has to be LOW!.