low oil pressure?

Hey guys, I just got my bike back up and running after last years spun rod bearing. I'm using my motor from 2 years ago that had a holed piston. Just put a good piston on the old connecting rod.

I have it filled to the top line on the oil sight glass but my oil light still comes on around 1300 rpm's and lower. I also hear a ticking on the top left side of the valves, sounds more to the exhaust side. Could this be oil starvation? I also just rebuilt my head last year, so all the valves should be in spec. I just slapped it on the different lower end.

It sounds like one of the oil passages to the head might be blocked.

well that's not what I wanted to hear. I just got it up and running. Where is the oil sensor? and does it sense oil level or pressure?

The oil sensor on your 650 is located directly behind the points cover (ref# 16 in the pic below), and is a pressure sensor.

It's possible that the wire attached to it might be loose or grounding out, and at low RPM's vibrates enough to break contact/ground out and flash the oil light.
It's also easier and less time consuming to check the sensor than pulling the cylinder head to see if an oil passage is blocked.

Post edited by: RetroRiceRocketRider, at: 2006/04/10 17:56

It's ref# 16 in the pic below.

well I messed with it some more and determined it only happens when the motor is at operating temperature. If it's cold and I start it, the light doesn't come on and I don't hear that ticking noise. Maybe as one of those o-rings gets warm it partially blocks off my oil passage? I gotta get this figured out so I dont' blow another motor. :laugh:

Go ahead and blow that motor, I have a 750 here :laugh:

It's possible that the ticking is unrelated to the oil pressure problem, and it's also possible that you have a bad oil pressure sensor. There is probably a spec in the manual for oil pressure sensor resistance, so you can check it with a multimeter, but sticking a mechanical gage on it to measure actual pressure would be the best idea.

As the oil warms up the thickness of the oil decreases, so pressure drops, although if pressure drops far enough to trigger a good sensor, then you do have a problem.

I'm reasonably certain that a restriction on a oil passage feeding the head would increase the pressure at the sensor, not decrease it.

I'm going to take a look at the manual and check out the oil path diagram.

Just checked the manual, and the oil pressure sensor is indeed on the main oil gallery, and the oil feed to the head branchs off the main gallery, so a restriction on oil flow to the head would increase the pressure at the sensor.

Looks like the problem is one of the following:

(1) Bad sensor (hope for this one)
(2) Weak oil pressure relief valve spring (probably not this one)
(3) Improper oil (if you didn't put 10 wt oil in it, then forget this one.)
(4) Clearances exceed service limits (remember that 750 motor I mentioned?)
(5) Clogged oil filter (oil filter bypass valve should mask this one)
(6) Oil pressure relief valve stuck open ( I don't hold out much hope for this one)

How many miles were on that bottom end?

Post edited by: steell, at: 2006/04/10 23:08

hmmm 750? I've got a new project lined up that is gonna need a motor, might be in touch there.

bad sensor? i'll check that with a multimeter pretty soon.

the oil pressure relief vavle was only a few months old last year and only 50 miles on it this year. So it's not that.

I'm running some 10-40 oil in it from walmart, but it is pretty black allready. So i'll change it and through in a new filter as well to rule those out. Maybe buy some better oil too, even though this stuff isnt' energy conserving.

what do you mean by clearances? piston? valves?
rings?

The bottom end only had about 13k on it, so it's not high milage at all.

By clearances I mean any lubricated bearing surface, like the main, rod, and cam bearings.
I fogot to mention that a partially clogged oil pickup screen could cause the problem also.

Here is my attempt to describe where the oil goes

Oil pan, through oil screen, through oil pump, then to the filter, there is a bypass valve located before the filter to bypass the oil if the filter is plugged, then to the main oil passage, relief valve is tied to the main oil passage and bleeds excess pressure back to the sump, one line comes off the main passage and feeds the transmission, the last one comes off the passage and feeds the head (oil pressure sensor is on that one because it's at the end of the main passage) the line that feeds the head also feeds the crank bearings (rod and main) and the primary chain.

At 13k miles you would not expect excessive wear of the crank bearings, but strange things happen.

I was following the diagram in the manual as I typed

I would rather have the 650 myself.

Between R4 and steel I can't think of anything else to check. I'm afraid it's a loose bearing some place. You should always check your clearances with some plastagauge when your putting a motor together. You said you just put a good piston on the old bottom end. Some of the bits from the piston had to go some where. Some of those little piston pieces may have damaged a bearing surface. On the one that spun a bearing I bet it was #2.
Mark

actually it was the #1 piston. I normally dont' over rev my bikes, but I ride them hard. So i'm not sure what happened there. I'll get some pictures up of the holed piston and hopefully I can find the pics of the spun bearing. I just changed my oil, actually went to synthetic since and 10-30 since it's a little lighter I hope it can flow easier through the passage ways. idk, i'm just hoping it's on the top end, and not the bottem end again.

Steell, check your pm's.