another oil light thread !

[hhshort]

My son has a 197?4 R75 frranken beemer that he rescued from the ARMA circuit and returned to street legal. it has been ridden off and on for the last 20 years with no problem. The amber oil light came on while cruising on the interstate. He shut it down immediately and we hauled it home. WE put a test oil gauge on it and it had oil pressure. We reinstalled the sender and the light comes back on. Some where he read that the light will come on if it over pressures. We now installed the oil gauge permanently. Cold pressure at rpm is 85 psi and higher. hot pressure at rpm is about 65-70. Idle pressure hot is 40 psi.

All the numbers seem a little high compared the the numbers in the specs. . It has 20-50 oil in it. The questions are: is there problem with over pressure? ( It is being ridden) Is there a reason for over pressure? Could there have been a modification to increase the oil pressure when it became a race bike?

PS the oil pressure sender is probably a VW sender bought at Auto zone years ago.

 

[jhall]

Interested

I am interested in our Airhead guru's input on this. Looking online at specs (60-74 PSI @4000 RPM), if your initial 85 is when the oil is still cool, that seems OK, since it drops to within spec after warm up. Most oil systems I am familiar with include a pressure relief valve but, when oil is cold, volume often over runs the PR valve, so pressure is a bit high. The 40 PSI at idle exceeds the spec I found (14.5-29 PSI @800-1000RPM). But again 'the devil is in the details' so, again, I am looking forward to what our gurus have to say on this.
As for the light coming on when at overpressure, in addition to low pressure, I have never heard of that on any system, but it seems a good idea. Hard to believe Airheads were that far advanced though. Looking forward to learning new things here.

 

[20774]

I would be inclined to go back to an OEM sender unit. As for over pressure, there is a pressure relief valve in the filter cavity...it should be opening around the 75psi level. If it's not opening, that could be a problem, but you won't get a light for that. Snowbum talks about the oiling system here:

https://bmwmotorcycletech.info/oilingsystem.htm

You should confirm that the ball/spring valve at the base of the filter cavity is working correctly.

I don't consider that the pressures mentioned are out of spec, except for being over 75 especially when hot...cold, that is to be expected. The light coming on at cruising speeds is distrubing.

 

[jhall]

Electric Gauge Accuracy

I would be inclined to go back to an OEM sender unit. As for over pressure, there is a pressure relief valve in the filter cavity...it should be opening around the 75psi level. If it's not opening, that could be a problem, but you won't get a light for that. Snowbum talks about the oiling system here:

https://bmwmotorcycletech.info/oilingsystem.htm

You should confirm that the ball/spring valve at the base of the filter cavity is working correctly.

I don't consider that the pressures mentioned are out of spec, except for being over 75 especially when hot...cold, that is to be expected. The light coming on at cruising speeds is distrubing.

Given the manual gauge readings, the OEM electric gauge seems suspect. One way to confirm or dispel, is to do as the OP did, and try a manual pressure gauge. Agree, the light coming on while running down the road is disturbing. Kinda like the dimly lit charging light, while underway, which is said to be 'fairly common on Airheads', wonder if same is true for the oil light?

 

[20774]

The OEM gage is mechanic as far as I know. Seeing the oil light AT ALL while at speed is not good...unlikely the alternator light. At least with the alternator light, if the battery is good, you can still ride somewhere for support...or a new battery. If the oil pressure is indeed falling below threshold at speed, you're not going to get too many chances at that.

 

[jhall]

OEM Mechanical Gauge?

The OEM gage is mechanic as far as I know. Seeing the oil light AT ALL while at speed is not good...unlikely the alternator light. At least with the alternator light, if the battery is good, you can still ride somewhere for support...or a new battery. If the oil pressure is indeed falling below threshold at speed, you're not going to get too many chances at that.

An OEM mechanical gauge (or any mechanical pressure gauge) would be plumbed into a pressure passage somewhere. I do not recall ever seeing one, but there's much I haven't seen. Where do they plumb in?
Thanks

 

[20774]

jhall -

I think we may be talking past each other. The OEM sender unit is a mechanical device...has an internal diaphragm...which opens closes contacts. There is power coming into it so when the contacts close, the dash light illuminates. So, it's mechanical-electrical?? I guess I consider it a mechanical device which has a passive electrical function.

#16 is the oil pressure switch...or sender.

https://www.realoem.com/bmw/enUS/showparts?id=0333-USA-09-1977-2474-BMW-R_100_7T&diagId=11_1726

 

[jagarra]

My pressure light comes on at the end of a ride when I pull up to garage and idle. Figured that is normal considering oil and bike would be hot. I ordered a new sending unit just to see if that made a difference.

 

[jhall]

Electrical Gauge

jhall -

I think we may be talking past each other. The OEM sender unit is a mechanical device...has an internal diaphragm...which opens closes contacts. There is power coming into it so when the contacts close, the dash light illuminates. So, it's mechanical-electrical?? I guess I consider it a mechanical device which has a passive electrical function.

#16 is the oil pressure switch...or sender.

https://www.realoem.com/bmw/enUS/showparts?id=0333-USA-09-1977-2474-BMW-R_100_7T&diagId=11_1726

I'd consider that an electrical gauge, since the gauge operates off electrical signal. In that case, again, my first course would be to validate with an actual mechanical gauge. Sounds like that is what the OP did, which is understandable.

 

[hhshort]

another oil light thread.

Thanks for the come back. I have read Snowbum's article on the oil system. The bike is up for an oil and filter change and that will give us a chance to check the bypass valve. That seems to be the only thing that could cause an increase in pressure. In any case the gauge will stay on the bike for a while. Will report is we see a change after the oil filter change

 

[grahamm]

if I was doubting the oil circuit I would check the oil flow to the rockers.... this at least is a indication that there is flow.

spark plug removed and grounded, valve covers removed... turn over with the starter to see if ample oil flow is getting to rockers.

 

[pglaves]

Try this:

https://www.toolots.com/wd-1003.htm..._PJGMNz8MH43xSw6bWMo2y_F4tdEdBjUaAjS5EALw_wcB