Oil pressure relief

[MrDavo]

That's not the oil pressure relief valve, but relief at having some oil pressure!

Last Friday I had my first ride on the K1, to get an MOT on the frame number (she passed, advisory was one loose spoke at the back, which shows they were thorough). About 5 miles, she ran as sweet as a nut, but on the way back the oil light started to come on  idling at traffic lights, then took more and more revs to go out. The nearer home I got the more the light came on, I limped back onto the drive seriously worried, and already trying to work out how and when the motor was coming out.

After some internet research (not a euphemism, for a change), I decided to check the oil pump O-rings, I think the bike was restored years ago, but barely used since (and I started to wonder if low oil pressure was why) and everything rubber on the bike is hard or perished - for safety's sake I changed the inner tubes as well as the tyres, and the cracked fuel lines - I'm waiting for the fuel cap gasket as that leaks now I have a fullish tank. The pump O-rings were Ok, but hard and flat, so I ordered a new set from David Silver at Stafford Show, they came yesterday, and I fitted them last night.

The wife came home late yesterday to find me despondent - O-rings fitted and oil replaced, I fired her up, the oil light went out, then came back on at idle, the warmer she got the higher the revs needed to make it go out. I checked for oil at the number 4 tappet cover, fine, but by I switched off she needed 2,000 rpm plus to extinguish the light. By now I'm thinking mains - the motor all seems freshly rebuilt, but mistakes can be made.

The last throw of the dice today was to try a second hand oil light switch I bought for £4 at Stafford show, mainly because I wanted the rubber boot, which is missing on my bike.

I am here to tell you how releived I am - the light goes out as soon as I fire her up, and stays out until I switch off. Ladies and gentlemen, we have oil pressure!

As I'm waiting for the DVLA to process my registration application (why do I expect that they are going to send the forms back with some new problem?) I can't legally go for a test ride unless I book another MOT, but I may be sneaking out later for a quick test after accidentally fitting the plate off another bike. Don't try his at home.

[AshimotoK0]

Nice one .. I remember I had Citroen car once and took it to the scrapyard to scrap  'cos the oil light was on and I suspected the worse. The guy at the yard was a really nice bloke and bunged an oil pressure switch in my hand to try out. Same as yours, oil light went out and so I drove it away. You see a lot of USA 750's with an oil pressure gauge fitted to the oil gallery blank off.
Your right about that cover boot, they always go brittle and crack near the large diameter end that fits over the switch.

Ash

[steff750]

  i bet you fitted a red plastic oil switch
you will find that the oil switch (black plastic) the oil light comes on sooner  than the red plastic switch,i had the same problem but i also checked it with a oil pressure gauge to be sure,and it runs at 40 psi so no worries here atleast

[MrDavo]

Correct on both counts, what confuses me is that switches on Fleabay advertised as genuine are black too. The red one I have just fitted came off a K2 engine, the wire boot and screw all look original so I am assuming that the switch is too. The old switch will be going on a shelf in my living room, to join a collection of small broken parts from blown up race bikes, crashes etc.

In the spring I had a similar drama with my 30 year old 911 - out on a drive in Buxton I stopped at a set of lights and was overtaken by a cloud of blue smoke, which I realized to my horror was mine! Looking underneath there was oil everywhere, and the red 'idiot' light had come on on the dash. I'm thinking mega pound signs and engine out just for starters. Any other car I would have switched off and called out the AA, but an aircooled Porsche has 3 oil gauges, for level, temperature and pressure, and they were all normal. It turned out the fault was with the idiot light switch, which when they fail leak oil which is under pressure. Yet again someone on an internet forum helped me out, and I fixed it myself for £17.

I shudder to think how much a garage might have charged me to sort that one out. 

The test ride went fine, I love the noise the HM300s make on the over-run!

[Bryanj]

Oil pressure switches have always been a common fault and you will find car ones fit BUT car ones tend to go out at a lower oil pressure than bike ones, i think it's something like 3psi and 6psi

[steff750]

  ive always thought that the black plastic switches are honda original hence they come on at higher psi than the red ones, even the handbook states ignore the oil light at engine idle but should go out as revs progress