CB400f -does anyone have an oil pressure gauge fitted, what readings do you get?

[400 Cafe Racer]

Hi Guys,

The idiot oil pressure light tells you very little. I wondered if anyone actually has an oil pressure gauge permanently fitted and what sort of readings are typical at different temperatures.

Thanks

Dennis

 

[McCabe-Thiele (Ted)]

Back in the day you could buy high pressure oil switches for a BMC Mini that went out when the engine was idling. Sometimes like a cylinder pressure gauge it's often best not to know. The factory dash oil pressure gauge on my W124 Merc had a maximum reading of 45 psi so anything higher was superfluous.

[400 Cafe Racer]

Back in the day you could buy high pressure oil switches for a BMC Mini that went out when the engine was idling. Sometimes like a cylinder pressure gauge it's often best not to know. The factory dash oil pressure gauge on my W124 Merc had a maximum reading of 45 psi so anything higher was superfluece.

Hi Ted,
Thanks.
Reliable information is always good, so you always knew if anything changed on your Merc.
According to Haynes manual it does not come on until until 4.3psi - in the danger zone, which leaves a lot to be desired in the way of information while riding, so it would be interesting to see users readings if possible.

[Nurse Julie]

Interesting. The oil pressure switch, being situated on the top crankcase only tells you that the oil pressure is high enough to protect the crank etc. All our bikes have oil jets fitted, which are oil restrictors, they restrict the oil going to the top end of the bike, camshaft etc in favour of keeping the components in the bottom end well oiled. Top end oil starvation can be as dangerous and expensive as bottom end oil starvation, I wonder why Honda, in this instance, chose not to have the oil pressure switch situated at the top end 🤔🤔🤔🤔

[McCabe-Thiele (Ted)]

I did fit a pressure gauge back in the late 70s, Smiths iirc, I seem to recall it used to run at 80psi, came in useful one day as whilst on a run down the motorway it suddenly dropped pressure like a stone, turned out the oil filter, which was a pattern filter, had collapsed and went into a spiral shape as it did so. Never fitted anything but genuine Honda since on a SOHC.

You did well to notice the drop in pressure on a gauge - they do not shout at you like a warning lamp!

[K2-K6]

" I wonder why Honda, in this instance, chose not to have the oil pressure switch situated at the top end"

The cylinder head is effectively "open bath" lubrication with the pressure just delivering the oil rather than being a constant pressurized film as the crankshaft bearings are. After the restriction going from gallery to the head there's not that much pressure to monitor,  if failure occured (blocked preventing oil getting out) the pressure would rise not fall,  but then if too high pressure was present the relief valve would open on the pump.  So you'd not see the error from monitoring system easily.

It does look odd though as essentially there are two different delivery systems combined and split as noted, base mains etc and head system all occupying the same engine 

[TrickyMicky]

" I wonder why Honda, in this instance, chose not to have the oil pressure switch situated at the top end"

The cylinder head is effectively "open bath" lubrication with the pressure just delivering the oil rather than being a constant pressurized film as the crankshaft bearings are. After the restriction going from gallery to the head there's not that much pressure to monitor,  if failure occured (blocked preventing oil getting out) the pressure would rise not fall,  but then if too high pressure was present the relief valve would open on the pump.  So you'd not see the error from monitoring system easily.

It does look odd though as essentially there are two different delivery systems combined and split as noted, base mains etc and head system all occupying the same engine 

  A few million years ago I worked for a motor parts wholesaler, and we did a steady trade in selling camshaft kits for the Ford OHC Pinto engine. I think I'm right in saying that they also used the "spray bar" system to lubricate the top end, but, I never did find out if the problem was down to poor lubrication or other factors.  I seem to have a vague memory that the cam lobes wore prematurely.

[Nurse Julie]

" I wonder why Honda, in this instance, chose not to have the oil pressure switch situated at the top end"

The cylinder head is effectively "open bath" lubrication with the pressure just delivering the oil rather than being a constant pressurized film as the crankshaft bearings are. After the restriction going from gallery to the head there's not that much pressure to monitor,  if failure occured (blocked preventing oil getting out) the pressure would rise not fall,  but then if too high pressure was present the relief valve would open on the pump.  So you'd not see the error from monitoring system easily.

It does look odd though as essentially there are two different delivery systems combined and split as noted, base mains etc and head system all occupying the same engine 

  A few million years ago I worked for a motor parts wholesaler, and we did a steady trade in selling camshaft kits for the Ford OHC Pinto engine. I think I'm right in saying that they also used the "spray bar" system to lubricate the top end, but, I never did find out if the problem was down to poor lubrication or other factors.  I seem to have a vague memory that the cam lobes wore prematurely.

On our SOHC/4 models, 99.9% of cam damage will be through oil starvation caused by a minute piece of debris in the restrictor jets in the oil passages which supply the top end.

[allankelly1]

" I wonder why Honda, in this instance, chose not to have the oil pressure switch situated at the top end"

The cylinder head is effectively "open bath" lubrication with the pressure just delivering the oil rather than being a constant pressurized film as the crankshaft bearings are. After the restriction going from gallery to the head there's not that much pressure to monitor,  if failure occured (blocked preventing oil getting out) the pressure would rise not fall,  but then if too high pressure was present the relief valve would open on the pump.  So you'd not see the error from monitoring system easily.

It does look odd though as essentially there are two different delivery systems combined and split as noted, base mains etc and head system all occupying the same engine 

  A few million years ago I worked for a motor parts wholesaler, and we did a steady trade in selling camshaft kits for the Ford OHC Pinto engine. I think I'm right in saying that they also used the "spray bar" system to lubricate the top end, but, I never did find out if the problem was down to poor lubrication or other factors.  I seem to have a vague memory that the cam lobes wore prematurely.

I remember this system well

Normal ford carp  design

I think the cause was infrequent oil changes that then caused the spray bar to get partially blocked combined with an cylinder head /OHC design that had the cam shaft spinning in “fresh air” rather than the cam lobes constantly dipping into some form of trough that held a quantity of oil so that the cam was well lubricated even without a spray bar system

Any lack of oil feed to the spray bar cam on a pinto, and the cam was then toast

If you look at the 400f engine as well as a spray bar there is a trough system too to keep the cams well lubed during any temporary oil starvation


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[400 Cafe Racer]

I had an amp meter and a oil pressure gauge mounted in a pod above the speedo/tacho so they were easy to see. The oil pressure take off was mounted where the current pressure switch was on a T piece so they both worked, it meant cutting out part of the chaincase guard but it did work.

Hi Oddjob,

Can you remember what variations there were on your readings with a hot engine, or when idling etc. Interested to  find our more.

Thanks

Dennis

[400 Cafe Racer]

It was a long time ago, late 70s or early 80s IIRC. The actual readings I don't accurately recall, more the position of the needle, IIRC the gauge went from 0-100 ( i just looked up a picture of one, I thought it went higher so that's why I said 80psi) and the needle used to sit almost vertical when running but a little past, which made me think 80psi sounded about right, but based on the pic 55-60psi is more accurate, it used to go down on tickover to approx 20psi and around 40psi when very hot but TBH it didn't sink that much as back then we all used 20/50 oil so it was thicker to start with.

Thanks Oddjob,

Good info, useful to know your experience. The gauge was a regular and important feature of most sports and race engined vehicles and I felt sure that several out of all the 400 users would have fitted one at some point.

I'm hoping there may be others to reply.

Cheers