I would have thought the pressure relief valve simply starts to open above the prescribed pressure for the relevant model, and vents oil back into the sump? The pump is chain driven, so the only way to affect the 'power' of the pump other than by engine revs would be to divert some of the output elsewhere.

The NC35 relief valve is 15220-MR8-900, and is not a supercession for the NC30 part (000), so I guess that means the engine was designed to run at a different pressure range than the 30? If so, do you know what that is, Neo?

edit: found it listed as 71-85 too....

Also, the NC30 non oil cooled model oil pump is a different part number to the NC35 one (15100-ML0-000 vs 15100-MR8-900). Drive chain and sprocket are identical. No supercession here either. Any idea what the difference might be?

I've no immediate plans to stick an oil cooler on my NC35, but if at some point I happened on the bits to do it, I'd want to make sure that the setup was delivering the correct pressure. The NC21 and 24 have oil pumps with different model numbers too, but the the whole family shares the same chain and sprocket. Each model appears to have a different pressure relief valve, so would the way to get the correct pressure if using a 21/24 pump be to fit the valve from a 30? I wonder if some property of the NC35 pump when compared to the NC30 pump for the non oil cooled version means it needs to run a different one?

thunderace wrote:

Neosophist wrote: Not sure what controls the oil pressure, thought it would be the pump but the part is the same.

The oil pressure switch regulates the oil pressure by sending a signal to cut the oil pump power when it reaches the setpoint.

The pump is driven by a chain from the engine, the switch lights the oil light when there is low oil pressure... I don't think it works as above on the VFR

Neosophist wrote:

thunderace wrote:

Neosophist wrote: Not sure what controls the oil pressure, thought it would be the pump but the part is the same.

The oil pressure switch regulates the oil pressure by sending a signal to cut the oil pump power when it reaches the setpoint.

The pump is driven by a chain from the engine, the switch lights the oil light when there is low oil pressure... I don't think it works as above on the VFR

OK fair enough. If it is chain driven, I would imagine there is a relief valve built into the sump or crankcase then.

thunderace wrote: OK fair enough. If it is chain driven, I would imagine there is a relief valve built into the sump or crankcase then.

It's in the bottom of the pump.

Looks like that is what controls the pressure then, explainig why they are different amonst the different bikes.

If you are conerned there will be wrong pressure with NC24 pump then fit the NC24 valve too :)

But if the NC24 valve is set to 62psi, then it won't make enough pressure for the NC30 or 35 that require 71-85, surely? NC21 at 76 fits into the 71-85 range though. I think I'd be happier putting an NC35 valve into a different model's pump, or using a pump that came from a Euro spec oil cooler fitted 30....

speedy231278 wrote:But if the NC24 valve is set to 62psi, then it won't make enough pressure for the NC30 or 35 that require 71-85, surely? NC21 at 76 fits into the 71-85 range though. I think I'd be happier putting an NC35 valve into a different model's pump, or using a pump that came from a Euro spec oil cooler fitted 30....

The pump that came from a euro spec NC30 is an NC24 oil pump.

Ive never heard of anyone swapping the valves when they have changed the pumps and nobody has had any trouble before.

Its not a dramatic change in pressure anyway, would be interesting to know why it was changed though, as all models share the same engine.

Do the 21 and 24 have different rev limits and/or power output compared to the 30/35? Allegedly, the latter are 59 and 53 bhp, but that's on paper and the same system says that all the range topping turbo sportscars of the same era like Skyline, Supra, NSX, GTO etc were 280, which is rubbish.... What are the 21 and 24 rated at? Also, maybe something else internal was changed, and required different pressure for optimum running? I guess only Honda really know...

speedy231278 wrote:Do the 21 and 24 have different rev limits and/or power output compared to the 30/35? Allegedly, the latter are 59 and 53 bhp, but that's on paper and the same system says that all the range topping turbo sportscars of the same era like Skyline, Supra, NSX, GTO etc were 280, which is rubbish.... What are the 21 and 24 rated at? Also, maybe something else internal was changed, and required different pressure for optimum running? I guess only Honda really know...

That is true.

The NC21/24/30 were all rated at 59PS from honda.

The legislation at the time of making the bikes was that no 400cc machine could make more than 53ps + 10.

So MFGs built everything to 59PS (53 + 5.3=58.8).

However, in 1992 the law changed and the 10% tolerance limit was removed, so bikes had to be 53PS if they were 400cc's.

Since then the law has been changed again and their is no power restriction. However, with modern day emission laws strining out a factory 400 to make more than around 60hp breaks the emissions laws.. but there are a few modern 400s in the mid 60's from the factory.

The NC21/24 came from a time when the law didn't dictate a speed limit, hence the bikes were unlimited, the clocks only go upto 180km/h like all JDM clocks but it will go off them quite easily. It does have a red SPEED over warning lamp that will illuminate at 80km/h alert the rider of breaking the then max speed limit for all motorcycles (80km/h).

So yes, no idea why it was changed, change it if you like but doesnt seem to make any difference.

NC30 revs 1000rpm higher than NC24/21 too.