Topic: CB750 oil flow rate

[23tbucket]

Just need a rough idea; Does any one know the flow rate of the Honda CB750 oil supply pump...say at 4000 rpm? I have the specs on pressures, but nothing else. I could open up a pump and do some calculations, but just maybe someone here can help. I also think the oil pump would be turning about 1000 rpm if the engine crankshaft speed is 4000 rpm? Is this correct? If so...then I could run a pump at the 1000 rpm and temporarily run a suction line into a jug of oil and the discharge into a graduated cylinder.

Thanks; Clifford

[Bodi]

I'm not so sure that trochoidal/gerotor pump flow volume would be so easy to calculate from looking inside one - see http://is.mfkg.kg.ac.rs/podaci/Lozica_Ivanovic/62/30-Ivanovic.pdf, it makes my head hurt! I've never counted the teeth on the pump or crankshaft gears either... but I'm curious about why you need to know the flow rate?
Plus there will definitely be some rotor leakage loss with changes in fluid viscosity and static pressure.
If I really needed a real world flow number, I would hook up an external graduated oil tank to the motor and measure it. If the scavenger pump return can be switched to another collector tank one could run the engine at whatever RPM desired and then swap the return line to the other tank, and measure how much oil is drawn from the supply tank in a known time (before the tank runs dry of course). I think this will be accurate on a 750, I'm not sure but I think the transmission is oiled from its scavenger pump outlet - not from the engine supply pump or a separate rotor set. This would be pretty much impossible on any of the other wet sump SOHC4 models anyway.

[23tbucket]

Bodi: Thanks for your reply. I guess it would help if you know why, I have a couple of SOHC's that the transmissions have been removed and block-off plates put in place where the tranny was machined off. This modification was fairly commonly done with midget racing  back in the day. An oil pump was usually driven off of the camshaft. I don't know what pumps were used or any other info.
  If an oil pump has too low of a flow rate....then the supply pressure won't be reached and engine damage will happen. If the flow rate is too high.....then the oil will overheat from being relieved inside the pump.

;Clifford

[70CB750]

If I understand you correctly, you need an oil pump on the camshaft to supply the same amount of oil as the original CB750 oil pump?

[mec]

only found some numbers for cb900 bol d´or:
41Liter/minute/7000rpm for engine
18Liter/minute/7000rpm for oilcooler

mec

[23tbucket]

70Cb750: Thanks for your reply. The camshaft driving the pump would work, but I am going to use a timing belt driven pump off of the crankshaft (more or less). By using belts, I can change the amount of flow somewhat by changing pulley sizes. Just would like some idea of where to start with this.

Mec: Awesome information. I think you have given me the information to get close. Some of the dual camshaft 1980's Hondas did use pumps with twin pump rotating assemblies as per the info you found...one section fed the engine internals and the other section pushed oil through an oil cooler. If I use a little bit less than the 41 Liters per minute at 7000 rpm (crankshaft), I should be able to size a pump and have it turn at a certain speed and get very close to supplying the  proper oil supply to the engine. Most external pumps run at a maximum of 4000 rpm and a minumum of 500 rpm. Most external pumps I have found will give two specs: displacement per revolution, and gallons per minute at a certain rpm. Easy  enough to do the calculations once you know what is needed.....at least it will get me close.
Thank you ever so much: Clifford

[70CB750]

You could always use original fuel pump than and modify it to work, input can be plumbed out, intake too, with a bit of creativity. 

Interesting problem, got pictures?

[TwoTired]

Pump flow rates don't mean a thing unless pressures are included in the spec.

Pretty much all pumps will flow the most with no resistance to flow offered.  It is what they do when resistance is offered that is important.   Flow rates and pressure for any given engine will vary with the clearances in the journals, and orifices in the pathways.

To wit, an old worn engine will have low oil pressure (and lots of oil flow), even with a brand new oil pump installed.  But, that flow volume is unlikely to reach the furthest path away from the pump, 'cause all the journals are loose.

Check out water pumps, for example.  Many have flow rates coupled to the amount of lift in can provide.  The lift is another way of saying back pressure.

Even the SOHC4 pump will flow zero if you block the output.  Well ok, the pressure relief valve will open to allow it to flow through the pump without hydraulic lock blowing seals.

Anyway, what you need is a flow rate with output pressure spec. 

[bjbuchanan]

Look at some of the oil pumps that remote turbocharger guys use and I agree with TT, you gotta know flow at some type of pressure or resistance

[23tbucket]

Yes ..you guys are correct on needing to restrict the flow to create pressure. Most engines should have around 30psi to 60psi of oil pressure at normal operating temperature and speed. The restriction in an oil flow is mostly determined by the engines design through orifices, and rotating assembly clearances. The relief valve is just needed if there is high restriction due to cold oil, tight clearances or a restriction of the flow that shouldn't be there. The relief valve protects the pump. Here is what I am getting at...if the pump flow is too low (or worn out) then you will never reach the required pressure. Likewise, if the pump flow is overly high the pressure will be obtained, but the oil will become heated due to the oil going through the relief valve over and over.

Here is what I am thinking of doing: Roughly size an external pump and the speed it needs to run at with the specs given by Mec. Adjust the relief valve spring and test so it dumps at a certain pressure beforehand. Put an oil pressure gauge in the galley. If the engine runs but doesn't get up to the proper pressure...then I may need to speed up the pump or find a larger one. If the engine is good and hot and has the right oil pressure...then I can take a stethoscope and listen to the pump to see if the relief valve is letting oil squeeze by (it will be making a high squealing noise). If it seems like the pump is returning too much oil then I can slow the pumps speed or get a smaller pump. For sure it is better to have a pump that flows a bit more than what the engine actually needs, but too big is not a good thing either.

Thanks for your comments...I am taking it all in.

[Don R]

 The imagination runs wild with the possibilities of such an engine. multiple engines and front to back mounting come to mind.

[23tbucket]

Thanks again fellows; I just found some information regarding sizing an engines flow rate. An oil pumps flow rate is often centered around how much oil is contained in a reservoir (oil pan, oil tank, etc.) You don't want a pump so big it empties the reservoir before the oil is returned...or too small of a flow that won't build up the needed pressure to enter all the engine bearings, etc. Better to oversize the pump....apparently the oil being bypassed via the relief valve does not heat the oil very much....so moot point on me.
 Boy, that 41 liters per minute seems like a lot...that is around 10 gallons per minute. A V8 chevy needs around 20 gallons per minute at 3000 rpm. But the honda, being a smaller engine and at twice the speed (7000 rpm) it does make sense. If the V8 could do 6000 rpm..it might need 40 gallons per minute?

[23tbucket]

Ah heck...everyone thinks I'm nuts anyway.....couple more pictures of what I started last winter:

[70CB750]

Wow, that's nice!

Will follow with keen interest.

[Vinhead1957]

Man I should of had a V8

[Don R]

Have you asked Russ Collins? He did it already.