Topic: sohc 750 oil pump

[honda 7]

I am wanting to know if there are any nos or after market oil pumps for the 750 1969/1974 sohc4. I am running an 836 in a roadracing sidecar and the low oil pressure worries me.I have been told that the oil pump rotor and ring out of a honda goldwing have the same diameters but are wider .There would be no problem to grind the width to the same as the 750 .Its only the pressure side of the 750 pump that is a problem.Hope someone out there can help. Scotty

[BLUE71TURBO]

 Brother, if your oil gauge is correct and pressure is low at idle and at high rpm's......It's the bearings in the lower end !   
 As the gaps between the bearings and the other componets widen more oil leaks out and the pressure drops. Some times a high volume oil pump can be installed to help " get by "  because it will pump enough so that oil will get to where it needs to.... but that is just a bandaid fix.  You really need to install new bearings as long as the crankshaft is in good shape or wait too long and have to rebuild the
whole engine due to lack of oil and major seizure of the whole engine.  You stated your racing this engine, man rebuild it or you and your partner are going down the racing road to HEAVEN OR HELL !!  IT'S YOUR'S and yer PARTNER'S LIFE !!   
    As far as i know there has not been any aftermarket oil pumps made for the cb750. There's probably some kind of mods that racer's
over the years have made to stock setups but i have'nt had any experience in that area of the cb750.  I'm sure some of the more experienced brothers here will chime in and share info on this subject.      GOOD LUCK !    JON G.

[Gonzowerke]

Hondaman says in his section of the faq that when he raced them, the stock oil pump was fine, he just chamfered the inlet. (If I remember Correctly)

[bear]

 I am running an 836 in a roadracing sidecar and the low oil pressure worries me.
 Scotty

G'day Scotty.
Sorry you didn't make it to Winton. Saturday was as wet as a shag, would have suited you Tasweegens down to the ground.
Never had a problem with the stock pump. As Jon G mentioned any pressure problems where usally conected with bearing wear or crank damage.

Cheers,
Brian

[spiritof67]

Somewhere out there somebody knows this one: I remember an article when the CB750 was still a new bike and people were racing them that there was another spring in the engine that was the same basic diameter as the oil pressure relief spring but stronger - and thus gave a higher oil pressure. It would've been printed in 1971 or '72. Has anybody found out which spring that is/ tried it? Maybe that would do the trick...

[Bill/BentON Racing]

That rings a bell.Will look.Bill

[lordmoonpie]

Somewhere out there somebody knows this one: I remember an article when the CB750 was still a new bike and people were racing them that there was another spring in the engine that was the same basic diameter as the oil pressure relief spring but stronger - and thus gave a higher oil pressure. It would've been printed in 1971 or '72. Has anybody found out which spring that is/ tried it? Maybe that would do the trick...

That's right I believe - there was a stronger spring in the honda race kit parts for the oil pump. Of course it's an obsolete part now but you can achieve a similar effect by pre-loading the standard spring with a small washer. Not as good as the stronger spring but it works. I have this arrangement in my CR750 engine...

[napoleonb]

David Silverspares had one on ebay a few months ago. The spring is indeed a kit item.
Perhaps you can have a stronger spring made by a manufacturer, that isn't really costly.

[ttr400]

I am by no means a 750 oil pump expert, but when I was investigating the 400F pump upgrade I bought many used 750 pumps. all the rotors had damage to them and were not usable for what I wanted to do. In the end I gave up on them and made new rotors for the 400F pump. I found in the 750 pump, the smaller rotor is the same as in the 400F pump. the larger rotor is the one I wanted for my mod, ground down in height. I believe the thicker rotor is for the return to oil tank?
For my CR replica I managed to get a NOS pump from a guy in Germany (Sandgus I think).
I bought the 970 spring that DSS had on ebay. I will check the difference to a stock spring and post some specs later.

Kevin

[spiritof67]

I've been trying to track this damn spring down for years - I know there was a "kit" spring, but my recollection was that there already was a spring in the standard CB750 that would do the job. After years of being told 'no there isn't", it's good to hear that the real answer is "yes there is".

Lord Moonpie, what washer did you use? Did you use a stainless washer? I am presuming you started with a brand new spring.

What was the original/afterwards oil pressure?

Anybody got one of these ("kit spring") that can be duplicated? Or can anyone figure out which is the existing CB750 spring that does the job? Either or all of these are things every CB750 owner should have available. After all, with or without a cooler, an oil cooled engine can always use a little more circulation - i.e., oil pressure.

Onward, stalwarts! The solution is near!

Spirit

[Jerry Rxman Griffin aka MuthaF'er]

I have some NOS springs for my NOS Leak Stopper but that won't help with what you're after. I plan on going through my oil pump in the very near future and I can try to ID "your" spring vs any others on the bike once I've seen it since my bike is still in a million pieces.

[spiritof67]

re: that last item, I used to have (but lost) a complete CB750K "exploded" engine poster which would have made it a lot easier to ID this little (but critical) part. I think the poster was a Honda showroom/parts counter item.

Of course, I let that, the "Honda Winners Are Here!" strip and the Dick Mann CR750 head-on poster get by me - "Ah, they'll always be available!". Right.

Spirit

[Sam Green Racing]

Hey Scotty, have a word with Mark, Hondaman on here. He was involved in midget racing where the motor had the gearbox removed. No gearbox = no oil pump, yes.
I seem to remember the pump on these motors was run off the end of the cam so there must be an alternative.
Thing is, if you have low oil pressure, you'll soon be needing a new crank and god knows what else, get new shells in that motor.

Sam.

[Bill/BentON Racing]

Sam,the midget motors had oil pump driven off rt side of cam.I have one.Have to weld boss on cam cover.Must work pretty good....they turn 14-15,000 rpms! Bill

[ttr400]

The specs of the 970 kit spring.
Length= 34.5mm
Dia= 16mm
Wire=1.8mm

Stock spring from a used pump.
Length=38.5mm
Dia= 15.5mm
Wire=1.5mm

Kevin

[Bill/BentON Racing]

Thanks,what kind of pressure increase with the 970 spring?

[kos]

Hey Scotty, have a word with Mark, Hondaman on here. He was involved in midget racing where the motor had the gearbox removed. No gearbox = no oil pump, yes.
I seem to remember the pump on these motors was run off the end of the cam so there must be an alternative.
Thing is, if you have low oil pressure, you'll soon be needing a new crank and god knows what else, get new shells in that motor.

Sam.

Yes Sam, you are correct the oil pump is still just a Honda OEM pump thou. Take a look for yourself.

KOS

[Bill/BentON Racing]

Looks like the one I picked up.Anyone on increase in pressure with the 970 spring? 5-10 psi?

[bwaller]

Yes Kevin if you had access to a spring pressure tester to compare the two springs it would be valuable info.

[ttr400]

I'll go over to my Friends shop, he has a valve spring tester, so I suppose that will do the job. will report back.

Kevin

[754]

Just curious what the NOS pump went for? was it just the pump unit, or was it with the base too?

[ttr400]

It was the complete oil pump. went for 349.00 Euro.

Kevin

[Sam Green Racing]

Hey Scotty, have a word with Mark, Hondaman on here. He was involved in midget racing where the motor had the gearbox removed. No gearbox = no oil pump, yes.
I seem to remember the pump on these motors was run off the end of the cam so there must be an alternative.
Thing is, if you have low oil pressure, you'll soon be needing a new crank and god knows what else, get new shells in that motor.

Sam.

Yes Sam, you are correct the oil pump is still just a Honda OEM pump thou. Take a look for yourself.

KOS

Dear Mr McGrew, please refrain from messing with my mind.
I know you did it beKOS you can but it gave me a head ache.
I started to wonder how much I had had to drink last night.
I closed my eyes but it was still there. It wouldn't go away.
Is that a straight 8, or two motors coupled together?

 

Getting back to being sensible, if that's possible If the stock pump is used and it's up to pumping enough for two motors, would it not be a good idea to mount a pump from the CB750A which I belive pumps a lot more than the standard CB750 pump?

I hate sidecar people, they to give me a head ache.

Sam.

[754]

 I bought a new pump in the early 80s, It was 75 or 78.00 Can, without the base...

[kos]

Hey Scotty, have a word with Mark, Hondaman on here. He was involved in midget racing where the motor had the gearbox removed. No gearbox = no oil pump, yes.
I seem to remember the pump on these motors was run off the end of the cam so there must be an alternative.
Thing is, if you have low oil pressure, you'll soon be needing a new crank and god knows what else, get new shells in that motor.

Sam.

Good eyes, I can't talk about this combination right now. Manifold made for these cam driven oil pumps is adjustable by just turn a set screw in. Oil pressure will not be a problem.

KOS








Yes Sam, you are correct the oil pump is still just a Honda OEM pump thou. Take a look for yourself.

KOS

Dear Mr McGrew, please refrain from messing with my mind.
I know you did it beKOS you can but it gave me a head ache.
I started to wonder how much I had had to drink last night.
I closed my eyes but it was still there. It wouldn't go away.
Is that a straight 8, or two motors coupled together?

 

Getting back to being sensible, if that's possible If the stock pump is used and it's up to pumping enough for two motors, would it not be a good idea to mount a pump from the CB750A which I belive pumps a lot more than the standard CB750 pump?

I hate sidecar people, they to give me a head ache.

Sam.