Topic: 1975 Honda CB750F Oil Pumps

[RodSOHC750]

Searching EBAY for used 1975 CB750 oil pumps.  I don't understand the HM751, HM345B, HM184, HM305, HM128B, HM640 etc. in the pump descriptions. What are these codes?

[Bigsam302]

I think that those numbers are just what the seller uses to label his parts. There is only one seller that uses them. It's a salvage yard. I've bought from them a bunch and that code means nothing to you.

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[RodSOHC750]

OK. That makes sense.  Couldn't believe Honda would make so many variances of the oil pump in one model year. 

[SOHC4 Cafe Racer Fan]

I think that those numbers are just what the seller uses to label his parts. There is only one seller that uses them. It's a salvage yard. I've bought from them a bunch and that code means nothing to you.

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b

Correctomundo

[Bigsam302]

There's nothing like being stuck on the side of the road after my antigravity battery exploded today. The scariest thing is sitting here fanning my bike and hoping that it doesn't catch on fire.

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[chewbacca5000]

Searching EBAY for used 1975 CB750 oil pumps.  I don't understand the HM751, HM345B, HM184, HM305, HM128B, HM640 etc. in the pump descriptions. What are these codes?

I got a nice one out of a 76f with 17,000 miles.   $50 to your door. 

[RodSOHC750]

Thanks. I was able to make a good one out of three.  None of the three pump lobe tip clearances met the Honda spec of .002 inch.  Most ranged from .004 to .008 inch.  Not much choice since I can't buy new lobes. Picked the smoothest lobes and replaced all rubber parts.

[HondaMan]

Thanks. I was able to make a good one out of three.  None of the three pump lobe tip clearances met the Honda spec of .002 inch.  Most ranged from .004 to .008 inch.  Not much choice since I can't buy new lobes. Picked the smoothest lobes and replaced all rubber parts.

Where did you find a Honda spec of 0.002" for the lobe tips? All my Honda manuals have shown this at 0.0138" since 1970, with up to 0.030" side clearance to the cover/body walls. From experience, I know that once the lobe tips are more than 0.010" the PSI drops to about 55 at hiway speeds on hot days (20w50 oils) and 25-30 PSI at idle (900 RPM) when hot. The only thing that seems to actually impact the oil flow is the side cover clearance: so long as this stays under 0.020" the pumps' overcapacity keeps plenty of oil rolling thru the engines (750 engines, not the 500/550, here...).