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Later Alloy Body Oil Pump in K0 Bomber

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AshimotoK0:
My understanding from  the Bomber experts on Hondatwins.net has always been  that fitting a later alloy body oil pump from a K2 onwards is the way to go to improve top-end lubrication.

However, I spoke with Jensen on the phone last night about various bike related subjects  and it seems that in his extensive testing of synthetic oils in the Bomber, he originally fitted a NOS CB500T pump but experienced wear and reverted back to the steel body one. I will ask him to comment specifically on this but meanwhile I went through his posts and pulled out some pertinent points and copied them into the attached document. He certainly is a fountain of knowledge on the CB450 DOHC and CB72/77.

I bought a later alloy body oil pump, used but good condtion, for my K0 and passed on a NOS steel body one that  I was offered fairly cheap ..  I think I will contact the guy again and see if he still has it 'just in case'.  Jensen told me that there were several modifications to the K0 pump. I suspect that the one I was offered was an upgraded part as it came from Honda's Service Centre that was in Nottingham in the 60's/early '70's.


https://www.dropbox.com/s/kb8pbuwl3a4jdxv/jensen.doc?dl=0

MrDavo:
I’m not sure where this leaves me, Ashley rang me about it while I was on to of a French Alp, skiing, as Jensen had given him the impression that some modification may be necessary to fit the later pump. I am now in Chambery airport waiting for our delayed flight home.

My 450 is a K1, it did have the early steel bodied pump, and I have fitted a later 500T pump to get more pressure, I’ve read a few threads about it.

The pump I fitted was from a low mileage bike, and doesn’t (yet) have a worn alloy body. I don’t think I have a clearance issue though, as mine is a five speed engine, reading Jensen’s document the problem arises when you fit the late pump with the four speed clutch.

I’ve kept the original steel body pump, I can always switch back.

Perhaps Jensen can comment if he sees this, I don’t want to pull my engine apart again if I don’t have to.

K2-K6:
Mr Davo,  off topic but we, yesterday, drove back past Chambery airport from the alps leaving Les Arcs in the morning to return UK.
Brilliant snow this year, some of the best for a long time. Where did you stay?

Back on topic,  some of the metallurgy in these areas can be the inverse of what would appear logical in wear patterns. A steel component may be worn by a softer material given the right circumstances. The cam lobes, also,  are lubricated in a zero pressure environment,  so increasing pump pressure will not improve local were rates. That specific point needs absolute flow to clear used / heated oil and replace with supply as fast as possible.
Pump pressure is similar to resistance in electronics,  I believe. The system will need lowered viscosity to get more supply,  only then would more pump capacity give a relevant increase in oil supply to the cam lobes.

Nigel.

AshimotoK0:
I sent Jensen a Facebook message and sure he will respond in due course.  he's been away on business so it may take him a couple of days to respond.

I read somewhere on HondaTwins that there was an official Honda Service Bulletin on the early pump. Someone had posted an image of it but it was Photobucket and no longer visible in the post. I will investigate further. The construction of the alloy body later pump is the same as the CB250/350K's  so I will have about half a dozen of them that  I can inspect. I think am going to grab the NOS steel body one if it's still available though.

jensen:
Hi, took a while to respond, but better late than not at all......

The intresting part is the spacer, which is't a standard one, it's thinner. I will find the pump somewhere in my stash and measure the parts... I will also make a better picture of the install guide as soon as I have the time.

btw, happy easter everyone !

Pictures :

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