Topic: Did this frame and bike exit the factory together? CB750

[70CB750]

Thank you, Dream, gotta compare pictures with what I have.  I am pretty sure the K0 oil tank does not have the oiler output.  Maybe it is aftermarket or some other variation.

[Geeto67]

I guess what I thought was a K6 oil tank wasn't.

Functionally speaking - does it make a difference? I mean we are talking about excess oil, the tank still vents to atmosphere - it just does it in a different way.

[Dream750]

I guess what I thought was a K6 oil tank wasn't.

Functionally speaking - does it make a difference? I mean we are talking about excess oil, the tank still vents to atmosphere - it just does it in a different way.

That’s a very good point.
 
It doesn’t make any difference for custom made K6 oil tank applications as the tank vent hose can be connected to the rear crankcase fitting and will function just fine.
 
In a stock application, I personally would hesitate to second guess the Honda engineers by using a stock pre K6 oil tank on a K6 engine. As there are internal/external design differences between the two types. One fitment problem that has to be addressed is a hose fitting size mismatch between the smaller oil tank chain oiler fitting and the larger crankcase drain fitting. And blocking these fittings off is probably not a good idea either. I wonder what would be the long term effects (if any) by using the earlier style oil tank that circumvents the K6 oil tank design? It’s really easy just to use a stock K6 oil tank for K6 engine swaps. This eliminates any doubts and the infamous oil overfill discharge which many pre K6 owners have experienced. I think the real difference here is up to the owner to decide.

[Terry in Australia]

Sorry Dream750, but what a load of bullschidt! The chain oiler on the K1-K6 had nothing to do with the oil tank! The chain oiler mechanism consists of a hollow threaded output shaft with an "O" ring and a screw to adjust the oil flow which comes direct from the crank cases.

My K1 Cafe Racer has a K6 engine in a K1 frame, using the original K1 oil tank, the only difference is that the crancase breather tube (which ALL CB750's have, regardless of model, except the auto) on the K0-K3 was smaller than the K3-K6, F-F3, and K7/8. All I needed to do was turn up an alloy "adapter" so the larger crankcase breather tube from my K6 would connect to the smaller hose from the K1 oil tank. ALL CB750 engines have a cam cover breather tube as well.

Mate, I don't know where you're getting your information from, but you're 100% incorrect! Cheers, Terry.     

[Dream750]

OK, Terry I’ll bite.

If the oil tank has nothing to do with the chain oiler feed, then please explain the purpose of the small hose connecting the oil tank to the crankcase.

(It's a pretty small OD hose designed to be relieving crankcase pressure into the oil tank separator)

[Terry in Australia]

The "small hose" is the crankcase vent tube mate, it was increased in diameter after the K3. It has NOTHING to do with the chain oiler. Cheers, Terry.

[70CB750]

Here is my K3 tank, there is no output you marked as oiler - whatever it really is.

I am pretty sure the K0 tank has nothing of that kind either but i will nor pull it just for picture.

As far as the chain oiler, Terry is right, it is a feature of the output shaft.

[Dream750]

Guy’s, looks like my terminology and description of “chain oiler” coming from the oil tank vent hose is not clear. The open end of the final drive shaft is hollow and receives it oil supply from the oil guide. The oil guide collects oil from the rear crankcase fitting via the oil tank vent hose. The chain oiler flow is adjusted at the end of the final drive shaft. I could be completely wrong here, but that’s the way I understand the description/operation of the chain oiler up to the K5. 
 
Perhaps these threads and pics will help better explain:
 
http://forums.sohc4.net/index.php?topic=98822.0
 
http://forums.sohc4.net/index.php?topic=95059.0

[ekpent]

Sounds pretty convincing to me Dream. Looks like MC has researched it pretty well also. Maybe another new tidbit of info to remember on these.

[Terry in Australia]

The oil tank vented into the atmosphere in the earlier models, with a separate hose that exited between the engine and the rear wheel. The oil tank vent was positioned at the top of the tank, not the bottom, obviously...........

The bottom hose is a crankcase breather that vents back into the oil tank, not the other way around, but some oil from the "oil mist" ran back and splashed into the oiler tray. The chain oiler worked primarily on oil splashing into the tray (inverted in Dreams's pics) and running out the hollow output shaft.

If this hose was only required to provide oil feed back to the chain oiler, then why was it increased in size when the chain oiler was deleted? By the way, the fitting for the chain oiler splash tray was retained in the later models crankcase castings, the only change to the internal crankcase venting was the larger diameter breather pipe. Cheers, Terry.    

[ekpent]

Its a tennis match and Terry has a good point also.   Mercy--------   

[Dream750]

It’s too bad the Honda shop manual left out the functional description and internal flow diagram of the oil tank, chain oiler supply and crankcase vent system. Had this information been included, all 750 owners could easily reference this as common knowledge. Instead we are left with trying to piece the parts together into a working system without a reference.  
 

[Dream750]

I am pretty sure the K0 tank has nothing of that kind either but i will nor pull it just for picture.

K0 tank pics:

[scottly]

K1 oil drain:

[HondaMan]

re: the chain oiler and crankcase vent: check Honda's Service Bulletins of the 1969-1970 era. Some dealers were chastised (including Brown's Sport Center where I worked then) for shutting off the over-effluent oilers to help keep customer's bikes clean, because Honda considered it to be in part a crankcase vent mechanism. When the larger 18T countersprocket came in the K2, the larger spigot on the back of the engine also appeared, because the chain oiler were being set (by the factory) to a lower setting to clean up the bikes a little. This was said to "balance the crankcase pressure more with the lesser chain oiler". (?)

That's all I had of it, except where I turned them down, anyway.   

[Terry in Australia]

That was probably a bit later Mark, because the early K0's didn't actually have chain oilers, their output shafts were solid. The chain oiler was brought in later to help combat the chain breaking issue. Cheers, Terry.