Author Topic: CB750 Engine Case Interchangeable  (Read 1413 times)

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Offline HondaMan

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Re: CB750 Engine Case Interchangeable
« Reply #25 on: January 31, 2019, 05:36:21 pm »
Would you be able to tell by these pictures which one I have? I don’t have your book but I’m ordering it now.

Those are the late style, like the K7/8 and [most of the] F2/3. If your engine number on the top case is parallel to the cylinders, it is likely the K7 or later F1 type. If it is perpendicular to the cylinders then it is the last year of manufacture: the final-drive shaft and bearing (and seal) from that type seldom fit the other cases very well. But, the final drive shaft and bearing can be easily swapped with a similar version (I have several) that will let you use a little earlier case if needed.

All this said: I am currently in the process of repairing some K0 (very early) cases that had a chain accident. It's expensive, running about $400 so far, but I think it will come out OK in the end. It takes time and patience, and expert welding and machinists who care to get it right. I am blessed to know a few of these around here!
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Offline oz750

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Re: CB750 Engine Case Interchangeable
« Reply #26 on: February 09, 2019, 02:38:29 am »
As this thread is very timely for me, I'll hop in, if you don't mind.
I recently purchased a K8, and decided to replace the worn chain, and found a large hole that had been covered with a coke can and fibreglass!

I can source a K6  cases in good nick, and my question is will my K8 internals fit into the K6.
I have made a better repair that is ok and oil tight,so the bike is rideable now, but will jump on the cases if the collected wisdom on this invaluable site is to go for it.
Thanks in advance for any suggestions/ help.

Offline bryanj

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Re: CB750 Engine Case Interchangeable
« Reply #27 on: February 09, 2019, 02:48:00 am »
Considering the K8 had the better chain that is pure PO neglect.
Check the part numbers for the respective output shaft bearings, if they are the same chances are good cases will swap.
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Offline 754

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Re: CB750 Engine Case Interchangeable
« Reply #28 on: February 09, 2019, 03:26:14 am »
You can run the K6 cases with output shaft, if you can live with  chain closer to wheel.
 You would need k6 sprocket carrier and spacer, chainguard may not fit.
I think you can transfer  the late output shaft into a K6, but you should check with a set of cases.
 The gear set driving the output shaft, on K7 and K8 have different tooth counts than K6 and earlier.
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Offline oz750

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Re: CB750 Engine Case Interchangeable
« Reply #29 on: February 09, 2019, 04:11:31 pm »
Yes I agree that it was a lack of basic maintenance that caused it. Thanks for your replies. I'll check the cases and see what they are like. As I am able to wait, it will be best to have patience and find the right cases or engine. Either way I will leave it a better bike than I found it.

Offline bamacb

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Re: CB750 Engine Case Interchangeable
« Reply #30 on: February 11, 2019, 01:13:50 pm »
Don't know if it will help , I assembled a bottom end yesterday using 72 cases with 78 trans. The only change needed was I installed the bearings and gear from the 78 on the 72 out put shaft. Dropped right in.

Offline smacd11

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Re: CB750 Engine Case Interchangeable
« Reply #31 on: February 11, 2019, 02:50:15 pm »
oz750, where are you located?  I have a set of K7 or K8 cases I could probably part with. I have both, one has broken mounts one looks good. Can't remember which one at the moment. They are in storage right now.

Shawn

Offline oz750

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Re: CB750 Engine Case Interchangeable
« Reply #32 on: February 12, 2019, 09:21:43 pm »
Thanks Smac. I am in Australia, but happy to pay freight over if cases are good. Thanks again for help.

Offline smacd11

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Re: CB750 Engine Case Interchangeable
« Reply #33 on: February 13, 2019, 05:11:30 pm »
It's -25 Deg C here - I'll try to dig it out in the next couple days and send you some pics.

Cheers,
Shawn

Offline oz750

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Re: CB750 Engine Case Interchangeable
« Reply #34 on: February 14, 2019, 03:22:04 am »
OMG I can't even imagine that! I hope you don't have to go outside.Much appreciate your help.

Offline bamacb

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Re: CB750 Engine Case Interchangeable
« Reply #35 on: February 14, 2019, 08:14:04 am »
This is what I know to be true . I have a 72,77,and 78 engine. I just finished the 72 bottom end using the 78 trans. The only thing needed was to change the output shaft gear on the 72 shaft using the 78 gear. The same is true in reverse order,early trans to late cases. I compared 4 output shafts,the bearings are the same as is the over all length. The gears are different as is the placement of the outer double row bearing. It stops around 1/4" sooner [closer to shaft end] on the 77/78 than the early style 72 does. In short you must use the shaft for the cases you have and the output shaft gear for the trans you are using. Everything drops in with no clearance problems.

 

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