K7 rear drum

[grewth]

Does anyone know if a K7/K8 rear drum will work on the earlier K series bikes please ?
Alternatively, does anyone have a K7 parts catalogue handy.
This evening, I have managed to find all my CB750 parts catalogues EXCEPT for the K7 one which has gone AWOL.
Rear hub part number from mid K1 production to K6 is 42601-300-030.
Can anyone give me a part number for the K7 hub please

 

[pickleknuckles]

You can cross-reference the parts here -
https://www.cmsnl.com/honda-cb750k7-four-usa_model14395/partslist/F11.html

I think the hub, drum, and carrier are different part numbers but still interchangeable, maybe. I know it's a common swap to use a later wheel on an earlier bike to fit a slightly larger tire.

 

[grewth]

You can cross-reference the parts here -
https://www.cmsnl.com/honda-cb750k7-four-usa_model14395/partslist/F11.html

I think the hub, drum, and carrier are different part numbers but still interchangeable, maybe. I know it's a common swap to use a later wheel on an earlier bike to fit a slightly larger tire.

Many thanks !
According to that link, the K7 hub has a different part number to the K1-K6.
Two different parts actually, ending 040 and 050 respectively, against the K1- K6 030.
I've discovered that the K7/K8 had wider swing arms and 10mm wider cush drive hub to accommodate the 630 size chain and sprockets.
Not sure about the hub width
I've also read that the CB750A had a stronger rear hub fitted, but no real explanation of why
this was needed
Looks like the only solution is to find a K7 hub and measure

 

[pickleknuckles]

Many thanks !
According to that link, the K7 hub has a different part number to the K1-K6.
Two different parts actually, ending 040 and 050 respectively, against the K1- K6 030.
I've discovered that the K7/K8 had wider swing arms and 10mm wider cush drive hub to accommodate the 630 size chain and sprockets.
Not sure about the hub width
I've also read that the CB750A had a stronger rear hub fitted, but no real explanation of why
this was needed
Looks like the only solution is to find a K7 hub and measure

I happen to have a k7 wheel in my shop. What exactly do you need measured?

 

[grewth]

I happen to have a k7 wheel in my shop. What exactly do you need measured?

Good question.
I want to find out if the K7 hub will work with a K2 type swing arm, axle, cush drive, brake plate etc.
I guess that the critical dimension is going to be outside face of the LH bearing to the outside face of the RH bearing.

 

[grewth]

I just checked the spacer tube which sits between the bearings on the CMSNL site.
42620-300-010.
This has remained the same part since 1969 according to my parts books.
Bearings also seem to be the same from start to finish (type 6304 and 6305), so I'm feeling hopeful that it might be a straight swap.
Unless anyone knows different ?

 

[pickleknuckles]

Good question.
I want to find out if the K7 hub will work with a K2 type swing arm, axle, cush drive, brake plate etc.
I guess that the critical dimension is going to be outside face of the LH bearing to the outside face of the RH bearing.

I'll measure it for you asap. I've got a spare K4 brake plate and cush drive stashed somewhere I can drop in too. I think the rubber bits are slightly different for the K7...like one piece vs two, maybe?
The K7 wheel has all but one rubber piece, I think.

Does the parts diagram show different/wider axle spacers for the early vs late bikes?

 

[grewth]

I'll measure it for you asap. I've got a spare K4 brake plate and cush drive stashed somewhere I can drop in too. I think the rubber bits are slightly different for the K7...like one piece vs two, maybe?
The K7 wheel has all but one rubber piece, I think.

Does the parts diagram show different/wider axle spacers for the early vs late bikes?

Thanks!
Comparing parts lists can be confusing.
To the best of my knowledge, the K7 swing arm is wider than the K6 on the chain side only, due to the change to a 630 size chain etc.
The K7 cush drive casting is 10mm wider, and presumably the axle and the spacer between the cush and the hub are also increased by 10mm.
The LH top shock mount on the frame was also moved 10mm outboard too.
The axle spacer between the brake plate and the swing arm is a different part number, and so far I do not know what is different about it.

 

[pickleknuckles]

I haven't gotten out to my shop (it's +30min away) so no kush drive on it yet.

Bearing face to bearing face thru the centers on my K7 wheel, is 111.3 mm, best I can measure. They're beat old sealed bearings and they're tight so one could be pushed in a hair. They're pretty sticky grimey too.

The hub, brake side bearing center to floor, is 120.5 mm. The bearing outer edge is fairly flush w the hub edge, but the floor at the drive side hub center might not be perfect.
Got 120.6 on another loose CB750 hub I have w no bearings. No clue what year it's from though.

The two brake plates I have here fit it perfectly and I know one of those was off my K4 and the other came w the other hub.

 

[grewth]

I haven't gotten out to my shop (it's +30min away) so no kush drive on it yet.

Bearing face to bearing face thru the centers on my K7 wheel, is 111.3 mm, best I can measure. They're beat old sealed bearings and they're tight so one could be pushed in a hair. They're pretty sticky grimey too.

The hub, brake side bearing center to floor, is 120.5 mm. The bearing outer edge is fairly flush w the hub edge, but the floor at the drive side hub center might not be perfect.
Got 120.6 on another loose CB750 hub I have w no bearings. No clue what year it's from though.
The two brake plates I have here fit it perfectly and I know one of those was off my K4 and the other came w the other hub.

Many thanks for making the effort !
Meanwhile I've been collecting more bits and pieces, and I now have a veritable smorgasbord of Honda CB750 parts to play with here.
I've got a nice K7 rear wheel c/w a rock hard old tyre (still holding air though)
I've got a rough K4 rear wheel with a 18" rim and tyre.
I've got the matching cycle parts from the K4, plus also a K6 swingarm to play with.
From first comparison of the K7 type hub, I'm thinking that it's actually a different casting to the earlier type.
It may not be an exact swap because it's machined differently in places, but I'm confident that with a little work it will fit.
I read somewhere ( possibly John Wyatt's book ) that the CB750A had an uprated ( stronger ) rear drum fitted, I'm thinking that the K7/K8 got the same item