Topic: '77 Cb750 to '76Cb750 Swap Issues

[Radski]

Besides a few bracket and bolt fitment issues I'm tremendously stuck figuring out what to do about the rear setup. Particularly with the sprocket carrier, axle length, spacers, front sprocket, and swingarm.

History: I put a '77 engine in a '76 frame. the hub I'm using is off the '77 along with the sprocket carrier and brake plate. the swingarms between the years are different with the '77 being longer and wider in areas. Now.... IF I wanted to change from the 630 chain that the '77's came with, to a 530....firstly what do I need to do for the sprockets? The offset is really throwing me for a loop. I'd like to do the smartest setup if possible and along the cheaper end if I can. Do I:

- buy a '76 sprocket carrier then just deal with getting the appropriate sprockets? (which would be....?) therefore using the 76 axle and spacers which I believe I have.
- use the '77 sprocket carrier but then change the sprockets to ?? for the 530 conversion? (a problem here is in the 76 swingarm with the 77 sprocket carrier there is literally no room for two spacers unless I machine them down?)
- use Cb650 sprockets which I've been reading with what year carrier?
- install the '77 swingarm (which the axle bolt is not moving in the frame near at all..stuck) and then deal with converting sprockets which are??and will the added length of said swingarm make any real difference?

Any suggestions or information would assist in making this swap and build more a sucess. Can anyone instruct me what to do here? Surely someone has done this before right?

[HondaMan]

A few questions to help clarify some details:
1. Is the '77 750 the K7 or the F2 model?
2. Is the '76 750 the K6 or the F1 model?

[Radski]

A few questions to help clarify some details:
1. Is the '77 750 the K7 or the F2 model?
2. Is the '76 750 the K6 or the F1 model?

1. the '77 is the K7
2. the '76 is the K6

not to get confused but as far as I understand..the '77 engine is the same as the '76 F engine?

[HondaMan]

not to get confused but as far as I understand..the '77 engine is the same as the '76 F engine?

Almost, but not quite. The final drive shaft is different, the clutch cover is different, the head casting is different (but can be made compatible), the sprocket cover on the engine is slightly different (to clear the offset sprocket) and usually lacks the rubber cushion on the rear support, the cam chain slipper tensioner is shorter (in most of the K7), and the bushings in the tranny gears in the K7 are cast iron, while some of the F1 bearings were bronze, ending the series with cast iron somewhere along the way.

Your main situation involves that final-drive shaft: the K7 usually (but not always!) has the big flat washer that bolts into the end of this shaft to hold the sprocket. This was a 630-chain-size sprocket. This sprocket was offset to the left side of the bike by setting it atop the modified shaft so the wider chain would not hit the inside of the chain guard enroute to the rear wheel. The chainguard was made slightly more squared-off on the top channel to help with this clearance, too. Then the rear (wheel) sprocket carrier was made to ride outboard by the same change, so everything would line up.

When you switch to 530 chain instead, a whole lot of things fall in your favor.
First: the 530 chain is made with more sideplate clearance (unless you return to an O-ring chain, which I do not recommend), which allows it to snake sideways without heating or large power losses. (BTW: this is not true of #50 chain, which does not have this sideways clearance).
Second: the 530 sprockets are narrower, easing the clearance problems all over this situation. You can get offset sprockets in 530 size if you stay with the K7 rear hub and just install a 530 sprocket back there, but this countersprocket can not be flipped over at 5000 mile intervals to increase its life, so it will live less long than the floating type would. Flipping the rear sprocket at these intervals will help somewhat.
Third: the modern 530 chain will carry 20% more power than the OEM 630 chain once did, even more if you use non-O-ring type. I can suggest using the Diamond Powersport (or if you can find one, the old XD or XDL type, on eBay) as being the most-forgiving of all the chains I have used.

Things to watch for: if you have the final-drive shaft that lets the sprocket slide all the way onto it, and is secured in a 'floating' manner, most of your grief (as described above) is missing. If you have the one that mounts the sprocket solidly on the very end of the shaft, using the large washer and a bolt, then all the above applies.

[Radski]

not to get confused but as far as I understand..the '77 engine is the same as the '76 F engine?

Almost, but not quite. The final drive shaft is different, the clutch cover is different, the head casting is different (but can be made compatible), the sprocket cover on the engine is slightly different (to clear the offset sprocket) and usually lacks the rubber cushion on the rear support, the cam chain slipper tensioner is shorter (in most of the K7), and the bushings in the tranny gears in the K7 are cast iron, while some of the F1 bearings were bronze, ending the series with cast iron somewhere along the way.

Your main situation involves that final-drive shaft: the K7 usually (but not always!) has the big flat washer that bolts into the end of this shaft to hold the sprocket. This was a 630-chain-size sprocket. This sprocket was offset to the left side of the bike by setting it atop the modified shaft so the wider chain would not hit the inside of the chain guard enroute to the rear wheel. The chainguard was made slightly more squared-off on the top channel to help with this clearance, too. Then the rear (wheel) sprocket carrier was made to ride outboard by the same change, so everything would line up.

When you switch to 530 chain instead, a whole lot of things fall in your favor.
First: the 530 chain is made with more sideplate clearance (unless you return to an O-ring chain, which I do not recommend), which allows it to snake sideways without heating or large power losses. (BTW: this is not true of #50 chain, which does not have this sideways clearance).
Second: the 530 sprockets are narrower, easing the clearance problems all over this situation. You can get offset sprockets in 530 size if you stay with the K7 rear hub and just install a 530 sprocket back there, but this countersprocket can not be flipped over at 5000 mile intervals to increase its life, so it will live less long than the floating type would. Flipping the rear sprocket at these intervals will help somewhat.
Third: the modern 530 chain will carry 20% more power than the OEM 630 chain once did, even more if you use non-O-ring type. I can suggest using the Diamond Powersport (or if you can find one, the old XD or XDL type, on eBay) as being the most-forgiving of all the chains I have used.

Things to watch for: if you have the final-drive shaft that lets the sprocket slide all the way onto it, and is secured in a 'floating' manner, most of your grief (as described above) is missing. If you have the one that mounts the sprocket solidly on the very end of the shaft, using the large washer and a bolt, then all the above applies.

I cant thank you enough for your wealth of knowledge. That definitely is the type of information I need.

Is this all using the '76 swingarm as well? (with the axle and correct spacers) Or should I try to get the '77 swingarm out of that frame and use it instead?

[Radski]

and how many teeth should I be looking at for a mid to high ratio for around town use but also cruising speed on a highway? I think stock on the '77 was 15 front and 43 rear(?). I spoke to someone at Sprocket Specialists and they gave their recommendations of maybe a rear that was up near 48.

[mAd mOrdigan]

The spacing of the 630 from tooth to tooth is wider than the 530 so the stock gearing of 15/41 I believe on the K7/K8 would translate to something like 17/48 on the 530 chain. Of course you can gear up or down a tad depending on if you want more top end or more acceleration and still be pretty close. Some are using 18/48 and I think you can even use 17/46.

[754]

 Use the 77 arm, move your shock out, is the very easiest.
 Run either size chain.
 If you don't do that I can run you thru it but it's work..

[HondaMan]

For gearing: the '77 engine has a lower primary drive ratio than the '76 K6 type does. Honda used the [rough] equivalent of the K1 gearing in the late engines to boost performance a bit. This gearing was lower than in the K2-K6 engines and bikes.

Here's the numbers:
The K1 (and warranteed K0 retrofits) used 17/48 sprockets with the 530 chain.
The "touring" gearing came along in the K2, with 18/48 sprockets on the 530 chain.

Here's the 'catch': the K7 engine's cam starts its powerband at about 5000 RPM, while the earlier engines come on about 4200 RPM with about the same torque. This is due to the cam timing, intake side. So, you may want slightly lower gearing to bring the power on slightly sooner: this was how the 15/43 sprockets came about for the 630 chains. If you use the 17/48 combination in your situation, the engine will feel more responsive, more of the time, especially when commuting in the below-interstate speed ranges.

I am the 'odd bird' of the 750 touring riders: I run 19/48 on my K2 when I go 1-up touring (80+ MPH out here in the West), and mostly 18/48 for commuting (never gets above 3rd gear then, though). I sacrifice a bit of torque in top gear below 65 MPH and have to use 4th then, but at 90+ MPH it sings a sweet song.

[Radski]

Thanks Hondaman. I havent purchased the sprockets yet or chain for that matter but I plan to as I'm getting close to that time.

I have swapped everything that I could over to the '76 frame. I've redone some connectors (plan to do the rest when I have the harness off the bike when powdercoating) and upgraded my fuse block. Went to ATC's and ended up mounting on the engine side of the battery box. Seems to fit well and its out of the way and near invisible, but able to get to if needed.

One issue that worries me is this. After much debate and opinions, I put the '77 swingarm on and for some reason it rubs the left side rear passenger peg mount triangle. Right side has at least 3/8 gap. Why is this? Is my frame slightly bent? Is it dimensions of the swingarm? I have no idea how to 'get the centerline' and use geometry to take measurements. Should I just heat up the triangle and bent is out slightly? Any help here would be great.

I'm mocking it up right now to see what tabs I want to keep and what I need relocated etc. Then the tear apart will happen to clean up the motor which I'm doing myself (exterior) so any suggestions here would be great too. Powdercoat some parts pieces and frame. I had some surface rust inside the tank but after a soak of Metal Rescue for 24 hours, the stuff worked like a charm! going to soak some parts bolts etc to clean them up too.

Thanks to everyone for your knowledge. You all are helping in this swap and build.

#odzilla

[Radski]

not to get confused but as far as I understand..the '77 engine is the same as the '76 F engine?

Almost, but not quite. The final drive shaft is different, the clutch cover is different, the head casting is different (but can be made compatible), the sprocket cover on the engine is slightly different (to clear the offset sprocket) and usually lacks the rubber cushion on the rear support, the cam chain slipper tensioner is shorter (in most of the K7), and the bushings in the tranny gears in the K7 are cast iron, while some of the F1 bearings were bronze, ending the series with cast iron somewhere along the way.

Your main situation involves that final-drive shaft: the K7 usually (but not always!) has the big flat washer that bolts into the end of this shaft to hold the sprocket. This was a 630-chain-size sprocket. This sprocket was offset to the left side of the bike by setting it atop the modified shaft so the wider chain would not hit the inside of the chain guard enroute to the rear wheel. The chainguard was made slightly more squared-off on the top channel to help with this clearance, too. Then the rear (wheel) sprocket carrier was made to ride outboard by the same change, so everything would line up.

When you switch to 530 chain instead, a whole lot of things fall in your favor.
First: the 530 chain is made with more sideplate clearance (unless you return to an O-ring chain, which I do not recommend), which allows it to snake sideways without heating or large power losses. (BTW: this is not true of #50 chain, which does not have this sideways clearance).
Second: the 530 sprockets are narrower, easing the clearance problems all over this situation. You can get offset sprockets in 530 size if you stay with the K7 rear hub and just install a 530 sprocket back there, but this countersprocket can not be flipped over at 5000 mile intervals to increase its life, so it will live less long than the floating type would. Flipping the rear sprocket at these intervals will help somewhat.
Third: the modern 530 chain will carry 20% more power than the OEM 630 chain once did, even more if you use non-O-ring type. I can suggest using the Diamond Powersport (or if you can find one, the old XD or XDL type, on eBay) as being the most-forgiving of all the chains I have used.

Things to watch for: if you have the final-drive shaft that lets the sprocket slide all the way onto it, and is secured in a 'floating' manner, most of your grief (as described above) is missing. If you have the one that mounts the sprocket solidly on the very end of the shaft, using the large washer and a bolt, then all the above applies.

Would I still then need to get an offset front sprocket? Am look at the JT338.17 for the front. Know is this will work? and the JT284.48 for the rear.

Also the way the drive looks, the sprocket fits on the arm but only so far. Then there is a washer that holds that on and the bolt to hold it all on together. Would this be the floating you speak of?

[Radski]

I've ordered a Bates Style front light and its working sweet. Havent done the turn signals yet as supposedly I need a diode or two in there to help with the directional flow. Got some mini deco turn signals as well but need to get brackets for them.

My problem right now is that the 2 1/4" tail light came with three wires... red, black and yellow. According to Dime City Cycles, the yellow = ground, red = brake light, black = running light.

When I turn the key ignition on, the light lights up but the brake lever is not giving it an order. I tried two different rear brake switches and neither worked. It is possible however that both switches are old. Additionally, I am not running a front brake switch as its not wired up. Hope that doesnt affect it.

Anyone have any suggestions to troubleshoot this rear brake switch problem?

The bike is coming along! Cant wait to post all the build pics in a Project Forum.

[Dolomite]

Check your grounds. There is a secondary ground in the wiring harness located near the ignition coils.

[Radski]

Check your grounds. There is a secondary ground in the wiring harness located near the ignition coils.

you mean the green wire thats actually attached to the frame at the coils? that one is firmly and cleanly attached. otherwise at the mess that was in the old headlight there are a number of green (I'm assuming ground wires) connectors. Double bullets and triples. But theres a couple that are empty but I still havent hooked up the turn signals which I assume thats where their ground wires will go.

[Dolomite]

Yes greens in the headlight are ground connectors. The other main ground is where the negative terminal hooks into the frame. If you've painted the frame at all make sure that ring terminal is clean and mates to a clean surface. I knew I had a ground issue when I did mine because when you hit the horn button, the tail lights came on

[Dolomite]

So also I had to do this same swap, but reversed. I have a 78 frame where the motor committed seppuku and ended up putting a 76 750k motor in it. The rear sprocket was changed to a 46T 530 feom JT, same offset and the front was replaced with a 530 offset from cyclex. I did however use my PD carbs. Those changes to the sprockets though were the only ones necessary for the swap. I do not know if this helps you at all, as the final drive shaft is the limiting factor and I don't believe they are interchangeable due to different oil seals. Perhaps the offset sprocket from cyclex can be put on backwards creating a negative offset?

[Radski]

So also I had to do this same swap, but reversed. I have a 78 frame where the motor committed seppuku and ended up putting a 76 750k motor in it. The rear sprocket was changed to a 46T 530 feom JT, same offset and the front was replaced with a 530 offset from cyclex. I did however use my PD carbs. Those changes to the sprockets though were the only ones necessary for the swap. I do not know if this helps you at all, as the final drive shaft is the limiting factor and I don't believe they are interchangeable due to different oil seals. Perhaps the offset sprocket from cyclex can be put on backwards creating a negative offset?

Yes i've had very similar responses about the sprocket changes from many people so I went with a 17T front and a 48T rear, both 530 and I wanted to reduce weight and seems like its easier to find more 530 parts. I havent put them on yet as I'm waiting for the chain now. FIngers crossed the advice I've been given works out!