Topic: New from NJ USA

[86FJNJ]

Combining two CB750 parts bikes into one bike, essentially 78F chassis with 76F engine. Seems like a very helpful forum so far!

[denward17]

Welcome from NC!

[HondaMan]

Welcome to the fun - from Colorado!

[Gary in NJ]

What part of NJ? I’m in Warren county and I’m restoring a ‘76 550F.

[86FJNJ]

I’m by Ringoes a bit south from you, hope to have it running by may but if not the Yamaha is up and running

[newday777]

Welcome aboard from southern NH.
I have a 78F I'm slowly restoring

[MD]

Welcome from -17 F, Minnesota,

-MD

[scottly]

Combining two CB750 parts bikes into one bike, essentially 78F chassis with 76F engine. Seems like a very helpful forum so far!

Be aware that the 76 engine's sprocket mounts about 10mm further in than the 78, causing a chain alignment issue. One way to solve this is with an offset sprocket.

[newday777]

Combining two CB750 parts bikes into one bike, essentially 78F chassis with 76F engine. Seems like a very helpful forum so far!

Be aware that the 76 engine's sprocket mounts about 10mm further in than the 78, causing a chain alignment issue. One way to solve this is with an offset sprocket.

Good catch

[86FJNJ]

Combining two CB750 parts bikes into one bike, essentially 78F chassis with 76F engine. Seems like a very helpful forum so far!

Be aware that the 76 engine's sprocket mounts about 10mm further in than the 78, causing a chain alignment issue. One way to solve this is with an offset sprocket.

Thank you! I had heard about this but am not at the point yet to get to sprockets, although I did order a 530 chain sprocket which was supposed to be for my 78 wheel but the sprocket is not as thick as the 630 sprocket that was on there and the threads to the bolts that hold the sprocket on stop slightly before the bolt would meet the sprocket, so I'm wondering if I got the wrong sprocket or if I need to add some spacers...would appreciate if anyone knows otherwise I'll deal with the sprockets in a few months when I get to that point

[newday777]

Combining two CB750 parts bikes into one bike, essentially 78F chassis with 76F engine. Seems like a very helpful forum so far!

Be aware that the 76 engine's sprocket mounts about 10mm further in than the 78, causing a chain alignment issue. One way to solve this is with an offset sprocket.

Thank you! I had heard about this but am not at the point yet to get to sprockets, although I did order a 530 chain sprocket which was supposed to be for my 78 wheel but the sprocket is not as thick as the 630 sprocket that was on there and the threads to the bolts that hold the sprocket on stop slightly before the bolt would meet the sprocket, so I'm wondering if I got the wrong sprocket or if I need to add some spacers...would appreciate if anyone knows otherwise I'll deal with the sprockets in a few months when I get to that point

Which 530 sprocket did you order, front or rear?

[86FJNJ]

Combining two CB750 parts bikes into one bike, essentially 78F chassis with 76F engine. Seems like a very helpful forum so far!

Be aware that the 76 engine's sprocket mounts about 10mm further in than the 78, causing a chain alignment issue. One way to solve this is with an offset sprocket.

Thank you! I had heard about this but am not at the point yet to get to sprockets, although I did order a 530 chain sprocket which was supposed to be for my 78 wheel but the sprocket is not as thick as the 630 sprocket that was on there and the threads to the bolts that hold the sprocket on stop slightly before the bolt would meet the sprocket, so I'm wondering if I got the wrong sprocket or if I need to add some spacers...would appreciate if anyone knows otherwise I'll deal with the sprockets in a few months when I get to that point

Which 530 sprocket did you order, front or rear?

I ordered the rear sprocket, I had heard the front needed to be offset 10mm so I was going to wait until I had the engine back in etc before ordering that.

[86FJNJ]

This is the sprocket I had ordered a while back, although the pattern on mine is not circles it's probably just a generic photo, but the part number is the same except I went with a 40 tooth.

Basically once i put the sprocket on the bolts that hold the sprocket on run out of thread before they squeeze the sprocket. This 530 sprocket is thinner than the stock 630 sprocket. So that's why I'm wondering if when doing a 530 chain conversion on a 78 CB750 do I need to add spacers between nuts and sprocket or between sprocket and hub assembly.

https://www.denniskirk.com/jt-sprockets/sprocket.p81060.prd/8106040S.sku

[scottly]

Both 530 and 630 chain are the same tooth width, 3/8", but the pitch, the space between the pins, is different: 5xx is 5/8", while 6xx is 6/8". The stock sprockets for your bike were 15 front and I believe 42 rear, for a ratio of 2.8:1. When converting to 530 chain, a 17 front with a 48 rear will give a ratio of 2.823:1.
Do you have the '76 rear wheel? The sprocket carrier mounts the rear sprocket in closer, but I don't know if it will fit into the '78 Comstar hub.

[86FJNJ]

Both 530 and 630 chain are the same tooth width, 3/8", but the pitch, the space between the pins, is different: 5xx is 5/8", while 6xx is 6/8". The stock sprockets for your bike were 15 front and I believe 42 rear, for a ratio of 2.8:1. When converting to 530 chain, a 17 front with a 48 rear will give a ratio of 2.823:1.
Do you have the '76 rear wheel? The sprocket carrier mounts the rear sprocket in closer, but I don't know if it will fit into the '78 Comstar hub.

Ha! I hadn't thought of that but I just checked and the 76 hub is shorter than the 78 and it does fit inside the 78 so it looks like I could use either 76 or 78 hub, I would just have to make sure the 76 or 78 spacer still work if I use the 76 hub on the 78 wheel. Although I also still have the 76 swingarm. I already replaced the wheel bearings in the 78 wheel and hub so I'd prefer to use that because  if I use the 76 I need to buy a new wheel bearing, but nice to have some options. but still prob easier to just buy a 10mm offset front sprocket if that's all I need.

[scottly]

If the '76 sprocket carrier fits the '78 comstar hub, that's the way to go. The '78 swingarm is wider on the chain side, so the '78 spacer should work; it's easy enough to check. This will allow you to use standard '76 sprockets instead of more expensive offset sprockets. Fitting the '76 swingarm to the '78 frame presents another issue, since the shock is also offset on that side.