1978 CB750K /1987 CBR600 Swing arm swap

troubletocome

troubletocome

New Member
Anyone have any experience or insight with this swap?

I have a CBR frame (sitting in the background) I am going to cut the mono shock brackets off of to use on the CB750 frame.

Any photos of the shock/ swingarm angle would be awesome.
2020-09-27 12.17.43.jpg
 
That's a really long bike. For swingarm droop start at 8 -10 degrees and see where that puts the top shock mount and work from there. Modern forks have less offset to create the right amount of trail with steeper rake than our old bikes, so that gives you some room to play with.
 
You have what you need right on the table...the Cbr frame. You need to copy the CBR geometry as close as you can. That may mean mocking up the CBR frame with swingarm and shock and then making a jig or sturdy template from it. It also may help to sit it so the steering head is at the correct rake for the frame and measure swingarm droop etc, that way.

Later, Doug
 
Also check your sprocket alignment between the 78 engine and the new rear wheel. The 77-78 750 engine is 10mm wider at the drive sprocket than earlier 750s. Honda changed the 77-78 swingarm and sprocket carrier on the wheel to compensate.
 
Rider52 said:
Also check your sprocket alignment between the 78 engine and the new rear wheel. The 77-78 750 engine is 10mm wider at the drive sprocket than earlier 750s. Honda changed the 77-78 swingarm and sprocket carrier on the wheel to compensate.
Click to expand...
Sort of but not quite. They modified the countershaft and ran a wider 630 chain on the 77-78, so they offset the sprocket and widened the cover to keep the chain from hitting. Converting to 530 chain and an offset counter sprocket allows you to run the early year stuff on the 77-78.
 
irk miller said:
Sort of but not quite. They modified the countershaft and ran a wider 630 chain on the 77-78, so they offset the sprocket and widened the cover to keep the chain from hitting. Converting to 530 chain and an offset counter sprocket allows you to run the early year stuff on the 77-78.
Click to expand...
Yes!
 
teazer said:
That's a really long bike. For swingarm droop start at 8 -10 degrees and see where that puts the top shock mount and work from there. Modern forks have less offset to create the right amount of trail with steeper rake than our old bikes, so that gives you some room to play with.
Click to expand...
Thank you!
 
Streetfighterkz said:
You have what you need right on the table...the Cbr frame. You need to copy the CBR geometry as close as you can. That may mean mocking up the CBR frame with swingarm and shock and then making a jig or sturdy template from it. It also may help to sit it so the steering head is at the correct rake for the frame and measure swingarm droop etc, that way.

Later, Doug
Click to expand...

Thanks Doug! I have a 86CBR i ride that I am comparing for angles. The shock is cantilevered so I am having some head scratching on the mounting angle of that.
 
irk miller said:
Sort of but not quite. They modified the countershaft and ran a wider 630 chain on the 77-78, so they offset the sprocket and widened the cover to keep the chain from hitting. Converting to 530 chain and an offset counter sprocket allows you to run the early year stuff on the 77-78.
Click to expand...
Super awesome and helpful! Thank you!
 
Rider52 said:
Also check your sprocket alignment between the 78 engine and the new rear wheel. The 77-78 750 engine is 10mm wider at the drive sprocket than earlier 750s. Honda changed the 77-78 swingarm and sprocket carrier on the wheel to compensate.
Click to expand...
Yes. Good to know! Thank you! I think I need to mount my engine before I finalize anything in this swap.
 
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