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Discussion Starter · #1 ·
I have an 85 Nighthawk 450 converted to a bobber with straight pipes. I'm trying to gear the rpms down as anything over 6,000 rpm is pretty painful....it goes from harley thumping to sport bike drone. Right now it seems to do 6k-7k around 60 mph if my speedo is correct. The bike has plenty of low end power for me, and the with the close gear ratios it seems like a like taller gearing would help.

I've already gone up to a 18 tooth front sprocket. The rear wheel is off a 450E and is a 34 tooth. I haven't seen a front sprocket bigger than 18, or a rear smaller than 34.....does anyone know a substitute that will fit?
 

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I think you've got the wrong approach. Your problem is noise levels not gearing. Add some HD Sportster mufflers and your problem will be solved.
Running an 18/34 sprocket set with a 130/90/16 rear tire at @60mph means the engine is running @4000 rpm in 6th gear. That's below the power band for this engine getting close to the lugging area which is destructive.
Use www.gearingcommander.com to sort out your ratios https://www.gearingcommander.com/
Now to address another issue you've brought up. You have the CB450SC engine/transmission ass'y running a CM450E wheel. That means the chain is out of alignment by 4.2mm's causing excessive wear and drag. You need to space the front sprocket inboard at least 4mm's to correct this. A 1" USS, not SAE, flat washer inserted between the sprocket and retainer will do this. Need to drill 2 holes in it for the retainer bolts and use 5mm longer bolts.
 

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Discussion Starter · #3 ·
22050353_10106185509845714_7642724549257842696_n.jpg

No real good place for mufflers....i thought eventually about having a custom set of pipes made to run down the rear frame rails....but for now will leave as is.

Long we've spoken about the chain alignment....you were kind enough to provide me a source for the washer even. I just need to finish mock up to see if how far out of alignment it really is, as the rear end has been converted to a rigid. Not sure the wheel spacing is the same.
 

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I knew your user name sounded familiar, lol, hard to keep track of all the bikes/names/questions and answers.
The rear spacing should be exactly the same as with a swing arm, otherwise the bike will be dog tracking and become unstable in turns. The front and rear wheel have to be on the centerline of the frame, it is critical.
 

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Discussion Starter · #5 ·
Thank you from all of us for your continued input and advice....it's invaluable to us newbies!
 

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Discussion Starter · #6 ·
I rode past a police radar speed sign today. The sign and the speedo both said 25 mph...so it's close.

At 60 mph, my tach says im turning 7,000 rpm. It is a 7:1 ratio mini tach.
 

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Somethings not right there. 18/34 sprocket set should have you down in rpm from stock not up. Possibly a bad tach?
 

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Discussion Starter · #8 ·
Possibly, however it does not bounce/hunt and moves smoothly. I think 7:1 is the right ratio....however at low idle it is showing 2,000 rpms.
 
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