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1978 Honda CB750K sprockets

This is a discussion on 1978 Honda CB750K sprockets within the Honda forums, part of the Manufacturers category; I just bought this '78 CB750K from my brother. He has brought this thing back to excellent condition and the ...


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Old 08-17-2008   #1
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Default 1978 Honda CB750K sprockets

I just bought this '78 CB750K from my brother. He has brought this thing back to excellent condition and the only complaint I have is that it runs at 4000 rpms at 60mph. I know the bike doesn't red-line until 8500 but I find it somewhat annoying to run a bike down the highway at that rpm level. I would like to change the rear or front sprocket and retain the original chain-size of 630. So far, I have found no sprckets available for the front that are larger than 15 tpi and that is the OEM size. For the back, I have only found
down to a 38 tpi. The bike came with a 41 tpi back sprocket. If I'm doing my math correctly, I will only gain about 7.5% rpm level with that sprocket or around 300rpm's. So instead of running at 4000 I will be running at 3700. I was hoping to get it down around 3200 to 3400 at 60mph. Does anyone out there have any experience with this model/year or know of any place to get more options for the 630 chain? I am VERY hesitant to go to a 530 chain because it is light weight and most-likely not as strong but maybe I shouldn't be worried about it. Any advice would be greatly appreciated. Thanks!
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Old 08-20-2008   #2
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Default 1978 Honda CB750K sprockets

Really, I wouldn't worry about that RPM. Those engines are designed for it. BTW my Ninja 500 is close to 5000 RPM at 60 mph and redlines at 11,000 RPM so it's no big deal to be cruising at what you are. You could go down a couple teeth on the rear but you'll loose acceleration. Also it lug the engine some at a cruising RPM which could make it run hot. I bought a 76 CB750K for parts that had 70k+ miles on it with the stock gearing. It did run good with no smoke or bad rattles (they all rattle some) and after a teardown of the engine the cylinders showed hardly any wear. I still have all the engine parts to use for my F model.

My 76 CB750F runs a 530 chain, they are plenty strong. Get a good chain and you won't have a problem. The 630 chain wasn't real popular.
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Old 08-26-2008   #3
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Default 1978 Honda CB750K sprockets

Thanks for the response! I just assumed that the speed limits being 55mph when the bike was built it might not be good for it to run it at 65 to 70 very long with the original gearing. You are the second person who told me they have run these bikes around 5000 rpm for an extended period of time with no problem. I'm probably being too cautious. Thanks again!
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Old 08-29-2008   #4
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Default 1978 Honda CB750K sprockets

Yeah they aren't like a car engine with a redline of 5000 rpm or anythin'. You have to look at other things too like how light the rotating internal engine componants are in a motorcycle compared to a car. One of the few motorcycle engines that aren't designed to rev high for long periods of time are Harley engines but again they make all their power down low in the RPM range or powerband.

Have fun with that CB750. I have one also currently in pieces but I've been inspired to uncover it and start back workin' on it. If you need any parts for it let me know. I got buckets of sites saved in favorites for the CB750's.
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Old 09-01-2008   #5
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Default 1978 Honda CB750K sprockets

Ok, I decided to buy the 38 tooth rear sprocket for a little help on the rpms even though I'm sure now that it would have been fine. I put the sprocket on as I suspected, my chain is too long. I thought I could make up the difference with the adjusters but it aint gonna work. My question now is, the original chain is a 630x88, it looks like my options are either a 630X86 or 630X84. I'm thinking if I reduced my sprocket by 3 teeth then I should be able to go down two "gaps" in the chain to a 86. Does this sound right?
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Old 09-06-2008   #6
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Default 1978 Honda CB750K sprockets

Yeah that sounds about right. If your chain is in fairly new condition you can get a chain breaker or have any bike shop press a link or 2 out of it.
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Old 09-08-2008   #7
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Default 1978 Honda CB750K sprockets

I put a smaller sprocket on the a rear as well. I wasn't worried about the RPM, I just got tired of the vibration when running the RPMs that high. Put the smaller sprocket on and it rode like a goldwing, well not really. It really is not worth it if you don't do much highway riding, you do lose some low end acceleration.
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Old 09-13-2008   #8
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Default 1978 Honda CB750K sprockets

On a similar note, I've found that acceleration on my CB350F is a much quicker if I shift at around 6000 RPMs as opposed to 4000. Given the way these engines are made, can they take getting up to 6 or even 7000 regularly?
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Old 09-13-2008   #9
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Default 1978 Honda CB750K sprockets

Oh yeah, as long as you stay below the redline you'll be fine. Now if you're going around all day at 9 grand somethings gonna give eventually. My Ninja 500 redlines at 11,000 rpms but I don't take it that high.
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Old 07-18-2011   #10
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I have used the #530 chain on my 121 HP Honda VF1000R V4.

Master link clip too.

No problem.
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