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I recently bought a 1982 CB750K and would like to know what RPM levels
other owners of this bike are seeing at 100 KPH and 120 KPH.
That equals roughly 60 MPH and 77 MPH.
This bike originally came with a 530 chain and 18/46 tooth sprockets.
Mine has a 630 chain with 18/46 tooth sprockets.
At 100 KPH I am seeing 5100 RPM and at 120 KPH seeing 6200 RPM.
This cant be right????
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That sprocket setting is way out. Original Sprockets are 15/44. Many years ago when my chain and sprockets needed changing, I went to a 15/40 rear sprocket and what a big difference, now at 100 KMH and 120 KMH its shows between 3000 -3700 rpm at those speeds. 140 KMH plus and its doing about 4200 rpm. Definately change the rear sprocket to a 42 or 40 and keep the front at 15. Any smaller and you wear out the front sprocket in no time at all. Too big a front spocket and you wont get the cover back on. I know as I have tried that experiement!!!!! Hope that helps, but DO change the rear sprocket as soon as possible
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I checked with the Honda dealer and he says that 18/46 530 pitch is right for a 1982 CB750K.
The final ratio 2.56 matches the final ratio listed in the owner's manual.
I still cannot believe that Honda would gear this bike is such an odd manner.
As stated the current sprockets and chain are 630 instead of the standard 530.
It is my understanding a 630 chain with say 100 links is the same length as a
530 chain with 100 links? The pitch refers to the width of the link does it not?
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Sorry but the Honda dealer is dead wrong !!! You would not even get 220 KMH out of it with those teeth on it. At 220 KMH the motor would be revving way off the red line. My book has written in it 15/44 and as I said in my pervious post I chnaged the rear sprocket and fornt plaus a new chain fto a 15/40/ Now I cruise comfortably all day at 120 KMH with the RPM only showing 3400 on the clock. 3000 at 1000KMH and about another 100 RPM at 110 KMH. HOnda road tests of this CB750KZ model reported 222 KMH at 9500 with the 15/44 set up. With the current setup I get over 50 MILES PER GALLON or 6 litres/per 100 Km. Keep to your existing setup if you want to have early termination of the engine. The pitch refers to the width is correct, so you can use the same chain minus a few links with a 15/40 set up or if you want a 15/42 set up is also available- same chain
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This post was updated on .
Not trying to start an issue since you are trying to help me and I am thankful for that:
Any pictures of the CB750KZ show that it came with ComStar wheels and double disc brakes on the front.
Mine is the CB750K with spoked wheels and a single disc up front. I have read that these were
different models and that would explain the different final drive ratios.
The 15/40 combination gives a final drive ratio of 2.67 which is different from the 18/46 ratio of 2.56. The 15/40 ratio would make the engine rev even higher than it is now.
The CB750KZ must have different internal trasmission ratios.
Regardless, I do need to reduce the rear sprocket count.
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It also looks like the CB750KZ had a 4 into 2 exchaust system while the CB750K had a 4 into 4 system.
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The 15/40 would make the engine rev LOWER than the current set up you have. The higher the rear sprocket the higher the engine revs the lower the rear sprocket the lower the engine revs as you are getting closer and closer to a 1 to 1 ratio which in essence would never even get the bike going. Mine has the Comstar wheels with a single front disc and rear drum on the rear. I do have a picture of my bike with the comstar wheels, but its on a disc and when I find it i`ll up load it for you. The gearboxes on all the 79 -83 CB750K and F series are exactly the same the world over . Its just the drive train thats different. I see that you have an 18 tooth front sprocket. If you dropped the rear sprocket to 42 teeth that will cut down the high RPM you are experiencing. The more teeth on the rear sprocket the higher the engine RPM . You only have to look at trail bikes - they have a massive rear sprocket, which gives them higher RPM but lower gearing for hill climbing
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The CB750K and KZ are one and the same bike !! The F model had the four into two exhaust. The Z was used on all southern hemisphere bikes to denote that it was the end of that series. Here is my Honda CB750KZ taken in Australia when brand new in 1982. This had a 15/44 sprocket set up and I eventually changed it to a 15/40 set up to lower the RPM at cruising speeds in the 100 -120 KMH area. Gives me over 50 Miles Per Gallon instead of the 42 I used to get.
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I am now totally confused since two of my local Honda dealers state the 18/46 and several online supply houses. The 18/46 ratio has the revs way too high for my liking so they are being replaced. The sprockets and chain should have a 530 pitch but they are 630 for some reason.
Thanks for all your help and if anyone has anything else to add please feel free to do so.
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I`m sorry to tell you that the people who have given you this information is WRONG I cant spell it any louder.ITS WRONG !!!! You cant run an 18/46 sprocket set up. The engine revs way too high and will eventually self destruct. I have had my CB750K since new and when I bought it , it had a 15/44 sprocket set up . That wasnt bad, and was good for quick acceloration and riding two up. But with your set up , what are you planning on doing - climbing Mt Everest ??????? Ideally a 15/42 or 15/40 is the way to go which is what I have been running for god knows how long, and never had a problem. I have been on this forum since it started way back in June/ July of last year, and no one has ever had the problems you are describing . In fact just about everyone over the past 10 months has said they run 15/44 or 18/42, 18/40 I dropped to a 15/40 for better fuel consumption and still use the 630 link chain - just had to remove three or four links to get it to fit properly and to leave room for adjustment
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I think I metioned that the CB750K and KZ are one and the same bike. The Z was used in the Southern Hemisphere to denote that this was the last of the CB 750 series. They both have the four into four exhaust system. Its the F model that had the four into two.
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Go look at my post of the 25th April at 1.34 pm and you will see the photo of my CB750KZ when it was half a day old . Its has the four into four system on it and is the same as the the CB750K There is absolutely NO difference in the KZ or K model. Its one and the same bike
 I have added the photo of my bike again in case you didnt see it in the other post
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I own a CB750FZ, 1982, Australian delivery.It has 18/46 sprockets, and while I was suprised at the gearing, I believe it is correct. This is confirmed in the specifications and article at www.motorcyclespecs.co.za, which also gives the reason for changing from a 630 chain to a 530.
1982 CB750F
1978 Triumph Tiger 750
197? Yamaha DT175
197? Hodaka ACE 100
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Well I dont know who suppplied your bike but mine was bought here in Perth frmo the Honda dealer - whi doesnt exist anymore, and it was fitted with a 15/44 sprocket set up. Also the website you give is a South African website and when I went to live in South Africa for 14 years, I took my Honda over to South Africa with me. There they were running 15/44 sprockets in South Africa and it was there that the genuine Honda O ring chain and sprockets had to be replaced under warranty, as they were knackered beyond belief. It was suggested to me that instead of going to the same set up, go to a 15/40 gearing and that dropped my RPM by over 1000RPM at the South African speed limit of 120 KMH. At that speed my motor was turning over at just over 3500 RPM. With the gearing you folks keep on harping on with an 18/46 or 48, no wonder the motor revs so high. ITS WRONG. Christ knows I have had an umber of Hondas in my life tme and two CB750KZ and an F model which had a 15/46 sprocket set up. I`m still riding my Honda with the 15/40 set up fitted in South Africa when I returned to Australia about nine years ago. All Honda`s in South Africa had a 15/44 sprocket set up and perhaps someone can tell me why my Australian Honda had the same gearing as the South African models when it was bought in Perth in 1982. Answer that one if you can. My handbook states 15/44 and so did my workshop manual , which went missing during the return trip to Perth
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Boys, this is getting a little out of hand considering the topic. There are many possibilities for the differences and to be truthful who cares.
This thread has helped me in understanding the issue so there has been value added. I checked the owner's manual and it lists the final drive ratio as 2.56 which matches the 18/46 tooth count. It could also match other tooth counts (i.e. 16/41 or 14/36).
Here is a great site that lists many ratios:
http://shop.wemoto.com/info.dyn?title=Sprocket_Gear_Ratios
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The Haynes manual for the CB750 DOHC 1978-1984 gives a final drive ratio of 2.533, equivelent to 18/46 sprockets. It aso lists US CB750C,SC with a ratio of 2.388. The genuine Honda factory manual for the CB750K shows 15/38 sprockets, which give the same 2.533 ratio. If anyone doesn't like their present gearing just change it!
1982 CB750F
1978 Triumph Tiger 750
197? Yamaha DT175
197? Hodaka ACE 100
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Heres another spanner to throw in the works. Check to see which model you have . There are nine variants. Here is the list: DK, DM, U, SA, CM, E, G, F, & ED. The DK, DM U CM & SA models are General, Australian, and South African. The E, G, F, ED are European Models only, and this maybe causing the confusion, I have just found my workshop manual for the Australian Model CB750KZ and it lists the final drive ratio as 2.533 (15/38) and the ED model has a final drive ratio of 2.40 ( 15/36). If I can scan the page that lists the final drive ratio, I will upload the page for all to see. America must have used a totally different set up to the Southern Hemispere bikes, and I`m running a 15/40 as against the original 15/44. So either way a 15/38 or 18/46 gives you the same final drive ratio. Just drop your rear sprocket by four teeth and remember to shorten the chain, otherwise you will have too much slack
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What RPM levels are you seeing at 100 KPH and 120 KPH with the 15/40 combination?
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At 100 KMH its doing just under 3000 rpm, - about 2900 and at 120 its sitting at 3400. 5th gear is now like and overdive, so when you want to overtake in hurry, I drop down to fourth or even third gear - depending on circumstances. 3rd gear now gets me to 150 KMH very quickly and fourth gear will take me past 190 KMH
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This post was updated on .
i have a 630 chain for strenth, came with a 520 setup. these motor produce alot of low end torque which stretches the shit out of chains lol yes i lost a tad bit of rear wheel HP but knowing my chain is not going to fail is priceless
i dont remeber the teeth count on the sprokets. but 50-60 mph is right around 5,000 - 5,500 rpms.
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