Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: bobv7 on July 18, 2020, 03:41:44 PM
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Afternoon All
Can anyone tell me what rpm I should be reading at 60mph in top?
Cheers
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CB500? 5000 rpm.
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The reason I ask is because I bought an after market matching speedo and tacho. The speedo looks like it's reading pretty close as they usually work off front wheel diameter anyway but I'm not so sure about the rev counter, but since I'm not going be red lining the bike every where it's not so important. There is a marking on the rev counter dial reading 1:4 so maybe it was intended to fit a twin and actually showing half the true rpm?
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My 550 is 4000 at 60mph.
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CB550s vary, some have 17 and 37, some have 17 and 34 teeth.
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Just had a look at mine it looks like 36 rear. So the least teeth on the rear the faster for same engine rpm?
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4000 rpm at 60 mph is about the same gearing overall as a cb750, isn't that a bit tall for a 550? 120mph at 8000rpm?
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I haven’t had the speedo or tachometer calibrated or refurbished other than new faces and painted, so cannot confirm accuracy. It maybe slightly above 4000 at 60mph. I will check tomorrow if the weather is kind.
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I put the various numbers on an excel spreadsheet.
Gearing between the crank and the primary shaft is the same on 500/550.
Gearing between primary shaft and clutch basket is different. Overall primary gearing 500/3.247, 550/3.063.
1-5 gear ratios are the same.
Standard front/rear sprockets are 500 17/34, 500 17/37. Delta says some 550s may be different, but I have no knowledge.
Rear tyre standard, 500 is 3.50, 550 is 3.75. Changing from standard sizes will alter gearing to rear and accuracy of speedo on front.
All in all the overall ratio on 500 to 550 is just about identical.
Should be 4000rpm = 51MPH. 6000rpm = 76MPH.
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Delta says some 550s may be different, but I have no knowledge.
The CB550K3-ED, say for continental Europe, had 17 and 34, like all CB500 models had. It was to market this particular model more as a tourer bike, to differentiate to the somewhat sportier CB550F2. In the rest of the world all CB550s had standard 17 and 37.
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The reason I ask is because I bought an after market matching speedo and tacho. The speedo looks like it's reading pretty close as they usually work off front wheel diameter anyway but I'm not so sure about the rev counter, but since I'm not going be red lining the bike every where it's not so important. There is a marking on the rev counter dial reading 1:4 so maybe it was intended to fit a twin and actually showing half the true rpm?
I fitted a pair of aftermarket matching rev counter/speedo to my 750 K2 just after I rebuilt it (while I was refurbing the original clocks) and the the rev counter read about a 1000 rpm high at 60mph
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Anything like these?
[attach=1]
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No, they where CB750K replica's (almost identical to the original's to the non expert)
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That is interesting on the proper gearing numbers. I didn’t get out on the bike yesterday not weather in the morning so decided to fit new fork seal that seemed to be leaking. (Can’t believe somebody put the one seal upside down) ooops!🤭🤫! I am now starting to doubt myself with mph/rpm, wouldn’t be the very first time I have been wrong.😂
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Riding the bike this morning and the rev counter was reading 3000 rpm at 60 mph. Obviously this set up is not a direct replacement for the standard one but it would be interesting to see if anyone can spot a relationship between the readings? I thought the rev counter might be reading half speed but not sure that matches up with what others are quoting. Ideas?????
If you missed it this the set up!
[attach=1]
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Hi Bobv7
I own a cb 550 k3 and at 60mph = 4500 RPM in top gear the gearing fitted to mine is
Front sprocket 17 Rear sprocket 37 but it does feel that it could do with another gear !
Hope this helps you
gromitdog
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That’s axactly what I thought gromitdog. I wondered if it was just after riding around on my touring bike.
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Guess it's all down to the gearing inside the rev counter body and not as I had hoped some logical correlation with road speed. Somehow I doubt I'll be risking the engine the way I ride so maybe it's not quite as vital a tool as it was when I was younger! Cheers for the feedback.
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See the post here where I worked out the whole thing👍👍
http://www.sohc.co.uk/index.php/topic,14633.15.html (http://www.sohc.co.uk/index.php/topic,14633.15.html)
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on my 550F I am getting 4000rpm at 55mph with 17/34 sprockets - I dont think the tacho is very accurate on these bikes though.
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Hi, Just had a good run on the K3 apart from losing the trim off one side of my tank, only to find it run over several times on the return journey. That aside I stated previously that I thought that I was at 60mph at 4000rpm and that is exactly what my clocks are telling me. I will check my sprockets and see what they are, but I have no way of telling if the clocks are accurate.
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Well thanks to the info received I've calculated that if I multiply my rev counter reading by 1.3333 it will be correct.
That is 60mph @ 3000rpm in top x 1.3333 gives a true reading of 3999.9rpm.
I'm sure that must mean something significant about the gearing inside the rev counter head, and I dunno how it helps but it was something to ponder on rainy day. ::)
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Hi,
I own a 1977 CB550K3 which was originally registered in the US.
At 4000 revs in top gear it is doing 50mph.
Dave
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I will check my sprockets and see what they are, but I have no way of telling if the clocks are accurate.
GPS? :D
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Just spotted this slightly old thread.
I wanted to check my newly damped tacho and nearly bought an optical tacho for £10 but there is a strobe phone app called Strobelight where you can set the rpm at say 2000 and then shine the phone light on the timing nut and play with the revs around 2000 until the nut appears stationary.
I’ve only tried it briefly but mine shows about 2,300 on the tacho at 2,000 on the strobe.
At about 5,000 on the tacho my Speedo reads about right anyway. I think if I set the strobe for say 1,000 the tacho would be about 1,300, which I will check sometime.
Slightly fiddly but cost £0!
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Out of the 10 SOHC's i have only one is spot on with the speedo and rev counter ;)
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I darent take my eyes off the road after all these years!! :-\