Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: paulbaker1954 on December 07, 2017, 01:51:10 AM
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Been playing with some numbers but now confused.
The tech spec I have shows the primary reduction ratio as 2.0 for the 500 Four but 3.063 for the 550.
I thought they would be the same so I am a little confused
Can any 4 gurus shed any light on this?
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According to the Honda Shop Manual, those figures are correct.
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550 has a different clutch to the 500 so hence the difference
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Thanks Bryan
Now that’s interesting as I have been playing with the gear commander site www.gearcommander.com
If you load their data for HONDA CB500 all the gear ratios are right except the primary reduction
Change the primary reduction to 2 and the calcs show a speed of 196.5 at 9000
What the hell am I doing wrong
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Are there two components to primary on that engine?
Does it drive crank to layshaft plus layshaft to clutch?
The 750 drives direct to clutch shaft from crank, and then again from gearbox to sprocket output.
The two combined in both bikes equals the primary reduction but the gearboxes spin at different speeds as far as I can see.
Proviso of counting chain and sprockets as secondary reduction.
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500/550 has primary chain reduction then gear reduction to clutch basket
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Sorry all I am still really confused
I am trying to calculate speed vs rpm for different wheel/ sprocket combinations and really confused
Is there a difference in the primary chain reduction between the 500 and 550 then.
Since both bikes have same gear ratios and very close final drive ratios (17/34 and 17/37) but hugely different primary reductions (2 for the 500 and 3.063 for the 550) I am missing something here in my calculations I can only assume therefore there is a difference in the primary chain reduction between the bikes but I have no data on what the primary chain reduction is in my tech specs
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I think primary chain is same but primary gear and basket gear vary
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Sorry all but I think I am not explaining my problem clearly!!!
I am trying to calculate road speed vs rpm for the 500 four and somewhere I am missing something
I have Avon 400/18 rear tyre which has a circumference of 82.9 inches and there are 63360 inches in a mile, so 1 rev of rear wheel is 0.0013 miles
For the 500, spec is a 2.0 primary reduction and 5th gear is a 0.9 reduction and final drive is a 2 reduction assuming stock 17 and 34 teeth as per spec. This in 5th gives an overall reduction of 2x0.9x2 which equals 3.6 so 1000 rpm equates to 60,000 revolutions per hour or 60000/3.6 =16,667 rear wheel turns which is 16667x0.0013=21.67 miles
So this means 21.67 miles per hour for every 1000 rpm which gives 21.67 x 5=108 mph at 5000 rpm which is clearly nonsense as I know it’s more like 12 mph per 1000 rpm
I am missing something obvious I know but dont know what
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I think primary chain is same but primary gear and basket gear vary
Chain is the same on the 500, 550 and 400. Just different gearboxes, clutch, sprockets and chain length .
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As Bryan says, surely there’s a reduction to the clutch basket?
As you say, there’s something missing. I rode my original for months with no speedo and always estimated speed at 12mph/1000
Sent from my iPhone using Tapatalk
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Can anyone confirm the number of teeth on clutch basket and primary shaft?
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I understand what you mean Paul, just not so familiar with the exact layout.
Primary reduction is usually given as crank to first ( in this case chain to the first shaft it's driving) then there is the reduction of that shaft driving the clutch through a gear set, so the clutch shaft speed into the gearbox has arrived via two reduction methods.
It looks like just the first stage is quoted, the others on here should be able to tell you how many teeth are on the crank and the other end of the chain. If that's a times two reduction, then you've got to then add the clutch gear set reduction to it.
I'm more familiar with the 750 which drives, crank straight to clutch in one chain run and no gears. Then, when leaving the box has a paired gear set to drive the output sprocket. How they quote these two units on both engines I don't know, but they are both altering the total output to final chain, and obviously not incorporated in the 5 gear ratios.
If that makes sense.
Nigel.
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Those figures for the 550. Give clutch reduction of 2.625 so there must be the other component on the primary chain to make total of 3.063.
If you work the 500 figures and assume 2 more teeth on the clutch, then that's going to be 2.826 on the clutch alone, so you still need the number of teeth for both primary chain sprockets to add to both of these illustrations to give total primary reduction.
May have found another error in Honda manual, the one that states primary reduction of 2.0 it just can't be that figure.
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The primary shaft gear, the very large one the primary chain runs on is the same for the 500 and 550, they share the same part number, the smaller one which sits inside the clutch casing is different, the 500 has a 23T gear and the 550 has a 24T gear. The 550 clutch basket has 63T but the 500 isn't shown in the parts book.
The 500 clutch basket has 64 teeth (just counted them on a spare I have) so what I am now missing is the number of teeth on the crank and the primary shaft where the primary chain runs.Anyone have these figures?
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Without those primary sprocket figures you can't be accurate, but if you try and just extrapolate the difference for that tooth change on clutch drive ( the others say it uses the same primary chain) then I've got something like 3.183 total primary reduction for the 500.
Worth running that figure to see what you get perhaps.
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Without those primary sprocket figures you can't be accurate, but if you try and just extrapolate the difference for that tooth change on clutch drive ( the others say it uses the same primary chain) then I've got something like 3.183 total primary reduction for the 500.
Worth running that figure to see what you get perhaps.
If we assume the quoted primary reduction of 3.063 for the 550 is correct with 24 and 63 teeth on the clutch reduction then the primary chain reduction works out at 1.167 ((3.063*24)/63)
This then gives a total primary reduction for the 500 of (1.167*(64/23))=3.247
So finally in 5th gear and standard 17/34 sprocket set I get a total reduction of 3.247*0.9*2=5.845
So with my Avon 4.0/18 rear with a circumference of 82.9” giving 0.0013 miles per rear wheel rev I get (60000/5.845)*0.0013) miles per hour per 1000 rpm = 13.34 mph
So finally at 5000 rpm I get 5*13.34=66.7 mph
Feels about right to me
Conclusion
Without accurate data on the 500 primary chain reduction I make the total primary reduction for the 500 as 3.247 NOT the 2.0 stated in the Honda tech specs I have!!!!
And finally just for fun for the 550 in 5th with a total reduction of (3.063*0.9*2)=5.513 and using same Avon tyres you get 14.148 mph per 1000 rpm i.e. 70.74 mph at 5,000
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Been away a while so just catching up. Indeed it's one of the many Honda mistakes. The 2:1 for the 500 is the final drive ratio. 34 teeth on rear wheel sprocket and 17 at the motor end.
I did a little excel spreadsheet on the 500/550s a while ago.
Both share 24 teeth on the crankshaft and 28 on the driven primary shaft gear.
500 is 23:64 driving the clutch basket and 550 24/63. So primary reductions are 3.246 (as quoted the June 72 test in MM) for the 500 and 3.063 for the 550 from crank to rotation of clutch basket.
Interestingly as the 550 has a 17:37 teeth arrangement (rather than the 17:34) on the final drive chain sprockets, but also has a slightly larger rear tyre specified as standard (3.75 instead of 3.50..2% larger) all the differences just about cancel out with the stock arrangement so 500/550 all should rev about the same. (about 62 mph at 5000rpm or 100kph as Delta will proudly tell us)
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Cheers Seabeowner at least it confirms my own calcs
Good to know I wasn’t going crazy then!!!