Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Lobo on April 15, 2019, 11:55:58 PM
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Apologies, likely discussed before...
Interested to learn the criteria in setting the red line (rev) limits on our bikes (or any i/c engine). Whilst I wouldn’t do it - would it be acceptable to take my 47yo K2 upto it’s limit? Is there a 5% rule (or suchlike) that is assumed the engine won’t operate @ the max rpm. Is there a ‘fat factor’... how much? What form would the failure likely take - valves first? So many questions...
Ta..
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As i remember the 500 handbook it said not to continuosly rev ABOVE the red band.
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Back in the day when people used to fit Yoshi big bore kits and cans etc, it was established by Pops Yoshimura that Honda purposely set the redline considerably lower than the motor could take. This was apparently to avoid too many engine failures. The first part of the standard motor to show it's limitations were the valve springs, rev them too high and valve bounce would occur. The bottom ends of the Honda fours appear fairly bullet proof. So along with Yoshi pistons and cam and valve springs the 750 bottom end could easily take 11,000rpm, and the 400 four a dizzy 14,000 rpm without any serious failures. I regularly used to thrash my 750F1 well into the red line with stock valve springs and never blew it. Provided the motor on your old K is in good condition, I see no reason not to ride it as Mr Honda designed it for, hard. But, if you aren't sure about it's condition, that's a different matter.
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Its criminal not to redline them at some point in a ride. :)
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My 400/4 loves a bit of red lining. But, i know that the engine is in excellent fettle since rebuild.
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Ride it like you stole it ::)
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Ride it like you stole it ::)
Ride the one you've stolen. Then the redline don't matter. Sorted. ;D
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It's easy to be brave with someone else's engine. What's it worth with a blown motor? Provided that the crankcase survives, can you get the bits to fix it? Only you know the condition of your engine but do you know the history and state of the internals? Do it, if you feel the engine is up to it but do it bit at a time. Softly, softly catchy monkey if you know what I mean. Am I still allowed to say that?
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...I’m with you Mr Sheene; after 60yrs I can’t sprint, and would likely end up in A&E if I tried.
Same-same my lovely old K2...
We’re growing old gracefully together 😂
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It's easy to be brave with someone else's engine. What's it worth with a blown motor? Provided that the crankcase survives, can you get the bits to fix it? Only you know the condition of your engine but do you know the history and state of the internals? Do it, if you feel the engine is up to it but do it bit at a time. Softly, softly catchy monkey if you know what I mean. Am I still allowed to say that?
It’s not about been brave with someone else’s engine. If someone asks for a opinion it’s what they get. It’s like going out with the prettiest girl in town and all she ever wants to do is hold hands. If that’s ok for you fine.