SOHC.co.uk Forums > CB750

Red line engineering

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Lobo:
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..

Bryanj:
As i remember the 500 handbook it said not to continuosly rev ABOVE the red band.

hairygit:
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.

Sent from my X6pro using Tapatalk

Moorey:
Its criminal not to redline them at some point in a ride. :)

Nurse Julie:
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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