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Offline macvit7906

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transmission questions -unknown gear ratios
« on: February 16, 2019, 10:32:58 AM »
Hi all,

Working on a project bike. The bike used to be raced, had things like RC ENG cam, lightened rotor, RSC pistons, etc.

The engine is supposed to be from a 75 cb750f, but while working on changing out the bearings, I noticed that the transmission gears do not look like the other cb750f stock transmission I have. The biggest difference are the dogs on the one gear.

Compared to the stock cb750f gear that has more of just splines that fit into the adjacent gear. see pics

After search around the internet it looks like this may be a later DOHC cb750 transmission?

Do any of you know for sure if this is a later cb750 tranny? Are there any benefits to having the DOHC transmission in an SOHC engine? Is this purely for racing or can I still run this for everyday riding?

Thanks!
« Last Edit: February 17, 2019, 02:56:20 PM by macvit7906 »
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Offline bamacb

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Re: transmission questions - benefits of a DOHC transmission?
« Reply #1 on: February 16, 2019, 01:19:29 PM »
Not sure what the gear is from but it would allow back cut/ under cut to be done. Much better positive engagement for racing. Should work for street but maybe someone with more information will chime in.
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Offline macvit7906

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Re: transmission questions - benefits of a DOHC transmission?
« Reply #2 on: February 16, 2019, 07:51:18 PM »
Quote from: bamacb on February 16, 2019, 01:19:29 PM
Not sure what the gear is from but it would allow back cut/ under cut to be done. Much better positive engagement for racing. Should work for street but maybe someone with more information will chime in.

Thanks for the response. mainly want to make sure street use is fine. I'm not sure if there are racing only gears and how I would be able to tell the difference.
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Offline bamacb

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Re: transmission questions - benefits of a DOHC transmission?
« Reply #3 on: February 16, 2019, 11:27:33 PM »
Looking closer that is a stock gear that has been machined down. Only reason I can think is easier engagement.
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Offline macvit7906

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Re: transmission questions - benefits of a DOHC transmission?
« Reply #4 on: February 17, 2019, 09:14:34 AM »
Quote from: bamacb on February 16, 2019, 11:27:33 PM
Looking closer that is a stock gear that has been machined down. Only reason I can think is easier engagement.

i see that too. interesting.

The two gears furthest to the left look to have different ratios as well.
This could be a k5 transmission with a ground gear for engagement.

Not sure if I wan to run it or not.
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Offline macvit7906

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Re: transmission questions -unknown gear ratios
« Reply #5 on: February 17, 2019, 03:00:38 PM »
very weird gear ratios after doing some counting.

on the mainshaft, gear m1 (furthest to the left)  has 24 teeth. Stock has 18.

M4 has 30, m2 has 27, m5 has 34.

final drive gear ratio is 48/56.

Honestly no idea what transmission this is, guess I'll play it safe and use stock.
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