Topic: Knowledgeable advice needed, PLEASE!

[Ricky_Racer]

I have a (supposedly) Yoshimura-built CB750 SOHC motor with Yoshi Daytona cam, lightened and balanced crank (viewed through the oil sump opening), Yoshi rods, and the most beautiful pro porting I've ever seen. Here's my request for info... Is it possible to determine if the motor has a close ratio trans without splitting the case? That may be a tough question, but you guys are the best CB750 builders I know of and I really could use some advice. Help! Anyone?

Much thanks. Ride well, everyone!

Ted

[MauiK3]

Take the plugs out, turn the sprocket or rear tire and record the corresponding turns on the crankshaft vs the output shaft for each gear. This will give you the crank to output shaft turn ratio.
The field service manual has the ratios for each gear that you should be seeing.
Be sure the engine is lubed up.

[Ricky_Racer]

Thanks, Maui. The motor is currently on a stand so I may try your technique. Are you in Hawai'i? I lived and worked on three islands for a combined fourteen years. Mahlo nui loa!

Ted

[MauiK3]

Maui, south side just north of Wailea.
Great weather, nice folks.

[MauiK3]

The town is Kihei

[scottly]

Take the plugs out, turn the sprocket or rear tire and record the corresponding turns on the crankshaft vs the output shaft for each gear. This will give you the crank to output shaft turn ratio.

That method doesn't take the primary reduction into account.
Ted, to get the most accurate measurement, I would measure from the clutch and count the rotations for one full turn of the output shaft. You would have to be fairly precise, like using a degree wheel, as the difference of, say a 2.5:1 ratio vs 2.45:1 would only be about 18 degrees, or about 3 minutes on the face of a clock.

[HondaMan]

...just don't turn the engine via the right-side crank nut (by the points - or whatever is there now?). That will bend that small shaft, altering the spark timing. Use the alternator's nut instead.

[MauiK3]

Yep, got that wrong
Here is a link that may help
https://novaracing.co.uk/honda-cb750-close-ratio-gearbox

[Jerry Rxman Griffin aka MuthaF'er]

I don't know about your tranny Ted but that B on the end of the cam verifies you do have a Yoshi Daytona cam.

Where is your new life taking you?

[Ricky_Racer]

You're correct, Jerry. It is a Daytona cam. And the rest of the motor just shouts Yoshimura including the rods. This was certainly a pro-built motor and I have no idea how much it would take to duplicate it today. It came to me in a very interesting early CB750 with an ARD mag and a set of 40IDA Webers. A seriously high-buck build!

I'm going to the Philippines. I was there six years ago but a bout with bladder cancer followed by COVID locking down the Philippines ended my plans to return there much earlier. Thanks for asking.

And everyone, thanks for responding to my request. I've recommended this forum to anyone who seemed serious about developing their SOHC skill set. Ride well, my brothers, but ride safely as well.

Ted