New guy to forum. Cb750 transmission swap with cb900c?

[Keegster96]

Hey guys!

New here and in the middle of building my 1980 cb750c back up after I seized one of my cylinders. Got a killer deal on a 1980 cb900f, that came with a spare, 1981 cb900c motor. I have taken both my cb750 and cb900c now and seems like everything should work now that it's swapped in there it for perfect. From what I have read the 900s and the 750 had basically the same bottom end, just trying to double check before I put it all back together. And the other cb900f is complete just skips out of 2nd gear so plan on fixing it and selling it whole. Only 12000 miles on it.

Thanks for the help

[TOOLS1]

A few years ago someone here did that same transmission swap. If I remember correctly, it was a bolt in swap. I am sure that if you used the search function here, you could find the thread.
TOOLS

[Keegster96]

This and other forums, along with all the manuals I can find, has led me to beleive this works. I just never found anyone that fully confirmed it works. Have a good feeling so think I'm just going to roll the dice on this one. I'll confirm if it works soon lol

[shinyribs]

I had a dohc engine that was a mix of 750 and 900 parts, but my memory is fuzzy. I'll research it a post back. But the 900C is a different animal. What exactly are you trying to swap around?

Half-caf was the fella that was working on a transmission swap with a 900C. Don't recall all the details but should be able to find his thread with his username.

[shinyribs]

Ok, so it was 750 cases with 900 trans, clutch, rods and cams. I thought that's what it was but wanted to make 100% sure.Everyone know the cams interchange, but apparently the trans/clutch will, too. Between the K and F models, at least.

http://vintage-and-classic-honda-s.456789.n3.nabble.com/Shiny-s-1980-CB750-F-happy-with-pods-td4044473.html

[shinyribs]

Here's where Half-Caf was playing with 900C and 750 trans parts. I didn't read all the info just now, but maybe this will help.

http://vintage-and-classic-honda-s.456789.n3.nabble.com/Half-Caf-my-80-cb750f-SS-cafe-project-td3333614i240.html

[Keegster96]

Thanks so much man! Emailed him just now. When I know for sure I'll throw it on this thread for everyone. Like you said it's a long way to the end lol

[09greyson]

I’ll let you guys know if the cb750f output shaft fits in the cb900c transmission. I’m currently converting my ‘81 cb900c into a cb900f, with some liberties (gsxr1000 front end and wheels, cb400sf swing [I like the dual shocks still], and a lot more wastes of money). I’ll probably have it in, in about a week and a half.

[Keegster96]

Well I know it all fits cus I put it all in the 900c. I have a good feeling it will work. Going to take some more measurements when I get home from work. Won't be home for another 6 days. So hopefully the gasket kit will have arrived and I can put it in and see if it works after that.

[Keegster96]

Ok so had everything back together the other day and wouldn't you know it everything works.... Just be sure that you switch the seal being the sproket with the one from the sproket drive transmission, it has a small ring on it which keeps it in place. I failed to realize this an now have the cases split once again. The motor had to come out again to paint it anyways, and now I can take this motor apart with a blind fold on lol. But can not wait to get this monster back together and on the road!

[TOOLS1]

COOL!! Do you have any pictures of the process?
TOOLS

[Keegster96]

Motor out of the bike. Get help I nearly died getting it out by myself

[Keegster96]

[Keegster96]

Here is a picture of it all pretty much back together. Cb750c transmission in a cb900c bottom end, now to see if it holds up to the power. I'm sure it will be good though. The one picture shows the lip on the gasket. Wasn't thinking and put the 900c gasket back in, needless to say there was an oil leak lol. Ordered all new seals since I have it apart again and a new gasket for the bottom end. It's farley easy to get at this part think it's like 35 bolts and then it should come apart. I'll give more updates when I'm back from work again and have it all painted and the new cr carburetors. 

On Thu, May 3, 2018, 2:50 PM Keegster96 [via Vintage and Classic Honda's], <[hidden email]> wrote:

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On May 3, 2018 2:50 PM, "Keegster96 [via Vintage and Classic Honda's]" <[hidden email]> wrote:

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[Keegster96]

Here is a picture of it all pretty much back together. Cb750c transmission in a cb900c bottom end, now to see if it holds up to the power. I'm sure it will be good though. The one picture shows the lip on the gasket. Wasn't thinking and put the 900c gasket back in, needless to say there was an oil leak lol. Ordered all new seals since I have it apart again and a new gasket for the bottom end. It's farley easy to get at this part think it's like 35 bolts and then it should come apart. I'll give more updates when I'm back from work again and have it all painted and the new cr carburetors. 

On May 3, 2018 2:50 PM, "Keegster96 [via Vintage and Classic Honda's]" <[hidden email]> wrote:

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[Keegster96]

Here is a pic of the old girl before I stripped it back down again

On Thu, May 3, 2018, 3:05 PM Keegan Lang, <[hidden email]> wrote:

Here is a picture of it all pretty much back together. Cb750c transmission in a cb900c bottom end, now to see if it holds up to the power. I'm sure it will be good though. The one picture shows the lip on the gasket. Wasn't thinking and put the 900c gasket back in, needless to say there was an oil leak lol. Ordered all new seals since I have it apart again and a new gasket for the bottom end. It's farley easy to get at this part think it's like 35 bolts and then it should come apart. I'll give more updates when I'm back from work again and have it all painted and the new cr carburetors. 

On May 3, 2018 2:50 PM, "Keegster96 [via Vintage and Classic Honda's]" <[hidden email]> wrote:

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[Keegster96]

Found out I'll need to grind a couple spots on the block

[shinyribs]

Good stuff, man. Thanks for following up with solid info. That'll be super helpful to someone in the future.

[Keegster96]

I hope so, I'll follow up in a few weeks when it is fully completed

[Half-Caf]

Hey Keegster, sorry I'm late to the party. As you found out most things are pretty much plug and play between the two engines. I also had to do some grinding to accommodate the proper clearance for the chain. Are you running the 900 oil pan with the oil cooler as well?

Another snag that I am sure you may have already run into is that the chain guard from the 750 will not mount up to the 900c engine. As such, I am currently looking into fabricating a chain guard of some sort. In the meantime I've managed to ride just fine without losing my foot