CB400 Hondamatic Question?

P

posibrian

Pub Flyer!!!
New member here but not new to motorcycles, I've grown up around them my whole life and I've had a few. I've been looking around Craigslist for a old CB or XS and I finally picked up a 1978 CB400A Hawk Hondamatic for super cheap. The one problem it has is that the engine needs rebuilt cause the PO ran it out of oil due to not pluging it up right after an oil change.

So now that you know the problem, here's my question!

Is it possible to convert the Hondamatic to a 5 speed or 6 speed? If so is it real difficult? If it's not possible then I can just basically throw in a different CB400 motor with a 5 speed correct? The only thing I can think of that might run in the way of this is the motor mounts not matching up right?

Thanks for all the replies in advance and look forward to my rebuild thread!
 
I don't think you can do just a transmission swap, but you should be able to throw any cb/cm 400-450 twin engine from 78-87.
 
+1 you can swap in a CB/CM450 from an 82+ and get an oil cooler, 5-6 speed manual, better oiling for the head, and more power. The mounts are Identical as the hondamatic motor. You can find those engines cheap too. I did this to my 81 after I had a piston go as it was much cheaper than a rebuild. You loose the kick start though.

Cheers,
 
Thank you both for the quick replies! I really appreciate it! ...will I have any trouble matching everything up for the wiring harness to the engine if I get another engine from 78-87?

Thanks again guys your awesome!
 
Not sure how much of the electrics are different, but I do know the hondamatics have a switch to make sure the side stand is up before you shift gears. You could probably jump those wires easy enough.

Edit: looking at my clymer wiring diagrams, it looks like there is the kickstand switch, "changing relay" and some differences in the CDI wiring (more connections).

Edit again: Found it! The automatic has a different CDI box because it has to run more advanced ignition timing when it is in gear to keep the bike from stalling, than when it is in neutral.
 
Yea I'm hoping its not to much of a difference. I was at this shop in Silverlake earlier yesterday and the dude said I'd have to change the brain out (the black box under the tank on the left side of the frame) ...So I found a 79 cm400 engine for cheap and I'm thinking about getting it but I need to make sure it'll work first before I throw the cash at the guy.

Thanks again for the quick response wood!
 
posibrian said:
New member here but not new to motorcycles, I've grown up around them my whole life and I've had a few. I've been looking around Craigslist for a old CB or XS and I finally picked up a 1978 CB400A Hawk Hondamatic for super cheap. The one problem it has is that the engine needs rebuilt cause the PO ran it out of oil due to not pluging it up right after an oil change.

So now that you know the problem, here's my question!

Is it possible to convert the Hondamatic to a 5 speed or 6 speed? If so is it real difficult? If it's not possible then I can just basically throw in a different CB400 motor with a 5 speed correct? The only thing I can think of that might run in the way of this is the motor mounts not matching up right?

Thanks for all the replies in advance and look forward to my rebuild thread!
Click to expand...


Your bike is stupid.
 
If it is any help to you I have a harness and a """"Black box"""" from a 78 400tII ,pretty cheap depending on where you live..
 
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