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Discussion Starter · #1 ·
Hey y'all. I am working on a 78 cb400A that i just picked up, trying to get her roadworthy, but something went wrong...

I am fairly well versed in smaller engines as i have had a couple mopeds, but this is my first larger bike.

The rundown:
cleared tank and carbs of old gas/sludge (carbs are probably going to need to be rebuilt)
new battery
oil change (new filter, gaskets, etc.)

took a while to get the bike to turnover, but finally success. it will not idle without giving a little throttle (maybe a 1/4 turn).
Basically i was just trying to burn off the seafoam gas through the carbs.
ran for about 2 minutes like this then a loud CLANK which killed the motor.

Now when i try the electric start there is just a click and all the lights dim. The kick start doesn't budge (it did before the CLANK)
I also noticed that after the clank i tried running through the gears and i could only shift between N and 1...it wouldn't click up to 2.

Did i kill the bike? Does it sound like i seized the motor or hopefully something less dreadful?

thank you for your time!
 

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There are so many things that can lock up the 400as that it would be hard to tell you what the problem is. The top end can be removed with out pulling the motor so I would start there and see if the problem is in the valve train or cam chain. But as you say it wont shift into 2nd gear I suspect the problem is deeper than that. Its not any good the way it is so I would bite the bullet and tear it down. But thats just me.

Bill
 

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Pop the plugs out and the left engine cover. You now have access to the rotor which enables you to turn the engine over by hand, it should rotate a bit stiff using both hands but fairly smooth. If it rotates and then suddenly sticks/stops odds are that the left rod bearing has failed.
 

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Discussion Starter · #5 ·
So i pussed out and just decided to take the bike in to a local shop to have everything checked out since i just bought it anyway...i figured they will give it a good once over. turns out they pulled the top end and nothing appeared to be seized, but the kick is still locked in place. they have basically left me with the option to split the case and see whats what and as they said, "get nickel and dimed" or find a new motor. I'm ok with dropping some cash on a new motor, but at this point if that is going to happen i am wondering if any other "A" motors can do a straight swap? like a cm400A motor or a 450A?

They are going through a few salvage suppliers, but if they can't find something i am trying to keep my options open.

thanks guys.
 

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Discussion Starter · #8 ·
I did a complete major overhaul on my 78cb 400 motor from crank brgs to new valve adjusters. About $1500 doing all work myself.Just to give you an Idea of cost.

Bill.
Thanks Bill. Yeah i think i may go with them replacing the motor, then i can keep the original (hopefully rebuild it myself so i can learn). They were saying they think they can find a new motor for under 800, i looked on ebay just to see what's out there and it shouldn't be too hard to do.
 
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