HELP, partial crank

[lemayspeed]

My cousin needs help, so i am trying...
82 XS400, nice bike, i might buy it from him, but gotta get it on the road first.
was running normal, then just stopped on him while doing 10-20mph, he isn't good at describing the event, so i went to take a look, only a partial electric crank, battery cable loose, i tightened that, still only partial crank.
took the generator sight cover off to turn motor, as it burns oil and was low, could turn it backwards about a 1/4 to 1/3 turn, and then forward same amount again. tried putting bike in gear and rolling, @ same amount of free play. I am wondering if maybe the starter clutch or something else, it shifts through the gears while sitting still, from what i have read, it looks like i have to crack the whole case to look at the starter clutch????'
hoping to not have to do that.
any help is much appreciated.
thanks

 

[xschris]

Is it a dohc bike or a sohc. But it sounds like something is broken in the motor.

 

[lemayspeed]

DOHC 12R is the prefix on the motor number, YICS

 

[xschris]

Maybe one of the dohc guys on here could shed more light on this issue but it sound like a engine tear down is in order Even if it is a starter clutch issue.

 

[16VGTIDave]

Sounds like a dropped valve or the timing chain failed. I agree with Chris, time for a tear down...

 

[Edgee2004]

If you cannot turn the motor than the starter probably can’t either, so I would start with the valves. Pull the valve cover off and look at the top of the motor. What do the valves look like from the top, is there one that is not riding on the camshaft? Next I would, just because the valve covers off, pull the camshafts and look at them. Then you can press on the valves to see if they move. If they do not you have a stuck valve. If it is a stuck valve than pull the head and rebuild it.
But I have a question when you turned the motor did you feel or hear it hit anything internally? Or is it just too hard to turn, try it again without the plugs to relieve the pressure. Also you doing all you’re testing in neutral right?

 

[Edgee2004]

http://www.yamahapartsnation.com/oemparts/a/yam/500423c8f8700209bc787b7b/camshaft-chain

check this site out for parts. I really like them and they ship fast. OEM parts cheaper than my dealer.

 

[16VGTIDave]

I'd strongly suggest NOT trying to turn over the engine (except gently by hand) until the problem is found. It would not be good to do further damage. Some parts are getting difficult to find, like pistons...

 

[Edgee2004]

yeah should have added that. gently.