Cant turn engine HELP ME PLEASE

CalgaryStreetBob

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1981-82 XS400 SOC Canadian version

the motor is out of the bike

THE PROBLEM IS
When I try to turn the motor to set top dead center I can not turn the crank shaft over.
I noticed the problem after I re-torqued all the bolts.
When I torqued all the bottom 6 12mm (socket) bolts to 20 ft lbs the engine seems to be too tight to rotate the engine.

HERE IS WHAT I HAVE DONE TO THE ENGINE

I have the engine out of the bike.
I just finished a full rebuild of the motor.
Complete tear down and build up.

The bottom of the original block was cracked where the kick start goes in.
So I got a new bottom end to the case.
I replaced all the original transmission parts into the new bottom end.
lots of lube and everything is turning properly.
Put both parts of the case together. clutches and alternator parts in.
engine turned no problem.

Torqued all bolts to spec. "I can not turn the motor over."
If I loosen the bottom 6 bolts the motor turns over. no problem
the case seems to be squeezing the main crank shaft too much.



I changed a few bearings
new clutch plates.
new gaskets
new piston rings
 

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Did you try and turn it with the head torqued and the cam off?
I just took it apart again and took out the cam, and put it back together and retorqued all bolts in the case.
EVERYTHING SPINS FREELY.

took it apart gain and reinstalled the cam,
retorqued all bolts to 5 ft lbs.
it spins.
large bolts are supposed to be 15-20 ft lbs.- anything above 5 ft lbs of torque is too much to let the cam spin freely
and small ones are around 6-8 ft lbs.

its almost like the PLANE BEARING (cam sleeves) are squeezing the cam too much when I torqued the 10 mm bottom bolts to spec...
. it doesn't make sense.

PS. I just got a new low torque, torque wrench. I'm not just eyeballing it.
 
Okay, so it sounds like the bottom end of the engine is fine. The issue could be one of three things - chain related, valve related, or cam bearing related.

First, make sure you are rotating the engine in the correct direction. Looking at the alternator end, you should only be turning the crank in the counter clockwise direction, never turn it the other way. Also, loosen up all of the valve adjusters fully before you do anything else.

Are the cam chain guides installed correctly? The bottom end of these has to sit in a pocket inside the case. Check that they are seated and that the chain tensioner is working otherwise the chain will kink and stop rotation.

Are the correct rockers installed in the proper locations in the cover? Make sure your rockers look like this:
Cam cover.JPG


Verify that the cam sprocket is timed correctly. With the engine rotated to the LT mark on the alternator flywheel as viewed in the timing window, make sure that the mark on the sprocket and mark at the end of the cam shaft are aligned and in the 12 o'clock position. You may have to rotate the engine through another 360 degrees to get this look.
Cam timing 4.JPG


If the cam timing is off or rockers out of position, you might have a valve open at the wrong time, hitting the piston and stopping rotation.

Finally, use oil or assembly lube on the cam journals and the corresponding saddles in the head and cam cover (the bearing surfaces have to be absolutely, positively clean before you do this). The cover also needs some sealing compound (Yamabond, Three Bond, Permatex Motoseal, etc) between it and the head before you torque things up, and don't use so much that it gets into and gunks up the cam journals. Make sure you have the two dowel pins in position. Torque the 8mm bolts to 16 ft-lbs and the 6mm ones to 7 ft-lbs.

If the engine rotated before tear down and you haven't changed or modified any parts, then the engine should rotate after checking the above. If it does not you will have to take the head back off and measure the cam and bearing saddles separately and calculate the clearances because something is really off.
 
Having just had to replace my cylinder head due to a crack, I had heard you can't mix random heads with random valve covers as the cam journals are machined as an assembly. They then stamp the engine number on both parts so you know you have a match. I purposely bought a complete matching assembly for this reason and had no issues. The numbers are between the intake ports. Oops, hit post too soon. If they aren't matched it is possible a slight misalignment of the cam journals could be clamping the cam tight and locking the engine.
 

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Having just had to replace my cylinder head due to a crack, I had heard you can't mix random heads with random valve covers as the cam journals are machined as an assembly. They then stamp the engine number on both parts so you know you have a match. I purposely bought a complete matching assembly for this reason and had no issues. The numbers are between the intake ports. Oops, hit post too soon. If they aren't matched it is possible a slight misalignment of the cam journals could be clamping the cam tight and locking the engine.
I was thinking the same. New bottom end is probably squeezing the cam 100,000 of an inch too much.
 
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