075 milling saw tight when pulling over (wont start)

[farmerjohn]

Hi, 
ill try and make this brief as i can. I bought a mill with 2x 075's (one on each end) one was running fine, one a bit rough.

after changing a lot of parts on both the one running rough was running perfect, 

the one that was running rough is now spot on.

the one that was running really well now seems to have a tight spot, after changing crank baring seals it seemed tight to pull (as if there was a hand break on !!!!)

this is what we did on the saw:

before i bought a clutch spanner i tried the old method to lock the crank of putting rope down the plug hole and turned to top dead center and got a bar on, there seemed to be a 10th of  turn then went tight again so i stopped as it felt bad and got a clutch spanner ordered, changed the seal, put all back together and it was tight.

after deliberation decided to remove the barrel and there seemed to be fibers between the barrel wall and piston, so presumed the rope had gone into the exhaust port and i had cut it with the piston, on inspection the chrome was flaking on the top of the barrel. so decided to change the barrel and piston (as we had changed this with great success on the saw that was running badly as barrel badly scored)

so, new barrel and piston in, oiled everything up, new gaskets, stretch bolts etc, went to fire and its still tight, took the spark plug out as even with de-compressor there is some compression and compared the other saw it seems to have a tight spot at top dead center as it changes direction, like  a notch!!!!
 my thoughts are, but i cant believe i could have done it so easily is that i have bent the crank or con rod. 
am going to split the saw (again) at the weekend i think, does anyone have and other thoughts?

or even if i get the crank off, how to check it or the conrod as the been could be undetectable to the human eye.

Any advice would be much appreciated as i just want to get milling and spent so much time and money and still am not up and running its frustrating

Edited May 31, 2018 by farmerjohn

[spudulike]

Highly unlikely that the rod or crank is bent, they don't go that easily. I would usually remove the flywheel and clutch, pull the plug out and the saw should turn over easily. 

Fitting the wrong seal can cause the crank to be stiff but would be at all crank positions.

If you remove the top end, it may stop the issue and if it returns when the top end is refitted, you are getting somewhere.

A bent rod becomes obvious if you lightly undo the top end bolts so the cylinder is loose and turn the engine over slowly, holding the top end lightly in place. The top end will rock from side to side of the rod is bent.

Most bent cranks I have seen have become obvious from the chain moving up and down excessively on the bar of the chain is loose, visually wobbly when the crank is rotated or impact between the coil and flywheel plus the engine will feel tight.

Are you sure the cord was removed fully and the seals were fitted correctly?