Topic: '75 CBFourF rebuild - engine won't rotate - WTF?

[seabird]

Save me from an early grave guys - here's the details:

rebuilt the engine (out of the frame) with new (STD) pistons,rings, wrist pins &circlips.
Cylinder block and Head on - it rotates as smooth as silk.
Fit the Rocker cover, adjust the tappets as per the book.
Socket on end of crankshaft:  Engine will rotate only around 45 degrees or so, then goes solid


My thoughts so far:

Valve head striking piston?
Cam chain locking up on sprocket(s)?
Camshaft position incorrect (no groove on end of camshaft - Haynes manual lies yet again)?

Words of wisdom and comfort needed urgently!!

Terry
(Seabird)

[MRieck]

Sounds like a valve hitting the piston(caused by incorrect cam timimg). Probably an exhaust valve is closing very late. Start again with #1 at TDC and remember(rule of thumb) that both rocker arms should be loose at this point. I'm curious though....if you install a head and all the valves are in the closed position it shouldn't turn over very easily secondary to high cylinder pressure when rotating the crank (none of the valves open to bleed pressure).

[seabird]

Thanks fellas - incidentally, I have the spark plugs out, so any resistance shouldn't have an affect when the pistons rise as the contained air in the cylinders will bleed away to atmosphere through the plug holes.

But the camchain sprocket misplacement does sound like the problem - I'll give it a go (again)!

Thanks again.

Terry

[Gordon]

Did you make sure to set the timing mark behind the points plate to the T" 1-4 and then line up the marks on the sprocket with the cylinder head? 

[seabird]

Yup!  It was the valve timing - reset the camshaft sprocket, timed on T1-4 - you could almost hear the poor thing sigh with relief (or was that me)?

And it's all there!  the thing rotates as I said, like silk, the rocker clearances almost fell into place!

I am a Happy Bunny  I'm now sitting with a glass of Talisker single malt and a small seegar, smiling smugly at a (soon to be) working engine.

Next task - the Clutch....(spooky music.....)

Many, many thanks guys - couldn't have stayed sane without you!

Terry
(Seabird).