Rebuilt motor won't turn

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PURPLECUDA340

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Lower end of my 1971 340 rebuilt by shop, I had to assemble upper end. Assembled cam, , cam sprockets,crank sprocket, timing chain (dot to dot) and was able to turn engine over with the crank bolt attached to harmonic balancer. Once I attached the new hydraulic rocker arm assy, I was unable to turn motor over manually with the crank bolt, even with 135 ft lbs of torque.......If I loosened the rocker arm shaft retaining bolts, I was able ,again ,to turn engine over with the crank bolt.........

Anyone have a clue as to what might be happening ?
 
Also , heavy duty valve springs, new retainers, etc....I'm afraid of strtching the bolt on the harmonic balancer if I apply any more pressure in an attempt to turn motor over.
 
PURPLECUDA340 said:
Lower end of my 1971 340 rebuilt by shop, I had to assemble upper end. Assembled cam, , cam sprockets,crank sprocket, timing chain (dot to dot) and was able to turn engine over with the crank bolt attached to harmonic balancer. Once I attached the new hydraulic rocker arm assy, I was unable to turn motor over manually with the crank bolt, even with 135 ft lbs of torque.......If I loosened the rocker arm shaft retaining bolts, I was able ,again ,to turn engine over with the crank bolt.........

Anyone have a clue as to what might be happening ?
Click to expand...
Sounds like your timing chain is out of sync and an open valve may be hitting the piston. Sometime back this happened to me. Everything looked right, but the wrong timing chain was in the box I bought. I have a Desoto hemi and somehow another chain was in the box. The Desoto uses a 318 timing assembly. The mark on the big gear was way out. Now I double check everything from autozone!
 
Is the cam sprocket in the right hole?? We had dads buggered up on his 273 and it was comp cams as well. They have 3 spots/places where it could be set at...advanced, retard and standard....yep we had it on retard and actually bent 2 pushrods turning it over by hand.
 
Are you running a really fat cam which might require valve guide machining and spring seat cutting. You could be in bind with the valve spring, interference between valve keepers and guide or just good old fashioned piston to valve contact. What pistons, flat tops, domes, valve reliefs cut in or not? Pull yer valve covers to check valve springs , if they're closed up , that's a problem . Not a 100% on wether you can see your retainers vs guide but something to look into. If the head side of things is ok. Then its time to clay your pistons to measure for clearance. Good luck.
 
Thanks for all your advice guys, I just pulled the head and noticed some slight marks on the pistons....appears to be piston to valve contact, thankfully ,never tried to start engine...I'm having issue resolved
Thanks
 
Double check the comp timing chain, I sent one back about a month ago for quality issues.
 
Had this happen on a slant build make sure your rod berings are seated correctly not a big deal until you go to start it, then it gets really bad. I would rather tear it down and start over than break it .
 
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