difficulty turning over engine
 

I have a 64 356SC. SC engine ran but fouled plugs badly... time to rebuild. Put known good C engine in; (stored indoors 4 yrs. but oiled every year and turned over by hand). The C engine has good compression (9.5) compared to the tired SC engine when turned by hand, sparkplugs in place, carbs removed. Starter can not turn C over fast enough to start when plugs are installed. Starter & bushing new 100 miles ago, and it turns over C engine very fast without plugs in. So no apparent conflict with valves hitting pistons. I have oiled cylinders thru plug holes. I can rotate by hand: slow with plugs in and noticably easier with plugs removed. When I use starter, it rotates very slowly but will fully rotate engine; and without plugs it spins very fast.

Any suggestion at to difficulty spinning engine with plugs in place?

6V or 12V?

6v system. Battery in excellent shape, just had shop load test it.

BTW. #0 GA wire to battery with new clamp on connector. My coil is disconnected.

Sounds like the starter motor is down on torque. I've got several 6V that test good, spin fine but low on torque when on an engine. Stoddard sells a 6V high torque starter that will spin anything.

Great to know. I'll pull the starter and have it tested for torque. I assume they can do a load test on it. Hopefully. I'll also lube the bushing while I'm in there.
Thanks for your input. I'll let you know how it turns out.

Make sure the battery negative cable connected to frame is clean and no paint where cable connects. Check all cable connections.