difficulty turning over engine

[dp4ta]

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?

[callard]

6V or 12V?

[dp4ta]

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

[dp4ta]

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

[callard]

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.

[dp4ta]

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.

[kltarga72]

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