My flathead is very tight after the recent rebuild. With the plugs out and the trans in neutral, I can turn it over with a wrench on the crank nut, but the new 6 volt starter will not turn it over even when I hit it with 12 volts. An old 12v start from an early 50s Merc will turn it over, but the battery runs down after a few seconds of cranking. Does anyone make a high torque 6v starter? Other than converting to a 12v system or push starting it, does anyone have suggestions of how to get the beast started so I can let it run and soften up a bit? I have faith that the rebuild was done correctly and don't think that the mains were over torqued, etc.

 

Over torqueing the mains would end up with twisted off bolts, if you didn't have anything to do with the rebuild, then you need to check some things out. Were the cylinders bored and new pistons installed, if so were the cyls bored and honed to the correct clearance? Was the crank turned, if so, were the correct clearance bearings used, were they plastigaged. A newly rebuilt engine should turn stiffly, but with a good starter and battery it should turn over well enough to start.

 

If the engine was painted after the rebuild, the paint could be insulating the starter enough to prevent it from getting enough current to do its job. That happened to me after the rebuild of the engine in my 47 COE. Scraping paint off at the starter mounting points and where the ground strap from the frame attached to the block fixed it up.

The engine for my 36 pickup sat for a long time after being rebuilt before I got around to installing it. So before trying to start it, I put the pickup into 3rd gear and towed it around with a tractor for 30 minutes or so just to loosen things up.

If you can turn the engine over with a wrench, then the starter should be able to do it easily. So my bet is on engine paint causing the problem.

Tom

 

Clean Cable contacts are one of the bigest culprits, make sure all contacts are clean. Also if you using 12 Volt Cable your having a lot of resistance, and they don't work well on a 6 Volt system.

Quick & easy way to determine if this is the problem get omeone to roll the engine then feel the Cables if they get warm then you have a contact issue, or improper size Cables. I use 001 size Welding Cable & have no issues.

If this is not the problem then time for a Starter rebuild, it happens.

 

5 star has a great point,you can put 12 volts into a 6 volt wire size but never the other way around. 12 volt systems use less amp's then a 6 and will over heat the wire,
the other point he made was the proper grounding of the starter on to much paint.

f5fordgirl has another good point, bearings being sized properly as I don't know of many shops that know how to properly build a flatie around this country any more. many don't plasticgauge the bearings and just slop a motor together
if you can't crank it with a 12 volt boost something is wrong, converting it to 12 volts helps, you don't have to change the starter it can handle it as is.

 

My issues were with paint and wire. Once I addressed those the starter did what it was supposed to do. Might not be your issue but I'd put it at the top of the troubleshooting checklist. Good luck.

 

I trust you checked the ring gap. Another thing other than cables,do make
sure starter end plates are clean they need a good ground to the housing,
thats how they work.