engine cranking speed

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Fred Hanks

Member
I just purchased a '41 Ford barn find that has a "8MC" merc motor in it that has been it for years...when I get in to start it she rolls over very slowly and finally starts. The 6 volt batt is putting out 6.5 volts, lights burn bright, what can I do to get this engine to roll over and start like a flatty should ?
 
Check your grounds, make them clean,brite,tight, be sure you are using the correct size cables, somtimes they get switched to the 12 volt ones over the years.
 
Fred Hanks said:
I just purchased a '41 Ford barn find that has a "8MC" merc motor in it that has been it for years...when I get in to start it she rolls over very slowly and finally starts. The 6 volt batt is putting out 6.5 volts, lights burn bright, what can I do to get this engine to roll over and start like a flatty should ?
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As mentioned make sure you have LARGE 6 volt battery and starter cables with ALL good clean, tight connections. These engines don't have to spin fast to start, you can start them with a hand crank. They should start on the first or second turn of the engine when properly tuned. The starter should turn crisp and not bog down, which indicates a voltage drop. You need the full 6 volts from the ignition switch to supply voltage to the coil. The starter load drops the coil voltage and if it gets to low it becomes hard to start. G.M.
 
As indicated, check / clean / replace grounds and metal they connect to. Make sure one of the grounds goes from / to the engine / chassis ( head bolt best ). More than one grounds a good thing. I have three, battery to chassis, engine to chassis, trans mount to chassis. Contrary to normal thought mode you need a heavier battery cable and starter cable for 6V than used on 12V. X2 to have the same impedance. Also old starter and battery cables have oxidation you don't see.
Go new.
 
Also, don't confuse the slower revs of the starter on 6v to be a problem. Your late model daily driver on 12v spins the starter smartly. 6v by it's very nature is going to turn the engine over slowly. Many confuse this as a problem and want to convert to 12 v and that opens a new can of worms.
 
Fred
starters use bushings which will wear, letting the armature drag on the winding shoes
causing the starter to slow down.
Bruce
 
I might be off base here, but the original motor may have had stabiliser bars which were left off when the later motor was fitted. You need to check for a really good grounding strap from the engine block to the battery ground.

Mart.
 
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