1970 MERC 500 THUNDERBOLT, TEST COIL?

[bill cook]

HOW DO I TEST MY COIL TO MAKE SURE IT IS GOOD?

 

[ledgefinder]

Re: 1970 MERC 500 THUNDERBOLT, TEST COIL?

The ignition coil should show 28-34000 ohms across the secondary windings and nil (about 0) across the primary. <br /><br />The coils inside the distributor-type thing should show 400 ohms red-to-white (disconnected from switchbox), same for red-to-blue. White-to-blue should show 10 ohms. Red-to-ground should be an open circuit, same with blue & white. <br /><br />The switchbox should deliver 140 volts to the coil (peak reading).<br /><br />I have a question for you about a motor I have. I think I have the same distributor (if you have the switchbox with the red, blue, white & green terminals). When you turn the pulley on the distributor, does it move smoothly or sort of snap-though? I can turn mine a little due to slack in the drivebelt, and it snaps through to another position so that the drivebelt is now tight on the other side. I can't tell if it just some magnets lining up inside the distributor, or whether I've got a bearing problem. <br /><br />I've had two other of these motors (a 71 and another 74) and never noticed this behavior. The thing ran fine for a week of vacation last summer - whatever it is doesn't seem to be getting any worse. I'm probably going to sell it & don't want to pass on something that'll just bust on the next guy. Thanks!

 

[bill cook]

Re: 1970 MERC 500 THUNDERBOLT, TEST COIL?

Hey ledgefinder thank you so much for all the help<br />I really appreciate all the good advice from you and everyone else.<br /><br />which are the primary and secondary coils? ie.... where do I hook the leads from the meter?<br /><br />as for your question my distributor rotates clockwise about 20 degrees (looking from the top of the motor down), but its a little stiff then stops and returns to its original position via some sort of spring mechanism I assume but it does not slip or click into another position.<br /><br />I may be wrong on this as obviously I am not a merc expert, but I believe this is how the motor alternates between cylinders at idle and slow-speed.<br /><br />I sure hope that helps you as you have been very helpfull to me.<br /><br />billy sea

 

[bill cook]

Re: 1970 MERC 500 THUNDERBOLT, TEST COIL?

Hey ledgefinder it's me again I misunderstood your question before. My distributor pulley also makes a little snap sound as it rotates<br />which appears to me to be magnetically induced<br />so I think your alright there.<br /><br />should I be taking these readings you suggested with the motor running? cause thats kinda my problem, my motor won't start! However I am borrowing a 1000 amp booster/starter to get my motor spinning faster hopefully then the magneto/igntion-driver will generate some spark for me. what do you think?<br /><br />thanks again<br /><br />billy sea

 

[ledgefinder]

Re: 1970 MERC 500 THUNDERBOLT, TEST COIL?

Thanks for the note on the distributor - good to know. <br /><br />Seems like the slow starter could cause what you're seeing (weak/no spark) - that ignition is self-energizing. Why don't you just rope start it. You can spin that thing a lot faster with a rope than with any electric starter.

 

[ledgefinder]

Re: 1970 MERC 500 THUNDERBOLT, TEST COIL?

Those resistances are taken with the motor stopped, voltages with the motor running.

 

[bill cook]

Re: 1970 MERC 500 THUNDERBOLT, TEST COIL?

ledgefinder I have the same type of switchhbox<br />red,blue,white,green, and ground. Tried rope starting, pretty tough. When I had the plugs out lubin' the cylinders it turned over real fast.<br />Put the plugs back slowed down again. Must have some serious compression, or did it jump timing?