Mounting Sierra aftermarket magneto coils on '57 Lark

[cheburashka]

I've decided to bite the bullet and replace the coils, condensers and points on my '57 Lark. I bought the aftermarket coils made by Sierra. I noticed that the stock coils line up perfectly with the raised boss on the points plate, and someone suggested that lining these up was an acceptable way to set the air gap between the coils and flywheel. How reliable is the machining on the Sierra coils? Can I trust them to be as accurately machined as the OMC factory coils? <br /><br />I've been unable to find the ring tool for aligning the coils, and since this is the only time I plan to do this (thus I won't need the tool for another fifty years) I'd like to go forward without the tool. I do have an extra flywheel. Has anyone cut a window into a flywheel to set the alignment on the coils? are the manufacturing tolerances close enough that a motor set up for one flywheel would work with a different one? <br /><br />Thanks for your help.

 

[Paul Moir]

Re: Mounting Sierra aftermarket magneto coils on '57 Lark

I find the Sierra coils to be superior in just about every way to the OEM ones. One point you might overlook is that the pin for the spark plug wire is threaded, so you have to screw it in to get it to seat completely. But once that's done it holds much better than the stock ones.<br /><br />You can safely aling the coils with the machined bosses. Very few people have ever used the ring. If you have a set of calipers handy, you can check your work. Face to face (ie, the ID of the alignment ring) the coils measure 4.472".<br /><br />A method I like to use for setting the coils perfectly is to run a layer or two of tape (building up about .010") over the face of the coils, and loosening their mounting screws a bit. Then install and rotate the flywheel, pushing the ignition coils back the tape width. (Do this with the throttle set to slow, and again with the throttle set to fast). Remove and tighten the ignition coils.<br /><br />If the armature plate has any wobble to it, err on the side of caution with the coils a little back from the bosses. If you're armature plate is wobbling, now's the time for Joe Reeves' fix for it.<br /><br />Manufacturing tolerances are very close, you can swap flywheels without any problems. I do hesitate to swap the steel starter rings on them though, as they seem to be balanced with the flywheel.<br /><br />I hope this helps, if you have any more questions please don't heasitate to ask!

 

[cheburashka]

Re: Mounting Sierra aftermarket magneto coils on '57 Lark

Fantastic. Thanks for the quick reply!! I'll try the tape method. It makes a lot of sense to me.

 

[Paul Moir]

Re: Mounting Sierra aftermarket magneto coils on '57 Lark

I'll warn you, that's just something I made up myself. There's no official sanction! Even the .010" is mostly assumed.<br /><br />Where most people run into trouble setting up these on Big Twins is getting the wiring tucked in very tightly so the flywheel doesn't rub against anything.