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January 21, 2024

Ignition System

The GT6 and it's kin all used the ubiquitous Kettering ignition system from the factory.  The heart of the system is the distributor, which in conjunction with the coil, produces a series of high voltage spikes that are timed and routed to the proper cylinders to initiate combustion.

I dug out my refurbed distributor.




There were a few chores to do before dropping that bad boy in place though.  First task was to prime the oil pump.  This isn't strictly necessary, since a crank over with the starter motor will do this, but I think there is an advantage to having all of the oil galleries already full on the first crank.

Dumped in oil until I got a good reading on the dipstick.  Filled the oil filter too.





The oil pump is driven from a gear that also drives the distributor.  That gear is driven by the camshaft.  The little fork on the bottom of the drive gear shaft mates with a tongue on the oil pump shaft.  To drive the oil pump directly, it just takes a shaft with a duplicate of that fork.  Spinning the pump with a drill motor pulls oil out of the sump.  It's obvious when the pump sees oil--the load on the drill increases, and oil will start to well up in the cavity.  I had one leak at the oil gauge line coupling that made a bit of a mess, but it was just that the tubing wasn't seated properly.




The next job was to set the drive gear float clearance.  The gear itself runs between the top flange of the oil pump shaft bush below and the distributor pedestal above, and needs a little room to make sure it isn't bound up. 

Setting this clearance is a little tricky, and the factory suggests sort of a round about way to do it.  They say to put a temporary spacer of known thickness under the drive gear, and place the pedestal in place on top of that.  The pedestal now won't seat, and the gap between the pedestal seating surface and the block is measured.  A little arithmetic then determines how much the pedestal has to be shimmed up to give the drive gear between 0.003 and 0.007 inches of clearance.  The actual shims provided look like paper gaskets, but they are very thin, and several of them are included in gasket sets.

I used that method, but found it just about as easy to use bent feeler gauges to set (or check) the clearance.




The gear then comes out so the temporary spacer can be retrieved, and the gear re-installed.  The position of the gear is important since it sets the timing for the distributor.  The pedestal and shims can then go on.




With the distributor in place, the spark plug wires could then be installed.  In the past, I've just bought plug wire sets specified for the car.  I was always a little disappointed though, since it looked like the sets were made up of a selection of wires of standard lengths, so most of them were longer than they needed to be.  I temporarily installed the old set of wires just to see how bad it was.




Not really terrible, but I thought there was room for improvement.  I bought some bulk wire, some terminals, and some boots.  The result looks more tidy to me.




Next up was the line for vacuum advance.  The little elbows are aftermarket items, but I got the nylon tubing elsewhere.




I followed the fuel line.




It looked fine, but my mind's eye saw something a little better.




Last up:  The tach cable.  I'd  ordered one almost a year ago, and finally brought it out to the light of day.  The first thing I noticed when comparing it to the old one was that it was two or three inches longer.




Well, maybe no big deal.  Let's install it.  This is when the heartache started.  The inner cable wouldn't go far enough into the drive spindle for the outer housing to seat properly.  The stickout of the inner cable appeared to be too long.




I cut off the end, and sealed it with a little TIG fusion tack.




But it still would not go into the drive spindle on the distributor.  Is the square section too big?  Let's compare to the original cable.  Original first:




The new inner cable is nearly 0.012" (abut 12%) larger than the one that fits.  So is it the wrong cable, or just mis-made?  I don't know, but I had had it so long, I didn't feel I could send it back, even if I hadn't modified it.  I ordered another one from a different supplier.




This one was two inches shorter, and fits fine.




All's well that ends well, I guess.




These were sort of nit-picky tasks, but not really hard.  I had probably less than $50 in parts and materials, not counting the oil or the bad cable.

Comments to Ed at elhollin1@yahoo.com

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