Erratic ignition on old inline 6

[Doug Redinger]

I am trying to track down a frustrating ignition problem on my 1963 merc 850 inline 6. Last time out last season I was running W.O.T down the lake doing about 5200 rpm when all of a sudden the motor backfired and stalled!! Tried restarting it and it did start, but it ran very, very rough. Turned out to be a spark plug had blown out of the spark-plug hole, threads were apparently partly stripped and the pressure and heat had eroded away the remaining aluminum allowing the plug to fall out. Must have been getting oxygen from around the plug and just finally melted out the plug hole threads. Anyway I repaired the threads with a helicoil insert and installed a new plug. When I went to start the motor this spring the motor fired right up, although it seemed to have a intermittent miss on 2,4,and six. I hooked up an inductive timing light on #2 and it would appear that #2 is firing at the same time as #1. I have a bright chalk mark on the flywheel timing #1 at TDC which is also the line stamped on the flywheel from the factory. #1 fires at or near this mark at idle, but so does #2 which should be 180 degrees off from #1?? Anyway I took apart the magneto and replaced the condensors, filed the points and regapped and synchronised the points. 90 degrees of dwell on each set and 60 degrees offset from each other. Replaced the wires from the point sets to the terminal block. Replaced the wires from the terminal block accross the top of the block to the coils. Tried a spare good coil in both coil positions!!! Still errattic ignition and missing. Installed new plug wires and swapped in a spare distributor cap I had!!! Still the problem persisted.I thought maybe I had a crack in the cap or some carbon tracking inside the cap, but saw no evidence of either on either cap!! Tried 2 other rotors I had on hand and still problems. Tried another magneto I had and used it with combinations of new rotors and both caps and still having problems. Also replaced resistors and wiring from resistors to coils and same result.

I Finally checked the base timing between the flywheel and the distributor pulley and the marks were all in allignment ( crankshaft center alligned with line on flwheel alligned with arrow on distributor pulley and center of pulley). However if I change the timing on the distributor pulley the motor seems to run better and miss less, although #2 still seems to fire at the same time as #1. About the only thing left I thought it could be is the flywheel is moving on the end of the crankshaft ( sheared woodruff key ??? )

Does anyone have any ideas as I am at my witts end with this thing (50-60 man hours) in just the last week on this thing.

Sorry about the long post but I wanted to give as much pertinent information as I could!! Thanks in advance to all!!!

 

[Laddies]

Re: Erratic ignition on old inline 6

Doug, start with a dwell meter and check the dwell on both sets of points, then run the engine at speed with it hooked up and watch for point bounce or misfire. While running have a voltmeter hooked on 1 coil at a time to make sure the ballasts are working OK if they allow to much voltage to the coils they will heat and misfire. If in the process the engine starts to misfire find out which coil when reverse coils to see if the trouble is in the coil or points and condenser.