Hello All:
 The first reaction you will have is: "Why doesn't this moron have the number off the existing magneto?" Well, my mind was tied in knots till I was 20 miles from the site when I thought to contact ACMOC. I am trying to get D6  # 9U6991 to run again after about 30+ years in the toolies. I removed the magneto and was able to gin-up a decent spark. Then I timed it per the operator's manual. However, it seems that the impulse coupling fires about 25 - 35* before TDC on cylinder #1, same with #2. I checked with a wire probe on the piston top and the spark occurs about 1/2 - 3/4" before TDC. The timing mark on the flywheel confirms this. Every time I try to light a fire, the damned thing kicks like a mule. Since the impulse coupling engages a gear, and the coupling is keyed to the magneto shaft, I see no way to fudge on the timing. The magneto also has no slots for the bolts to finesse the timing by rotating the mag a bit; It's mounted totally stationary to the engine. I will have a parts book in a few days, from eBay, and will have the Bosch and maybe the Cat# by tomorrow afternoon, in case anyone can confirm or deny it is correct for the machine. I am ASSUMING (yeah) the thing must have run in the past with this magneto, but "assuming" can get a fellow in trouble. Any advice or input is much welcome.

Thank You,

Jeff

I am still have a magneto AMERICAN BOSCH CATERPILLAR for D6 and he has good spark but he is missing the gasket cap

Correct magnetos for the D318 are....
American Bosch MJK 4/2 360 D410
Wico XH-2839
Fairbanks Morse FMXF2B36D

Thank You Gemdozer and Old Magnet. You both replied a few months ago when I needed a mag for D8 1H3647. The D6 parts book arrived shortly after I posted yesterday and it appears that a Cat# 7F9937 is the correct unit. I'll check the Bosch number for a match to 4/2 360 D410 per Mr. Magnet. The D8 magneto I bought from Mr. Gemdozer works fine on the starting engine, but starting the diesel was delayed by a nasty foot long "Mother Nature" block drain behind the instrument panel. That's now half-assedly corked-up with JB Weld. If it holds coolant and runs good, we will get it welded and fixed correctly. I am posting videos of all the fun on: www.youtube.com/@oldiron
All the Best,
Jeff

Thank You so much for the information. Checking the magneto on the machine, it is a MJK 360C 410, NOT a "D410" as you say is correct for the machine. That would explain it not firing at TDC or thereabouts. It was firing about 20 - 30 degrees before TDC and, of course, just kicked every time instead of trying to run. If the owner wants to invest the cash, I'll be looking for a 360D unit. The machine has been sitting in the weeds with the hood off for many years, but the diesel is not locked-up. The carburetor was badly corroded and may not function even though I did manage to free the float and poke the crud out of the jets. I will need a magneto just to get to the next potential trouble spot.

 Thanks again,

Jeff

Had that trouble on my 75, damn thing wouldn't start, timing was always off, reset it and off again, took mag apart, RC-2Q, found out it had too long of an armature shaft, about only an eigth inch but enough that it held the impulse far enough away that it would scrape past the impulse trip latch on the mag housing and throw the timing off and not trip the impulse, had Mark's Magneto put the correct, shorter shaft, armature in and worked great.

The "C" model is fine. They came in "A,B,C,D" models as time progressed.

I appreciate the update. So you say the C version is also correct. That leaves me scratching my head RE the consistant early firing that prevents it from starting. Any additional thoughts?

Thanks,

Jeff

Timing gear is off a few teeth? Installed wrong at one time?

WOW! That could get nasty in a hurry. The machine does not show any sign of being reassembled and then refusing to run. It, according to the sketchy memories of some family members, worked for years at the ranch, and was then set aside. Some time later, an attempt was made to get it running, and a replacement magneto was offered by a fellow Cat owner nearby. The thing refused to start and the fellows gave up in disgust and left all the sheet metal scattered around in the brush. Guess I'll just keep thinking on the subject.