Replacing the Magneto on an 084

[Papee]

Notes: Please read all posts in this thread before doing anything to your motor when making this switch. I have a summary post on the second page.

If you've seen my embarrassing moments thread you have seen that my mag has gone bad on my motor. Questions or maybe just reassurance have arisen. The mag I am using as a replacement is a Slick mag, a little different than my original,nothing to do with my questions. They are generally the same.

on the mag there are tabs or keyways on each, one of the tabs having a (-) mark on. I am assuming that if I put the drive gear on the same way that I took it off the other one with these marks aligned, it will be timed right? There are marks on my flywheel and a (.) mark on the magneto drive gear so I'm figuring as long as I put it together the same way I took it apart It should be timed the same as it was before?

On another note, I went down to Saturn Surplus to pick the mag up this morning and he mentioned another carb that may work for this motor. It has an accelerator pump and came off an engine a bit larger but still a direct fit for the stock intake. I'll start another thread on this carb when I have this thing back together and have had a chance to run the boat.

[Duane Scarborough]

Papee,

I "thought" that I had photos of the timing marks. I took things apart, took photos, and sent them to Buster "way back" when he had some mag timing questions.

The only one I can find is SO blurry. Even I can't figure it out from THAT photo, and I was the one who took the photo.

I'll keep looking.

Duane

[Papee]

I'm pretty sure I have all that right Duane. Before I took it apart I turned the crank to the timing marks. I'm just not real clear how this magneto works. Does the mag fire 4 times per revolution of the crank? I guess I need to know where number one is as far as cyl # and on the mag. My new mag is different, it's a slick mag. I can kinda guess by the length of the plug wires on the mag, two are longer.

My guess is that it may fire 4 times and you have to get the mag timed to #1 then install it aligning up the timing mark. On the mag, I would also guess that since the layout of the spark plug wires on the mag are the same the wires would go on the same way. I have the old mag labeled so I could them back the same way I took them off. If all my assumptions are correct all I need to know is where number 1 is as far a cyl and mag #1.

EDIT: Here's all I found in the manual I have posted in the specs thread.
d. Installation. (figure 4-25
(1) Rotate starter rope pulley (29) until both rockers on number one (1) cylinder (30) dose, and stop when timing
mark on camshaft gear (31) is present.
(2) Hold end of high tension wire from number one (1) terminal of magneto (12) 1/8 inch from magneto case.
Turn magneto gear clockwise until magneto impulses and spark occurs. Turn magneto gear (28) counter
clockwise until magneto gear (28) timing mark and camshaft gear (32) timing mark are aligned. Install
magneto (12) and gasket (29) (3)Install screw (22), washer (23), and lockwasher (24).

[Papee]

Ok, I found number one cyl on the engine circled in red in the pic by using this I can find out which is number one on the mag.

[Papee]

Ok I think I have it. After looking at both mags, the old one in the first pic I determined the one marked to be number 1 by the tags I put on the wires when I removed them. looks like I had them right but started with the wrong number one. I labeled the cyl at the rear left side number 1 and the actual cyl 1 I had marked 4. I wuz backwards.


On the new mag number 1 is marked.

[Duane Scarborough]

Papee,

Glad you've got it figured out. From what I determined way back, the mag turns at half the speed of the crankshaft, so it only fires 2 times per crank revolution. (or when each cylinder reaches the end of the compression stroke).

If you look VERY carefully, the cylinder numbers are cast into the case, just a little above where the cylinders meet the case. At least it is on mine. But you REALLY have to look for them. When I finally found them, I highlighted them with a paint stick, so they'd be easier to find in the future.

Duane

[Papee]

I just went out and cycled the mag. It sparked on number one the first time I turned it. It took 4 turns to get it to fire on number 1 again. Now if the heat wave would just quit I could get it on.

[2006rubicon]

I think I have something for you, I just bought a 4A084 that had a dead fairbanks morse mag and picked up a slick replacement, It came with these instructions. I set cyl #1 on TDC and impulsed the mag until #1 fired per these instructions, then because I don't have the inline timing light shown in the army manual I got creative by taking an old plug wire off the fairbanks and put it on cylinder one and then stuck the exposed tension springs together between the old and new wires, then clipped my trusty ole craftsman timing light inductive pickup right over the junction between the two wires, (inductive pickup didn't work over the braided radio suppression covering, imagine that!) then adjusted the mag with the engine running until the timing marks were correct, just like a regular automotive distributor. I was advanced quite a bit, but I never did find the tiny dot mark on my mag gear. Apologies for the size of the pic,my computer apparently suffers from gigantism.
Also-anyone else see the typo in the original military manual? I saw that too when I was farting around with my magneto trying to change it out. I've heard of having both valves close, but dose? Then again, the military does have some wierd lingo going on sometimes.

[Papee]

After you posted this I looked in the box and there was a sheet like that under the package. Looks like I did everything right. It's been raining here all day so I haven't got out to work on it. Add to that I am working on a new bathroom for the wife so I have to sneak out to work on it.

[Papee]

Just putting some info here so it's easier to find. I am working on getting the engine running again. I can get it to pop a few times but it won't start. When I went to hook the spark plug wires up the one on the new mag (short leads) were different. I came back in to find the firing order and cyl numbers. I found the firing order now I have to find the cyl locations.

a. General.
Engine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41084-2, -3 and -4
Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4 cycle gasoline powered
Number of cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4 (horizontally apposed)
Horse power rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20 at 3600 r.p.m.
Fuel pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diaphragm 3.0-4.5 psi outlet pressure
Air cleaner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dry models 4A084-2, -3 and -4
Spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Shielded
Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-.033 in. (.071-.083 cm)
Magneto contact
Gap, Fairbanks Morse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..015-.019 in. (.030-.48 cm)
Gap, Slick Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .008-.012 in. (.020-.030 cm)
Valve tappet clearance cold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..007-.009 in. (.017-.027 cm)
(Intake and exhaust)
Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Centrifugal
Oil capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 quarts (4 1/2 gts. with oil filter change)
Alternator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 volts alternating current (ac)
Starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 volts direct current (dc)
Regulator-Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 28.5 ± .5 volts at 1.5 amps
Firing order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1-4-2-3
b. Dimensions and Weight Models 4A084, -3 and -4.
Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20 in. (50.8 cm)
Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28.50 in. (72.4 cm)
Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22.10 in. (56.13 cm)
Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., . . . . . . . . . . . . . . . ..265 lb (120 kg)

[Papee]

Ok I found that the cyl numbers are stamped on the case just above each cylinder. here's what I have.

[Papee]

Now I"m totally confused.

It looks like the slick mag turns CCW with the rotation of the motor. The Fairbanks I took off looks like it turns CW. Who knows which way the slick mag turns or maybe someone that has a slick mag can post a pic of where the wires run?

Now I've also noticed that there are two marks on the cam gear the is a (V) and an (o). When I took it apart the dot on the mag gear was aligned with the (v). I hadn't move the engine at all then installed the mag gear dot on the V

[Duane Scarborough]

Papee,

If I remember correctly, the Slick does appear to turn opposite to a Fairbanks. I don't think it's really opposite, but some weird thing in the Fairbanks distributor cap.

Mine is a 4A084-4, which came with a Slick mag.

Looking at the cap, from the rear, 1 is at about 4:00, 4 is at about 8:00, 2 is at about 10:00, and 3 is at about 2:00.

So, from the perspective of looking at the cap, it rotates CW. From the same perspective, the crankshaft is turning CCW.

The cylinders are numbered 1 on the right front, 2 on the left front, 3 on the right rear, and 4 on the left rear.

Firing order 1-4-2-3.

Hope this helps.

Duane

[Papee]

Thanks Duane, I had to walk away from it a few times today. I was looking at the gear on the mag but I musta got crossed. I am about the same way as you describe. I did have the rotation in the wrong direction, I've tried it both ways. I put it back to what you described and I got a little more action but it didn't start.

After it tried to start I choked it a bunch and it would try. I pulled one of the plugs and it was bone dry. I tried dumping some gas in the carb but with it horizontal it's hard to get much in. It tried more when I dumped the gas. It has always started easy but it just don't seem to be pulling the gas in like it normally does when it's choked. It is a new carb and was running fine when it shut off. I did check the old mag and it is not firing so I did troubleshoot the mag right. Maybe I also have carb or fuel pump problems. It will be a new day tomorrow.

Since I have the new Tillotson carb here I'll just put it on and see if that takes care of it. I do think the mag is timed right and the wires on correct now. Oh BTW, I am pulling the thing over with the rope, I have the starter off after more problems with it.

[2006rubicon]

Oh BTW, I am pulling the thing over with the rope, I have the starter off after more problems with it.

I feel for you there, I'm doing the same thing for now! One thing I did notice on mine, it ran really snappy with way too much advance, near as I figured I had close to 40 degrees in it!!!! but it did sound good! When I tried to fire it up for the first time it kicked back so hard it ripped the rope out of my hands and popped every joint in my arm, my shoulder STILL hurts from that. When I finally did get it running and was able to put the timing light on it I was able to see it was way off and backed it down to 15 degrees, but I had to put the original flywheel and housing back on to do that. I'm gathering your setup has the timing mark somewhere else. The slick instructions say you can time the mag using the P terminal and a light and that tells you exactly when the points open and the mag fires, but I don't get where the power for that test light comes from and I hesitate to put power into a magneto, my understanding is that is a big time no-no. Dumb question here from an even dumber guy, but, in regards to yours, is it possible you have TDC #1 on the end of the exhaust stroke (true TDC), and not TDC on the compression stroke (when you're supposed to stick the mag in). I only ask because I had a heck of a time getting the marks on the gears to line up like the manual says they're supposed to , I never did find the one on the mag gear. I did the wrong TDC thing at first and everything wound up being 180 degrees out. Then it sat there and popped and farted but never started. (hey that rhymes!) After I figured out my goof and the timing adjusted it fired right up without kicking back, but I still have to pull that chord like it owes me money!

[Papee]

I was out today and looked at putting the Tillotson carb but it is clocked different, it is turned and isn't an exact fit. I put the stock carb back on and it did try to fire, it made about 2-3 rotations each time and sounded like it wanted to run. The carb seems to be working right now. I'm just not sure where I'm at, too much gas choking it or too little. I'll let it sit overnight and give it another whirl tomorrow. I feel a little better now since it's so close to starting.

I'm still searching for more information on the marks on the flywheel but I did put it back the same way I took it apart so it should run. On my flywheel someone put yellow paint on the marks. There is a (0) mark and a (V) mark on the flywheel.

As far as adjust the timing, When I was pull starting mine all the time I adjusted the timing on the water to how it ran the best but it was harder to start like that so I turned it back.

[2006rubicon]

I'm still searching for more information on the marks on the flywheel but I did put it back the same way I took it apart so it should run. On my flywheel someone put yellow paint on the marks. There is a (0) mark and a (V) mark on the flywheel.

are the marks on your front flywheel? my rear flywheel didn't have an O and a V, it looks like this:
http://dl.dropbox.com/u/484139/DSC03429.JPG
probably the O and V on yours are the equivalent thing, O being TDC and V being the 15 degree mark. Then again, if your engine fires up tomorrow, does it really matter? Keep us posted and good luck!

[Papee]

The marks I am talking about are on the cam gear. The way it looks, I didn't check to make sure, but looks to be 180* from each other.

[Papee]

Well it's running again! It's running rough though. I checked all the plugs and they seem to be firing ok. I do have the mag turned ahead as far as I can get it and I need to have the choke on most of the way to keep it running.

[2006rubicon]

The marks I am talking about are on the cam gear. The way it looks, I didn't check to make sure, but looks to be 180* from each other.

Ahhh OK, that makes perfect sense now. I think you nailed it then. Follow my logic here-If the marks on the cam gear are 180 apart, then when the 0 on the cam is in line with the mag gear but the mag gear dot is on the opposite side, the engine is should be true TDC (end of exhaust, start of intake) Conversely then, the V would be TDC compression stroke, ie-when you want to fire the mag. Now if that V mark lines up with the dot on the mag gear, then the built in 15 degree advance in the mag will cause it to fire 15 degrees before TDC, which causes the the timing to perfectly line up with the IGN mark on the flywheel, which is, no suprise, 15 degrees before TDC. (THATS why my marks didn't line up AND why I was so advanced when I did mine, I'm a tooth off, but I must have offset it because I rotated the mag enough when I timed it with the light to compensate and hit the timing scale anyways.) So lining up the dot and the V will put you exactly where you need to be. You're right, it's gotta be a fuel issue then!