Needing detailed magneto timing help for 1918 Excelsior twin

[ronj]

Im trying to set my timing not sure to use front cylinder or rear for TDC mag timing Does front ht lead go to front cylinder the guy who rebuilt mag I think he has them backwards from all the info ive seen timing marks on gears are no help there are several
Does #1 cam on interrupter go to #1 cylinder # 2 to back cylinder
Any help would be appreciated
Ron

[gharper]

Ron,

First, check out this thread from a while back regarding magneto timing. I posted a comment there explaining my method. http://www.antiquemotorcycle.org/bbo...magneto+timing

If you have a Bosch or Berling magneto, the rear wire goes to the rear cylinder, front wire to the front cylinder. ASSUMING you have the correct mag for the engine, the cam marked I should go to the rear cylinder, II to the front, the rear was considered the #1 cylinder. The most important thing is to set the timing when set at full advance and CHECK IT ON BOTH CYLINDERS. You'll be amazed at how far off it can be on one cylinder and perfect on the other. It may require some gentle dressing of the leading edge of the cam that is firing early in order to get it just right, and this takes time and patience! I can't stress enough how important it is to get it set right, and equal on both cylinders.

The only timing marks to worry about are the ones on the pinion gear and the cam. On the X, the only other marks are on the mag gear and the timing case. I wouldn't rely on them at all, who knows what parts are swapped from what machine.

Call if you need more eXplination.

gene
720-341-5606

[exeric]

I hope my post isn't going to muddy the water, but I think it will apply to ronj's problems. I’ve been having a lot of magneto trouble of late, and having mental problems understanding the timing of this Excelsior. I hope the following makes sense and I hope my pictures and text clearly show the sequence of firing on the front, and rear cylinders. The magneto is a Bosch ZEV, 45 degree, clockwise rotation. Any help will be greatly appreciated, and even if you make me look like a moron, I'll be a happy moron if we can figure this out.



1. This picture shows the pinion gear, and cam gear timing marks in alignment, and the rear intake lobe in the same position as Excelsior’s timing drawing.



2. This picture shows the firing position of the rear cylinder. Both valves are closed, and the piston is 3/8” before top dead center.



3. You can see the fiber is just on the cam and should fire the rear cylinder.



4. This picture shows the problem I am having. The piston is 3/8” BTDC, and both valves are closed but you can see the fiber is well past the cam lobe for the front cylinder.

So, I have tried numerous 45 degree timing housings, both clockwise, and anti-clockwise and every one is off. What am I doing wrong.

[Robert Luland]

Nothing for Nothing But I'd pull the mag and move it a tooth. Bob L

[Tommo]

Eric,
As you have a degree plate on the engine can you tell us how many degrees of rotation there is between the opening of the points on each ramp.
I think this may help.

[exeric]

Thanks for the reply Peter. Do you mean the degrees between when the points open on the rear cylinder (both valves closed, and piston at 3/8" BTDC) and when they open on the front (both valves closed, and 3/8" BTDC)? Should that be 2 complete revolutions plus 45 degrees? Remember Peter, you are talking to a complete idiot here so you'll have to dumb it down.

On a different note, In the event that all of my point housings are wrong, I have made this new housing, and I can attach the ramps where they will open the points at the right time. This whole episode really pisses me off because I supposedly have a 45 degree, clockwise rotation magneto, with a 45 degree C.W. point housing.

[exeric]

I thought about your question Peter, and I think I misunderstood. I just now checked the degrees between the points opening from the rear ramp to the front ramp and I come up with 315 degrees.

[harleytoprock]

Eric, The first thing I'm noticing is that your timing mark for the rear is 40 degrees BTDC but the timing mark for the front is 30 degrees BTDC. It's hard to see your front TDC mark but this what I think. Also is it possible that the lobe you are declaring as rear is really the front on the interupter?

[Tommo]

Thanks for that Eric and I suspect you have a miss match of parts.
Harleytoprock's comment is relevant also. Pull the no 1 pick-up off and make sure the brass strip on the slip ring is visible. If its not you're using the wrong ramp on the interrupter ring.
I need to do some maths with the 315 degrees and will get back to you.
By the way did the bike run with this mag and if so what were the problems it demonstrated

[gharper]

Eric,

I suspect that you are using the front cam to time to the rear cylinder and visa-versa.

When I set the timing, I prefer to actually measure piston position relative to the cylinder head rather than using a degree wheel. This can get tricky with a single piece cylinder/ head assembly, more so with the early X having the lower tank tube right in the way. I use a depth gauge, set at 0 when at TDC, then back off 7/16" or .4375". I use a bit more advance because I'm a mile high (no pot is legal in Colorado now jokes please!) and typically ride up in altitude, plus we have better fuels today and tend to run the engines faster than back in the day. I was able to dial the timing on my 19X to within .007" from one cylinder to the other, pretty close for that old thing! If using a degree wheel, that's fine, just be sure the math is correct and exactly the same front and back.

Lets say you get the timing on the rear cylinder set just where you want it. Rotate the crankshaft 360 + 45 degrees, or 405 degrees. This is where the front cylinder should be at the same position relative to TDC and the points should be just opening. Rotate again 360-45 or 315 degrees and the rear should fire again. Another way to look at it is this: look at the spacing between the 2 cam lobes of the mag and note rotation,. Pick a cam lobe, then follow in the direction of rotation toward the other cam lobe. The smaller gap is the gap between the front and rear firing position, the larger gap is between the rear and front cylinder. For degrees of point rotation, use the same #s as above and divide by 2 because the mag rotates at camshaft speed. From your 3rd picture it looks to me like your mag is off by 180 degrees. You are setting the timing to one cam, then the space to the next cam lobe is the smaller gap, which is wrong, it should be the larger gap. After the rear cylinder fires, the points breaker needs to traverse the larger gap (360+45/2) to get to the front cylinder cam. Then the breaker traverses the smaller gap to get to the rear cylinder (360-45/2). So, set the crank so the rear cylinder is at 3/8" btdc and rotate the mag only until the breaker is hitting the front cam in the mag. Clear as mud? This should get you close.

Once you have the correct cam set to the correct cylinder, or at least close, then set it to fire on the front cylinder. Remove the front high tension pickup and look inside the hole, the brass track should show on the collector ring, Bosch should have the front wire to the front cylinder, rear to rear. If this is good, now the fun begins, carefully dress the leading edge of the cam that fires too early until it is dialed in to match the other. These are very hard and you will need a stone or emery board. Patience is definetly a virtue for this task!

Once set properly, all this work pays off. It's amazing how slow an engine can idle, how easily it starts and how much more power it has when the timing is correct on BOTH CYLINDERS!

Good luck! Gene

[exeric]

Well, it looks like it's all going to work out. Thank you Gene, and Peter for your knowledgeable insights. Peter, I took the #1 pick-up off, and lo and behold; no brass contact. I was timing the wrong cylinder with the wrong ramp. Gene called and gave me some more tips, and advice on how to really dial it in. It never ceases to inspire me that this stuff is pushing 100 years old and yet is still functional, and servicable. Thanks for the help.