I'm no magneto expert, but I have stumbled through the timing process a few times over the years. But as I sat in the shop last night setting up the mag on the A10 rat bike, it occurred to me that there has to be a better way! And the last time I did this there was no Britbike.com, so I thought I'd ask.
So, here's my drill. Mount the mag. Set the points at .012. Clean and check the cam ring to see it's close on both sides. Lube the mag ring. Check for spark. Set up the advance (manual on this one).
Then, set the crank position at TDC and rotate backwards to 3/8 inch BTDC. I have never set up a degree wheel for this and use a dial indicator to find TDC and a piece of steel rod to measure BTDC. Loosely position the fiber gear on the mag shaft and screw on the nut.
That's where I am right now. This part always puzzles me. There is no real difference in electrical potential between point closed and points open, so the only way I've ever used to find out when the points open is the old cigarette paper method. There's got to be a better, more accurate way, doesn't there?
Considering that I won't be following up with a strobe on this, it is particularly important to get it pretty close on static timing. If I could just get some sort of electrical indication of when the points open, perhaps a continuity light or buzzer, like we do with regular points ignition, that would be close enough.
Is there a way to do that? Would pulling the ground brush do it? Any other tricks?
I did a search for previous info on this on the board, but didn't find anything. Appreciate any help I can get on this!
Jim-I've tried a few times with a multi meter myself but no luck. Two things I do differently-I use a .003 feeler guage instead of paper and I fit a degree wheel to the crank on the drive side. 3/8 in. is 29 BTDC I think (?)got it written down in my book at home.Much easier than sticking something down the plug hole I think. Good Luck
Last edited by MikeG; 03/30/102:05 pm.
1960 BSA A10 2007 Suzuki Bandit 1957 A10 (Used to be a Triumph here) 71 Norton Commando
On normal coil ignition I used a buzzer on the points, you didn't have to be looking at it which seemed an advantage over the bulb. I had a 2v battery and buzzer in a box with 2 wires with clips on.
Yeah, I do that as well on a point ignition. My multimeter has a buzzer built in. Nice! However, the Mag doesn't seem to give you that option. The electrical circuit is the same with the points closed and open. I have not found a way to electrically differentiate between open and closed.
Jim-I've tried a few times with a multi meter myself but no luck. Two things I do differently-I use a .003 feeler guage instead of paper and I fit a degree wheel to the crank on the drive side. 3/8 in. is 29 BTDC I think (?)got it written down in my book at home.Much easier than sticking something down the plug hole I think.
Thanks. I'll try the thin feeler guage. I haven't "rolled my own" in many years, so I wasn't looking forward, at my age, to going in to the drug store to buy cigarette papers!
As for the piston travel measurement, I use the fixture for my dial indicator that screws in to the plug hole. I found a steel rod that is a nice sliding fit, and I've marked grooves at the TDC position and at 3/8th inch above. I know the angle messes with the distance slightly, but I just add a bit to make up for that. At least this is consistent and measurements are the same every time. I can also use this as a TDC finder by dropping the rod a bit.
I suppose I should set up a degree wheel, but I expect you made up a special one to fit the cush drive on the end of the crank?
Actually the "fag" paper is supposed to be .002" and that is what I use. Next you have to set the 3/8" before TDC with the piston rising. This is very important as it takes up all of the wear in the timing gears.
I use a wooden BBQ skewer and a Stanley Knife blade (Carton knife to some).
Bring the bike to TDC in the normal direction of rotation. Pop the skewer in the plug hole, lay the blade flat on the fin then rotate the skewer against it. Pull the skewer out and make a second cut 3/8" above the TDC mark you have just made. Make them fairly deep. Rotate the engine backwards to BDC , put the skewer back in the plug hole and cut it off just clear of the plug hole. Place the blade back on the fin pressed lightly against the skewer. Slowly rotate the engine till you feel the blade "drop" into the grove you cut in the skewer. Set your points to .002" at this position. Pop the skewer into your tool box, now renamed to "timing tool". With a little practice you will be able to do it with your eyes closed which will stand you in good steed should you need to check the timing on the side of the road on a dark night. As for using a timing disc on the cush drive, a strong magnet works wonders with a thin plastic, card board or aluminium disc, used in conjunction with a fold back clip on a fin with a bit of wire hanging off it for a pointer.
I have a Norton and a Velo with mags and here is how I do it. There is some work the first time, but after that it is a piece of cake. By the way, this assumes that you are starting with a clean, lubed mag with a good oil seal. First, set the gap, then take the central bolt out. if you take the central bolt out, you can use a continuity test light to determine exactly when the points open. Use a Sharpie to mark the housing where they open on each side. By putting a straight edge across the marks and the center bolt hole, you can tell if the points are opening 180 degrees apart. If so, fine. If not use a stone or a dremel to grind the cam ring back to as close to 180 degrees as you can. Obviously this is easier to do with the mag on the bench instead of in the bike. Check the gap again. If you aren't getting the same gap on both sides, split the difference. In other words, if you are looking for .012 and when you set it on one side, you are getting .016 on the other side, set one side at .010 so the other is at .014. Now make a positive stop by beating and drilling out the inside of a sparkplug. Tap the inside for a carriage bolt and a lock nut. Take ot the spark plugs and install the stop in one of the plug holes. Put your degree wheel on and set it to where you think TDC is. Now back the crank to about 70 degrees BTDC or so. Ease it forward until the piston hits the positive stop. Note where this happens. Now back it up until it hits the stop again. Note the reading. If you guessed right on TDC, it should stop at the same reading ATDC as it did BTDC. TDC will be precisely halfway between the two readings, so adjust the degree wheel until you have it reading correctly. This will probably take a few tries. Now rotate the crank to whatever reading it is supposed to fire at. Loosen the locknut on the positive stop until it just kisses the piston at the appropriate reading BTDC, install the magneto with the ignition advance locked (if it has one, I use half a clothes pin to lock it)without the center bolt. Use the continuity light to make sure that the points are just opening. Don't forget to put the center bolt back and unlock the ignition advance before you try to start it. If you did everything right, the next time you want to check your timing, you won't need to use the degree wheel. You just thread your now locked in the right position positive stop into the sparkplug hole, rotate the engine forward until it stops, take the center bolt out of the mag and put your light on it. If the light is on, but then goes out as you rotate through the ignition advance, you are good. This way tells you exactly when the points are breaking, and you don't have to worry about corrections for the angle of the sparkplug hole or any issues with actually finding TDC. My bikes start and idle very nicely.
Thank you kindly sir. You are exactly the guy I was hoping would see this post. The center bolt! Never would have guessed that one! I just went out and tried it, and sure 'nuff. It works! I never was comfortable with the cigarette paper method. Always seemed too much like guess work to me. Just one question: Once you've removed the center bolt, there isn't any risk of losing position on the shaft, is there? As I recall, isn't that a keyed straight fit on the shaft?
I also like your carriage bolt method of TDC and Advance. Once it's set you're good to go, and the round head should give consistent piston height.
Very nice stuff, Ed. Appreciate your taking the time to enlighten me!
The points plate is located by a key and held in place by a taper fit, so it shouldn't move. I use the head of the carriage bolt on the top and round off the end that the piston hits with a file. One thing I forgot to mention, if you occasionally dribble a little 3 in 1 oil onto the cam lube felt, the fiber heel doesn't wear and your timing doesn't change. By the way on the A10, don't skip making sure both sides fire exactly 180 degrees apart. It will make a big difference in how it runs. Glad I could be of help.
By the way on the A10, don't skip making sure both sides fire exactly 180 degrees apart. It will make a big difference in how it runs.
Thanks Ed. One more question. When I'm turning the motor to check that the points open 180 degrees apart, how do you make sure the mag doesn't fire off a spark and fry your continuity light? Does removing the center bolt disable the mag or do you have to ground something else to make sure this doesn't happen?
Right about the centre bolt.Not quite so right about stoning the cam;although it will work. The cams are usually quite accurate (unless somebody has been stoning them).If you get variation in timings,and especially different gap either side,it is because the housing that holds the cam is not square to the armature centreline. Try unbolting the cam housing.Rotate it 180 degrees and bolt it back.This won't fix it,but it will tell you if the cam housing face is out of square (some turning require to fix) or if it is the face on the main body that is out of square (easily fixed with a file). Even just replacing bearings can effect this squareness.