So I am finishing up some maintenance on the bike including new pushrod tubes and seals....twice. I also decided to replace my timing advance springs since one was buggered up. I was watching William on one of the Boxer2Valve videos and he was setting up timing so I thought I would check mine just for fun. I started with the static test and found that when the points open I had the dot from the F in the window but I should have an S . Doing some more research I saw people say the static timing is less important so I went and bought a timing light and checked idle timing. Much to my confusion at idle I was seeing the F at the top of the window. Also when I bring the RPMs up I lose the F all together. The only way I was able to get the S in the window at idle was to crank the advance dial on the timing gun all the way up past 60 degrees. Am I doing something wrong? The engine wouldn't even run if that were true, right?
Here's a video. It's very hard to see but you can just make out the F in the window.
https://photos.app.goo.gl/CRgEw5Mdwx4W9Nk87
Full album here:
https://photos.app.goo.gl/20Upno9AmXd3G4Ps1
Very nice bike !!
Sometimes it's helpful to remember that the marks are only a helpful aid, but they are NOT the absolute authority. That place of honor belongs to the pistons. You are timing the ignition spark to the position of the pistons within the cylinders. If the flywheel was ever removed to reseal the main shaft or seal the oil pump (both of which should be done with every clutch job), then the flywheel could have been re-installed in the wrong position.
An easy way to test this theory is to remove both plugs, place the gearbox in high gear, and bump the rear wheel until a slender screwdriver inserted through the plug hole is pushed outward to its maximum position. At that point you should be able to look in the timing window and see a third flywheel mark "OT". OT can be construed to mean On Top, that is to say both pistons are at Top Dead Center (aka TDC). The OT mark may not be dead center of the window, but it should be visible.
An Airhead uses 5 flywheel bolts, so if my theory is correct then your marks could be at least 72° off their true position.
It's not impossible to time the ignition with the marks in the wrong place, but it certainly won't ever be easy, quick, or fun. And having to set up a degree wheel on the front of the engine will preclude any "quick pre-ride spot checks". It may even screw up your valve adjustments.
I'd like to know what you find.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Ok, so I got my mechanical advance springs in and rebuilt the advance assembly and put it back together. Once that was back together I checked the top dead center vs OT position. It's dead on. So I took a closer look at my advance timing plate and found that it seems to be cranked all the way to one side. I'm thinking about loosening it up and turning it the other way and checking static timing. Like I said it runs as is. Should I mess with it or just not touch it? Hmmm......
You should remove the front engine cover, get all the tools to set the ignition timing in place, and put a box fan blowing on the engine.
Then crank the bike, and with the engine running at idle, then move the bean can while you look for the "S" mark. This may take awhile. Final setting is done at high RPM with the "F" mark (and ignoring where the S mark ends up). We are only doing the major portion of the work at idle to delay the build up of engine heat... and hopefully delay the inevitable burn your going to receive from the exhaust pipe. 😛
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Two questions...
• What was the outcome of this ?
The only way I was able to get the S in the window at idle was to crank the advance dial on the timing gun all the way up past 60 degrees. Am I doing something wrong? The engine wouldn't even run if that were true, right?
• I never heard of a timing light "with an advance dial". Can you please explain ?
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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