airhead timing mystery

[sbosbach141157]

I have a 1983 R80RT that has a timing mystery. When I first took possession of the bike, I checked timing and found the large "S" and three horizontal timing marks on the flywheel just like Clymer's illustration in the shop manual. It was set considerably advanced, so I set about to do a full tune up, starting with torquing the heads, adjusting the valves (which were quite tight) and re-timing the engine. Now I couldn't find the large S mark and the triple horizontal marks. Instead, the bike timed up with a small "s" mark with a single horizontal line under it. I know there were triple marks at first, as I carefully drew an illustration of where the lines were in relation to the timing mark on the case.
The carbs were balanced after this and the bike runs well. What happened to the triple timing marks?
Steve in Austin

[nealart]

Hmmm - do you also own an older airhead that you might be confusing with this bike?

[20774]

Anything more that you did as part of the "full tune up"? And how are you checking the timing...with a voltmeter, 12v test lamp, or with an inductive timing light hooked around the spark plug lead?

There's only one S-mark that I'm aware of. The small S you might be referring to is likely the full advance mark...I think it is a Z for your bike.

Sounds like what's happening is that your bike is "timed" to idle at the full-advance mark which is extremely advanced. The larger S-mark with the horizontal lines is still there but because of the advance in the timing, it's already gone past the timing window and now not visible.

Something has drastically changed, or you turned the timing of the ignition the wrong direction.

[sbosbach141157]

Kurt,
Thanks for the ideas. I am using an inductive timing light using the left spark plug. the bike has electronic ignition, so I can't do a static test with the equipment I have. I even watched visually as I rotated the flywheel by hand with the rear tire off the ground and could only see the OT and S marks as a pair and then the Z mark as it came around.
The advance seems to be working normally and the bike runs well except for what seems to be higher than normal vibration at most speeds. The timing marks also seem to be blurred, but I haven't had enough experience with timing the bike to know what is normal. From the forum I know that blurred marks indicate timing chain or cam problems with this bike.
Is there anything that could have come loose on the flywheel to lose the marks?

Steve

[20774]

Steve -

Those new-fangled electronic ignition bikes, eh? Maybe someone can help with problems on timing and setting it on your year bike.

Here's what I'd do from a static point. Pull the left spark plug, put it back in the end of the cable, and lay the threads of the plug back down on the engine fins...ensure that the plug is grounded. Put the bike in a high gear, turn the ignition on but don't start the bike. Then slowly turn the rear wheel until the plug fires. Stop and check the timing hole...see where the S-mark is. Better yet, have someone do the wheel turning and you watch the timing hole. Watch all of the timing marks come around and identify at what point the plug fires. That will be your idle setting. If it's not at the S-mark and just a little off (hopefully), then your timing needs to be adjusted.

As for blurry timing marks, on my bikes that's typically an indication of a bent camshaft nose. The points/advance is run off the extension of the camshaft. If it is not running in a pure line but rather wallows a circle out in space, that will cause differential timing. Since our bikes are a wasted spark system, both plugs fire at every rotation of the engine...one cylinder will be compression the other will be on exhaust, ie, a wasted spark. But if the camshaft is slightly bent, then the firings won't be perfectly on top of each other. Yes, a timing chain can contribute to that as well, but for low mileage bikes it's likely something else. I have an aftermarket electronic ignition system on my /7 which has eliminated any double images because I can adjust the firing points of each cylinder individually.

RE: the flywheel...in your bike, you have the second generation flywheel or clutch carrier as it's called. It's not the big massive heavy spinning disks that were in the bikes prior to '81. Still, your flywheel is bolted to the rear of the crankshaft and there's nothing to come loose or off. If the flywheel came off, you'd have many, many problems. If the bike has never been apart or if no one has ever been into the clutch area, my guess is there's nothing wrong with the flywheel. Something has gotten off in the timing area.

Someone mentioned on another forum that setting the valves can change the engine timing. I'm having trouble seeing how that can happen as one system is mechanical and the other system is electrical. But you initially said that you first adjusted the valves and afterwards, you began to encounter problems with timing. Again, not sure how those are related...

[tghsmith]

timing light is fine to use, power it from somewhere else than the bike(battery charger, good battery in a car next to the bike) sometimes the bike can cause flakey readings, set the Z mark in the window at 4k rpm and see what shows up in the window at idle. should see the S marks if the advance unit is not sticking or frozen up.

[rocketman]

I'm wondering if those "triple" S marks were just multiple images like from a bent nose cam or timing chain problems, it could the the tensioner is not working right to take up the slack. I would try taking off the timing cover, remove the plugs and then use the hex nut in the alt. to move the valve cam, if there is any play in the chain then you should see a "dead" point where moving the cam does not immediately result in piston movement. Put a straw or chopstick in the spark plug hole and move the piston to somewhere in the middle of the stroke, since at TDC there is a moment of non-movement of the piston as the crank comes around which could give you a false reading. Using the midpoint of the piston movement would prevent such a false reading. With the piston at the mid point move the timing cam back and forth while looking at the piston movement, be cafeful though as the alternator bolt could come lose when moving it in the normal tightening direction since they are reverse threaded (I beleive). If there is slop or a "dead" point when going from one direction to the other you know you need to check the chain/tensioner.
RM

[sbosbach141157]

Thanks for all the replies! I am fairly certain that the timing is on the money and the advance is working properly. Thanks Kurt, for the confirmation of no loose parts coming off the flywheel! I don't understand the disappearing marks, but I can't complain too much as long as the bike is running well. I have used both the bike battery and a second battery off the bike with no real difference noticed in the timing window. I'll eventually get around to checking the timing chain tension, as I have had enough experience with engines to know how little it takes at the timing chain to make the engine run like crap.
Steve
83 R80RT

[tghsmith]

1983 has a bean can, no nose shaft to get bent, 3 marks at the S and one mark at the Z(full advance)need to know what rpm the marks are being seen at.

[rpeckham136133]

1983 has a bean can, no nose shaft to get bent, 3 marks at the S and one mark at the Z(full advance)need to know what rpm the marks are being seen at.

The three marks are there for a reason: the center one is the "S" mark, and the two marks to the side are the acceptable limits for the differential timing.

You might try putting the inductance pickup on the other plug wire to see if there is a difference.

It sure sounds to me that you are seeing just one of those marks, the one that coincides with the strobe. You should be able to see which one it is by varying the engine speed, and as the timing advances, the "S" mark should roll up (towards the seat).

:whistle

[20774]

You might try putting the inductance pickup on the other plug wire to see if there is a difference.

Something else I've heard is to reverse direction on the inductive pickup...sometimes they're directional. Mine is not, but see if there's an arrow on the pickup or read the directions. My guess is that if in the wrong orientation it might not work at all as opposed to only work in a partial or delayed sense.