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How to tell TDC on Compression vs Exhaust stroke

23K views 16 replies 8 participants last post by  dcpppf  
#1 ·
Hey guys,

So the short story is as I am doing a valve clearance job I got tired and dumb and turned the crankshaft by hand without the cams on and lost track of what stroke I was on. Now, I know from the marks on the generator to find TDC and 125 BTDC but I'm not sure how to know if this is on the compression stroke or the exhaust stroke. The cams need to be placed on the compression stroke and I can only imagine bad things happening if they are placed in on the exhaust stroke.

My understanding from the service manual is the ignition timing is based on the crankshaft position sensor among other variables. Is there a way to make sure I am on the #1 cylinder compression stroke and not exhaust stroke? I'd much rather have spark on compression than exhaust.
 
#2 ·
After furious googling my current plan is to
1. Install the cams in one of the 125 BTDC positions
2. verify I can crank by hand without issues
3. leave valve cover off
4. connect spark plug to ignition coil #1, ground the spark plug to chassis, leave spark plug in open view out of engine
5. Leave fuel tank off, sitting way far away, plug or tape off spark plug ports
6. Connect ECU, turn on bike
7. Crank engine while Recording spark plug and camshafts on a slow motion video.
8. Review video. If spark on #1 happens when cams display compression stroke, good. If cams display exhaust stroke, remove cams, rotate crank 360 degrees
9. reassemble, remember this lesson for the next one.
 
#3 ·
In case anyone comes across this later. I did the method above and it sparked at both compression and exhaust strokes. So... put it together and give it a start? I'm thinking with this new information the ECU recognizes when it starts what stroke it is in.
 
#5 ·
Do not turn it over on the starter. If the cam timing is out the valves could contact pistons and bend. Turn it over gently by hand and observe the cam lobe/valve position on number one cyl on the comp stroke. They should be closed. Then time according to the manual.
 
#6 ·
180 out is when the #1 lobes face in. Lobes face out, the crank is @ TDC, the crank is on the next [power] stroke past TDC for #1. Lost spark is a set of points firing twice. Sequence fire (some ign systems) is a single spark where the cam sensor calls the sequence.
 
#8 ·
Ah. See I didnt know about lost spark. I thought for some reason that it would only fire once per cycle not twice. If that were the case, and I thought it was, then firing on exhaust only would result in knock on compression without spark and/or ignition with open exhaust valves. Neither of which I was wanting to see.

Spark on both was great to see and hear. I was worried for nothing.

Thanks to everyone who responded.

Now i just got to figure out how to keep the damn new valve cover gasket on the cover while installing it, damn thing keeps falling off and I'd rather not put everything back together and have an oil leak from the valve cover.
 
#11 ·
Who said the 09 had points. I showed two types fire. Look at the 3-sparksticks showing single fire. No cam sensor, possible dual fire... depends on tone wheel design too. Only a slow-mo vid [at the tone wheel knows for sure] watching spark in the view as well.
 
#17 ·
Wish I knew about this thread a couple of years ago when I did the same thing during my first personal valve check on this bike. I had to phone a few friends to convince me of the wasted spark haha. Convincing myself "it didn't matter" was pretty tough! Good stuff here.