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confirming tdc

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Top Dead Center

So I've seen a bunch of threads on finding top dead center, and I've been told that using the marks on the flywheel would be the most accurate way to find it. Can someone confirm that these pictures are an accurate depiction of tdc?

When I look up at this angle, looking square at the notches, the |T is lined up with the notch. Doesn't show in the picture cause of the shadowing, but it's there.

IMG_1083.jpg

At the same time, this is what it shows on the crank gear. This is looking straight on, so the hole is about 2 teeth off from the arrow. Does this seem right?

IMG_1086.jpg

Thanks!

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Those pictures are too blurry to see the marks. The second flywheel mark when lined up with the notch in the LS case is the generally the most accurate TDC mark to see. Remember the eng rotation is CCW on the LS and to use the second flywheel mark. The RS marks should also be lined up at the same time. The marks can be alittle tricky too see just because of how low they are and you need to be level with them to get an accurate view of how well they are lined up.

If you want to be at TDC on the compression stroke then the cam marks need to be lined at the same time the crankshaft marks are. Hope that helps

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Those pictures are too blurry to see the marks. The second flywheel mark when lined up with the notch in the LS case is the generally the most accurate TDC mark to see. Remember the eng rotation is CCW on the LS and to use the second flywheel mark. The RS marks should also be lined up at the same time. The marks can be alittle tricky too see just because of how low they are and you need to be level with them to get an accurate view of how well they are lined up.

If you want to be at TDC on the compression stroke then the cam marks need to be lined at the same time the crankshaft marks are. Hope that helps

Ok, so this is what the first one looks like if the mark wasn't in shadow.

IMG_1083-1.jpg

I rotated the rear wheel forward to line it up, so everything was moving CCW on the LS when the |T on the flywheel was lined up, but the right side when viewed from eye level is 2 teeth off.

Since I've heard that going by the flywheel is a more accurate method, that must mean there can be a discrepancy between LS and RS right?

Thanks for the reply TDW!

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To me it looks like you are using the first mark on the FW (Left side case) to line up. It sounds like your process is only taking you to the first mark also. There is another one about 3/8" behind the first one.

Like TDW said, be sure to use the second mark on the flywheel, you can think of it as the second mark from the front of the bike also. The first one is 10 or so degrees BEFORE TDC and the second one is TDC. Both the LS and RS marks should line up if you are using the correct mark on the LS flywheel.

Yes, the flywheel marks should be used to find TDC, much more accurate, and if you working on the cam chain you need to watch it so it stays lined up while you put the chain on.

Also as you put the chain on make sure you keep the slack to back (tension side), otherwise it'll be off a cog off when the chain slack moves to the tension-er side of the chain and you'll have to redo.

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That picture that you posted of the LS case and flywheel was taken at a strange angle and also cant see the marks on the flywheel at all, thats why I said it was too blurry.

There shouldnt be a difference between the LS and RS timing marks being lined up at the same time, IF there is I would first check the flywheel, key, and crankshaft slot by removing the flywheel.

What kind of mods does the bike have?

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To me it looks like you are using the first mark on the FW (Left side case) to line up. It sounds like your process is only taking you to the first mark also. There is another one about 3/8" behind the first one.

Like TDW said, be sure to use the second mark on the flywheel, you can think of it as the second mark from the front of the bike also. The first one is 10 or so degrees BEFORE TDC and the second one is TDC. Both the LS and RS marks should line up if you are using the correct mark on the LS flywheel.

Yes, the flywheel marks should be used to find TDC, much more accurate, and if you working on the cam chain you need to watch it so it stays lined up while you put the chain on.

Also as you put the chain on make sure you keep the slack to back (tension side), otherwise it'll be off a cog off when the chain slack moves to the tension-er side of the chain and you'll have to redo.

Hey MajHazrd, so should I be looking at the marks on the outer ring of the flywheel, |F |T, and lining up to the |T which is the second mark? OR, do I use the second of these two marks which are on the inner ring of the flywheel, and have no labels to them?

IMG_1089.jpg

The above picture is what I saw when I went back and rotated it via the crank on the right side. I went around once and it skipped past the mark. Went around a second time and was able to stop it on the mark:

IMG_1092.jpg

Thanks!

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those pics make it look to me like the marks on both sides line up right.

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That picture that you posted of the LS case and flywheel was taken at a strange angle and also cant see the marks on the flywheel at all, thats why I said it was too blurry.

There shouldnt be a difference between the LS and RS timing marks being lined up at the same time, IF there is I would first check the flywheel, key, and crankshaft slot by removing the flywheel.

What kind of mods does the bike have?

I had the flywheel off ealier, as I was replacing the cam chain, and when I put it back on, it fit into the key on the crankshaft. Is there anything else that has to be lined up when it goes back on?

Bike just has CCC mods done.

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those pics make it look to me like the marks on both sides line up right.

Ok, then I think was just using the wrong marks on the flywheel. If I go with this I'll just need to adjust the chain over a couple teeth to line up the cam again.

Thanks for all the help guys.

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Sorry I was gone for a while.

I just happen to have my flywheel laying on the bench in the shop. I see the F and T marks you are talking about... don't use those.

Just for clarity:

Yes, use the two on the edge of flywheel with no marks in your last picture. In your picture the first one from the left is Before TDC for spark timing and the second one is TDC for aligning the cam with the crank.

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What gets guys messed up is there are TWO tdc's, compression and overlap. If the both intake and exhaust valves are not loose when the "marks" line up, you need to roll it around 360deg and check again. For just checking valve clearance you can just line the cam sprocket up with the head surface and make sure lobes point the right way, don't really have to pull those side plugs off.

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I would never time an engine off of the lobes pointing the right way.... you could be one to two cogs off one way or the other and never know it.

I also never use a mark on the chain to re-time the cam, there is a chance that the chain could come off the crank gear and jump a cog. I've had it happen.

But then I'm an engineer, its in my personality to precisely check settings 3 times. :banana: I would be constantly asking myself, "Are you sure the time exact? Aaaah its close."

IMHO - Don't leave something as important to performance and valve/head clearance as cam timing, to chance!

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I would never time an engine off of the lobes pointing the right way.... you could be one to two cogs off one way or the other and never know it.

I also never use a mark on the chain to re-time the cam, there is a chance that the chain could come off the crank gear and jump a cog. I've had it happen.

But then I'm an engineer, its in my personality to precisely check settings 3 times. :banana: I would be constantly asking myself, "Are you sure the time exact? Aaaah its close."

IMHO - Don't leave something as important to performance and valve/head clearance as cam timing, to chance!

I know what you mean about trying to cut corners when getting the valve timing right, like marking one of the chain links-not a good idea. The cam lobes pointing rearward is just an indication that your close to TDC on the compression stroke is all. I also dont understand why some guys use a straw thru the spark plug hole-seems like a waste of time to me. Doesnt take long at all to check the marks on the crank and cam for being correct.

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I would never time an engine off of the lobes pointing the right way.... you could be one to two cogs off one way or the other and never know it.

For adjusting the valves, the engine does not have to be exactly at TDC for a perfect valve adjustment. Proper adjustment can be attained as long as the rocker arm roller tip is on the base circle of the cam.

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For adjusting the valves, the engine does not have to be exactly at TDC for a perfect valve adjustment. Proper adjustment can be attained as long as the rocker arm roller tip is on the base circle of the cam.

Still quicker and easier to just look at the timing marks on the cam gear and be sure, than it is to evaluate weather or not the rocker roller is on the base circle of the cam lobe. Guess timing marks are just alittle confusing for some people, but the timing marks were put there as a reference point for that reason.

Can you imagine how difficult or tricky it would be without timing marks?:banana:

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