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Old 12-30-2007, 08:19 AM   #1
creola OP
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XT225 TDC Marks

The TDC marks on the flywheel of my 2007 XT225 are not at all similar to those referenced in any official documentation I have seen.

Yesterday I did the initial valve check at 528 miles at what I assumed was TDC. The intake was within spec and I had to adjust the exhaust because it was .0.05mm to loose.

The radial marks on my flywheel consist of an elongated H followed by a lone l. Therefore, I have three radial marks from which to choose, not the often referenced one radial mark followed with a T.

Per a photo documented method I chose the middle of the 3 radial marks.

Later I read that the TDC mark is the third radial mark.

If needed I will pull the spark plug and set the TDC by the SSBB method. However, I would rather ride today than pull down the bike.

So can anyone document for me the correct TDC radial mark on an '07 XT225?
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Old 12-30-2007, 06:26 PM   #2
DaveRMS
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http://www.xt225.com/forums/ubbthrea...=10228&fpart=1

Quote:
these are the 3 radial groves on the flywheel, the one in the middle is top dead center (TDC), however a four stroke engine may read bottom dead center ( Im not that sure about this statement). However, it is not important. What is important is to check the exhaust gap while you have the center groove visible. If you can get a .003" feeler gage in the gap your at TDC. If not rotate the flywheel another 360 degrees anti-clockwise and check the gap. This time it will be there. So, you have a 50/50 chance of getting it right the first time. By the way dont use the rachet function on your tool. Once you see the flywheel notches, just spin your tool one full revolution to see notches again!
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Old 12-30-2007, 09:51 PM   #3
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Quote:
Originally Posted by GSNorCal
That reference quote is great!
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Old 12-31-2007, 05:45 PM   #4
creola OP
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Actually, I believe he is incorrect. At least for the '07 XT225.

Here are my results:

My '07 and I suspect other years' models do not have the radial mark and the T on the fly wheel. Instead my XT has the elongated H, consisting of two radial marks connected with a horizontal line, followed in a CCW direction by a lone radial mark.

The elongated H is fact used for timing the engine and represents the acceptable firing range.

The lone radial mark is TDC. I determined this using a dial gauge to observe the movement of the piston. On three occasions the maximum piston extension occurred at the lone radial mark. That is sufficient data for me to conclude that TDC occurs at the lone radial mark, provided you are on the correct stroke.

The piston travels an additional 0.13" vertically as the flywheel is rotated, CCW, from the middle radial mark to the third radial mark.
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Old 12-31-2007, 06:43 PM   #5
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interesting. I'll have to double check our 2005 then. We haven't used it since we did the adjustment.
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Old 01-01-2008, 03:26 AM   #6
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Unless your valves were at the loose end boundary of the range they should still be alright.

On my first attempt while using the middle radial mark as TDC, the exhaust was at 0.24mm so I reset it to 0.17mm. A couple of days later, when I decided the middle mark was possibly incorrect and performed the dial test, using the third or lone radial mark the exhaust valve gap had only increased 0.01mm to 0.18mm in the additional 0.013" the piston travelled. The intake gap also increase 0.01mm.


So if your valve gaps were at least a couple of points below the maximum they should still be alright.

I always determine the actual gap verses just checking the max-min gap.
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