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Discussion Starter #1
Hi all,

I"m timing the camshaft to the crankshaft and have some questions. On my flywheel there are the T and advance marks and of course the engine has to be at TDC to time the camshaft properly. My first question is that the piston is as at TDC on both the upward and downward strokes, but which one is true TDC, the upward or downward stroke of the piston, and which do I use to determine TDC? (Cylinder jug exposed for clarity) Secondly, there are no other marks on my flywheel other than the T (top) on the left side and the advance marks on the right side of the flywheel. When I look in the timing inspection opening on the flywheel cover, the T never lines up in the inspection hole, neither do the advance marks, why is that? Thirdly, once I determine true TDC, I can just mark it with some paint or scratch a mark, so what is the purpose of the timing marks if one cannot see them through the inspection opening on the flywheel cover? Thanks for everything, I'm new to mechanics so thanks for sharing your knowledge.
 

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Discussion Starter #2
I think the flywheel may have been removed in the past and put on slightly off of what the factory set the timing to. I don't think it affects the performance of the atv, I just have to mark the new TDC and BTDC marks with paint or etch a mark into the flywheel is all, that's why I'm not able to see the markings on the flywheel through the inspection opening on the flywheel cover. I could also remove the flywheel I suppose and realign everything to factory settings so that the "T" lines up in the flywheel cover inspection hole.
 

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Discussion Starter #3
oh and I read that TDC is determined on the compression (upward) stroke and not on the downward stroke when the piston is at the top of the cylinder jug. TDC also has to be determined when inspecting and adjusting the valve clearances of the intake and exhaust valves. The way that my particular flywheel was put back on by a previous owner really threw me off, but you should be able to see the timing marks on your flywheel through your inspection opening on your flywheel cover (recoil starter housing) if it's installed on your machine correctly; if it's not, you can just reinstall it so the factory etched in timing marks line up with the flywheel inspection port or just mark the new TDC and advance marks yourself with paint, for example. I think this is all correct but some verification and/or other pointers is appreciated and welcomed.:)
 

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The flywheel CAN'T go on the crank in a different position. Its keyed.
If you turn the engine to TDC the "T" mark will line up with the timing mark. You can verify TDC with a straw in the sparkplug hole on top of the piston.
 

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Discussion Starter #5
oh ok, thx, so the flywheel is on correctly, good to know. But why doesn't the "T" mark or the advance marks on the flywheel line up in the timing inspection hole on the flywheel cover? I tried lining up the "T" mark manually so that it lines up in the inspection hole but it wants to move left or right and is very sensitive, I have to balance it perfectly with my hands for the mark to be visible through the opening, the marks never line up if I pull the pull start, even very gingerly. So what is the purpose of that inspection opening if I can't use it?
 

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There is top dead center and bottom dead center twice for each complete combustion/exhaust cycle - timing is done at TDC and there is only one TDC - whether it is TDC of the combustion stroke or exhaust stroke is determined by the camshaft that is turning 1/2 as fast as the crankshaft - crankshaft makes two full rotations for each one rotation of the camshaft.

The 'T' mark wants to move due to the pull of the flywheel magnets on the stator, so on some machines the flywheel has to be held while on others it stays in place.
 

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Discussion Starter #7
ok, thx latebird, so when I'm ready to time the camshaft to the crankshaft, I have to anchor the flywheel in place safely so that the "T" lines up in the inspection hole? Any suggestions on how to do it safely, I know enough not to put a screwdriver into the flywheel holes as damage to the stator can result. I"ll just have to leave the flywheel cover off then until the engine is put back together then I can seal it up with a gasket maker, it would've been a lot easier if the timing marks had lined up in the inspection hole in the first place lol
 

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Discussion Starter #8
actually, the flywheel stays in place quite well once I perfectly line up the "T" in the flywheel inspection hole so long as I don't bump it with the flywheel cover and knock things around, thanks again for everyone's info, learning lots every day!
 

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As a mechanic, I remove the flywheel cover (recoil starter) and find TDC with a probe inserted through the spark plug hole - the novice should use a soda straw or plastic instrument that will not damage the spark plug hole threads, valves or piston if the unforeseen should occur - when I have determined TDC, I mark the engine case (if no factory mark is present) so I can put the flywheel at the TDC position easily and quickly.
 

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Discussion Starter #10
Thanks for the info again latebird. One last thing, in the photo, you can see the automatic compression release mechanism of the camshaft, my question is, is it in the correct position? I think it is, in this position it can interact with the small cam sprocket pin when it's rotating in normal operation but if you're new to mechanics like myself, one can never be sure 100%.


IMG_20200318_154316672.jpg
 

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The pin is a stopper - it cannot move beyond that point - off the pin is correct at rest, against the pin when running
 

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Discussion Starter #12
sorry, so in the picture, that small latch should be on the left or the right side of the cam sprocket pin?
 

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Can't say - I never paid attention to it as I have never removed or installed those parts - maybe on of the other guys on here could answer that?
 
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