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Old 06-22-2009, 06:05 PM   #1
cbr600F4
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Question Timing help

Ok here is the deal. I rebuilt by honda 200 fourtrax 4 wheeler this past weekend. I tried to make sure that I lined everything back up to the marks on the cam sprocket. I must have been off by a bit. The 4 wheeler will start up, but I can tell the timing is off.

When the piston is top dead center, only the exhaust valve should be open, or both should be closed, right? I think I saw the intake valve a bit open at top dead center and this is my problem.

Feel free to give me some advice on how you would set the timing. Keep in mind this is a one cylinder engine (old school and simple) and 2 valves.

Thanks
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Old 06-22-2009, 06:08 PM   #2
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At TDC, the valves should not be tight. Both should be closed, and a certain amount of play per repair manual(adj valves)


Pull the plug, put an extention or something in it and turn the engine. When the rod stops going up, turn it just a little more... there is some slop due to the joints at the piston for when the rod comes around the crank.

^^that's very generic description; there may be specifics or crankshaft markings to easily set up TDC. Remember one top cylinder position is w both valves open, the other is with them both closed(four combustion cycles, two rotations.)
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Old 06-22-2009, 06:20 PM   #3
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Quote:
Originally Posted by CaligoneTx View Post
At TDC, the valves should not be tight. Both should be closed, and a certain amount of play per repair manual(adj valves)


Pull the plug, put an extention or something in it and turn the engine. When the rod stops going up, turn it just a little more... there is some slop due to the joints at the piston for when the rod comes around the crank.

^^that's very generic description; there may be specifics or crankshaft markings to easily set up TDC. Remember one top cylinder position is w both valves open, the other is with them both closed(four combustion cycles, two rotations.)
Thanks

On more question, isn't there a stroke where only the exhaust valve should be open (exhaust stroke)

If this is true how would i know if i am on the compression stroke (both closed) or the exhaust stroke?
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Old 06-22-2009, 06:24 PM   #4
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Intake, compression, ignition and exhaust...

there is a small overlap between intake and exhaust, so the exhaust will close as the intake is opening.

If you pull off the valve cover the cam, pushrods, whatever it has should not be pushing on the rockers/valves. if it is, the timing is off or you are 180 degrees out and on the wrong stroke.

The easiest way to find it is to put a compression tester in the spark plug hole, take the gauge off and put your thumb over the hole. As you crank the engine it will get hard and that is the compression stroke. you let off your thumb and the air rushes out.
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Old 06-22-2009, 06:38 PM   #5
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Quote:
Originally Posted by CaligoneTx View Post
Intake, compression, ignition and exhaust...

there is a small overlap between intake and exhaust, so the exhaust will close as the intake is opening.

If you pull off the valve cover the cam, pushrods, whatever it has should not be pushing on the rockers/valves. if it is, the timing is off or you are 180 degrees out and on the wrong stroke.

The easiest way to find it is to put a compression tester in the spark plug hole, take the gauge off and put your thumb over the hole. As you crank the engine it will get hard and that is the compression stroke. you let off your thumb and the air rushes out.
The good old thumb trick, forgot about that one. I will try this next weekend. I will update this thread.

Thanks for the help man
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Old 07-05-2009, 11:51 AM   #6
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Quote:
Originally Posted by CaligoneTx View Post
Intake, compression, ignition and exhaust...

there is a small overlap between intake and exhaust, so the exhaust will close as the intake is opening.

If you pull off the valve cover the cam, pushrods, whatever it has should not be pushing on the rockers/valves. if it is, the timing is off or you are 180 degrees out and on the wrong stroke.

The easiest way to find it is to put a compression tester in the spark plug hole, take the gauge off and put your thumb over the hole. As you crank the engine it will get hard and that is the compression stroke. you let off your thumb and the air rushes out.
Did the thumb trick and adjusted the cam shaft. took two tries, but got it done. Timing is dead on. Thanks again Cali
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