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Old 07-06-2013, 04:12 PM   #1
WantToRideMoar OP
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Honda XR600R valve timing question

I've got the Clymer manual for my new-to-me 1993 XR600R sitting here in front of me, and a task for myself after experiencing some hiccuping power while on the highway this morning.

I'd get intermittent failure of the bike to deliver power on a combustion stroke, at 5500 RPM and higher. This resulted in some stuttery cruising on the highway on the way to a ride this morning.

I've owned this bike for a little over a year and I've so far focused my maintenance tasks on tires, oil changes and a speedometer install. Never been into the engine itself thus far.

I can find TDC by inserting a chopstick through the sparkplug hole and watching it rise/fall as I cycle the piston from the left side of the motor. I see the intake valves rise during one cycle and the exhaust valves rise on the second cycle.

My Clymer manual says:

Quote:
9. With the ignition timing mark on "T", if all rocker arms are not loose, rotate the engine an additional 360* until all rockers have free play.
I've rotated the engine probably 7200 degrees so far, and the rockers have no free play. Unless I don't know what "free play" means.

What is meant by "free play" in the rockers? Them sumbiyatches are tight and have no rattle to them at all.
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Old 07-06-2013, 04:37 PM   #2
whisperquiet
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If the rockers have any free play at all (at TDC), you can feel movement as the rocker should have at least some clearance between the valve stem, the rocker arm, and the camshaft on which it rides. Here is a good tutorial on this:

http://www.4strokes.com/tech/honda/setvalve.asp

Your valve clearances may have closed completely up and have no "free play".
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Old 07-06-2013, 05:35 PM   #3
CycleDoc59
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The manual means that on one cycle, TDC occurs
at "overlap", where the intake is closing while the
exhaust opens. This is not where the valves can
be checked. On the next cycle (engine rotated another
180 degrees), TDC occurs at the top of the compression stroke,
so both valves are closed. (air shoots out of the plug hole
during this stroke, making it fairly obvious)

At this point there should be a bit of play at each
valve rocker, and where valve clearance is checked
and adjusted if necessary.... If there is no free play
at all, the valves cannot fully seat resulting in loss
of compression, plus dirty and/or burned valves and seats.
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Old 07-06-2013, 06:20 PM   #4
WantToRideMoar OP
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K, now I'm confused.

Linked article says:

Quote:
You want to adjust the valve clearance on the compression stroke, that is when the intake valve has opened and air has been sucked in, then the piston rises up compressing the air. Rotate the motor with the kick starter so that the exhaust valve has just open, and then shut and the intake valve is just about to open. You will feel with the screw driver that the piston is at TDC and the ‘T’ mark will show through the LHS inspection hole. This is not the correct TDC. Rotate the motor a little further and you will notice the intake valve open up. Keep rotating slowly and you will feel the piston rise again to another TDC. This is the correct TDC to adjust the valve clearance from. If you look through the LHS inspection hole now, you should see the letter ‘T’, but it might not be perfectly lined up the groove in the case cause the kick-starter spring won’t let it sit perfectly. I used a length of string to hold the kick-starter at the perfect angle to line up the two marks. There should be play in all the valve arms at this point. There are several marks, so be sure you have the ‘T’ mark. The key things to remember are the T mark must be lined up, and there should be some play in all 4 of the rocker arms.
I have no freaking idea how anyone is supposed to rotate the engine with the kickstarter and micro-manage lining up the T-mark through the sighthole on the opposite side of the bike... Why would you write a how-to as weird as that rather than using something simple like a freaking wrench so you can sight the T-mark? What am I missing? Seems you don't have any business adjusting valve clearance if you don't have a socket wrench.



And there is no rotating slowly... something is springloaded in there to force the thing to cycle hard through TDC after a certain point. I can't freeze it at the T-mark.


I'm going to give it another try tomorrow morning... there was no play in my rocker arms at either of the TDC positions so I may have messed up and timed on the exhaust stroke. I don't know, it was 100+ degrees out today while I was doing this and I drank about a gallon of water while working.

Just to be sure I understand...

1. Pick the TDC stroke where the intake valves have opened and the compression stroke has happened, not the TDC stroke where the exhaust has just happened and the intake is about to.
2. Try to center perfectly on the T-mark. Somehow. Even if the bike won't let me.


However, CycleDoc, you said:

Quote:
The manual means that on one cycle, TDC occurs
at "overlap", where the intake is closing while the
exhaust opens. This is not where the valves can
be checked. On the next cycle (engine rotated another
180 degrees)
, TDC occurs at the top of the compression stroke,
so both valves are closed. (air shoots out of the plug hole
during this stroke, making it fairly obvious)
Doesn't it need to rotate 360*, not 180? The T-mark should always be an indicator of TDC? Can the T-mark drift off TDC and need to be recalibrated?

And.... assuming I did do everything right today (too hot right now and second guessing myself), would valves with insufficient clearance cause the skipped combustions I was experiencing on the highway at 5500 RPM?
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Old 07-06-2013, 08:13 PM   #5
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Old 07-07-2013, 03:13 PM   #6
WantToRideMoar OP
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mcma111, thanks for your advice and conversation yesterday. Really appreciated.

All done with the valve clearancing now. Going to take it out in a little bit here to ensure the problem is resolved, run up and down the highway a bit to see if the stutter is gone.
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