Valve Clearance Issues - Honda CG 125

[rpsmith79]

Following on from my recent topic on what i thought was electrical issues with my bike, i have followed the advice given by Teflon Mike (yes i really did read through all hos posts ) and i seem to be having issues setting the valve clearances

Let me elaborate

I got the rocker off, turned the engine to TDC, loosened off the locknut and adjusted the clearances, they were quite a way out it seemed as i had to turn them out quite some way

After that i turned the engine over again 1 full turn, and the clearances were now massive (a good few mm each), so turned the engine 1 full turn again and they were back to the proper clearance (0.08mm), 1 full turn again and they are massive

What is going on.......................... HELP PLEASE

[Baggyman]

4 stroke - goes around twice per bang. Only one of those is TDC. Suspect you were on the other one (BDC).

If the plug is out (makes it a lot easier to turn) you should be able to see/feel the piston with something gentle when it is at the Top

Don't drop anything down the plug hole
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Old fart
Baghira, modded GS1000 and the T150 I bought in 1978 when I was 21

[rpsmith79]

[Teflon-Mike]

Without the book, you would check the tappets on the rock.. that is with the piston at TDC on the compression stroke, when both valves aught be completely closed.

Book instructions to use timing marks will be more scientifically finding same point in the combustion cycle.

One full crank rev will take you from TDC on compression, to TDC between exhaust and induction, when both valves will be open.. exhaust about to close, inlet having started to open, and you'll have pressure on the valve stems from the cam, and you 'aught' have no clearance gap on either.

Four 'strokes' to a combustion cycle.... piston strokes; one up, one down per rev, two revs per cycle, four strokes.

Cam shaft is driven at half crank speed so it revolves once to complete one combustion cycle, for two crank revs, four strokes.

Make sense?

Have you re-checked cylinder head stud torques, post replacement and 'first run'?
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[rpsmith79]

Yeah, panic over, looks like i had adjusted them at BDC rather than TDC, unfortunately though that doesn't help me in finding the route cause of the engine cut out as i don't now know if the clearances were correct or not before i incorrectly adjusted them at BDC.............arse!

Ahh bugger, forgot to check the head stud torques, will give that a go tomorrow, only takes a few mins now to take the rocker cover off, i could almost do it blindfold now, lol

[neptune8]

I always use the "feel the piston position" method to find top dead center. Remove the plug, and use a plastic drinking straw down the plughole to feel the piston. rotate the engine by turning the rear wheel with top gear engaged. The worst thing that can go wrong is you bend the straw. Turn the engine until piston is at or very near the top with both valves closed. Looking at the cam profile, it does not need to be precisely at top dead center. I personally think that you still have a charging problem, based on battery voltage readings.
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Enjoy yourself, its later than you think

[Baggyman]

much easier to get it from pictures - just google 4 stroke cycle and it will all fall into place. Words just confuse things.

another way to look at it is that you want clearances there when it is "off the cam" - i.e. the lumpy bit on the camshaft is not trying to raise that particular valve. as long as the lumpy bit is pointing away from where the rocker rides the cam, you will be getting it right
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Old fart
Baghira, modded GS1000 and the T150 I bought in 1978 when I was 21

[rpsmith79]

Cheers everyone, like they say, every day is a school day

[Robby]

Sounds like you adjusted them at TDC, just TDC on the compression stroke. The crank will go around twice for every one revolution of the cams.

This is why you set the crank to the T mark, and then look at the timing mark on the cam to line it up with something.

For future reference, valve clearance are never that far off unless someone messed with it. If the gap is meant to be 0.1mm and you can't get any of the feeler gauges in, you're out by 360 degrees on the crank.

[rpsmith79]