While doing some close up photography for a project I realized something. You need not expose the flywheel to use the timing marks to set your valves. While some of you may say "duh" I know a lot of folks still go to the trouble.
First of all, the cam rotates half as fast as the flywheeel. I put a piece of tape on the variator (light blue), lined the small sprocket holes (red) up with the head, and rotated the engine twice. On one full rotation of the engine the large reference hole (yellow) is exposed, on the next it's 180 degrees away and hidden:
The line next to the T mark on the flywheel was in this position in both of the previous pictures:
So lining the timing tab up with the T mark only means the two small holes are lined up with the head. To get the valves oriented correctly you only need position the large reference hole on the cam sprocket away from the head and ignore the T mark. Here's the cam sprocket with the large reference hole unexposed (yellow arrow). You can see by the red arrows the cam lobes are pushing on the rocker arms making the valve set impossible:
Here the engine is rotated one full turn and the cam sprocket 180 degrees. The large reference hole (yellow arrow) is now away from the head and the cam lobes are well away from the rockers (red arrows) allowing for a valve set:
SO POSITION THE TWO SMALL HOLES ON THE CAM SPROCKET IN LINE WITH HEAD AND THE LARGE HOLE AWAY FROM THE HEAD TO SET YOUR VALVES. It is not necessary to expose the flywheel on a routine valve adjustment.
Position your cam sprocket as pictured above.
The cam sprocket does not have to be exactly in this position, if it's a couple degrees off the lobes will still be well away from the rockers.
So what are the timing marks for anyway? If you're reassembling the engine the T mark means the piston is at the top. There's some variation on the marks from engine to engine but on mine when the flywheel is oriented with the line NEXT to the T (yellow arrow) and lined up with the timing tab (red arrow), then the piston is at the top:
The cam sprocket can then be installed with the timing lines oriented parallel to the top of the head and the large reference hole exposed. This will be TDC of the compression stroke:
I'm going to delete the part about the T mark on the Scooter Doc valve set tutorial. It's a waste of time to bother with exposing the flywheel. The other way to set your valves is rotate the engine until one cam lobe fully pushes on it's rocker arm, then set the other valve. Rich
That is all fine and well Rich, IF you haven't taken the Cam off and the chain is nice and tight. BUT what if you are haveing some starting problems or some nasty backfireing or loose of power and you suspect the timeing. So you look and the chain and it happens to be really loose due to the tensioner going south so now you suspect it might have jumped a tooth one way or the other. You do want to check the Flywheel and see if it is by the first line between the T and the Arrow and the Cam lined up at top dead center. In that case checking the Timeing Marks on the Flywheel is a must do. Also it is a good Idea when all is correct to mark the Flywheel were the timeing mark is pointing to on the Flywheel as well as the CAM and Chain mark one tooth and the Link it sits on. That way if you happen to every need to take the Cam or chain off you will get it right the first time and not be one tooth off. my .02 Alleyoop
I agree with everything you said Alley but for a routine valve set without the problems you mentioned using the timing mark is a waste of time. In fact, I think it's confusing to a lot of novices. How many folks have obsessed about the timing mark drifting a bit one way or the other when they're doing the set when it really means nothing? However, I would say that marking where the tab orients on the timing marks before there's any significant wear on the bike is a good idea. Where the tab sits for one GY6 engine might not be the same as in a manual. It would really help to know what is specific for your bike if doing a rebuild. Rich
For a rebuild I always use physical Top Dead Center...the timing marks are inaccurate and confusing, IMHO.
To set the valves in a routine adjust.. I use a rollover method..it accounts for cam wear etc. and is easy...
1. Remove the spark plug or back it off so it leaks compression 2. Remove the valve cover. Remove the fan cover 3. Using the cooling fan with a wrench or turn with your hand, rotate the engine CLOCKWISE 4. Watch the valves. 5. When the INTAKE valve, the top one, is all the way open (the rocker arm is pressed all the way down) stop rotating the engine 6. Loosen the locking nut (9mm) on the EXHAUST valve, the bottom one, and using a feeler gauge with oil on it, turn the adjuster screw until it is .005 inch... 7. Tighten the locking nut and re-check the gap to .005"
8. Rotate the engine again, CLOCKWISE until the EXHAUST valve is fully open (the rocker arm is pressed all the way down) 9. Now adjust the INTAKE valve, the top one, and set it to .004 inch 10. Tighten the locking nut and re-check the gap to .004" 11. Replace the valve cover 12. Screw in the plug, replace the plug boot and start up the engine...
On some engines if you find there is too much valve tapping, you can back it off these settings by .001 INCH or so.
Some people set both valves at .004 INCH…
Last Edit: May 14, 2012 12:16:16 GMT -6 by sprocket
Post by trailheadmike on May 14, 2012 16:13:32 GMT -6
If you don't mind taking a step back for me, when I adjusted the valves on my 257cc Linhai type last year I found TDC by using the arrow marking only. I did not expose the timing chain or anything. I couldn't have done anything too wrong since my scooter works fine, but am I to understand from this string that the arrow is actually not a proper way to go? I learned how to do it from the internet in the first place so I could have taken the advice of a dunce, making me a dunce once removed. Thanks in advance so I'll know for the next time.
2008 Vog 260; Dragon Custom Exhaust
13,335 miles, learning how to become a mechanic with each one.
Yup Rich and the GY6 is not a Honda engine either like you will see all over the internet...they had a similar engine but it is not a GY6...all the oil flow was external to the block and many other differences.