Valve Clearances And Confusion

[ferg]

Background: I'm in the process of doing the valve clearances on the CG before it goes up for sale. At first it seemed easy. This was the first time I had attempted it but it was quite a simple process..... or so I thought.

Problem: I have the "T" mark aligned to the casting mark, measure up and adjust. Simple yet..... Why does the clearance change for each rotation?

There seems to be a 'tight' measurement and after a full 360 rotation a 'loose' measurement. This repeats after every rotation, tight, loose, tight, loose and so on. I understand that looser valve clearance is better than them being too tight so I set them up on the 'tight' rotation meaning that there was the 0.08mm gap in the tight and then a whore of a gap on the 'loose' rotation.

When I put it all back together again however it sounded ridiculous. I've never heard the mythical bag of spanners but I'm guessing they sounded very similar to each other.

So I took it apart again and set it up on the 'loose' rotation, this means that in every second rotation (the tight one) there is no play. I don't think this is right either however?

I tried starting it but I was being eaten by midgies and needed a break. It was however not really playing. Could this now be due to the clearances being too tight and so a loss of compression?

Questions: Why does the bike seem to have two differing rotations? Is this the norm? Is this anything to do with the whole four stroke cycle? Am I going to have to make up a setting that gives the best of both worlds? Why did I bother taking it apart in the first place?!

Answers and discussion would be gratefully appreciated.

Yours,

Tappety McTight

[BudgetBoy]

PIP's video expalins it very well IMO. You get a tight reading when its pushing on the rod and a loose reading when its not.Set it when its PUSHING on the rod.Metal expands when hot and the noise you are hearing will get quieter or disappear when warm.

[alexp5]

Make sure the piston is at TDC on the compression stroke (rockers loose) If the rockers are tight, rotate the crank 360 degrees and realign the marks, then check and adjust clearances.

[ferg]

This is still confusing but thanks for the time so far guys.

So by aligning the "T" mark as directed and having the bike at TDC there is still a margin for error? As in it could still be on the wrong stroke? Hence why I am getting two different stories in terms of clearances at the valves as in one stroke has them loose and one tight?

If that's right though does setting them on the 'loose' stroke mean that they will be kept open when they shouldn't? Like I said I set them on the 'tight' stroke and there was far too much valve train noise. I have set them at this setting now, on the 'loose' stroke, will need to see if I can get it going again. I didn't give it much effort last night but it did make me wonder about it messing with the compression etc....

[alexp5]

Are you making sure the motor is cold first..?

Here's a link that should explain things for you: http://hondacg125.awardspace.com/valve_clearance.htm

[ferg]

Yep completely cold. I am following everything by the book, advice etc. In theory this is a simple job and not beyond what I can do but...... what's been said doesn't actually fit with what I'm seeing! Cheers for the link, I've seen it before and looked back at it when I was getting such different results!

[stretch]

The "T" mark you talk of is on the cam or crank?

If on the crank, then you can have it there but it doesn't mean the cam is in the right spot, like millemille is saying, 2:1 ratio crank to cam all of that.

[ferg]

Simple as that indeed. Thank you all for that. I wonder why it said nothing about that in any of the guides I read, including the Haynes manual? There is only ever mention of getting it to TDC by using the marks at the crank end, not which TDC. Is it just a basic bit of knowledge that I've somehow missed out on? Glad I noticed and asked though. You lot are incredibly helpful Thanks for the education.