Another Q on valves

[James England]

Hi again Folks

I have another question before getting the things together to check/do my shims.

As the valves wear into the seats, the cam gaps get smaller. Right? Which means that progressively thinner shims are needed to get the gap right.People have mentioned noisy valves as an indication that the gaps are wrong. Why would a valve get noisier as the gap gets smaller? Old-fashioned tappets get quieter as the gap is reduced.

Or is it that the gap usually gets bigger, due to wear on the cam lobe and shim? In which case the solution would be thicker shims?

[BA80]

There are 2 schools of thought on that question James. The most popular opinion is that they close up as the seats wear.

I tend to agree with the lobe and shim wear however I have had to adjust in both directions.

I believe it's a bit of both and like any non hydraulic setup, it needs regular care.

[James England]

So do they always get noiser as they wear then?

[BA80]

Re read my post.

[CatatonicBug]

So do they always get noiser as they wear then?

No. When I adjusted mine, they started to rattle like never before! What you said makes perfect sense - as the gaps get smaller, the rattle gets quieter, to the point that there is no gap between the cam lobe and the shim, making no noise at all. No noise = Bad thing.

[James England]

Re read my post.

I just did. So you've adjusted both ways. Were the valves noisy on all the ones adjusted then, regardless of clearances. do you think? Or just those that had got bigger...?

[James England]

No noise = Bad thing.

Thank you. That's what i've been trying to get at. Effectively then, some noise is good. Mine do make some noise but I don't think it's excessive (pardon the pun). I'll measure the clearances cold and see what's what.

[crazy steve]

No noise = Bad thing.

Yes, if your motor is getting progressively quieter, it's time for a valve adjustment!

Yamaha reduced the intake clearance in '80 from .006"/.008" down to .004"/.006", pretty much to reduce valvetrain noise; maybe they got complaints? This gives you options; you can run the big end of the 'looser' early spec if you're willing to put up with the racket and not have to adjust the intakes as often. Or you can run them with the tighter late spec and gain just a bit of valve lift....

[James England]

Yes, if your motor is getting progressively quieter, it's time for a valve adjustment!

Yamaha reduced the intake clearance in '80 from .006"/.008" down to .004"/.006", pretty much to reduce valvetrain noise; maybe they got complaints? This gives you options; you can run the big end of the 'looser' early spec if you're willing to put up with the racket and not have to adjust the intakes as often. Or you can run them with the tighter late spec and gain just a bit of valve lift....

I wouldn't want to risk burning a valve. My engine doesn't sound like a bag of spanners, just the usual top end 'rustle' of most bikes. I really ought to speak with data, as they say, so I'm going to measure the clearances tomorrow when the engine is thoroughly cool. Again, I'm not going to fix it if it ain't broke! I think I'd prefer to keep it within the original tolerances; too much gap must be better than too little.....

[DGXSER]

The 80-81 change in clearance also had to do with the change in size of intake valves, and the cams changed a bit as well. So it is a little more complicated than they just wanted to quiet things down.

I agree that the noise will disapate as the gap shrinks. And I have never had a valve that was to loose, but more than half that were to tight.

For my engines, I set the valves per the spec for that year engine.

[James England]

Follow up

Well, taking a deep breath, I checked the valve clearances today and found that only one of the eight valves was correct. The other seven were all too tight, which I took as a kind of good sign because it's consistent. Not having the Motion Pro 'Grind it Yourself' valve tool, I removed the cam caps and top chain guide. I must say, I found it heavy going and a real pain to get the dots lined up on the camshaft and the crank at the T position when putting it back. I ended up taking the exhaust sprocket off but getting it back proved to be fiddly because, of course, the camshaft always has one lobe pushing on a shim and kept it lifted. Then when I got it back in, the dot was out! I got there in the end but reckon I'll use the valve tool next time.

I have a collection of 24 spare shims, although, after shuffling the ones already in the bike, I only needed to swap two from the collection.

Since the general consensus seems to be that the gaps get smaller (mine certainly had) and the shims need to be thinner and thinner, then I have a lot of shims that I'll probably not need to use, so if anyone needs some and has any swaps, please let me know.

All the gaps are now correct and, although all the swapped shims were for thinner ones, the engine sounds quieter...... I could immediately tell the difference in tuning though and had to raise the tickover slightly. Just been for a fast burn and all is well. I can't say I notice any performance difference but the gaps weren't massively out in the first place.

Thanks everyone for the input. I'd never done this before and felt slightly apprehensive. Needless to say, having this forum is very reassuring indeed

[Geezer]

Back when I was turning wrenches for a living I found that 60% of the time valves would tighten up and the rest of the time they would wear loose. In all the engines I tore down and all the shims and cams I measured I didn't see the cause. I assumed that there must be a bit of valve stem compression going on but I never proved it...

Geezer

[SFerinTEXAS]

I assumed that there must be a bit of valve stem compression going on but I never proved it...

That could well be the case. Glass is a liquid that that stays solid because it is below its melting point. With enough steady concentrated pressure over time it will deform. Probably the same with steel but at a slower rate. And consider the pressure and heat the valves go thru.