Challenging a common belief...

[trbig]

Valves....

I've always been told and heard that the valve clearances get tighter on these bikes over time, I've just never experienced this. All the bikes I have seen with a few miles on them need thicker shims. A bike with a lot of miles get noisy in the top end because the larger gap between the cam and shim lets the cam lobe slap the shim.

I've always heard that the clearances SHOULD close since the valve opening and closing sets the valve deeper in the head over time. I've just never experienced this.

What's your thoughts and experiences? Have you had to shim with smaller shims the majority of the time?


Tod

[petejw]

I had three intake valves close on me after about 3 years
after having the head fully serviced and not checking the clearances.
Nothing wrong with the compression test either to indicate the valves were closed.
When I was an auto mechanic many years ago, I think
the wear was more with the valve rockers, resulting in a larger gap compared to the valves wearing into the seat, I think this would be worse with the introduction of unleaded fuel. Leaded fuel lubricated the valve and seat.

[b.walker5]

Mine have tightened up due to the valves stretching slightly over time. In my experience I've found that the shims dont really wear but the cam lobes can, and open up the gap, if the top end lubrication isnt quite what it should be.

[TADracer]

I have always wondered about this too. Seems like it depends where the wear (say that five times) occurs. If it is in the cam lobe, shim or the top of the valve stem or the bearing surface in the bucket then the gap should get larger. If it is in the valve seat then the gap should get smaller.

I have actually never replaced any shims due to wear. Now I have adjusted to the tight side and have replaced a shim or two for that purpose but never for wear.

[trbig]

In my experience I've found that the shims dont really wear but the cam lobes can, and open up the gap, if the top end lubrication isnt quite what it should be.

The cam lobes have nothing to do with the shim clearances. You measure to the back of the lobe with it facing away from the shim. Also, your valves aren't going to stretch.

I have drilled a hole through the shim bucket and I think that the buckets are as tough as the shims.. and the shims, I have never heard of one having any wear to them. Both the shims and buckets are made of some pretty tough hardened steel.


Tod

[DGXSER]

When I checked and adjusted my shims about 3k miles ago now, I wound up using smaller shims on all that changed IIRC.

I have had some folks tell me not to reuse shims because they are worn down from prior use and will not match the printed thickness. IMO, so frickin what! I'm measuring a gap, if it gets the gap correct, I do not care what is written on it. Might make my job little harder to get the right replacement next time I change them out if it is truly worn. Like Tod, I do not believe they wear much if at all. I saw the shims that came form en engine that had obviously seen some miles and honestly a little abuse. And they still did not appear to be worn to me.

I do agree with putting the number side down though so you can at least read the number next time.

[trbig]

Well, with all the used shims I have, many have unreadable numbers on them. They have all apparently wore down to the exact half size... oh never mind. The shims don't wear, the softer cam lobes will. Take your used shims and measure them and see if they've gotten any thinner than the number stamped on them over the years.

If you get new ones.. great... but don't be scared of the used ones.


Tod

[Pat Kelly]

Back when I worked at a Fiat dealer I measured the shims taken out after valve adjustments. If the measured thickness was different than marked (or someone put it in upside-down and wore the markings off) I would re-mark them. Sometimes they needed re-marking but usually not.
I would swap shims with customers doing it themselves at no cost. They had enough other problems .

[Geezer]

I've often ended up having to measure shims that were put in upside down and the marking were gone and I do believe they wear but not that much.

In my experience about half the time valves wear tight and the rest of the time they wear loose. If there is more stem stretch the valve will be tight but if the seat wears more, the valve will be tight. You don't see too much shim or cam lobe wear unless there was an oiling problem.

Geezer

[dbeardslee]

After lapping the valves I checked my clearances after 6k miles. All the intakes had closed some and needed one size smaller shims except one that needed two sizes smaller. All the exhausts were still in spec. I'm still wondering why the intakes would wear in faster than the exhausts.

[b.walker5]

..... Also, your valves aren't going to stretch... Tod

They do... Well document and researched. Significant problem in race engines with doulbe springs. Long spindly, hot lengths of steel under spring pressure being closed at speed against a hardened steel face. Measure a new valve against a used sometime. Difference can be several thou.

[jmnjrpa]

Yeah, they can stretch, expecially if you ever ran lean. The valves are made of very good steel but a lean running engine can melt one. Normally you find the valve face has cupped from being pulled into the head in this instance. Also the metal EXPANDS due to heat when operating, but then contracts when it is not. The molecular expansion is a particular problem in the machining industry.

[trbig]

Then I stand (Or sit) corrected gentlemen.. Thank you.


Tod

[Ivan]

Back when I worked at a Fiat dealer I measured the shims taken out after valve adjustments. If the measured thickness was different than marked (or someone put it in upside-down and wore the markings off) I would re-mark them. Sometimes they needed re-marking but usually not.
I would swap shims with customers doing it themselves at no cost. They had enough other problems .

I had an X-1/9. I know exactly what you are saying. It was a toss up whether the starter went more times a month than the valves needed adjusted.

Now, if I could find another one, I would graft an XS1100 engine in it, and make it lighter, more powerful and damn near bulletproof.

[Ivan]

They do... Well document and researched. Significant problem in race engines with doulbe springs. Long spindly, hot lengths of steel under spring pressure being closed at speed against a hardened steel face. Measure a new valve against a used sometime. Difference can be several thou.

Hence the reason the old guys back in the day used to grind the tip of the valve down when they ground the face.