why do valve clearances tighten up over time?

[ninjaneer]

So I can add Valve Clearance Adjuments as another notch in my DIY Success Stories Belt. :eclipsee_gold_cup: And as maleko89 and one2dmax forcasted, I found my clearances either w/in tolerance or too tight

In the bikes I have done, intakes tighten a little bit and the exhaust valves tighten even more. I have yet to see valve adjustment too loose.

...
Mark is correct. Usually they all tighten up. I read somewhere that I think Damon F. said one tightened and one loosened. BUT, if you think about how the cams are oriented compared to the valves. As they wear and slowly shift deeper into the heads the clearance on the cams is reduced so thinner shims are needed.

I would not consider it normal for the clearance to increase (about the only way this would happen is if the base of the cam was getting worn off). If this did indeed happen the you would have either a sticking bucket which wasn't rotating properly (the buckets slowly rotate as the engine is running) or a lack of lubrication (which would eat the lobe off first).
Sean

So my question: Even though, Sean provided an explanation, my naivety is preventing me from picturing the disappearing clearances. :ummm: Could anybody elaborate a little more on this manifestation? :worthy: Thanks all.

 

[Rusty McNeil]

Yes Damon's engine video states that one loosens and the other tightens.

I have to agree with Sean and Mark, due to the whole geometry of the setup and the wear points (valve seat) if they do anything they'll tighten unless some other unusual anomaly is occurring.

I haven't adjusted enough of them to really know what actually happens though.

If I had to guess the exhaust valves tighten more/faster due to the heat factor accelerating wear.

 

[maxcruiser]

As the valve seat in the head and/or the valve itself wears, the valve seats in the head further, therefore the valve stem is pushed higher up towards the cam lobe, reducing the overall clearance between the two.

Hopefully, this will help you understand why clearances usually tightens up.

Mike

 

[paulibiker]

I can see them tighting up due to valve/valve seat wear but every bike (none of them Maxs) that I've done most valve were loose.:hmmm:

Why do valve clearances loosen up over time?

 

[one2dmax]

Possibly on older bikes with 2 valves that have larger seating surfaces the stem actually wears more then the seating surface/face of the valve. Also, on push rod bikes the ends of the rods tend to wear out the rocker arm and this causes more slop then the wear of the valves can make up for.

 

[ninjaneer]

...Hopefully, this will help you understand ...

Mike

actually, that does help. thanks!


Regards from my Taptalking Hercules Android

 

[dannymax]

The valve seats wear at a much faster rate than any other component in the VMax valve train because the heads are made of the softest material....much softer than the valves, buckets, shims or cam lobes....which are hardened steel, heads are cast and therefore quite porous by comparison.

 

[PATMAX]

My Honda Element has the same condition on the exhaust side only. As the valves wear into the head, this allows the valve stem to creep closer to the cam lobe, reducing clearance. So when resetting clearance or as I like to say, "Clarence", set on the wide side of specs and give yourself more time between adjustments.
So, did you borrow a cam tool or buy one? I can't imagine anyone doing it without taking advantage of Sean's kit. Unless Kyle would help out on a Tech Day.
By the way Greg, how long do you think it would take to do again now that you did it once? Just curious but not bi-curious.
PATMAX

 

[Rusty McNeil]

The valve seats wear at a much faster rate than any other component in the VMax valve train because the heads are made of the softest material....much softer than the valves, buckets, shims or cam lobes....which are hardened steel, heads are cast and therefore quite porous by comparison.

When I did my heads it looked like the valve seat was an insert into the cast material of the head.

Still, I'm sure like you said they're softer than the other compnents.

 

[dannymax]

When I did my heads it looked like the valve seat was an insert into the cast material of the head.

Still, I'm sure like you said they're softer than the other compnents.

That makes sense as cast aluminum can almost be whittled with a butter knife!

 

[ninjaneer]

My Honda Element has the same condition on the exhaust side only. As the valves wear into the head, this allows the valve stem to creep closer to the cam lobe, reducing clearance. So when resetting clearance or as I like to say, "Clarence", set on the wide side of specs and give yourself more time between adjustments.
So, did you borrow a cam tool or buy one? I can't imagine anyone doing it without taking advantage of Sean's kit. Unless Kyle would help out on a Tech Day.
By the way Greg, how long do you think it would take to do again now that you did it once? Just curious but not bi-curious.
PATMAX

I borrowed Kyle's shim kit. Speaking of which, I need to get it back in the mail. So, how long if I had to do it again, good question...It took me the better part of two hours to get the covers off. I'd say another two or three to fit in the adjustments, and a whopping 10 to get things back together. But as you may be alluding to, I was taking careful steps into the unknown, measuring and remeasuring, stumbling over the mistakes of consulting the intake shim table instead of the exhaust table and using the feelers' metric numbers as the English numbers in the tables; plus I took additional reassembly steps of a carb rejet, the opportunity to clean up parts and pieces that are difficult if not impossible to get at, and rerouted some of my personal wiring. Now that I've done it, maybe an hour to get at the shims, maybe an hour put in new ones, and maybe three hours to reassemble cleaned up parts. I must say after the first cylinder, I started to getting pretty good by the last one. I even redid the first one because I finally understood how to judge the feeler's resistance when pushing and pulling it in to and out from between the lobe and shim.

 

[Fire-medic]

And next-time you won't be intimidated by the job. The first time I did my KZ1000 it ran so-much better, or was it all in my head? I only had two which were out, so not-too-bad.

Did you 'mike' the shims coming-out & going-in, & compare the readings to your calculations?

SOunds like your desire to detail things took the most time!

I borrowed Kyle's shim kit. Speaking of which, I need to get it back in the mail. So, how long if I had to do it again, good question...It took me the better part of two hours to get the covers off. I'd say another two or three to fit in the adjustments, and a whopping 10 to get things back together. But as you may be alluding to, I was taking careful steps into the unknown, measuring and remeasuring, stumbling over the mistakes of consulting the intake shim table instead of the exhaust table and using the feelers' metric numbers as the English numbers in the tables; plus I took additional reassembly steps of a carb rejet, the opportunity to clean up parts and pieces that are difficult if not impossible to get at, and rerouted some of my personal wiring. Now that I've done it, maybe an hour to get at the shims, maybe an hour put in new ones, and maybe three hours to reassemble cleaned up parts. I must say after the first cylinder, I started to getting pretty good by the last one. I even redid the first one because I finally understood how to judge the feeler's resistance when pushing and pulling it in to and out from between the lobe and shim.

 

[bazwell]

I'll throw in a little more knowledge into the fire. I got nothing better to do right now. :rofl_200:

Old cast iron heads used to seat the valves directly onto cast iron. It could almost handle it... provided you added lead to the fuel to lubricate the valve seats. :biglaugh:

Aluminium heads needed to have hardened valve seats inserted. They are even called "valve seat inserts", and are made out of some pretty hard alloys.
Therefore, aluminium head motors don't need lead, at all. Many of them can handle LPG as a fuel too, which is much more abrasive.
(However, if you were building a motor specifically for LPG you could change the valve seat inserts on the exhaust side to an alloy that has a higher nickel content, as the nickel lubricates.)

What everyone said about the valves and seat wearing is spot on. That's why valve clearances usually become closer. Camshafts wear, but not usually on the base circle, more at the pointy bit, which does not affect valve clearances.

Valve trains that use rockers are different, because the rockers can wear at both ends, and they can wear the rocker shafts and bushes (and the top of the valve wears a bit on all motors too). So when you add up the little bits of wear on rockers together sometimes they can wear faster than the valves and seats. In this case, the clearances become more. Rocker shafts are bastards for wear. The worst design is side cam engine with pushrods, rockers and rocker shafts. Funky old pommy motor cars were quite often like this.

So, the best motors (like the v-max :biglaugh usually have buckets and shims. Less moving parts, less wear, longer intervals between adjustments! :eusa_dance:

 

[MaxMidnight]

A valve seat insert.

and its relationship with the valve and guide.