Valve recession?

[Katman]

Does anyone have any interesting theories as to what causes valve recession?

Interestingly, I've only ever come across it occuring on inlet valves.

[Ocean1]

Which sort? The seat insert sinking deeper into an alloy head or the seat itself getting eroded away?

The second became more of a problem on exhaust seats when unleaded petrol came along. But I stopped being concerned about such things about then.

[schrodingers cat]

<iframe width="420" height="315" src="http://www.youtube.com/embed/sEf8va1S7Sw" frameborder="0" allowfullscreen></iframe>

Also

<iframe width="420" height="315" src="http://www.youtube.com/embed/cfGg15WgSEU" frameborder="0" allowfullscreen></iframe>

Notice the valve gear rotates. Thats where lead was so effective in minimising the scuffing.
Nowdays the material spec of the valve vs the seat gets to deal with things

[Katman]

Which sort? The seat insert sinking deeper into an alloy head or the seat itself getting eroded away?

The second became more of a problem on exhaust seats when unleaded petrol came along. But I stopped being concerned about such things about then.

It's not the seat that wears - it's the valve face that hammers itself into the seat.

It's happening in motors that have been built well after the advent of unleaded fuel.

[Ocean1]

It's not the seat that wears - it's the valve face that hammers itself into the seat.

I've seen both. My KTM head is currently on the bench waiting for new valves, the intakes were worn beyond what I considerd recoverable. Got some nitrided stainless steel jobs for it.

I worked with an aircraft engine builder once, they had issues with valve and seat wear relating to the effects of various additives in different fuels well before the general automotive industry did. He explained it as almost a micro-forging of metalic wear particles into the seat face, welding the valve to the seat. The valve lifting again tore the welded patch apart. Made sense of what I saw in those days, and I'd say whether the wear was on the seat or the valve probably depended on the respective materials.

[Katman]

This is the type of wear I'm referring to.

<img src="http://media.noria.com/sites/archive_images/Backup_200309_natural-fig1.jpg"/>

[Ocean1]

Yep, that's it.

Although in passing; that is not what I'd call a "normal" valve profile.

[Katman]

Yep, that's it.

Although in passing; that is not what I'd call a "normal" valve profile.

No, I think a cartoon artist drew those pictures.

[ducatilover]

This is the type of wear I'm referring to.

Looks like a Cluedo piece.
My theory would be the valve being made of a softer material and the valve being exposed more directly to heat than the seat, the seat has more ability to absorb impacts because the energy can be channeled away from it, whereas the valve cannot.
But, I'm no genius.

[Katman]

Looks like a Cluedo piece.
My theory would be the valve being made of a softer material and the valve being exposed more directly to heat than the seat, the seat has more ability to absorb impacts because the energy can be channeled away from it, whereas the valve cannot.
But, I'm no genius.

Interesting theory.......



.....but, as mentioned, I've only ever seen it happen to inlet valves (which obviously run considerably cooler than exhaust valves).

[ducatilover]

Interesting theory.......



.....but, as mentioned, I've only ever seen it happen to inlet valves (which obviously run considerably cooler than exhaust valves).
You're right there, but they're only cool when the intake charge enters the cylinder, but I suppose that debunks my heat theory. Damn.
Could cam ramp profiles have anything to do with it, or it could purely be the lack of lead?
I vote: Two similar motors with fresh valves (two GN250s or some other cheap shit), run one on lead additive and one on normal 95, compare after X distance. I'll supply one of them

[Ocean1]

Interesting theory.......



.....but, as mentioned, I've only ever seen it happen to inlet valves (which obviously run considerably cooler than exhaust valves).

As I said, the 525 is getting stainless items, intake valve wear is apparently a KTM weakness and informed advice is they last much longer. And yet they're not as hard. Go figure.

Does that indicate a galvanic issue?

[Katman]

I find myself wondering whether inlet valves are made with the same carbon content that exhaust valves are.

[caseye]

Speaking from past experience with the coal burner, 1981 TR1/ XV 1000cc, for novices.
After 107,000 K's she needed 1 new valve guide insert.
All valve seats were re-cut and lapped in ( yep they still do that).
Nothing else, no apparent excessive wear and I've run her on 91 No Lead for last 4 years or the last 30 odd Thousand K's.
When I did run some lead additive because someone else with a similar age bike did, it seemed to upset her terribly, so I stopped using it.
Have heard anecdotally that this is actually becoming more of a problem than most might have expected.
Mates in engine reconditioning areas in cars, boats and aircraft.
Perhaps they're just not making valve stems as hard as they used to Katman?

[nzspokes]

Ive been told it can happen due to aggressive cam profiles where the cam follower comes away from the cam as the profile drops. This causes the valve seating speed to be excessively high.

Not sure if this is true or BS but another way of looking at it I guess.

[Katman]

Ive been told it can happen due to aggressive cam profiles where the cam follower comes away from the cam as the profile drops. This causes the valve seating speed to be excessively high.

Not sure if this is true or BS but another way of looking at it I guess.

Yeah, nah.

I've seen it in an array of motors - all with standard factory cams.

[Motu]

Valve problems before unleaded fuel was of two types, and depended on seat width. Wide valve seats...eg BMC, would burn exhaust valves and seats, and sometimes on 30 degree inlets (GM) we would see burnt inlets. Narrow seats (American) would have big recession on inlet valves - very much so on Holden engines. Nothing to do with fuel, very much to do with seat width, and possibly spring pressure. Calling Max Headroom, I know he was working in engine reconditioning shops in this era.

That recessed inlet valve is exactly what you would see on any red Holden engine...and Falcon, Chev etc.

[Katman]

.....and possibly spring pressure.

Now that's interesting.

That's the theory that I heard today that prompted this thread.

If spring pressure had dropped though, wouldn't it result in less hammering effect?

[nzspokes]

Yeah, nah.

I've seen it in an array of motors - all with standard factory cams.

I had been told it was common on kawasaki gpz motors. But that could also been someone looking for a head job on my old bike. It ran fine.

[mossy1200]

I dont think it will be long before we get a double dip recession and you will see even exaust valves will be effected.

[Katman]

I've seen it often in the 4 cylinder 250 motors and always put it down to the sort of revs they pull but today pulled the head off a TL1000S that shows the same problem.

[mossy1200]

I've seen it often in the 4 cylinder 250 motors and always put it down to the sort of revs they pull but today pulled the head off a TL1000S that shows the same problem.

Would it make sence that a high reving 250 will strike twice as often but a large valve will strike less often but with a larger mass and heavier spring causing damage also.
It would also make sence that the seat is reinforced by the surrounding casting but the valve isnt so the impact shock is spread over a huge area. idd also suspect that due to the valve being a cheaper repair than a demolished seat that the modern design would be to make the cheaper to replace part the weakest link for warrenty reasons. Therefore aftermarket valve maybe stronger but when failure does happen later on the repair becomes more costly. This most likely wont happen untill the motor is shot though because your already on a second set of valves at this stage having replaced the original set.

[bogan]

Is it possibly something to do with the temperature gradient on the intake valve? Top is cold, bottom is hot, conflicting expansion from conflicting temperatures pre-stressing the valve and meaning it'll take less stress to deform it. Coupled with the other theories put forward it might explain why it happens to the intake and not so much the exhaust.

[Katman]

Is it possibly something to do with the temperature gradient on the intake valve? Top is cold, bottom is hot, conflicting expansion from conflicting temperatures pre-stressing the valve and meaning it'll take less stress to deform it.

Nice theory.

:niceone:

[Motu]

The engines prone to valve recession were of American design, with hydraulic lifters and so fairly slow on lift and drop, and low max revs, so spring pressures were pretty mild. The English who preferred wide seats had higher tuned engines with more aggressive cams and double springs as standard. Rather than spring pressure, it's loading on the seat itself... a narrower seat means more pressure on the seat, and less area for heat transfer.

In a modern engine the same things apply, but cams are much more aggressive in profile, lifting and dropping the valve at a much faster rate....the timings are much milder, but the valve opening and closing are very much faster - the valve is at max opening for a longer time.

[Ocean1]

Now that's interesting.

That's the theory that I heard today that prompted this thread.

If spring pressure had dropped though, wouldn't it result in less hammering effect?

If the spring pressure is low the valve won't follow the cam when it closes, so there won't be any nice gentle touchdown, it'll slam. I hear that's a problem with the CRF intake, the fix there seems to be to use the OE valve and upgrade the spring.


It would also make sence that the seat is reinforced by the surrounding casting but the valve isnt so the impact shock is spread over a huge area. idd also suspect that due to the valve being a cheaper repair than a demolished seat that the modern design would be to make the cheaper to replace part the weakest link for warrenty reasons. Therefore aftermarket valve maybe stronger but when failure does happen later on the repair becomes more costly. This most likely wont happen untill the motor is shot though because your already on a second set of valves at this stage having replaced the original set.

In the old days you'd get guys cutting seats for well oversized valves. They'd often grind right through the hardened cast iron surface, resulting in rapid seat wear. Now almost everything is alloy with hard seats, and yes it makes more sense to sacrifice a valve than a seat. Actually with modern materials I don't think either should need looking at for at least 100k. Competition engine's a different kettle of fish.

[mossy1200]

Maybe the damage on the valve is happening in the BOOM not the impact so big thin wide valves and high compression are a factor or light thin small motor valves.

[pete376403]

Is it possibly something to do with the temperature gradient on the intake valve? Top is cold, bottom is hot, conflicting expansion from conflicting temperatures pre-stressing the valve and meaning it'll take less stress to deform it. Coupled with the other theories put forward it might explain why it happens to the intake and not so much the exhaust.

I'm wondering this as well, the inlet valve head gets cooled by the incoming air/fuel them exposed to combustion temperature thousands of times a minute, where the exhaust valve gets to stay at a more constant (although elevated) temperature .

[pete376403]

Maybe the damage on the valve is happening in the BOOM not the impact so big thin wide valves and high compression are a factor or light thin small motor valves.

But when the "boom" takes place the valve is on its seat, so supported physically and heat can transfer through the seat into the head.

[Katman]

Is it possibly something to do with the temperature gradient on the intake valve? Top is cold, bottom is hot, conflicting expansion from conflicting temperatures pre-stressing the valve and meaning it'll take less stress to deform it. Coupled with the other theories put forward it might explain why it happens to the intake and not so much the exhaust.

Actually.......


.....nice theory, but.......



.....if it were that simple why wouldn't the problem be more widespread?

[pete376403]

Actually.......


.....nice theory, but.......



.....if it were that simple why wouldn't the problem be more widespread?

Maybe it is? How many car motors ever have the head off before they finally make it to Pick-a-Part? When I was working as a mechanic (Mitsi/Chrysler dealership) a valve grind was par for the course at around 50,000 miles, especially on Hunters and Avengers.

High performance bike motors, such as motocross singles are expected to be rebuilt every ?? hours, so maybe the valves get replaced before recession is obvious

[Katman]

Maybe it is? How many car motors ever have the head off before they finally make it to Pick-a-Part? When I was working as a mechanic (Mitsi/Chrysler dealership) a valve grind was par for the course at around 50,000 miles, especially on Hunters and Avengers.

High performance bike motors, such as motocross singles are expected to be rebuilt every ?? hours, so maybe the valves get replaced before recession is obvious

Thing is, it's not something that occurs unannounced.

As the valve recesses the valve clearance reduces to the point of affecting the running of the motor.

[bogan]

Actually.......


.....nice theory, but.......



.....if it were that simple why wouldn't the problem be more widespread?

Yeh, that was just the theory of why it happens more often on the intake side. Other theories like valve bounce or whatever would still need to cause a large stress to begin with.

[gammaguy]

Does anyone have any interesting theories as to what causes valve recession?

Interestingly, I've only ever come across it occuring on inlet valves.

times are tough,the recession affects everyone,even valves.:bleh:

inlet valve seats are often softer,so recess more readily

exhaust valves protrude into the hot gas stream so it is more likely the valves themselves which erode

in my time I have seen both types,inlet and exhaust,valve and seat.

the causes are many and varied,but poor maintenance is the root cause of most of it.

[Crasherfromwayback]

I find myself wondering whether inlet valves are made with the same carbon content that exhaust valves are.

Is it happening with titanium valves at all?

[Katman]

Is it happening with titanium valves at all?

Not that I'm aware of.

[Crasherfromwayback]

Could the lead in the old fuel be softening the impact on the inlet valve? And if they're built with the same material now as they were before not coping?

[Paul in NZ]

Now that's interesting.

That's the theory that I heard today that prompted this thread.

If spring pressure had dropped though, wouldn't it result in less hammering effect?

Not really - the spring pressure drops and then the valve can bounce when it closes resulting in multiple closures. In (say) a triumph twin the valve timing is such that most of the noise you hear at idle is reverse pressure on the timing gears as the cam goes over centre before TDC so there is a lot of spring pressure. It was always the thing back in the day, put in a hot cam and stronger springs etc???

There is a fair bit of metal crashing into stuff....

I agree with Motu. Old BMC and english stuff you were forever grinding / replacing valves. I don't see it as much on my Triumph now. Maybe due to the fuel? However the 98 leaves a horrible carbon mess in the head which might help coat everything (I dunno)

[ducatilover]

Could it also be a clearance issue? When I pull my valves (if I can rig a spring comp.) I'll be able to tell you, one of the exhaust valves was too tight when I got it, the other three valves too loose, so one valve has been running hotter.
With the 250cc motors, most people tend to avoid doing clearances because most n00bs are not willing to pull the cams and measure shims, where-as with a mototr like my 600, you can tell it has been maintained correctly, 73ks and the cearances were still spot on, same with my CB400 super four, both of these not exactly low revving motors 5-7krpm at 100k, so doing lots of revs everywhere, like a 250 doing 8-9krpm at 100.

Should I pull my valves out to see if the clearances has made one wear more/abnormal?

[Katman]

I discovered the problem on this motor during the valve clearance inspection.

Seven valves were within spec while one was too tight.

After going down three shim sizes and finding the clearance still too tight I realised that there was something amiss.

After pulling off the head with the tight valve it turns out that the other inlet valve has also started to show signs of doing the same thing (even though it still measured within spec).

One would assume that the inlets on the other head will be likewise.

[ducatilover]

I discovered the problem on this motor during the valve clearance inspection.

Seven valves were within spec while one was too tight.

After going down three shim sizes and finding the clearance still too tight I realised that there was something amiss.

After pulling off the head with the tight valve it turns out that the other inlet valve has also started to show signs of doing the same thing (even though it still measured within spec).

One would assume that the inlets on the other head will be likewise.
So each could be a possible causation for the other? Valve wear obviously = clearances get tighter and if one had set the clearances wron = valve wear.
This orcourse doesn't mean much as that shouldn't really be limited to the intake... unless bad mechanics don't believe in exhaust cams?

I reckon Bogan's theory is pretty on to it. Mine are just ramblings of an idiot on meds:lol:

[bsasuper]

Having worked in the engine reconditioning industry, its really the quality of materials used, and accurate machining.If the seat/valve isnt machined correct it will wear faster, subaru was a great one for having out of round seats from the factory.Of course when unleaded fuel was cut, there was no lubrication and cusion effect of the lead, and the lead substitute which was usually potassium, did not work well.One bright spark kiwi came up with the fuelstar tin treatment canister, which did work but was priced a bit high.Ferrari was using hollow valves filled with sodium decades back to keep the heat down, correct spring pressure is vital to keep valve rotation to a minium as well.Interestingly diesel inlet valves suffer even worse than petro as the fuel in injected direct to the cylinder so the valves dont get the cooling/lubrication effect of the fuel,I wonder how the direct injection petrol engines will last?Camhaft lobe wear is more of a problem these days.(who measures lobe wear when doing a shim check).

[Subike]

after reading this thread, and understanding most of it
I wish to hear opinions about using different grades of petrol .
IE , Regular verses Higher octane.
I understand lower compression engines do not need the high octane fuel, to operate efficiently.
that a low compression motor will only need 91 octane to do its job properly.
If a person was to use 98 octane in the same motor,
would there over time be a detrimental effect to the valve gear and combustion chamber of the low compression motor.
My thinking is that unburnt fuel could build up as carbon, or sooty deposits, eventually lowering the efficiency of the engine.
Thus increasing engine wear, by "washing" the cylinders of lubricant and or clogging the exhaust with unburnt fuel deposits.
Decrease engine power, and lower fuel economy being the result of using the wrong fuel for the engine.
Opinions please?

[Katman]

My thinking is that unburnt fuel could build up as carbon, or sooty deposits, eventually lowering the efficiency of the engine.
Thus increasing engine wear, by "washing" the cylinders of lubricant and or clogging the exhaust with unburnt fuel deposits.
Decrease engine power, and lower fuel economy being the result of using the wrong fuel for the engine.
Opinions please?

Interestingly, the TL motor that started this thread is showing signs of dirty (but not at all recessed) exhaust valve faces.

[bsasuper]

Carbon buildup in the combustion chamber and on the back of the valve, is two things, poor quality fuel and oil from the engine.If you want to see less/no carbon buildup , use caltex fuel.

[Subike]

Carbon buildup in the combustion chamber and on the back of the valve, is two things, poor quality fuel and oil from the engine.If you want to see less/no carbon buildup , use caltex fuel.

Is this because Caltex use stricter quality controls on their production process and delivery?
Or because the additives they use are more engine favorable than environment/ sales promotion propaganda favorable.
I believe that Caltex oil products are better quality than most that are available on the market.

[bsasuper]

I always filled my work car up with caltex, 4 years later I had a look down the inlet, valves were clean ,I mean zero carbon buildup.A bike I purchased used had carbon buildup on the valves, so I used only caltex fuel, I checked 3 months later and carbon was gone,the techron additive they blat on about actually works.

[jonbuoy]

Maybe some of the carbon build up is down to how the engine is run, a good run up to the blood every now and again helps clean the system out.

[SS90]

This is the type of wear I'm referring to.

<img src="http://media.noria.com/sites/archive_images/Backup_200309_natural-fig1.jpg"/>

As a sideline to my day job, I restore ultra light weight Italian 4 strokes (50 to 100cc 4 strokes from the early 60's mostly) things like Moto Morini Corsarinos as an example.

Quite often I come across rooted inlet valves, it would seem that valves where a problem on such small "performance" bikes.

Generally, inlet valves (actually all 5 I am currenly doing) look exactly like the computer image

A while back I mentioned to a highly experienced machinist (no google searches in his day) as to why they all looked like that (bearing in mind these bikes generally have not run since the 70's at best, so unleaded fuel is not the culprit)

His opinion is that simply rich running was/is the cause, and this ties in with the fact the the old carbs on these sort of bikes where shit when they where new, and they are no better now.

Rich running may or may nit be your cause, but it certainly is for the old Italian ultra light weights I see, and the valve damage seems neigh on identical.

[Crasherfromwayback]

His opinion is that simply rich running was/is the cause, and this ties in with the fact the the old carbs on these sort of bikes where shit when they where new, and they are no better now.

Rich running may or may nit be your cause, but it certainly is for the old Italian ultra light weights I see, and the valve damage seems neigh on identical.

What's his reasoning for it?

[scumdog]

Maybe it is? How many car motors ever have the head off before they finally make it to Pick-a-Part? When I was working as a mechanic (Mitsi/Chrysler dealership) a valve grind was par for the course at around 50,000 miles, especially on Hunters and Avengers.



Way back then I got the impression that a fair number of those valve grinds at 50,000 miles were done simply because 'That is What You Do' at that mileage rather than obvious evidence of a need for it.

And I use to worry about that sort of thing back then too.

Now I just drive/ride 'em until 'something' happens.

And so far the only obvious sign of valve-seat recession on zany of our vehicles was on Mrs Scumdogs little Anglia when the valve-clatter disappeared - and so did the compression and smooth idle.

SO...I re-set valve clearances and all was sweet for another year or so.

[ducatilover]

I wonder how the direct injection petrol engines will last?Camhaft lobe wear is more of a problem these days.(who measures lobe wear when doing a shim check).

Why wonder now? Look at the valves on any GDi Mitsi, shocking heaps of shit those.
And yes, I measure my lobes :2thumbsup