Understanding Valves


21 replies to this topic
  • boer

Posted October 13, 2006 - 07:49 PM

#1

So I was reading through my manual and was trying to put my mind in the cylinder head to understand some issues :thumbsdn: , namely what causes the valve clearances to increase and decrease or the side effects this has :thumbsdn: .

After looking at a sectional view of the setup, I have some questions for you experts:

1a: What causes smaller valve clearances: Does the valve become longer over time (creep or inertial loads)? Does the valve seat further into the head bringing the valve closer to the camshaft?
1b: What are the side effects of smaller valve clearances: Due to the clearance being smaller, actual lift of the valve will be more? Less lubrication between camshaft and and valve lifter? Less room for thermal expansion?

2a: What causes bigger valve clearances: Wear between camshaft and valve lifter or valve head, cotter etc? Excessive camshaft bearing clearances?
2b: What are the side effects of bigger valve clearances: Due to the clearance being bigger, actual lift of the valve will be less?

Look forward to the knowledge I will receive on this :devil:

  • Seabass

Posted October 13, 2006 - 08:13 PM

#2

Where's Indy when you need him!!!!

  • Audun

Posted October 14, 2006 - 02:11 AM

#3

Hmmmm.. Dont know how to quote but here is what I belive is the answers!
1a)
If the clearances is decreasing-> the valvesprings are pushing the valves up, and this force is pushing the valve seats against the cylinder head and thus making the cylinder airtight and allowing compression. Here there is litle lubrication and the friction is higher. This leads to a wearing effect on both the cylinder head and the valveseats and this means that the valve seats have to go further up to tighten the sylinder-> then the valvelifters are pushed further up-> less clearance..

2a)
If the valve clearance is increasing-> this is a result of the wearing as a result of the friction between the camskaft and the valvelifters. This is usualy the problem when breaking in the bike.. As for me.. Ive just installed the hotcam ex, and the cam was originaly anodized, and now i can clearly see that it is worn since the anodization is gone and the camchaft is metallic. My experience is that this effect stops after break in, or is a smaller effect than the one causing deacreasing clearances

This is also the effect that is causing youre engine to lose some compression. There is ofcourse other effects as carbon deposits and so on.

As for effects, if the clearances are to large or to small, this will cause the valves to open to soon og to late. The camshafts are also designed to work together and thus the clearances are important to get as much power as possible. Also, to large or to small will give an increased wear rate because of a unfavourable movement between the valvelifter and camshaft

To small clearance will open the valves to early, and as an example, letting pressure out of the cylinder to early->giving away power

To much clearance will give a small valve lift and thus not allowing enough air flow.


Hope I could help.
"My engrish are good not!";)

  • Indy_WR450

Posted October 14, 2006 - 04:11 AM

#4

For the most part the valve stems do stretch but the seats get pounded as well so the clearances can go either way but are usually gong tighter on our bikes due to the seat being pounded. That is why after adjusting 4 times the valves are usually do not seat well and you run the risk of potential failure at the valve neck. Use Genuine Yamaha Titanium valves or like I did I went to SS valves for durability. :devil:

  • MountainMax

Posted October 14, 2006 - 04:16 AM

#5

if the valve clearance is non existant, the valves can float (stay open a bit) and you can loose compression, However seems the Yamaa's are not as prone to adjustment as you would think, once a year maybe after breakin. i bought a hotcam shim kit and so far only used one shim out of it, lol...

  • boer

Posted October 14, 2006 - 06:04 AM

#6

Use Genuine Yamaha Titanium valves or like I did I went to SS valves for durability. :devil:


Does Yamaha sell the SS valves or are they from aftermarket supplier?

  • thillsam

Posted October 14, 2006 - 07:08 AM

#7

Overall these are good explanations, but there are a few terminology errors.

...This leads to a wearing effect on both the cylinder head and the valveseats and this means that the valve seats have to go further up to tighten the sylinder-> then the valvelifters are pushed further up-> less clearance...


You have confused the terms here: the valve seats are the steel inserts pressed into the cylinder head. The valve faces, or sealing lands, are the ground sealing surfaces on the tulip of the valve - the onces that are perfectly conical when the valve itself is new, and slowly take the impression of the valve seat as they sink further into said seat and clearances tighten.

...Ive just installed the hotcam ex, and the cam was originaly anodized, and now i can clearly see that it is worn since the anodization is gone and the camchaft is metallic. My experience is that this effect stops after break in, or is a smaller effect than the one causing deacreasing clearances...


This is not an anodic coating or surface treatment(only non-ferrous metals can truely be "anodized" by definition). Most cams are either through-hardened by a heating and cooling cycle and then black-oxide coated for corrosion resistance during shipping/storage/sitting on the retail shelf...OR...made from a material that can be flame-hardened on the outside, very similar in result to case-hardening.

Either process leaves about a .0001-.0003 thick oxide layer on the surface. This wears through quickly(especially in an abrasion wear scenario like seen in most rocker tips without rollers) and the exposed 'metallic' material is the hardened base material. This is what exhibits true waer resistance. If you can detect the few hundred thousandths that occurs in the first ride on a new cam with your feeler gauges, that's an impressive feat.


...This is also the effect that is causing youre engine to lose some compression. There is ofcourse other effects as carbon deposits and so on. ...


Unless the valves are being held open by zero or too-tight clearance and/or have burned thear sealing surfaces, this does not cause loss of measurable compression. If the valves are sealing and have any clearance at all, and compression is measured to be low, there is something else amiss with the engine - head gasket, worn rings, leaking sparkplug, etc.

...As for effects, if the clearances are to large or to small, this will cause the valves to open to soon og to late. The camshafts are also designed to work together and thus the clearances are important to get as much power as possible. ...


Many tuners, those who understand anyway, know that one can shift the torque curve of a given engine up or down by timing the cam or cams differently relative to the crankshaft and/or relative to each other, respectively. This was the only difference between the early WR and YZ models - the intake and exhaust cams were timed for less overlap to spread the torque curve out over a broader range at the cost of peak horsepower numbers.

You can accomplish the same thing, albiet a little more subtle, with valve clearances alone. Leaving the intakes looser, perhaps 25% looser(.008 instead of .006, for example) than the factory recommends always moves the torque curve down, creating a motor with more grunt and less torque in the higher revs. This is for two reasons: 1.) Opening timing is delayed, and shortened. Look at the specs for a cam that is designed for low end grunt, and you'll st the at the valves(especially intakes) open later and for not as long as a cam designed for high RPM breathing... and... 2.) Lift is lessened *slightly* although .002-.004" less lift is a very negligible difference for a valve that moves, say, ~.380". The real effect is on the timing...

...To much clearance will give a small valve lift and thus not allowing enough air flow.

This is only true when it comes to peak power numbers, not in terms of rideability or useful torque.

If you know you're engine and how hot it runs, you can set exhausts a little tighter and it will rev harder and higher at the cost of bottom end torque for reasons opposite those listed above - as long as the clearances don't go to 0 or positive and result in burned valvesw hile you're trying to run it that hard...



To answer one of the original questions:

1b: What are the side effects of smaller valve clearances: Due to the clearance being smaller, actual lift of the valve will be more? ... Less room for thermal expansion?


Yes, and yes. Valve clearance exists ONLY because of thermal expansion of the valve - no other reason. This clearance is in theory large enough that when the engine and valves are at their very peak temperature, the valve will still be held against the seat in the head by the spring and the rockers or cam will not be holding the valve open slightly(and by slightly I mean maybe a few millionths of an inch, up to maybe .0001")

Another thing to consider is heat. Valves must rest in the seats and touch them in order to evacuate heat. When you used to hear about "burned valves" on engines of the past, much of that had to do with the lack of metallurgy - seat materials and valve materials simply couldn't evacute the heat of combustion fast enough to keep the sealing faces from degrading really fast.

In modern engines, valves typically only "burn" because the clearances are set too tight or have crept to a tight setting through neglect for the peak temperatures they see and they are held away from the seat as a result - they have no place for the heat they've absorbed to go, and the stem can only carry so much heat to the valve guide for dispursion. The faces soften enought that they begin to distort and leak and it goes downhill from there...

  • thillsam

Posted October 14, 2006 - 07:29 AM

#8

Does Yamaha sell the SS valves or are they from aftermarket supplier?



I highly reccommend Kibblewhite Black Diamond SS valves. I had a set in my CRF450 for over 250 brutal racing and riding hours and never once had to change a shim...I will be overhauling the Sherco soon and it's getting a set as well, although the stock valves are SS in it was well...

Kibblehwites are available through their website(http://www.blackdiamondvalves.com/) or through any Parts Unlimited dealer...like the TT store...

  • boer

Posted October 14, 2006 - 08:43 AM

#9

Thanks for the replies guys. Thillsam you really know your stuff, and you bring it across so logically :devil: I have a new perspective now on the functioning of valves.

So, in a nutshell unless you have serious wear between lifters and the cam increasing the clearance, the most likely change in valve clearances will be the clearances becoming tighter? :thumbsdn:

Can the corrections be done by reworking (fine water/emery paper) the existing shims on a flat surface to be thinner or should one buy new shims and replace the old ones? :thumbsdn:

  • MountainMax

Posted October 14, 2006 - 11:47 AM

#10

yeah, the Honda valves are high maintenance, I would only buy them if you had a honda, Yamaha valves are fine.

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  • thillsam

Posted October 14, 2006 - 04:12 PM

#11

Thanks for the replies guys. Thillsam you really know your stuff, and you bring it across so logically :devil: I have a new perspective now on the functioning of valves.

So, in a nutshell unless you have serious wear between lifters and the cam increasing the clearance, the most likely change in valve clearances will be the clearances becoming tighter? :thumbsdn:

Can the corrections be done by reworking (fine water/emery paper) the existing shims on a flat surface to be thinner or should one buy new shims and replace the old ones? :thumbsdn:


Yes, most valves tighten as a resutl of their sinking into the seats and the stem furthering itself up into the valve guide, tightening the clearances meant for thermal expansion.

Yes, most 9.48mm OD shims are through-hardened, meaning you can lap them thinner(as thin as you want, really) although you should lap the number side, so the next person that does it isn't driven crazy trying to find out what shim some loony put into their motor when they order a thinner shim only to find out you've lapped the shim number they took out thinner than the next few sizes down...LOL

I used to use a set of diamond hones, avaialble from MSC tool or any other reputable machine shop supply house. Those shims are probably ~50+ Rc, very very hard - ten munites of lapping on old-school emery cloth will get you about ~.0005-.0010 of of a shim = very slow wihtout somethign more agressive. Be careful also to keep the faces of the shim parallel, do circles or figure-eights with perfect vertical pressure on the shim.

If you have access to any precision surface grinder, you can get your valve clearances set so close it's silly!

IMHO valve clearances are far more important on a multi-cylinder engine where it's relaly important to have everything matched as closely as possible. On 4-valve or 5-valve single-cyl motors, it might even be advantageous to have one intake valve a little looser to induce a "swirl" in the iinitial part of an intake stroke...maybe...LOL

Why no one but Honda has built a motorcycle engine with variable valve timing is beyond me...not to mention a single cylinder with the concept...

  • boer

Posted October 14, 2006 - 08:00 PM

#12

Are the manufacturing tolerances of the individual items in the valve train tight enough so that all bikes come from the factory with the same valve shim thickness? I would imagine they vary by not more than 0.1mm or am I wrong? :devil:

As the shims are hardened and I do not trust my own handwork with small shim a am considering using new shims. The reason for asking is that I do not want to buy a entire valve shim kit only to use one or two shims.

What did you guys find installed as stock (this way we can see what the difference is)?

The other option is checking the valve clearances, if out, removing the cam, lifters and shims and then knowing what size shim to get. The problem is having to rebuild it all and wait for shims to arrive (2-3 weeks) :thumbsdn:

  • OneToGo

Posted October 15, 2006 - 05:40 AM

#13

Some very good info here.

Two Q not worth a new thread.

1? Do the intake valve clearances generally decrease quicker than the exhausts?
2? Does the centre intake valve clearance pack down quicker than the outers?

I have observed the above on my 06 WR, and yes, immaculately clean filter!

:devil:

  • LimyWPom

Posted October 15, 2006 - 09:47 AM

#14

I experienced the same valve clearance adjustments as OneToGo on my 05.
A question for Indy or thillsam, through ignorance I always assumed that the Ti valves would be harder than SS valves, is the only benefit less weight for the titanium? :devil:

  • Indy_WR450

Posted October 15, 2006 - 05:30 PM

#15

Titanium is lighter and allows the bike to rev quicker and higher rpm. The Kibblewhite SS valves use heavier springs and result in a slightly slower reving engine. SS valves are harder and last longer but tend to float easier at higher revs.

  • waynus

Posted October 15, 2006 - 11:26 PM

#16

Have you boys thought about asking your local bike shop if they exchange shims. Mine does and they charge @ $5 each to swap. Handy if you can get your hands on a micrometer to check them when you are swapping.
Wayne

  • Audun

Posted October 16, 2006 - 03:01 AM

#17

Have you boys thought about asking your local bike shop if they exchange shims. Mine does and they charge @ $5 each to swap. Handy if you can get your hands on a micrometer to check them when you are swapping.
Wayne



Hehe, maybe in the rest of the world but not in norway.. Here they charge about 100-140$/hour for the work.. And I suppose they carge me about 700$ to do it for me.. For my R6 they said they charged 1200$ to adjust the valves, and afterwards he had tha balls to tell me it was a nice price! Darn i can do it myself in max 3 hours!

And for the WR, with some skill you can do it in about 1 hour, np!

  • OneToGo

Posted October 16, 2006 - 05:10 AM

#18

Some very good info here.

Two Q not worth a new thread.

1? Do the intake valve clearances generally decrease quicker than the exhausts?
2? Does the centre intake valve clearance pack down quicker than the outers?


I have observed the above on my 06 WR, and yes, immaculately clean filter!

:devil:


Hey INDY, now we have your attention, what about these two Q? above.

Thanks, looks like I'm not imagining it..
:thumbsdn:

  • Indy_WR450

Posted October 16, 2006 - 11:29 AM

#19

The exhaust valves generally need more adjustment.
The center intake valve on the 5 heads also seems more prone to adjustment then the other intakes. Not sure why.

  • kobernik

Posted October 16, 2006 - 12:03 PM

#20

I've also found (as well as a few other wr owners I know) that the middle intake valve and seat seem to wear faster then the rest which causes the clearance to tighten up.

I've found just the opposite of Indy in that I rarely have to adjust the exhaust valves compared to the intakes.

I like to give my valves too much clearance rather then too little. It doesn't seem to hurt anything (except maybe a little performance loss) if they open a bit wide. Not enough clearance is bad news i.e. valves don't close = no compression.

My 99WR has close to 15,000 miles on it. You can imagine I've done a few valve adjustments (plus one top end rebuild).




 
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