Temperature effect on valve adjustments?
 

You always read that a motor should be cool before valves are adjusted. What about those of us living in the frigid north? If your garage temp is 40 degrees as opposed to "room temp", do any changes need to be made in the tolerances? IE. Make them tighter than usual?

Yes, it makes a difference. I would set them to .003 inches if the temp is below 60 degrees. I don't think I'd set them if it were below 40 degrees.

-Andy

Any further thoughts? I have gotten mixed replies on this question...

As the temp increases, parts expand. As it gets colder, they shrink, right?

So, what is .004 at 70 degrees, is .005 at 40 degrees? .006? It can't be that much of a difference, because when the motor hits 250 degrees or so, at most the valve clearance should go to .001-.002 as parts expand, right? Assuming expansion is linear based on the temp...

So, if I stick with .004 at 40 degrees, at temp, the valves may be slightly loose, right?

For most cars, you see a recommended "range" in the workshop manuals. The pelican parts manual and bruce andersons book only mention the .004 figure...

Any thoughts appreciated. Motor is in the garage, on a stand, and the temperature is unlikely to hit 70 degrees any time soon...

Bo

When the temp is up to operating temp the valves are running as wide as .3mm an you still dont hear them.
Bruce

Bruce, does the gap get LARGER at higher temps? I though that as the cam lobe expanded, and the valve stem itself, that the gap got smaller???

Interesting topic. I get completely opposite replies from folks when asked...

I have to write it off to the aluminum expansion but at 200F the .1mm setting I have dial guaged @ .25 to .3mm. Yes the gap gets larger with increased temp change
Bruce

You are correct about the expansion of the aluminum. However your conclusion is wrong. As the aluminum gets hotter it expands and moves the rocker arm away from the valve. The rocker arms are suspended in an aluminum housing. You can readily measure a difference by doing a valve adjustment check on a warm vs cold motor. The first time I noticed this was when I set my valves to .004 on a 40 degree day. The engine was noisy after that and I checked my clearance on the engine when it was warm (had run a couple hours before). Clearance was around .006.

-Andy

Thanks to everyone for their input. Sounds like it should be reasonable to proceed...

Bruce, thanks for the input. I am suprised the clearance is as high as it is, when warm. You would think that the optimum would be much smaller, or close to nil, when warm.

Eagledriver... I am suprised you could tell the difference between .004 and .006... seems both would be within range...

The previous owner did the valves recently, and when I started the adjustment, I could not get the .004 guide into the gap, suggesting it was in fact tighter than that...

Last question, Is there a range for the gap that is suggested, rather than just .004? I would assume .002-.004 in either direction is within the error range?

Another possibility for thought only is the thread pitch is 1 mm, the lash setting is .1mm.
Now what to do with that information???
Bruce

Just honor the age old tradition of wheeling your engine into the living room / Kitchen and working on it there.

MY Favorite is the shots of the engine stand on Slate tile floor, second only to the engine sitting over a pristine brilliant white carpet.

"But Honey, the engine is perfectly clean! There's no danger at all.. whoops, I dropped a rocker arm loaded with assembly lube on the white carpet.."

Valves get "tighter" with age as the seat wears from the pounding of the valve. This causes the stem to sit up higher into the port of the head and the clearance to the rocker arm to be reduced

Valves get "tighter" with age as the seat wears from the pounding of the valve. This causes the stem to sit up higher into the port of the head and the clearance to the rocker arm to be reduced


Yes, this is correct and the idea that "noisy valves just need to be adjusted" is usually false. Chasing noise by closing the clearances is bad advice. Noise from wear in the guides and rockers cannot be adjusted out. The valve clearance gets wider when the engine is hot. The clearance spec is not about thermal expansion, it is about the amount of time the valve gets to sit down and give off heat through the seat. The factory spec should be considered the minimum and there is no good reason to ever set them tighter.

Paul

I can confirm that the lash increases with temperature, as I once replaced a broken rocker on a hot engine at the track. To set its lash I measured a couple of nearby, hot, valves, and used a thicker feeler gauge to do the reset on the new one.

Paul - I'm not sure I buy seat time as the reason for the factory lash. Cam shape has more to do with that, does it not? And the amount of time a valve is closed varies widely with cam specs. Certainly a standard is needed to set cam timing.

Best rationale I have heard deals with ambient temperature: set valves at room temperature, then take car to Alaska or Finland (or Gunnison, Colorado) in winter. On start-up of frosty car, rocker might not get off the base circle at 30 below F if you fudged the clearance to get more performance by keeping valves open a little longer.

VWs used 0.006," but there was the expansion of a longish aluminum push rod to deal with there. The Elgin 315 cams in my 2.7 race motor are set at 0.008" lash. Why Dema felt that was needed (his other cams have more normal lash recommendations) I don't know, though I faithfully follow it. Certainly can't have had anything to do with worries about sub-zero temperatures. Maybe the shape of the cam ramp.

I think it is easy to get the lash correct within 0.001" using the traditional "how hard is it to slide the feeler through" method. But I've never seen a tolerance given either. Maybe they believed mechanics would come close enough - within 0.0005" or so.

Walt

Walt / Bruce

When you say you've measured the valve clearance on a "hot engine" with a feeler gauge, don't forget that the "hot" portion of the valve head and stem inside the port (exposed to exhaust gasses) has already cooled down by several hundred degrees °C from its true operating temperature (and has therefore significantly decreased in its length), during the time it takes to stop engine, remove covers, measure lash.

Some rough calcs give about 0.35mm expansion/contraction for this "hot" part of the valve alone (L=40mm, 500°C, 17.3E-6mm/mm/°C for stainless)

I'd content that the actual operating valve clearance in a running engine, as opposed to a "hot" stationary engine actually decreases with increasing temperature.

Cam opening ramps are designed to to limit the impact speed of cam lobe on the rocker during takeup of the lash (clearance), allow for expansion of the hot valve, and allow for a small variation of the adjustment of lash.

So here's a confidence test for your assertion that the clearance expands, which I DO NOT RECOMMEND......set all of your lash clearances to zero on a cold engine (or hot stationary engine) and run it - I'm fairly certain that will burn every exhaust valve, and it will run like a POS all the way to destruction !!!

John

Out of curiosity, does anyone know the valve lash spec for desomodromic Ducatis? They have 2 rockers per valve to worry about and no springs. Do they have "zero" lash so that the valve stays seated during combustion? That might wear the cam base circle a little more.

Hot part of valve
 

Ducati Desmo
 

Ducati's nominal desmo valve clearance specifications, applicable to all desmo engines:

Check clearances with the piston at TDC Compression.

Intake:
opener - .1mm (.004 inch)
closer - NIL to .02mm (NIL to .0008 inch)

Exhaust:
opener - .1mm (.004 inch)
closer - NIL to .02mm (NIL to .0008 inch)

Experience has shown that it's better to leave a little more clearance on the Exhaust opener. And trying to set a zero clearance on the closers is generally hopeless and *always* leads to some binding somewhere. It is much safer to run loose than tight. So the specs I've used for Ducati desmo valve adjustments for the past 25 years are:

Intake:
opener - .1mm (.004 inch)
closer - .025mm to .06mm (.001 inch to .0025 inch)

Exhaust:
opener - .15mm (.006 inch)
closer - .025mm to .06mm (.001 inch to .0025 inch)

Openers are simple: they're like any rocker arm opener setup but you set the clearance with a shim.

Closers take a little more thought. The critical situation for the closing rocker is that it should never be so tight as to try to pull the valve any closer to the valve seat than fully closed. Ideally, you should check closer clearance all the way around the closer cam's circumference (pretty easy to do on a belt drive machine, harder on a bevel driver) to ensure that machining irregularities never allow the closer to attempt a negative clearance around the full cam run.

TAKEN FROM HERE http://www.ducatimeccanica.com/desmo_valves.html

So, if the clearances tighten as the engine warms, would that not cause the closer to stretch the valve?

Hello Walt,

I have worked with many different mechanical valve trains, with factory specs from 0.004" to + 0.020", and wondered the same questions. Valves, especially exhaust valves, need to get rid of heat and most of that goes through the seat when the valve is sitting down and closed. A good example of this can be found on the Porsche designed TAG turbo engine, where the exhaust valve seat had a groove to circulate coolant and 10% of the water pump output was directed to the exhaust valves. Porsche's recommendation of 0.004" is just about the tightest I know of, and considering the air cooling of the heads, recommending tighter clearances is just bad advice. If someone is that anal about valve noise, they should get something with hydraulic valves.

Factory specs for valve clearances, like many things, involve several issues. Jaguar, for instance, used 0.006" and 0.008" for many years, winning LeMans 5 times, testing engines at WOT for several days, but when the road cars came up against US cars with hydraulic lifters, customer complaints made them tighten the specs, then drill the lobes for oiling, then redesign the lobes for quieter running at 0.012"-0.014". These cams have exactly the same duration at 0.050", but are 40 degrees different at zero lash and have the same performance. Quieter valves with wider clearance and entirely a marketing decision based on customer desire. OEM's have to balance noise, adjustment intervals, and longevity into their specs. Most OEM's that make recomendations for racing (few) specify wider clearances to help get rid of the extra heat with more seat time.

Fleiger - on the desmo, the opener clearance will tighten, and the closer clearance will expand with increasing temp.

These are interesting theoretical arguments. I have no doubt that the exhaust valve does get hot and expand. The valve lash spec is actually .1mm plus or minus .05mm (.002-.006 inches). I've seen this published in a book and on this forum.

-Andy

I'd content that the actual operating valve clearance in a running engine, as opposed to a "hot" stationary engine actually decreases with increasing temperature.


Are you suggesting that they start out small (cold), get tighter when really hot, then get larger than cold when only warm ?

All of the hot running clearances I've measured have been wider than cold. Have you ever actually measured any ?

The valve lash spec is actually .1mm plus or minus .05mm (.002-.006 inches). I've seen this published in a book and on this forum


Which book would this be, the factory manual and spec book I have just say 0.1mm ?

Paul - I'm simply suggesting the RUNNING lash clearance gets smaller and smaller with increasing temperature on a RUNNING engine, and that the component with the greatest influence on lash is the expansion of the valve between it's cold and operating states.

When you shut down a running engine, the valve loses its heat very very quickly, much more quickly than the heads/cams/followers, and I contend that by the time you get to measure the clearance, the valve would have contracted significantly, thereby INCREASING the HOT stationary measurement (as you and others have found) at the time the measurement is taken.

My point is that the clearance you are measuring, is NOT the running clearance, which is significantly less than the setup or hot measured (feeler gauge) clearance.

I've never measured the RUNNING clearance or HOT stationary clearance. I have no doubt the HOT stationary clearance exceeds the COLD stationary clearance.

Hope I've clarified

John

John,

No, my point about your theory is simple. How can the cold clearance get smaller when really hot and larger when warm ?

Paul

I'm saying that the increase in clearance that you measure between cold (0.1mm) and hot (0.25mm-0.35mm when stationary) is all but taken up by the valve head and stem expansion when it's running at 500°C+.

Are we on the same page ???
John

But valves are usually stainless steel, right? The coefficient of thermal expansion for stainless steels is "nothing" compared to Aluminum. The combustion teperatures would be mostly touching the stainless steel so I think the difference between a running engine and a hot stopped engine would not be so great, as the Aluminum would still be "warm". The Aluminum would not see the swing in temperature. Valves, cams, and rockers should not expand much- most of the increase in lash would be the Aluminum cam carrier heating and expanding.

I am not sure about the thermal conductivity of stainless steel compared to Aluminum, or Titanium, for that matter. The stainless steel may hold on to the heat longer than the Aluminum.

It would be interesting to examine an engine with DFLs and ceramic/DLC coatings on the pistons, combustion chambers, and exhaust port liners (like the 964). That would block some of that heat and would be a good way to test your theory.

I'm saying that the increase in clearance that you measure between cold (0.1mm) and hot (0.25mm-0.35mm when stationary) is all but taken up by the valve head and stem expansion when it's running at 500°C+. Are we on the same page ???


John,

Your theory seems to be that there is a sudden, disproportinate, expansion of the length of the valve during running that closes up the clearance and disappears as soon as combustion stops ? And it is kind of like Schrodinger's Cat, if I want to measure it, it's not there.

My questions would be , how much how and quickly ? Since this stem expansion would have to be greater than the actual measured hot stationary clearance, why doesn't the same expansion take up the guide clearance and ruin the seat fit ? Around 75% of the heat goes through the seat not the stem and the stem tip would not be +500 C. I have stood next to engines on a dyno that have had the clearances checked immediately after shut down, so your expansion would have to disappear in seconds. I think this is a complex issue involving the net expansion of several components. It is somewhat counterintuitive that an air cooled engine would have such a small exhaust valve clearance spec. I have other engines with sodium cooled valves that are water cooled and they have much wider (0.020") exhaust clearances. Guide clearance spec however, is wider for the air cooled engine. I do not know of any auto engine with a tighter exhaust valve clearance spec that the Porsche factory spec of 0.1 mm, have never seen a range published by Porsche, and have never seen an OEM recommend diffferent clearance specs for minor changes in ambient temperatures. Have You ?

I think the main variable in the different clearances spec is to prevent closing up of the gap to zero in between the service interval.

Paul

The steel valve cannot be expanding more than the Aluminum cam carrier or Aluminum head. The steel holds on to the heat longer, too. Valve lash immediately after shutdown should be the same as running at operating temperature.

When the engine is still, it is heat soaking since the oil and airflow has stopped. This causes temperatures to spike a little while after shutdown. Lash should be the same or greater as running, assuming lash grows with increasing temperature.

.004" cold to .012" hot is my belief. Here is a plot of a 906 intake cam at the valve. The green line is .012" lift and the blue line is at .004". The factory designed the "clearance ramp" long enough to keep the valve seating velocity low, hot or cold.

There is a 56 degree change from cold to hot going from .004" to .012" on the 906 intake. My guess is the engine really wakes up when it gets hot.

http://drcamshafts.com/pbbs/906.JPG

I found a reference for the expansion of a valve stem when running. It is from Philip Smith's "Valve Mechanisms for High Speed Engines", what I would consider a good source. I have all his book and they are not at all error prone. The expansion of the stem under operating conditions is 0.0005" (ferritic) or 0.00075" (austenitic). There would have to be an expansion in excess of 10-20 times this stated figure for the hot running clearance to be less than the cold clearance spec, using the actual, measured hot stationary clearance.

From the reverse engineering department, Crane cams recommends subtracting 0.012" from the MFG hot valve lash spec when assembling a cold aluminum engine, when the MFG does not specify a cold clearance. This is in the ball park.

And from the truly bizarre department, we have the Chrysler slant six. In this case, the MFG, and I must say in 1959 they were riding the crest of the wave that top fuel engine still enjoy, recommended setting the exhaust valve lash to 0.020" while the engine is running, a perfect test for this theory. Not having done this, I spoke to someone with +40 years with this motor and they confirmed that the running clearance varys less than 0.002" after the engine is shut down.

You can see this exercise in action at :YouTube - valve lash on my 73 dart

This is .0005" per inch right?

Its normal to see timing cards with an additional .002" on the exhaust side vs. the intake because the valves can grow.

On all aluminum sprint car engine, the .012" number is a good rule of thumb. I like to give these guys a hot lash setting, and tell them to start it up .012" tighter and check it when its hot.

Hello John,

No, in this case he is talking about the total expansion of the valve in relation to the guide clearance. The issue we are discussing is whether the heat of combustion causes the valve stem to expand enough so that the actual clearance when running is smaller than the cold clearance adjustment. My experience with measuring hot clearances suggests not. Most of the other engines I know have higher clearances for exhaust valves, in the 911 that is not the case, and may have more to do with the expansion rate of the aluminum, not the steel valve.

I can't really understand what your chart is saying, both lines look brown to me. Can you give me a hint ?

Wow, that slat six information brought back memories. I ruined a set of feeler guages setting the clearance on a running slant six. They were my dads feeler guages and he wasn't amused! Setting the clearance actually wasn't that hard. The problem was I was stacking thinner guages to get the proper number and the thin guages stretched and deformed.

-Andy

Must be nice not to have to worry about clogged cam spray bars, center-lubed cams, or oil line restrictors. Just take the valve cover off and start 'er up.:rolleyes:

Ducati Valve Adjustment
 

Compare that with this: 4V Desmo Adjustment - Ducati.ms - The Ultimate Ducati Forum

Unfortunately, many of the photos are lost in cyber space, but here are a couple:
http://forums.pelicanparts.com/uploa...1262994937.jpg
http://forums.pelicanparts.com/uploa...1262994950.jpg


and a video: YouTube - cjayheff's Channel

Only the Italians could design a system where you must remove the cams and finger followers to change shims and valve lash. :p

Don't drop a valve (into the cylinder) if you are doing this with the heads on the engine.:eek:

The up and down lines, the green one is at .012" lift and the blue one at .004". The graph lines are the brown ones. The arc looking one is the valve lift curve, the other one is velocity. Between the green and blue lines the velocity curve is constant at around .0005" per degree. I assume from this design, Porsche expected to see a .012" hot lash when the engine was warmed up and making power.

Only the Italians could design a system where you must remove the cams and finger followers to change shims and valve lash.


Oh, give them some slack, they make excellent castings, nice shoes and decent wine...... The British made engines where you have to remove the head and grind the stems to set the valve clearance (Aston Martin ) and we Americans made engines that the crank and pistons have to come out to remove the valves (Miller, Offenhauser). Nobody's perfect. If you like Desmos' look into Michelat's 1914 Delage Type S engine..... the French invented everything and then what happened ?

Bo: Thank you for starting (if inadvertently) one of the rewarding discussions we get from time to time.

John JCGE: The graph you posted of valve temperatures is interesting. And looks like it is drawn from measured and slightly scattered data, then with a curve fitted? Seems logical: coolest on head near edge where heat can leave via the seat, and on stem hottest where farthest from either guide or seat cooling. Any more info on how this was derived? Just curious, as beyond quantifying heat at the valve and its distribution (valve closed? open? average?) I'm not sure just how it fits the lash discussion.

John D: On your graph, what are the units on the vertical coordinate? Zero something is part way up?

One trace looks like it is the cam lobe (nice bell curve). What is the other?

On the cam trace, the angle (tangent, differential) at any point is the acceleration?

Am I correct that more lash = less valve open duration? So the 906 would wake up because there was too much duration (overlap?) until hot? Would spend less time at the early and late small openings with lower flows, and more in the fat part?

This may be helping me visualize part of Paul's point: as the lash opens with heat, the valve stays closed longer (thus cooling more). The low angle of this ramp area means a small change in lash leads to a relatively large change in seat time?

I still don't quite understand why you can't do with the grind shape what you can do with altering lash as far as seat time is concerned. What good is the part of the ramp the rocker/follower never sits on?

Paul - As always, you inform these discussions with varied experience most of us (me, anyway) don't have. I like the idea that valve lash specs are related to anticipated service intervals. Having ground some seats and valves, I know that lash reduction due to wear (more like pounding) in these areas is certainly real.

Your post gave me a flashback to the last time (now long ago) I adjusted valves on a V8 with the motor running. Was easy, though depended on sound and not measurement as I recall. Can't hardly do that on a 911. For that matter, how would one quantify running lash? Something stroboscopic? And indirect, equating seat/open time to lash?

Same Smith of Design and Tuning of Competition Engines?

Walt

What good is the part of the ramp the rocker/follower never sits on?

Same Smith of Design and Tuning of Competition Engines?


Hello Walt,

Less acceleration and noise, like the quieting ramps that Jaguar developed in their parabolic cams to reduce noise at double and triple the earlier non parabolic cam clearances. Not a performance issue, a marketing response to the hydraulic lifter.

Same Smith, his +200 page tome on the poppet valve has been out of print for a while. I had to buy a zerox copy from a peg legged pirate 25 years ago. It has every wacky idea tried until 1967, and gets into the valve temperature and expansion rates of the sodium filled valves of the last of the highest spec piston aircraft engines before the jet took over. There is some recent work trying to understand the heat transfer at the valve seat, the finish of the surfaces, the mysteries and the mechanisms involved, but you can find a similar discussion on page 800 of the "Modern Gasoline Automobile of 1916". This book is truly amazing and I'm sure Harry Miller had one in his pocket.