Temperature effect on valve adjustments?

[bpu699]

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?

[Eagledriver]

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

[bpu699]

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

[Flat6pac]

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

[bpu699]

Originally Posted by Flat6pac

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...

[Flat6pac]

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

[Eagledriver]

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

[bpu699]

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?

[Flat6pac]

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

[RichHawk]

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.."

[Flieger]

Originally Posted by bpu699

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...

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

[psalt]

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

[Walt Fricke]

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

[jcge]

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

[Flieger]

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.

[jcge]

[jcge]

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

[Flieger]

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

[psalt]

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.

[jcge]

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