1000 miles @ 3700 rpm in 100 degree heat

car-reras · 06-27-2003, 07:36 PM

I just drove my 82 911SC 1000 miles over 8 days in 100 degee heat at around 3700 rpm. I can really hear my valves compared to the begining of the trip. Will an oil change silence the valves, or will an adjustment also be necessary? Last one was around 7000 miles ago.
Thanks,
Derek

Eric Mckenna · 06-27-2003, 07:50 PM

good question! I'd like to know the answer to that as well...
anyone?

VincentVega · 06-27-2003, 09:03 PM

What kind of oil are you using? Just curious. At that temp and rpm I would at least use a good 20w50. 7k miles is half way to a valve adjustment. Thick oil can quiet a noise, but does nothing to fix the reason for the noise.

Good luck!

dd74 · 06-27-2003, 09:33 PM

I notice a distinct difference in my valves in warm weather as opposed to not-as-warm (they're louder), but I don't worry as much. As long as nothing is really clattering, which I think you'd know and feel, and the car has its usual amount of power, things are good.

If the temperature gauge suddenly starts climbing, then I'd be concerned, or if the oil pressure dropped dramatically or was low to begin with.

GSpreeman · GSpreeman's Garage

I just did an oil change with Castrol 20-50 and my engine, including valves, is much quieter now.

RoninLB · 06-27-2003, 09:47 PM

Quote:

Originally posted by car-reras

I just drove my 82 911SC 1000 miles over 8 days in 100 degee heat at around 3700 rpm. I can really hear my valves compared to the begining of the trip.

I know all about big mile rides.. did one last year, and posted all about the big big miles..

anyway, I had a couple of exhaust valves that needed a tweak after about 14k miles on the big roads.. desert/mountains/etc... I only did the loose ones.. using the wiggle test.. then rode home from la la land.. and maybe big extended heat thins the oil beyond routine rides and thins the valve guide film/don't really know.. but I can relate.....................Ron

Type911 · 06-28-2003, 05:39 AM

Derek,
What were your oil temps during your trip? Do you still have the stock trombone or has the cooler been up-dated ?

thanks,
Chris
82 911SC

billwagnon · 06-28-2003, 06:49 AM

I don't understand.

I thought as the valves wore, they seated farther down the exhaust/intake ports, lengthening the effective length of the valve stem and resulting in LESS noise, as the gap between the lifter and the valve stem closes.

Kurt B · 06-28-2003, 07:33 AM

Interesting bill. Dangit, I'm so confused on the whole "what valves do when they fall out of adjustment". I've heard they get louder. i've heard someone say "they'd be so tight after that long [between adjustments]..."
What DO they do. Get louder and looser or quieter when they fall out of adjustment?

Tinker · 06-28-2003, 08:55 AM

Kurt,

Valves can either get tight or loose.

Tight can be a result of slight wear on the valve or valve seat.
Loose due to the adjustment nut backing off slightly or wear in the valve stem or rocker.

Remember that as the engine/valve gets hot, the gap increases not decreases.

Tinker

cstreit · cstreit's Garage

I would think a slight amount of valve seat wear and also wear on the top of the valve would mean the valve would sit closer to the rocker, and therefore be tight...

speeder · 06-28-2003, 10:50 AM

Quote:

Originally posted by Tinker

Remember that as the engine/valve gets hot, the gap increases not decreases.

I believe that it is just the opposite, heat makes things expand, not shrink, so valves get longer, not shorter with heat. Otherwise you would adjust valves hot instead of cold, the idea is not to have less valve opening when motor warms up.

bsaffin · 06-28-2003, 10:55 AM

Quote:

Remember that as the engine/valve gets hot, the gap increases not decreases.

I've struggled trying to wrap my head around this. It seems intuitive in one sense that the gap(s) increase when things get hot (i.e. valve guides), and so with hot oil, and increased gaps the oil usage would increase. But, doesn't metal expand with heat, so any gaps should actually decrease when the engine warms up?

...Bruce

Tinker · 06-28-2003, 12:56 PM

Chris,

Valve seat wear results in the valve being sitting deeper in the head....increasing, slightly, the valve stem height and reducing the valve clearance, all things being equal.

A greater clearance between the rocker and the valve stem or the adjusters would result in a greater valve gab. Maybe if they wore evenly, the net result is no change.

I also thought that heat would cause the gap to decrease as metal expands, but it`s not so. The gap INCEASES.

If you doubt me, check in any Haynes manual or owners manual that gives the valve clearance for both hot and cold. The cold value is usually less by approximately 0.05mm.

Tinker

Chuck Moreland · 06-28-2003, 01:15 PM

Quote:

Originally posted by speeder
I believe that it is just the opposite, heat makes things expand, not shrink, so valves get longer, not shorter with heat. Otherwise you would adjust valves hot instead of cold, the idea is not to have less valve opening when motor warms up.

The change in valves lash is the "difference" between expansion of the valve stem and expansion of the head. Head expansion moves the valve seat and cam farther apart, hence loosening the lash. Stem expansion tightens the lash.

Since the head is Aluminum or Magnesium it has a greater coefficient of expansion than does the steel valve stem. The head wins this little race so the valve lash gets greater with temperature.

speeder · 06-28-2003, 02:15 PM

(In my best Col. Klink voice), "verrrrrrry interesting".

Tyson Schmidt · 06-29-2003, 11:26 AM

Chuck's right, except that it's more the cam tower expansion than the head, but I think he was including that as the head.

The valves do indeed either tighten or loosen, depending on what is wearing the most. The valves will tighten up if the valve face and seat wear, and will loosen if the rocker arm bushing, rocker shaft, elephant's foot, and valve stem tip wear. It all depends on the conditions inside that particular cylinder. Is it running lean, or rich. What type of driving it's being subjected to. The oil used, the fuel used, etc, etc, .....

It's very random on a 911, but on some cars, it's as regular as clockwork. Isuzu Trooper 4 cylinders will tighten up the exhaust valves completely in about 20K miles but the intake valves loosen. They didn't have the proper hardness in the valves and seats to take the heat of the exhaust. The intakes, cooled by incoming air, had no valve seat recession, so the other type of wear won out, and the intakes loosened up.