Valve adjustments (loose or tight)

[tobluforu]

Well I decided to adjust the valves on the 72. I forgot what a time consuming job this can be; dirty to. The silicone gaskets on 2 of the covers ripped apart. I'm pretty sure this is because I torqued the nuts to much last time. So here's a qustion regarding adjusting the valves tight or loose. 4 of the valves were tight. I adjusted them all and then went around and checked again. I decided to adjust them a little on the loose side this time. Feeler gage slides right in and drags just a tad. So if you change nothing else on your car, in other words you just adjust the valves, how does the engine perform if the valves are loose or tight? Will it perform better if loose or tight? What happens internally? More gas or less if adjusted loose or tight? Better expulsion of gases? Does anyone see where I'm coming from?
Thanks.

[A Quiet Boom]

Well, tight can be very bad because if they're to tight they wont seat entirely and will burn up. The valves get most of their cooling from contact with the seat. Loose is usually better but too loose can damage the valve tips and even the cam because you're hammering the valves open rather than pushing them. The way you've set it sound about right to me. The amount of play in a valve adjustment won't affect max opening by much but it will affect at what degree they start to open as well as close, loose valves open late and close early making the cam seem more mild but this is really only noticeable when you're talking about race cams, it's hard to tell the difference with a street cam.

[BGCarrera32]

The advice given to me by more than one expert mechanic (by saying that I mean they have rebuilt many a 911 engine) is that you should adjust them to a tight .004". Keep in mind they have a +/- .002" tolerance either way. I would think that too tight is worse than too loose, but when you think about how everything wears over the next 10k mi or whatever your interval is, the valves need adjusting because they get loose, not because they get tighter over time. I do my valves without any oil on the feeler gauge, and there is a healthy amount of drag on it when I pull it through.

-BG

[Darkmoon]

Are you sure thay get loose over time? After looking at the way they work, I would think they get tighter over time as metal the surface area of the valve closing against the metal surface area of the head continuously bangs together cycle after cycle. When I think about it, immediately after a "good" adjustment, as the lobe of the cam falls, allowing the spring to pull the valve towards the head, the distance between the valve and the head decreases at a controlled rate until the lobe is bottomed out. At this point the only mechanical energy left is the spring. ( there's the .004" gap)The spring pulls tight and the valve "hits" the head. After doing this 2700 times a minute X 15,000 miles, that's in the ballpark of 41 million cycles assuming 2700 rpm = 60 miles an hour. (give or take million)

As the metal at the valve deforms and breaks away, the valve seats lower in the head. Wouldn't this cause the tip of the valve stem to get closer to the rocker? (.0035")

I don't know, I just made my first adjustment. To you long timers out there, do your valves get tight or loose over time? If loose, (.004" grows), what is causing this? What am I missing.

Thanks.

[tobluforu]

Thanks all! It seems that all the times I have adjusted my valves, they are always tighter then when I adjusted them before.

[A Quiet Boom]

I've had a lot of vehicles with mechanical adjusted valves and every one of them including two P-car motors loosened with driving. My drag car had a huge cam that required adjusting every other weekend. My Nissan's valvetrain is very similar to a P-car and it loosens up over time also. If you think about it you have wear at the cam and the cam follower, wear from at the valve tip and rocker tip, I would think those would wear more culmualtively than valve seat recession.

[ed martin]

I'm currently in the process of adjusting my valves on my 73.5 T. Interestingly the original owners manual has some very succint and concise explanations, such as how valve adjustment is integral to the timing. Also, according to the manual loose valves result in an overly lean conditon which leads to gray plugs instead of their proper brown color. To my way of thinking as far as whether valves loosen or tighten over time, it seems to me that as time and miles progress, the head/cylnder arrangement would have a tendency to expand or loosen- come apart. Therefore it would to my mlnd seem logical that valves would tighten, being compressed by the expansion. This I think would hold true unless in the locknut process of securing the valves, insufficient torque was applied, thereby resulting in loosening over time.But out of all this I do have a question. Would it not make sense to make sure that the heads are sufficiently torqued, or retorqued before adjusting the valves?

[A Quiet Boom]

Ed,

Head torque has nothing to do with valve lash on a 911 engine, the lash is completely localized to the heads and cam housing. A loose cam housing could adversly affect last but it would affect othe things as well. What causes the valves to loosen over time is the wear on the valve tip, adjuster tip, the cam itself as well as the follower. It is also possible to under torque the locknut but that has never been the case for me. To put this into perspective, I meantioned my old drag car. It had a very radical cam, in fact as radical as Lunati could custom make it for use with flat tappets, combine that with triple valve springs and the was tremendous pressure being exerted on the wear surfaces. On a pushrod engine like that you also have wear on the pushrods themselves. It's not any one thing that wears but instead the combination of each part wearing that adds up to looser lash. A 911 being an overhead cam design is inherently better for many reasons, first it has less moving parts to wear out, second thermal expansion has a much smaller effect when the cam is mounted in the head, and third less wear surfaces to "loosen" up. Think of just the cam and follower, you have a cam lobe with a flat follower sliding over it thousands of times per minute under pressure from the valve spring, it's unreasonable to think that these parts aren't constantly wearing each other down.

[aigel]

The clearance gets to be less over time. The valves 'sink' into the seats, especially on the exhaust side. This sinking is much more than the wear any other components see (which would move things the other way).

If you go too loose, you will have noise and loose power (less lift). I disagree with the earlier post, this is SIGNIFICANT power loss, and your engine will sound terribly from rattling valves.

Set the valves tight. If you do not have much resistance in the gauge, pulling int back and forth, your error in the measurement is potentiall much larger (e.g. dirt, cocked gauge, small bow in the gauge etc.), and you can really be on the loose side. Remember, there is no way you can compress that gauge down significantly and end up too tight.

George

[raceman]

l`ve been adjusting these things for a while,my own car and plenty of others.l`ve found that sometimes they`re loose,other times tight even though l adjust them the same way every time.Every engine is different.l tend to adjust on the tight side of.004 though because l don`t like noisy valves and they just seem to run cleaner that way.Worn valve guides will make a precise adjustment impossible though and in that case a little looser is better.

[A Quiet Boom]

Originally posted by aigel

If you go too loose, you will have noise and loose power (less lift). I disagree with the earlier post, this is SIGNIFICANT power loss, and your engine will sound terribly from rattling valves.

By loose I didn't mean that loose I just meant the loose end of the spec. Also if you crank down too much on the adjusted with the feeler gauge in there you can actually push the valve open, the when you remove the gauge the valve will shut and take up the lash or worse not shut all the way. Besides I'm past due on a valve adjustment right now and I can hear a faint tick that wasn't there when I last adjusted them. Either way it doesn't really matter to me enough to continue arguing about it, I've built a lot of different performance engines over the years, most of them with mechanical followers or tappets and in my experience the valves get looser not tighter. In the end it doesn't matter whether they get looser or tight as long as you adjust them on time. Now where's that gasket set........

[aigel]

Originally posted by A Quiet Boom
By loose I didn't mean that loose I just meant the loose end of the spec. Also if you crank down too much on the adjusted with the feeler gauge in there you can actually push the valve open, the when you remove the gauge the valve will shut and take up the lash or worse not shut all the way.

I hear you. And yes, you can push them open. But you won't be able to move the gauge then.

And you are right, just like oil changes, just do them frequently, dont' worry about the oil.
George

[Jadams1]

When do you guys adjust your valves, every 10,000 or 15,000 miles?

[Rot 911]

Originally posted by Jadams1
When do you guys adjust your valves, every 10,000 or 15,000 miles?

Every 15,000 miles. When I did my engine rebuild I used a dial indicator to find out exactly what the drag should feel like when I used the .004 feeler gauge. So I set the valves using a dial indicator and then tried to replicate the setting using a feeler gauge. Turns out to be a lot tighter then I ever thought. At .004 on a dial indicator, you can only slide the feeler gauge with some difficulty. Much more than just what some describe as a "magnetic"drag. And when the feeler gauge is out at .004 on the dial indicator it is almost impossible to reinsert the feeler gauge. When I tried to go with just using the feeler gauge I could never get the valve reset to .004. Was always .005-.006. But like a previous poster said, the correct setting is .004 +/- .001.

[targa911S]

better to hear em than smell em.

[cowtown]

Jerry Woods gave me this advice: If you can get the feeler in there, the gap is wide enough. Get them as tight as possible while still taking the feeler.

That advice has served me well for 8 years, and really simplifies the psychology of the situation.

[tobluforu]

Wow! Since my car is still apart, looks as if I will adjust them again since I adjusted them on the loose side this time.

[Darkmoon]

Has anyone ever tried using .005 feeler guage as a nogo limit gauge? The idea is if the .004 fits and the .005 doesn't, then you're not too loose.

Just asking here... I'm still pretty new to this stuff. I just realized you are supposed to have 6 shims on the pulley...

[aigel]

Originally posted by Darkmoon
Has anyone ever tried using .005 feeler guage as a nogo limit gauge? The idea is if the .004 fits and the .005 doesn't, then you're not too loose.

Just asking here... I'm still pretty new to this stuff. I just realized you are supposed to have 6 shims on the pulley...

Dang, I am impressed, you aren't new to technical problems, for sure! Yes, that is a very common trick among hobby mechanics to make sure you aren't too loose!

George

[Darkmoon]

Thanks.