DonE

Ah...got it. Thanks

DonE

I just completed the first valve lash adjustment since the rebuild. I tried two new methods (to me) - backside and Rob's suggestion of using a dial indicator.

After finding that I needed to bend my feeler gauges for the backside method, I ditched that method because I didn't feel comfortable sliding the feeler in between the cam and rocker arm on the opposite side. Not a good reason, but there you go.

I next tried the dial indicator. Way cool as far as accuracy is concerned. I however found that it took a lot of time moving the indicator aside, adjusting the screw, then moving it back into place. In addition, placing the point of the indicator on the screw took time because swinging the indicator back to the same place was impossible and the slot in the screw kept moving with each adjustment. If I had the patience, this method is superior for accuracy.

So, I ended up doing the rest of the valves the good old fashioned way. I then measured my work with the dial indicator. I tried adjusting the rockers by feel then checked with the indicator - off by .003 more and .001 less on three rockers. Anyone else adjust their valves by feel? I know of two builders that do.

FYI - all the rockers measured between .008 and .012, so they all loosened up since the rebuild. This was the first oil change (2nd filter change) since the rebuild and over 1300 miles, it used less than a quart - Penzoil 20w50. Mobil 1 15w50 went back in.

m42racer

It reaaly is important to set the lash to the correct amount. More important is to make sure the cold setting represents the hot lash. The hot lash is the running lash and its this amount that is calculated when the Cam is designed. Having the hot setting of, will start or delay the Cam motion. This changes the whole Valve geometry and changes the design and the performance. Hot lash is always given. Make sure yoyr cold setting represents what the Hot setting will be. Different usage, different engine configs, etc all will make this number different. So is adjusting the cold lash one way or another better. Maybe not if the hot lash is not correct. Accuracy is the name of the game. Thise that do it by feel have no idea what they are really doing. They are just saving thier time. What else are they saving on. Whatever way you use, make sure the hot lash is correct. When watching those I trust do this work, its always done on the engine staand, then after the engine is warmed up on the dyno the covers are removed and the hot lash is performed.

When rebuilding the engine, always check and chase the Rocker threads. Replace the adjuster screws idf there is any bind. Loose adjusters make the job alot easier.

DonE

I've never heard of a hot lash adjustment.

m42racer

Hot lash is the same as running clearance that is designed into the Valve motion. The reason its done when cold is to save time and effort. There is no other reason. The lash should always be done hot or at least rechecked and reset if necessary. The correct contact the Rocker makes to the cam lobe is the lash setting and this has to be done only when everything is hot and expanded.

JasonAndreas

The valve clearance specification (0.1mm) from Porsche has always had a cold engine reference temperature (actually room temperature 68F/20C like most DIN specs). They could have specified a measurement taken at 100C/212F or higher but the odds of even the best engine builder or mechanic taking repeatable measurements would be about zero.

m42racer

What is the difference between taking a repeatable measurement hot or cold? The best engine builder would know the difference and would know to do it hot. If they cannot get the hot lash to repeat, then I would figure some of the other critical measurements should also be questioned.

The factory would have measured the hot lash on a stock engine and then measured it cold and supplied the cold lash number for ease. No other reason. The issue here is the difference in these engines now. Some are producing alot more performance, therefotre more heat and the expansion rate will be bigger. This will then take some performance away from the Camshaft as it will be set in a different place.

Rob S

I agree with Jason, here. The factory valve lash spec is a "cold" spec. Though the cold lash spec was likely given so that (if adhered to), the hot lash would be correct, I have never seen any figures for what the hot lash should be. I can't imagine how the average (or even above average) mechanic could reliably set the lash at some temperature other than room temperature, especially on a 911. Just to get the valve covers off of a 911 or 930 engine that has just been running takes a fair amount of time (and is a pain when everything is hot). To adjust the valves takes even longer. All during this time, the temperature is dropping, so you would be chasing a moving target, and the lash adjustment would not be equal from valve to valve. With tires, it makes sense to set the pressures hot (because the measurement can be made so fast); but with 911 valves, it makes more sense to set the lash cold, because there's no good way to do otherwise, and there are no specs to follow at elevated temperatures.

Don, I still need to take a pic of my fixture; I don't know what you used to make your dial indicator measurements. You're right; the act of moving the indicator out of the way is necessary and takes some time. But with my fixture, it's pretty fast, and I guess I've gotten practiced at it. I'd say to set the indicator over a particular valve takes 15 to 20 seconds each time. To remove it takes a couple of seconds. To me, this is not objectionable. And like you noticed, it needs to be swung completely out of the way when the adjustment is made. If I find a valve that needs to be adjusted, I move the dial indicator out of the way and "guess" at a new lash setting. And I comletely tighten the lock screw each time before re-installing the dial indicator. I then re-measure. If it's wrong, I guess again, completely tightening each time. I find this works best.

I usually let the dial indicator plunger ride on the head of adjusting screw, but I sometimes use the face of lock nut. I make no effort to have it placed in the same spot each time. I don't care where the "zero" is on the indicator dial. I put the dial indicator in place and makes sure the plunger is somewhere in the middle of its travel, , I rock the rocker arm through its motion (without bumping the dial indicator) and watch the needle swing on the dial. I'm looking for a relative change of 0.004 in. on the dial.

As I said in my first note, I absolutely can't use a feeler gauge on 911 valves. I've tried and tried, and I can't get it to work at all. I don't know how you guys do it. But I understand that's how it's usually done.
Oh well...

Rob

nathanUK '81 930 G50

Rob & Jason, they were my exact thoughts too on the warm clearance settings (not knowing the exact temp of things), or hot as Simon puts it (in the UK we have warm clearances for most cars as well as cold, but of course only cold for the 911).

Rob, as for using the feeler gauge my mechanic had some difficulty in getting the feeler gauge in the gap, infact I did it for him mostly but that might just be that my hands are smaller. Also the more wear on the base of the adjusters makes the blade more difficult to enter the gap...
Was that your problem/difficulty?

JFairman

I have no problem with the proper feeler gauge in a 911 motor.
I've adjusted valves on a lot of different cars and motorcycles though so that helps I guess.
There's not much room in there, but I move or slide the feeler guage side to side while feeling the right amount of friction or drag on the blade, then tighten the adjuster lock nut while holding the adjuster screw with a short screwdriver while the .004" blade is in there.
Then check that the drag feels right again after that and if it gets tighter after tightening the lock nut then I repeat the process till it feels right.
New locknuts tighten down nice without trying to turn the elephant foot with it.
Overtightening the lock nuts will tweak the threads and make it almost impossible to get them tightened and adjusted right.
The threads on the elephant foot last longer than the threads in the lock nut.
Replacing them makes the whole thing so much easier and quicker when they get used up.

m42racer

I think you guys are missing my point here. Cold settinmg are given in order to make the adjsutment easier. I get that. But when fitting Cams other than stock, the Hot lash is always supplied or should be. The running clearance is what is caklculated when designing the Cam. My point is all of these engine operate a different temperatures with different boost levels etc, so all of this talk about how to check the clearances one way or another and setting the factory cold number accurately is not what it all seems. Maybe your Cam should have 0.012" Hot lash. Maybe yoyur engine runs hotter than another one. So what should the cols lash really be? Who knows unless you check it hot and hot is what your engine runs at. The position where the Rocker strikes the cam lobe changes with lash and this change makes a big difference in how the Valve motion is started and how the Cam reacts to the engine.

If you have a Cam from a aftermarket company I would bet it comes with Hot lash measurement. If it didn't, it should have.

loot87

But isn't hot lash going to vary by the temperature? How do you know your temperature during the hour or so that it takes to check it?

m42racer

Yes exactly. This is my point. The right and wrong way to do the cold lash is not as important as measuring the hot lash. If you do the lash cold and by feel, or by the typical way, and some say its not so accurate, so what. maybe the hot lash is off to. What about engines that produce 500+HP and thiose that produce alot less. The temperature is different and so may be the Cam design. There is no number that covers all.

Rob S

JFairman,

I, too, have used feeler gauges for decades with no problem in other settings.The problem I have in getting the feeler gauge to work right on a 911 is that the holding tools essentially have a lever arm that have prevented me from sliding the blade of the gauge so that I'm confident I have the right "drag" on the blade. Plus, I got questionable results when I checked (using a dial indicator) the work done by someone who used a feeler gauge. Your observation about damaged threads on the locknuts was interesting. I've experienced some difficulty with "sticky locknuts" too, but I never really thought about replacing the nuts.

M42,

I think everyone agrees that the hot lash is an important parameter, but in reality, your suggestion for measuring or adjusting it is just too academic. Unless you can produce some specs and a practical procedure to accomplish the adjustment hot, then it's all a dream that no one can ever live. For a 911 engine, especially one in (or even out) of a car cold adjustment is the only option available. (How many people have engine dynos?). A cold measurement may achieve the correct lash in a less direct manner than a hot measurement, but unlike a hot measurement, it can actually be done.

To that end, here are some photos of the fixture I bought years ago from Performance Products. I don't think they sell it anymore. I'd be interested if anyone knows where to get one nowadays.

Rob

srf506

I have absolutely no idea why you'd try and do a "hot" adjustment. In all of my years racing and everything else I've never even seen a reference for what the "hot" values would be. There's just too much variability in trying to adjust it hot. Doesn't mean you're not right on other makes and models, but on a Porsche 911/930 I've never even heard it referred to.