Valve clearance: 1.5mm+ intake and 1.70 exhaust

[dtw]

Just clearanced the motor. Comes in with no issues on intake at all; exhaust is close at 1.7mm. Per Anderson, this is fine (he recommends 1.5mm intake and exhaust); per Dempsey it needs a shim (2mm exhaust min clearance). I'm thinking of running as-is versus additional shimming. Thoughts?

[kstylianos]

what kind of RPM's is this motor going to see?

[dtw]

According to Crane, peak HP rpm is 6,200. So a bit beyond that?

[jluetjen]

Your talking about valve/rocker clearance right? Once you've gotten in there to get the measurement, the adjustment is pretty trivial. I don't even bother checking how bad they've gotten, I just readjust them to spec. If they are OK I leave them, if they are tight or loose against the shim I adjust them.

[dtw]

I'm referring to valve/piston clearance, sorry for the confusion.

[kstylianos]

If this is going to be a relatively lower RPM motor, then the less chance of rod stretch. If you are using lightweight valve train wear (titanium retainers), less chance of valve float. I believe BA's recommendations were for stock motors (stock RPM's and valve train).

[Wayne 962]

1.5mm and 2.0mm is what most people recommend in the biz...

Why take chances with your $$$ rebuild?

-Wayne

[dtw]

I'm talking to respected people in the biz and getting conflicting answers, which is why I posted. Where are you obtaining your 2.0 exhaust valve clearance spec? Is it from the spec books? I have hunted high and low and can't find mine.

Just got off the phone with my machine shop. When I told him I was at 1.7, he said "Nah, that's not right at all...you're running .5mm shim? Go back down to .25mm and tighten up that gap some more."

He was joking of course, and assured me that .060"/1.5mm is fine for the exhaust, and that at 1.7mm I should be just fine. So here I am with conflicting data from reputable sources...?

[Wayne 962]

Who is your machine shop? Call Walt at Competition Engineering and ask him. Call Jerry Woods or Bruce Anderson and ask him. All of these guys recommend the same thing, 1.5mm intake, 2.0mm exhaust.

It's not in the spec book because it's not a spec that you can measure when the engine is assembled new. It's a function of machining changes that the factory didn't consider when writing it's spec books. This is why I address this info in the Engine Rebuild Book.

It's your $$$ - take your chances, but you will always be afraid to drive the car really hard - trust me on that...

-Wayne

[jhelgesen]

Shoot Dave, what a small world. I was about to post about the exact same thing.

I'm checking the valve clearance on my 3.0 tonight. I got one exhaust valve that is measuring at 1.75mm. All the other intake and exhaust are 2.0 or more.

I'm reinstalling the heads on my 3.0, so the cams and rockers were never disassembled, and I didn't have any machine work done, I haven't changed anything.

So will 1.75mm work?

[Wayne 962]

No, it won't work. Why isn't anyone listening?

-Wayne

[dtw]

Come on Wayne, read my posts. I'm not "not listening". I'm trying to make sense of two conflicting inputs.. It concerns me that you say Bruce Anderson indicates 2.0mm. Page 179 on the 2nd ed. of his book says "Minimum clearance should be 0.060 inches (1.5 mm) for the valves." You asked about my machinist - he's David Brown of Speedwerks. He's built everything from Type IV motors to 962 motors. He's also saying that anything above 60 thousandths is gravy, and yes, he was speaking specifically about street motors.

John, when you say that you checked clearances on all the valves- did you do 1-6? If so, may I say I'm impressed. That's a lot...a LOT...of work. It does concern me that you have an outlier in your readings. What method did you use...turning the lash screw? solder? clay? I'd recheck timing on that bank. My right side bank came up at 1.45mm on the first pass...turned out the timing slipped on the final torquing, and we somehow missed it when double-checking with the dial gauge.

Some tips I've picked up while timing the cams...
-always come at the Z1 mark from a clockwise turn on the pulley....and make sure there is no chain slop as you approach the reading. Best practice is to come at the reading from a full 720 past the previous reading.
-assembly lube on the cam seems to give inconsistent dial gauge readings due to the thick, viscous consistency. Best results seem to come from using a very light skim of motor oil on the lobes, and giving the motor several rotations to allow the oil to evenly distribute itself.

[jhelgesen]

Yep, I did all the valve 1-6, intake and exhaust. Wasn't that much of a PITA.

I agree with you Dave on making sure you only go clockwise on the rotation. Counter-clockwise makes the chain tensioners really flex.

My method was I turned the screw in at Z1 and counted my turns. Least amount of clearance was about 15-20 degrees before Z1.

I'm considering taking the Hydraulic tensioners back off the engine and testing again with the solid tensioners I had on when setting the cam timing. I'll check the cam timing again, but I had two gauges on the engine and both were reading dead nuts on .040" when I was done.

Would be really cool if I had a temporary oil line set up that I could pump the tensioners up with pressure while testing.

[Tyson Schmidt]

DTW, if you need extra clearance, do what I did, and retard the cam timing. The spec for my Elgin-Solex cams was 4.2-4.6mm. I set it at 4.0mm, and ended up with 2.2mm clearance on the exhaust side and 1.8mm on the intake side.

It runs fantastic. Check out the Reseda Dyno Day thread on the 911 technical forum for my dyno sheet. Good reading for you, since you're building an exact replica of my engine. The dyno runs were made with MFI and a factory sport muffler.

[Wayne 962]

Hi again. There is no real downside performance hit when you modify your engine to make sure that you have this clearance. While I'm sure that some engines will work fine with these small clearances, it is really worth the risk? Particularly on an older mag-case motor there will be a bit more risk as the engine seems to expand, contract and deform quite a bit more.

The answer is simple, 2.0mm clearance is the sure-fire way to go. Anything less is riskier.

On a 3.0L engine, this clearance should be really, really big. A close tolerance on a CIS engine usually indicates that there is something really wrong. These close tolerances are typically only seen on 'S' cam motors or engines with really aggressive cam and piston profiles.

When I was up at Bruce's and Jerry's class last December, I confirmed the 2.0mm clearance number with them.

-Wayne

[Wayne 962]

Originally posted by jhelgesen
I agree with you Dave on making sure you only go clockwise on the rotation. Counter-clockwise makes the chain tensioners really flex.

It does not sound like you are using the correct method to time your camshafts. As detailed in the Engine Book and the factory manuals, the chain should be tensioned separate from the tensioners. I.E. use a pair of Vise-Grips or a chain tensioner clamping tool. Otherwise your chain will be too loose, and you won't get accurate readings.

You can't accurately time your cams using the chain tensioners alone.

-Wayne

[jhelgesen]

Wayne,

I'm going step by step, word for word from your book.

The engine is #6290079, should be a us spec 3.0. Cams are 930.148.08.

I set the cam timing with a pair of solid tensioners, both measured .040".

Then I primed and installed the hydraulic tensioners.

Next I checked the valve clearance. When I said the tensioners are flexing, its when I was checking the valve clearance.

With no pressure on the tensioners, will this affect the outcome of the valve clearance?

[Doug Zielke]

You can't accurately time your cams using the chain tensioners alone.

-Wayne [/B]

I have always wondered about this.
So....what happens to the timing under actual operating conditions, with the tensioners installed?

[Tyson Schmidt]

It moves around quite a bit. Especially when revved abruptly and released. Ever run one with the cover off? The tensioner gets a workout.

I've never done this with a pressure fed tensioner, and I'd assume that it would hold the chain more consistently tight than a hydraulic tensioner.

I believe in Bruce Anderson's book, he mentions that it can actually be beneficial power-wise. The cams would retard slightly at higher revs. I think he was describing the slight power loss from the gear drive set-up, which kept cam timing dead-on, and did not benefit from this "poor-man's Variocam" effect.

[dtw]

Tyson,
Holy crap. I was hoping for 170 flywheel...that's insane. You must love that motor.

What induction setup have you got? I have swapped out all the T kit for "e" stuff...pump, t-bodies, intakes, diz rotor, etc.