Cam timing termanology

[quattrorunner]

I'm just going to be honest here. I'm over my head with this step(cam timing). I have my dial gauge set up but I can see how I could screw this step up easily. My main issues I'm having is that I don't understand what is meant by "dial indicator shows that the valve has movedthe amount indicated for the intake valve stroke un overlapping TDC with 0.1mm valve clearance". I read it over and over and my brain just won't process this. Plus I didn't expect the valve to spin the dial 9 times. I'm a little freaked out by this step if youcant tell. Help?

[Flat6pac]

.1mm is the valve adjustment (valve lash)
The dial guage sits on the spring retainer. turn the pulley 1 revolution to Z1 and then the valve is opening to a measured amount. Move the pin to get the number you need.
The dial guage will measure the movement of the valve and that is the measurement youre setting with the pin
pin both the cams with the dot up. Set 1,2,3 side and then move the guage to 4 and turn the pulley 1 revolution and set the valve movement to match the other side.

Bruce

[quattrorunner]

Alright I watched a YouTube video of the procedure and feel like I do know what to do. But......one final issue is how to know how many times the dial indicator should turn over for my application. I have a 76 3.0 turbo using sc cams freshly ground. Watching yh video, he was timing a 68 higher lift cam and he measured 5.25 turns or millimeters if I'm not mistaken. But that's just it, I feel like im mistaken especially since read that for a sc cam it's .1mm TDC? Now u know how to do it but just don't know how many revolutions or milimeters.

[quattrorunner]

And sorry I'm on my phone hence the misspelled posts, sorry

[quattrorunner]

I guess I don't know the number I need or how to measure that. If I can get this I will have this build licked. Thanks.

[2.70Racer]

It is sometimes difficult to process written instructions, when a picture by comparison is so simple.
Something like writing instructions on how to tie shoe laces without a picture.
Remember the 4 cycles; intake, compression, ignition and exhaust.
The .1mm valve lash (gap), for both intake and exhaust, is set when the piston is at TDC compression stroke.
Cams are timed at the other TDC, when the exhaust valve has almost closed and the intake valve has just begun to open, (overlap). 360 crankshaft degrees after TDC compression.
You set the dial indicator against the intake valve when the intake is closed, with the indicator stem compressed about one turn of the dial and the dial rotated so the needle points to zero.
The intake valve is closed until a few degrees before V1 overlap.
As you turn the crank clockwise to TDC overlap, the intake valve is supposed to begin to open just before TDC overlap.
As the intake begins to open the dial indicator turns backwards from zero. The indicator stem is moving down with the valve, as it should. The needle turns backwards from zero toward 9 then 8 then 7.
When it reaches 5 the valve has opened .050", when it reaches 4 the intake valve has opened .060".
Let's say you are setting cams for a 1980 SC, the spec is 1.4mm to 1.7mm at TDC overlap.
Convert to thousandths of an inch, 1.4mm=.055", 1.7mm=.067".
So the dial indicator needle would back up to .045" for .055" and continue back to .033" for .067".
Midway is 1.55mm, or .061". As the needle is moving backwards it would read .039" for .061".
This sounds more difficult than it really is. Move the cam and watch the indicator needle and it become obvious. No need to count revolutions as the dial indicator needle has only moved about 2/3rds for a dial indicator using one complete turn for .100".

[boyt911sc]

Originally Posted by quattrorunner

I guess I don't know the number I need or how to measure that. If I can get this I will have this build licked. Thanks.

quattro,

Post a picture of your dial indicator and we will try to explain to you how to read or interpret the numbers. You are not alone and it is very common people get confused in reading the measurement specially for first timer. Once you decipher how to read the initial setting, interpreting the final setting is simple. HTH.

Tony

[quattrorunner]

Here is my dial. And thanks for all the help. I'm sure I can get this tonight.

[MBruns]

1 full rev of that dial is 1 mm, that has a full range of 25mm, if your cam timing spec was say 5.5mm at overlap (360 deg from Z1) as you turn the engine through it should sweep the dial 5 full turns plus another 1/2 (starting with the dial indicator preloaded a little and set to "0" before you turn.
Mike Bruns

[2.70Racer]

Since your dial indicator is calibrated in mm's, ignore all the conversion to inches. Sounds like you are getting there. Good luck.

[quattrorunner]

I just turned the crankshaft till the dial read 1.55mm and adjusted so it's at TDC with this value. is it really this simple or could I have f-ed it up? First time was past TDC slightly and now it's correct but I'm just not sure its right as I've never done it before. Did I miss anything? Thanks

[Daviboy]

quattrorunner you have got it. I too was over thinking the whole procedure but it really is that simple as long as you end up within the specified range for you cams thats it. Thing is when you do the left bank the dot on the cam has to be facing down ask me how I know....

[304065]

This may help visualize what is going on in the engine

Green= power, Gray= exhaust, Blue= intake, Red= Compression



You can see where the timing point is, it's at overlap TDC. Overlap TDC is like a road sign in the middle of the engine's two-revolution complete cycle-- one where you can clearly see where the crank is positioned, and one where both valves are open a little bit. All you are doing with the measurement is turning the cam so that one valve is sticking down into the combustion chamber a predetermined amount, so that you know the position of the cam.

Does this help or does this make it more complicated?

[quattrorunner]

It helps, it all helped me a lot. Thanks for all who have held my hand through this step. This step has haunted me for years, keeping be from doing a porsche 911 build till now to be honest. I got it and now the tough part as Wayne pointed out in his book is holding the gear/cam still while torquing it! It's also doable but difficult.
I'm super happy with my progress and couldn't be happier that I have tackled this project. I wouldn't have tried it if I didn't have this forum though, well I probably still would have but I would have bugged some guys I know that know this procedure.
Anyway, I feel like getting another engine that need building and doing that too. Kidding of course but you understand my excitement.
Thanks guys our the best

[Eagledriver]

Just do one more check before you move on. Make sure that number 1 and number 4 are timed 360 degrees from each other. In other words, number 1 intake valve should not open at the same time as number 4, they should be apart by one turn.

-Andy

[Flat6pac]

+1 on checking the 1 and 4
If youre TDC on 1 the intake valve is loose (has valve lash) the #4 is moving from about 30degrees before TDC. The rotor should be pointing to #1 when installing the distributor.
If 1 is tight and moving then #4 is loose with valve lash and the distributor rotor should point to #4

Bruce

[930LDR]

Doug - The explanation below is great. I've been doing a lot of reading and research as I embark on this and nothing really gave me cause to think about the fact that the gauge would be moving backwards and that the reading on the face of the gauge that I am really looking for is the inverse of my target.

Thanks!

Originally Posted by 2.70Racer

It is sometimes difficult to process written instructions, when a picture by comparison is so simple.
Something like writing instructions on how to tie shoe laces without a picture.
Remember the 4 cycles; intake, compression, ignition and exhaust.
The .1mm valve lash (gap), for both intake and exhaust, is set when the piston is at TDC compression stroke.
Cams are timed at the other TDC, when the exhaust valve has almost closed and the intake valve has just begun to open, (overlap). 360 crankshaft degrees after TDC compression.
You set the dial indicator against the intake valve when the intake is closed, with the indicator stem compressed about one turn of the dial and the dial rotated so the needle points to zero.
The intake valve is closed until a few degrees before V1 overlap.
As you turn the crank clockwise to TDC overlap, the intake valve is supposed to begin to open just before TDC overlap.
As the intake begins to open the dial indicator turns backwards from zero. The indicator stem is moving down with the valve, as it should. The needle turns backwards from zero toward 9 then 8 then 7.
When it reaches 5 the valve has opened .050", when it reaches 4 the intake valve has opened .060".
Let's say you are setting cams for a 1980 SC, the spec is 1.4mm to 1.7mm at TDC overlap.
Convert to thousandths of an inch, 1.4mm=.055", 1.7mm=.067".
So the dial indicator needle would back up to .045" for .055" and continue back to .033" for .067".
Midway is 1.55mm, or .061". As the needle is moving backwards it would read .039" for .061".
This sounds more difficult than it really is. Move the cam and watch the indicator needle and it become obvious. No need to count revolutions as the dial indicator needle has only moved about 2/3rds for a dial indicator using one complete turn for .100".