Degree Wheel for Cam Timing?

[Tippy]

Originally Posted by Spenny_b

Ah mate, very kind of you to say, and also to imply I'm not a rookie...but I really am....versus some of the pro's and wisened folk here, I'm barely off first base!

HAHA, come on. Give yourself more credit! You're sliding in for the home run on your projects!

[911pcars]

Measuring TDC with a dial indicator gets you pretty close, but the crankshaft can move several degrees while the piston is stationary at/near TDC.

The recommended procedure is to use a positive stop described by ChrisBennet (post #9). However, introducing a hard stop through the spark plug hole can be risky if the valve train is intact (possible valve interference).

The slim probe on this "through-spark plug" tool seems to avoid potential contract with opening and closing valves that might not clear with larger stops. Back off the valve adjustment to limit valve lift.


With #1 head removed, a simple TDC tool can be made with a flat plate bolted across the top of the cylinder and a bolt and two nuts through a hole in the middle as a piston stop. This is a commercially available TDC plate.



Sherwood

[jamesjedi]

All good points raised. I do have a performance cam. I am interested in doing it accurately without buying the Stomski Digidix. That said I am not sure it is truly needed, but the degree wheel is not expensive.

I do see that they are used by others.

[Spenny_b]

I like the look of the spark plug stop tool, however, I struggle to get my head around the fact that the dowel-based cam sprockets only allow you to "use this hole, or that one"...it's not that granular, unlike other vernier cam sprockets with infinitely adjustable inner/outer halves, with 3 or 4 bolts that lock one to the other. I'm surprised somebody hasn't developed these for our (aircooled) engines; maybe they're used on the water cooled lumps, no idea.

[ChrisBennet]

Originally Posted by Spenny_b

I like the look of the spark plug stop tool, however, I struggle to get my head around the fact that the dowel-based cam sprockets only allow you to "use this hole, or that one"...it's not that granular, unlike other vernier cam sprockets with infinitely adjustable inner/outer halves, with 3 or 4 bolts that lock one to the other. I'm surprised somebody hasn't developed these for our (aircooled) engines; maybe they're used on the water cooled lumps, no idea.

It isn't obvious, but if you treat the holes like short "slots" you can get finer adjustment than just putting the pin in the hole and torquing it down. Getting the cams timed th same side to side is generally considered more important than their absolute value. I like to use 2 dial indicators, one on each bank. That way if I run out of adjustment in the sprocket "slot" on one side, I can adjust the other side "back" to make them even.

[Trackrash]

I agree, the one locating pin seems suspect in terms of accuracy. Turns out on my motor the Z1 was spot on.

[Spenny_b]

Originally Posted by ChrisBennet

It isn't obvious, but if you treat the holes like short "slots" you can get finer adjustment than just putting the pin in the hole and torquing it down. Getting the cams timed th same side to side is generally considered more important than their absolute value. I like to use 2 dial indicators, one on each bank. That way if I run out of adjustment in the sprocket "slot" on one side, I can adjust the other side "back" to make them even.

Yup, exactly what I did; 2x Mitutoyo Digimatic DTI's on Z-blocks one on each bank simultaneously. A razor blade held on the crankcase to mark my absolute TDC (case parting line nowhere near accurate enough, IMHO), and I was successful in getting exactly 1.26mm on both banks - exactly what I was aiming for with max advance on 964 NA cams, so was chuffed with that...all inside a couple of hours one evening.

[Speedy Squirrel]

I found all of these insights very interesting. I am curious, do any of you turn the engine backwards when timing the cams, or always clockwise?

[911pcars]

Originally Posted by Speedy Squirrel

I found all of these insights very interesting. I am curious, do any of you turn the engine backwards when timing the cams, or always clockwise?

For accurate cam timing, always in the normal direction of rotation.

Sherwood

[boosted79]

If you miss the TDC mark you can turn backwards (CCW) but go quite a bit, then go CW again to sneek up to the TDC mark. This makes sure all slack is out of the chains as a result of turning CCW.