Cam timing

[don hopkins]

Does anybody have any special tricks they use when doing cam timing? I have to do it and it scares me a little.

don

[911pcars]

Here's one for background.

http://members.rennlist.org/911pcars/camtiming-1.htm

Sherwood

[Eagledriver]

Just take your time and think about what you are doing 3 times before doing it. You'll have no problem. Things to keep in mind:

The cams turn once per two crank turns.

The cams turn opposite to the direction the crank turns.

The piston chases the exhaust valve closed as it approaches the overlap measurement.

The intake opens as the piston approaches TDC on the overlap.


Good luck and let us know how it goes.

-Andy

[snowman]

Take your time, it ain't magic. Just follow the instructions. Then double check, and check again. It should become clear to you after you have done it and double checked it. Do not attempt without a dial indicator. They can be had for about $10 to $20 so do not let this prevent you from doing it correctly. A degree wheel can also be used to help. THey only cost about $15 or so.

Get Waynes book and the factory book. Get help if needed as this is really critical to get right, but don't fret either, it ain't rocket science.

[sand_man]

Originally posted by snowman
Take your time, it ain't magic. Just follow the instructions. Then double check, and check again. It should become clear to you after you have done it and double checked it. Do not attempt without a dial indicator. They can be had for about $10 to $20 so do not let this prevent you from doing it correctly. A degree wheel can also be used to help. THey only cost about $15 or so.

Get Waynes book and the factory book. Get help if needed as this is really critical to get right, but don't fret either, it ain't rocket science.

Where does one acquire a degree wheel? Almost EVERY early VW engine that I built (and there were several) had a degree'd crank pulley, but I haven't been able to source one for my 930.

[bbh03]

As long as it is for reference and not precise angular measurement, print an accurate degree wheel on heavy weight paper and paste it on.

[sand_man]

Okay...I hadn't thought about doing that, but is there a more permanent (accurate) solution?

[911pcars]

A permanent degree wheel isn't a requirement. Almost all hot rod parts stores carry versions of a degree wheel you can temporarily attach to the crank or flywheel. For the pointer, use welding rod, coat hanger or a pointed piece of sheet metal.

Since we rely on TDC as a reference point to time the cams, an important thing to check is whether the TDC mark on your pulley really represents TDC. It could be off for one reason or another.

Before the chains are attached, one can fabricate a mechanical stop for the #1 (or #4) piston near TDC. A threaded bolt/locknut through a piece of bar stock positioned across the top of the cylinder with the cylinder head studs works.

Rotate the crank (manually) clockwise until the piston comes up against the stop. Mark the pulley. Rotate the crank in the opposite direction and repeat.

TDC is exactly half way in-between the two stop marks. Ideally, this should be the existing notch in the pulley. If not, cut a new notch with a triangle file, then add a dash of white paint. Subsequent cam timing is thus more accurate. You can purchase an official piston stop also from the same degree wheel sources.

Sherwood

[sand_man]

Thanks, Sherwood! I found some on Summit Racing's site!

[camgrinder]

http://www.tavia.com/free_degree_wheel.html

[helidoc]

Originally posted by camgrinder
http://www.tavia.com/free_degree_wheel.html

Amazing what you can find on the internet. Wish I had seen this before I spent $40 on a wheel.

[sand_man]

FANTASTIC! Thanks, John!