Cam Basics

 

    What is a cam and how does it work??  The camshaft is the internal component that times when the intake & exhaust valves open and close as well as provides the mechanical motion to get that done.  The cam in an air-cooled VW motor is driven by a gear on the crankshaft at a ratio of 2:1 (2 turns of the crank for every 1 turn of the cam).  

    There are two basic types of cams available today.  The earlier "FLAT" cam and the later "DISHED" cam.  Flat and dished refer to the area where the cam gears attach.  Flat cams came stock on all pre-'71 VWs.  Most aftermarket cams built on new billets are of the "flat" variety.  These can be identified by either three (3) bolts OR three (3) rivets which hold on the cam gear onto the cam.  Dished cams came stock in the post-'70 VWs and are easily identifiable by the distinct "dishing" of the center where the cam drives the oil pump (see photo below).   Dished cams also have four (4) rivets which hold the gear to the cam.

cam-grind-ID.jpg (43713 bytes)

    Cams come in virtually infinite grind profiles.  I pretty much know my knowledge limitations, so I won't try and explain all the technical stuff like duration, lift, overlap and the like.  If you need advice as to which cam is right for your application, go talk to the cam maker or a respected engine builder for that.  To find out what grind of cam you have if you're in doubt, check the center and it should be stamped in there.  The above photo shows that this cam is a "D-10" grind from Delta Cams in Tacoma, WA.

1 - cam-heel.jpg (34290 bytes),      2 - cam-flank.jpg (37870 bytes),      3 - cam-nose.jpg (32932 bytes)

    Cam lobes have 3 basic parts: 1 - the "HEEL",  2 - the "FLANK", and 3 - the "NOSE

1 - cam-intakelobes.jpg (28756 bytes),      2 -  cam-exhaustlobes.jpg (24578 bytes)

    The above photos show which cam lobes control which functions.  photo 1 shows which lobes control the INTAKE valves,  Photo 2 shows which lobes control the EXHAUST valves.  Since you have only 4 total lobes to control all 8 valves, each lobe controls two different valves simultaneously.  In these photos, the TOP 2 lobes control the valves for cylinders 1 & 3.  The BOTTOM 2 lobes control the valves for cylinders 2 & 4.

 


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