Checking Cam Clearances & Installing Double Thrust Cam Bearings



    Before you install a camshaft, you should check a couple different areas to ensure that you are within specs and also to ensure that you won't run into any interferences with other moving parts.  

    Checking the cam's thrust clearance with your new cam thrust bearing is a must.  Too little clearance could cause binding or a seizure of the cam, while too much could cause excessive noise and wear on the cam gear as well as lifters.  

    Checking only takes a minute.  All you need to do is place your cam thrust bearing on the cam and slide a feeler gauge between the bearing and the cam's thrust shoulders.  For a new or reconditioned unit, this clearance should be between .0016" and .0051".  See photo below:

cam-thrust-clearance.jpg (34116 bytes)

    Now that your thrust is within specs, let's check to be sure that your cam lobes don't interfere with the lifters when they are in the full-OUT position.  Since I'm using only a very mild lift performance cam, I've got plenty of room.  You folks running high lift cams, be sure to check this closely.  Any interference will require you to have the lifter bosses cut down to provide enough clearance so that things don't touch.

cam-lifter-clearance.jpg (43484 bytes)

    I always use double thrust cam bearings when I build a motor.  Double thrust cam bearings are simply a set of bearings which have two (2) bearing halves which have the thrust wear surfaces.  The cam drive gears are "helical" gears meaning the gear teeth are cut at an angle.  This provides nice smooth and quiet operation, but it also loads the thrust shoulders.  VW recognized this and provided a thrust surface on one  (1) bearing half.  One half is adequate for a stock configuration engine running stock valve springs and such, but can be a little minimal when building a high performance engine.   Besides, it only costs an extra $5 or so to upgrade; Don't be cheap!!  Just do it!! :-)

   To run this style of bearing, you will need to slightly modify your engine case in order for them to fit properly.  The modification needed is a notch for the bearing tang to fit into.  No big deal I assure you.  First loosely lay the bearing into the bearing saddle and with a marking pen, mark the area where the notch needs to be made.  Then using a 1/8" thick bastard file held on end, carefully file the area.  Check periodically to ensure you don't file too deeply.  Once it fits just as the opposite side you're done.  No problem!!  Some folks just file off the tang on one bearing half but I prefer to add the notch.

 dbl-thrust-no-notch.jpg (38439 bytes)             dbl-thrust-notch2.jpg (26880 bytes)             dbl-thrust-notch.jpg (30144 bytes)             dbl-thrust-installed.jpg (37110 bytes) 


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Revised: August 29, 2003 .