8 Doweling Your Crankshaft

Saving a damaged crankshaft or strengthening your good one

 

    Your flywheel is held to the end of your crankshaft by one large nut. called a "gland nut".  This gland nut presses the flywheel tight against the end of the crank, but that pressure alone is not sufficient to hold the flywheel in place when torsional loads (twisting loads) are put on the crank and flywheel during engine operation.  On a stock VW, what keeps the flywheel from spinning on the end of the crank is 4 dowel pins.  When the correct torque is applied to the gland nut, these dowel pins virtually hold the flywheel in place for years of trouble-free service.  

    Now, if you significantly up the horsepower output of your engine or do not torque the gland nut correctly and it comes loose, those 4 little dowel pins are not going to hold anything.  The engine that is pictured in this article had the flywheel come loose which damaged the original 4 dowel pin holes.  If I couldn't 8 dowel this crank, the only other option would be total disassembly and replacement of the crank.  It was pretty bunged up, but was savable.

4 dowels.jpg (51454 bytes)            4-dowels2.jpg (58605 bytes)

    Here's a look at the end of the crank and all the damage to the dowel pin holes.

    Here's a photo of the 8 dowel jig set that I used to 8 dowel this crank.  The holes in the jig are drilled so that there is one hole that is not perfectly centered like the others.  This ensures that the crank/flywheel can ONLY go together one way every time once it's been drilled.  I bought my jig from CB Performance for around $25 or so, but they are available from most retailers.

jig-set.jpg (32217 bytes)

    Start by placing the jig onto the flywheel and getting that drilled.  I have 4 dowel pins that I keep in my jig all the time.  This ensures that the jig will not move during the drilling process.  They are a tight fit and actually need to be tapped with a hammer into place.  I used a drill press to  drill the flywheel because it was convenient.  However, you can use a hand drill.  The jig is thick and hard enough that it will adequately guide the drill going in and won't make off-center holes.

    Once the flywheel is done, the crank is next.  Remove the flywheel seal and end play shims since you will want to replace the seal anyway.  Tap the dowel pins in the jig with a drift punch so that they are sticking out the other side of the jig.  Then position the jig onto the crankshaft and lightly tap it into place with a hammer.  

    With the jig firmly in place, You can begin drilling your first hole.  Be careful not to drill too far into the crank.  Stop frequently and measure the depth of the hole with a similarly sized bolt.  To get an accurate measurement you may need to remove the jig from the crankshaft.  BE SURE TO PUT IT BACK IN IN EXACTLY THE SAME SPOT.  Once you have the first hole drilled to the correct depth, re-install the jig and place your drill bit into the hole.  Now wrap a piece of masking tape around the drill bit where it comes out flush with the end of the jig.  Now continue to drill the other 3 holes to the same depth using the tape as a depth guide.

drill-crank.jpg (40997 bytes)            drill-crank2.jpg (51130 bytes)

      Once all the holes are drilled, you need to tap dowels into ALL the holes on the crankshaft.  Carefully look at the dowels to determine which is the offset dowel and match that up with the offset hole in the flywheel.  You will need to check/set your endplay on the crank and get it back to factory specs (.003" - .006").  Once endplay is properly set and a new seal is installed, torque the flywheel to the correct torque (250 ftlbs).

finished-crank.jpg (59134 bytes)

    With this simple modification that you can do yourself, you can repair an otherwise damaged crank or strengthen your existing crank and be ready for the drag strip. 

 


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