Tuesday, November 21, 2006

VW - Pulling Dowels

Pulling Dowels

(I’ve) tried everything but the last dowel refuses to come out.

The dowel may have picked up a bit of debris when it was installed, causing it to wedge. Heating it in an oven may help. Your torch provides only localized heat, it gets the surface too hot by the time the heat penetrates to the root of the dowel; heating in an oven allows the heat to soak in.

You can pull any dowel simply by grasping it with a collet-type puller and vibrating the crankshaft with an air-hammer. The usual method is to use to a blunt-nosed chisel in the air-hammer, inserted into the pulley retainer bolt’s thread bore so the blunt-nosed chisel rests against he bottom of the hole. The crankshaft is supported in a padded vise, the collet-puller is tightened onto the dowel pin and pulled firmly by hand as you rap the thing with the air-hammer.

No collet? Then use vise-grips. Dowels are hardened. You can’t mar a properly hardened dowel with vise-grips. Some guys don’t even bother with a collet (i.e., a gripper that grasps the full circumference of a shaft. VW dowels come in three diameters. You’ll need a different collet for each size.). Instead, they take a pair of cheap vise-grips with soft jaws and drill them for the size of dowel they want to grip, less a few thou.

No air-hammer? Then use a regular hammer. Just be sure not to damage the crankshaft by hammering on it. No heavy blows. Pretend you’re an air-hammer.

Why does it work?

I don’t know. Different mass-ratios or something. But it does work . . . all mechanics and machine shops pull dowels this way. Or maybe not all, seeing the trouble your local shop had with it. I’d better make this a public post.

If sleeve retainer was used to secure the dowel-pins you’ll need to heat the crankshaft to at least 450 degrees. Do this in an oven, where you can control the temperature. Let it heat-soak at least an hour to be sure the heat has penetrated to the dowels. After getting out the dowels, put the crank back in the oven, bring it back up to 450 degrees, let it heat-soak about an hour, then shut the oven off and leave the crank in the oven 24 hours or until the thing is stone cold.

(Revision Note: Despite a number of messages from ‘professional’ mechanics saying they’d never heard of a ‘dowel puller,’ such tools are in fact commonly available and every engine overhaul shop usually has one. They are available from Proto, Snap-On and most other suppliers to the trade. The dowel puller usually consists of a number of collets in SAE and metric sizes, which screw into a slide-hammer. When the slide hammer can’t win the dowel free, the trick with the air-hammer is used.)

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