[T3] Fan Housing Screws

Jim Adney jadney at VWType3.org
Sat Sep 17 11:15:08 PDT 2016

On 17 Sep 2016 at 15:36, Know One wrote:

> Some of the screws holding the fan housing together have serrations.
> I've added a picture of a screw to the album with the cool tins.
> https://www.flickr.com/photos/52053275@N00/albums/72157670647048993

VW used 2 kinds of M6 slotted head screws in the initial engine 
assembly: plain thread and thread clearing. The screw in your photo 
is not a VW part.

The thread clearing screws had a single kerf at the start of the 
thread and were used when the female threads were in painted parts 
where the thread would have paint in them. The single kerf acted like 
a cheap tap to clear the paint out of the threads. As you suspected, 
once this is done, there's no need to use anything other than a plain 
thread screw.  

When I assemble an engine, I'll use a variety of screws, including 
hex heads in locations where experience has shown that they are 
really hard to get a screwdriver on once the engine is in the car.

I would not use the screws shown in your photo because they have lost 
a lot of their holding ability because so much thread is missing, 
like maybe 30% or a little more. Those kerfs are also likely to allow 
water to enter more freely and promote corrosion.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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