HVX MODS on big-bore strokers
Oil for the right-hand half of the crankcase arrives there via the
channel behind the #2 cam bearing. When building a high-reliability
engine a standard procedure is to increase the cross-sectional area of
that narrow channel.
While this improves things, the amount of oil that can reach the
rocker arms is severely limited. A modification to the tappets
improves that situation but only up to the amount of oil available.
To increase the amount of oil, one of the steps in the HVX mods is to
create a second oiling channel to the right-hand case half. This is
done by connecting the tappet oil gallery on the right-hand case-half
to another source of oil. This is done by connecting the tappet oil
gallery to the oil gallery behind the #3 bearing shell. This
procedure is illustrated in the FILE archives of this Group, and
consists of drilling two new oil passageways.
This procedure dates from the late 1960's. At that time the only
crankcases available were of German manufacture. Today, crankcases
come from Mexico and the quality is not as good as the German cases,
especially when it comes to performing the HVX modification. A
warning to check the case before drilling is included on the drawings.
Unfortunately, on Mexican crankcases the deep hole in the casting
where you need to extend the tappet gallery may be so deep that it is
impossible to perform the modification due to a lack of depth of
To say this another way, you can RUIN THE CRANKCASE if you fail to
ensure sufficient metal depth BEFORE doing any drilling.
There are various methods of repairing a crankcase that has been
damaged in this way but the only method suitable for a FLYING
Volkswagen involves welding. If you can not find a qualified weldor
to make the repair you should bite the bullet and buy a replacement
I mention this now because in the past week I have received TWO
messages from competent builders who have encountered crankcases that
could NOT receive the HVX modifications due to insufficient metal
depth. Both were Mexican crankcases, apparently of recent
A word to the wise should be sufficient. MEASURE before you drill or
you may find yourself with a junked crankcase on your hands.