From: bmrfamly_at_nwlink.com (Dan, Marilyn, Anathea, & Phil Patzer)
Date: Mon, 27 Jul 1998 07:26:36 -0700
Subject: all BMW oil holes in pistons
I am continually amazed at the "Kreosote" (by-product of water vapor &
oil vapor) I find on head bolts, and in the head bolt holes within the head
when replacing seeping head gaskets.
I always try talking the owners into replacing the piston rings as the
same chemical process that fills the head bolt holes also fills the oiling
holes within the third ring groove (the oiling ring) on the sides of the
I always DRILL out the holes and often have to use the drill-press,
instead of the hand drill, as the Kreosote plugs are so solid.
The purpose of these holes is to supply oil to the oiling rings (the
piston bottom acts like a funnel capturing oil sprayed from the sides of
the connecting rod bearings at their crank journals). The oiling ring has
calibrated openings and two "squeegie" edges. Often these are multiple
piece devices which eliminates the large end gap if the segments are
Inadequate oil delivery because of plugged holes leads to rapid cylinder
wall deterioration. This is indicated by loss of "honing" marks and the
presence of vertical scoring.
Caught early enough, the cylinders can be honed, and the rings, and crank
bearings can replaced with hood and block in place. Severe scoring will
not hone out, but requires boring for larger pistons. This is very costly
and the block must be pulled.
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the CyberWrench 425-259-3601 72' tii touring K75RT 85' 732i R100RS
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