> Question - in drilling out the port are you concerned about the chips
> falling into the overdrive?
I'm sorry I was not clearer, Tim. The port I was talking about is located
in the valve stem itself, so you simply pull the stem out (using a magnet or
bent paper clip) to make the mod. Clean it afterwards, so no contamination
to the OD. It's also kind of tricky to drill, so it's probably better to
use a small grinder (Dremel). There is a photo of a modified stem at
http://tinyurl.com/286t7wq
(Not my photo, don't recall where I got it. If anyone recognizes it as
theirs, please let me know and I'll be happy to give due credit.)
When the OD disengages, the valve stem drops, which opens the top of the
stem to the oil. The oil from the pistons then has to run out through that
port (and the clearance around the stem) for the OD to disengage.
Triumph also used to recommend motor oil for the A-type ODs, there was even
a 1954 service bulletin saying to use only motor oil if OD was installed.
(Although oddly enough, they specified detergent oils, like Shell X100.)
But somewhere around 1960, they changed to requiring GL4 in both OD and
non-OD gearboxes. Supposedly that was because they were seeing too many
failures of the thrust washers in the gearbox (which are a weak spot).
But if it works for you, then certainly you should use it.
-- Randall
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