I recently had to replace the throttle valve ($108) on my 1972 Tii (71,000 mi.).
It turns out that there are two steel bearings (steel on steel) which guide the shaft running from the throttle valve to the injection pump that are not lubricated. The absence of lubrication causes severe wear of the shaft and bearings, results in considerable play in the shaft, and makes mixture adjustment imprecise and idle erratic.
These bearings are pressed into the throttle valve housing and are not available as replacement parts through either the dealer or bearing supply houses. I attempted to have a machine shop line-bore the throttle valve casing, turn the injection pump shaft, and fabricate appropriate bearings but to no avail. The machine shop estimated that it would cost on the order of $100 to do the required work and suggested that for a few dollars more the replacement part would be a more prudent investment.
I talked to the dealer about the problem when I picked up the new part and he mentioned that failure of the throttle valves on Tii’s with 65,000 mi. and above seems to be a growing problem. He’s replaced 3 this year. Not only do the injection pump shafts fail, but the air regulation butterflies tend to stick because of a similar lack of lubrication. The moral of the story is, lubricate those bearings!
(Note: I find a 5/32 in. Allen wrench wired to a piece of coat-hanger works well as an injection pump alignment tool [BMW tool #6075]).
Author: Rob Woolley