Quote:
Originally Posted by Lycoming-8
I believe that the "butterfly" valve was installed at the factory to help prevent the engine from running backwards. There was some discussion about this some time ago, may have been related to the run-away threads. Looks like these were also installed in the 220D's as well.
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It's installed on the W123 240Ds to restrict the intake for more exhaust gas flow into the intake manifold. If it were to prevent reverse running, it would have also been on the 77-81 engines and the OM617 engines as well.
It's on the W115 220/240D because the injection pump is pneumatically governed instead of mechanically. EDIT:
200D, 220D, and early 240D tuning guide
The engines cannot run backwards.
AFAIK, the only on-highway engines that are physically capable of running clockwise and anti-clockwise are the Detroit 2-stroke series engines.