"Not Exhangeable Retrospectively" in BMW Parts Speak

[E36Ron]

After searching all over the Internet to clarify what is meant when a BMW part is listed as "superseding but not exchangeable retrospectively," only to come up more unsure than when I started, I would like to post a definitive answer: it means the new superseding part cannot be used in place of the old, superseded part, at least without modifications.

In other words, for English speakers, it does not "supersede" the old part in the manner we are used to, of being able to replace the old part with the new. I know this makes no sense to many of us -- then why call it "superseding"? -- but it appears to be a quirk of language translation.

I asked a prominent European user of this Forum, who explained that the original German, "nicht rückwirkend austauschbar," literally translates to "not retroactively/backwards interchangeable." He further said: "So it's best to treat superseding parts that are marked as "non exchangeable retrospectively" as incompatible (with the earlier part).

"How incompatible the parts are, depends. Some are totally different, some can be used with modifications and some are compatible apart from a minor detail. There's no telling."

So there you are -- use a later part marked as "not retrospectively exchangeable" at your own risk. Getting final clarification of this saved me a lot of money I might have spent in my enthusiasm to make just one more improvement to my BMW. ​

-- E36Ron

[shogun]

yes, nicht rückwirkend austauschbar = not retroactively interchangeable.
For example my 11/88 E32 750 has a cylinder head cover cyl. 1-6 p/n 11121720338, p/n used till April 1990, from 04/90 11121725808 , Non exchangeable retrospectively with old p/n 11121720338,
the reason is clear, the old cover till 04/1990 has the oil filler cap built into the cover, http://bmwfans.info/parts-catalog/E3...er_head_cover/
the newer version has the oil filler cap in front of the engine , no oil filler cap in the cover http://bmwfans.info/parts-catalog/E3...er_head_cover/

when parts are improved and will fit as replacement, like the chain tensioner for the M70 from April 1990, then there is mentioned Exchangeable retrospectively .Old partnumber 11311720414 http://bmwfans.info/parts-catalog/11311725682/

[MauiM3Mania]

Thanks for clarifying that.