Just wondering how many miles most can go with normal oil changes 300, 400,000 mi ? I know they are strong but what is the average they really need to be replaced , checked ? Is it the guides and chain that wear together or a combo of one before the other . How many of folks out there have gone this many miles without replacing the chain or guides ? This seems to be relatively one of the very few parts that amazes me about these engines. Thanks.

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A couple of Ford pickups F 150,250, 350 missed.
1983 240 D 256,000 miles ,auto, ac.