20-05-2021, 10:08 PM
Exactly when cranks exceed the fatigue limit is unclear. For failure it is reckoned to take 1 to 10 million cyles just above the limit, but at 100,000 miles a seven crank has done more than 500 million revs.
Provided there is no pinging and the spark is not very advanced the wide throttle low speed loading on a small bore engine is not formidable, and the cycles do not clock up as they do at steady high rpm.
Remarkable are modern large bore engines which attain very high cyl pressures at their typical operating speeds of just 2000 rpm or so.
It is surprising how well many of the 1960s engines survived at 4000 rpm. my 1964 Minx at 180 000 has done a lot of running at 60mph, although the stroke is same as Seven..
Provided there is no pinging and the spark is not very advanced the wide throttle low speed loading on a small bore engine is not formidable, and the cycles do not clock up as they do at steady high rpm.
Remarkable are modern large bore engines which attain very high cyl pressures at their typical operating speeds of just 2000 rpm or so.
It is surprising how well many of the 1960s engines survived at 4000 rpm. my 1964 Minx at 180 000 has done a lot of running at 60mph, although the stroke is same as Seven..