03-05-2022, 10:55 AM
I reckon that an engine, rebuilt with new everything should last about 40,000 miles before a re-bore becomes necessary. At that mileage, the bottom end, with modern oils should still be fine, although the rear main may benefit from a new bearing. This is based on my use of a Seven in the seventies and eighties, where it was my only transport. In those days, valves were an issue - with leaded petrol, frequent attention was necessary as the lead deposits lifted the exhaust valve off its seat, causing it to burn.
If you use a well fitted air filter, the mileage will go up, perhaps 70,000?
I have a pre-war book on engine rebuilding that reckons 2 1/2 thou bore wear for every 10,000 miles so this tallies quite well.....
Vintage blocks seem to be made from better quality cast iron, so may last a little longer.
If you use a well fitted air filter, the mileage will go up, perhaps 70,000?
I have a pre-war book on engine rebuilding that reckons 2 1/2 thou bore wear for every 10,000 miles so this tallies quite well.....
Vintage blocks seem to be made from better quality cast iron, so may last a little longer.