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When I was racing my GT6 in the TSSC challenge trophy in the 80s, all the 1500 Spitfire guys were having their cranks cross drilled for better BE lubrication. Apparently, this is the big deal, when Triumph increased the size of the crank journals in circa 1971, (and therefore the wiped area of the shell bearings) they neglected to improve the lubrication in line with this. So the crank oil pathways are the same size as those on the "small crank" 1300. Which is something of a recipe for failure, if not total disaster. Made worse the more you use the rev range. Cross drilling the crank addresses this lack. It's not a cure, only a total redesign could do that, but it does help, or so the race boys swore, back in the day!
Further, the last increase in capacity, from 1296 to 1489cc was done the "wrong" way, making what was already an old style, long stroke "undersquare" engine even more imperfect. It's a fact of life, long stroke engines are hard on cranks, short stroke engines (like the famous PCF 1500 Ford motor) are hard on pistons. Personally I find pistons easier to replace than cranks, you don't have to pull the engine out! Also the short stroke engine is much more free revving. But we work with what we have!
Steve
To be fair to the 1500, it is actually OK for road use, well at least for someone like me who brought up on diesels. Plenty of low down torque, even if you can't really rev it and to be honest that is what you want in a road engine, power low down.
OK ideally it would have been nice if Triumph had designed an engine that could run in 4th on a motorway all day without blowing up; so I do have to concede it is a bit flawed.