Focusing on the base engine design only, here also is a much simplified timeline of evolution. The D24/T/TIC family engine design falls into four basic categories.
Original design 1979-1980: Naturally aspirated only, with 11mm inhex non-stretch head bolts and corresponding configured block/head/headgasket. Solid lifters. Larger prechambers than later engines as well.
First update 1981+: Changed to longer, 12mm TTY "stretch" headbolts (some folks replace these with ARP or Raceware head studs). Solid lifters, and this basic design also was available from '83 on as a D24T turbo engine, with related changes as described in posts above.
Second update 1987+: Changed from solid lifters, mechanically adjusted with shims, to hydraulic lifters needing no periodic adjustment, although it can be a good idea to replace these lifters proactively at higher mileages as they can wear out internally. Available in this configuration as D24, turbo D24T, and turbo intercooled D24TIC.
Third update ~1995+: Redesigned front timing belt system on the very late production engines as described above.
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86 745 D24T/ZF 345k lifted 2.5"
83 764 D24T/M46 155k
Last edited by v8volvo; 07-26-2021 at 10:42 PM.
Reason: prechambers
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