The story
History: facts, each with its source
Wikipedia describes the R family as inline fours built from 1953 to 1997 to sit lengthwise, notably in the Celica and the Hilux, which the US knew as the Pickup. The 3R pushrod engine went into the Corona and the Hilux; the overhead-cam 8R, 18R and 20R followed.1
Wikipedia says the 20R and the overhead-cam R engines after it did much to establish Toyota's reputation for reliability, which had been indifferent at best. The 20R got a stronger timing chain and reinforced lower block bearings.1