whats the difference between red and blue 253

[HK1837]

That is right. Once they are rebuilt they can be anything. Only things that can't really change is the late red and blue engines have longer valley head bolt bosses, and the early reds (pre HJ production) have a neoprene rear main seal.

[Kingsandman]

My bad, its a red block ive just scraped blue paint off and found the original red, the engine no qr588710 casting dates 18j4 , does that eng.no corospond with cast date.cheers andrew.