Engine stripped for rebuild, strange marks on bearings etc

[Lee H]

Hi all,

Just bought a rev 3 turbo lump and then bought a GT3071 on impulse so decided I had better strip the engine and throw some forged pistons in with the power i'm planning to run.

Stripped it over weekend and was a little disappointed to find a score down one of the bores. Can feel it with my nail but not sure if it warrants a rebore or not. Picture below.

Also the bores are a funny colour in places, not sure if this is normal.







Then moved on to looking at the crank and big ends. Crank looks ok but the big ends have some really funny marks on the upper bearing of each rod.









Anyone have any ideas what would have caused this? Don't want to repace them for the same to happen again. Funnily enough number 4 was in the best shape and this is the furthest from the oil pump so if it was an oil issue i'd expect the opposite.

[Adam W]

A vertical score that you can feel means that it definitely needs a rebore IMHO, sorry :(

Those marks on the shells (or is it on the ro material itself? hard to tell from the pic) are heat marks, I can't offer any definitive advice as I haven't seen those before, but maybe detonation has been hammering the rod own onto the crank?

[adamh]

2nd that it needs a rebore, probably get away with 0.5-1mm. the wear marks on bearings don't worry too much about it if the cranks good. Thing to do get compressed air down that crank oil feed hole make sure all journal feeds are clear.
the reason #4 cylinder has least wear on the big ends is its farthest away from the flywheel, the largest mechanical load is applied at the flywheel end for that reason you will find the Main bearing is 3-4mm thicker in width at 1st position after fly (#1cyl) , but the rod bearings all stay the same width.