Discussion and questions related to the course Practical Engine Building
A few weeks ago my CA18det spun a rod bearing. The aftermath was a damaged crank and connecting rod number 2. The damage took place while drifting in third gear on a track with a lot of direction changes. I did was above 5000 rpm for several minutes
I run everything stock inside the motor. only mods are gt2560r turbo at 1 bar of boost and a nistune board. Engine was in mint condition with every bearing in the center of advised Nissan tolerances (0,018mm-0,045mm).
After breaking I checked everything again: bearings and crank where stil in good condition (except rod 2 point offcourse). Allthough some main bearings show slight wear damage at the sides. I cant find the exact reason for failing but i assume connecting rod fastener as the cap of the rod doenst seem to fit proper anymore. The rod bearings were to damaged to be usefull in determing the cause of the damage.
The engine did have a lot of blow by (piston rings at 3x max tolerance advised by Nissan manual). Cilinders are stil in perfect condition so i assume ring wear.
and i dont run extra ventilation on the engine.
I now have a different crank and connecting rod and i'm checking tolerances with new stock Nissan bearings:
-main bearings come at 0,045mm clearance
-rod bearings com at 0,045mm
would this clearance be acceptible ?
I'm going to guess that the reason for your failure may have been oil surge. This would be quite common with a lot of direction changes, particularly at sustained high rpm/high load. I'd be at least logging oil pressure after your rebuild so you can see if this is the case, or even better would be to address the oiling system with a baffled sump.
The recommended clearances are relatively tight for a performance engine, particularly if you were anywhere near the tight end of the range. You haven't mentioned a power level however with the 2560 at 1 bar I'm guessing it's not massive. I'd suggest you target around 0.050 mm on the rod bearings and 0.050-0.060mm on the mains. I'd also recommend a good quality full synthetic oil in the 10w40-15w50 range. This will provide you a thicker oil film to help protect the bearings but nothing will save you from oil starvation.