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The advantage of a cross-drilled crank is that you can more than one exit hole on the crankpin, offering superior lubrication.
But - to service a crossdrilled crank, you must unplug it because the outer radius region behaves like a centrifuge and collects dirty sludge from the oil, like this.
Any good race crank manufacturer will always cross-drilled. The position of the oilway on the crankpin is very critical, because if the bearing load is too high at the exit point, the oil pressure will be insufficient to let the oil out at all at main oil gallery delivery pressure.
The oilway mods shown in the photos have been done by me on virtually every crank I've ever prepped. The factory chamfer/radius on the drillings can vary from huge to OK to almost non-existent. I absolutely am sure that my preparing the journals in this way has contributed to the survivabality and reliabilty of GC engines over the years and is well worth doing. It takes time. An early crank like 131 2 liter which has 2 drillings per main journal compared with the later 2 (eg: Integrale) and is thru drilled on the crankpins (compared with the later ones which were only drilled to the centre) - takes me 3 hours or more. One slip iwith the tools and the rank is ruined.
- 2 liter Fiat TC crank - the sticky sludge traps particles from polishing, grinding & other crank mods, it can only be removed by unplugging the crank. All Fiat TC cranks are crossdrilled = race quality.
- crank sludge.JPG (71.71 KiB) Viewed 11376 times
- Massive Vauxhall 2.3 liter 'HSR' crank below the Fiat 2 liter (arch enemies in world rally in the 70s, Chevette vs 131). The Vauxhall crank is not crossdrilled. Cheap, nasty, avoid.
- Vaux 2.3 HS crank v Fiat.JPG (34.06 KiB) Viewed 11369 times
- Excellent drawing of a cross-drilled crank by member Jason Miller. Be careful when cleaning, the connecting drilling sometimes extends beyond the journal centreline.
- Cross-drilled crank JM.JPG (75.08 KiB) Viewed 11314 times
- GC mods to oilways. Keyhole helps entry of oil into crank and radius on crankpin (big-end journal) helps it disperse over bearing. Polish well. NO SHARP EDGES!
- crank prep 001.jpg (111.7 KiB) Viewed 10599 times
- GC tap/plug op involves removing factory staked plugs in webs, threading at 7/16UNC (all three taps are needed plus tapping lubricant) and plugging as in crank at left.
- crank prep 002.jpg (108.11 KiB) Viewed 10601 times
- This is not GC prep and no way good enough for a finished crank, a quick 10 second attack with a carbide burr, devoid of radii and sharp edges, it will shred the bearings in no time.
- crank prep 003.jpg (115.89 KiB) Viewed 10584 times
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