12g1505 fatigue life
Turbo Mini Forums

I'm in the process of building a k head 1275 motor and have recently got hold of a 1505 crank in a bunch of parts.

I understand that this crank doesn't have the rolled fillet radii as seen on the later CAM6232 A+ cranks.

So my question is: in a motor that will frequently see 7.5k rpm, is this crank suitable? Are there any definitive cases of poor fatigue life on these cranks at those sorts of loadings?

Thanks
Andrew

Vizard states in the yellow bible a tuftrided large fillet radius crank should survive for 120 hours at 6200rpm on a 90hp engine.

Then again it also states the fatigue life of a crank at between 8500 and 9000rpm is about 250 miles, still 250 miles is a hell of a long time keep an engine at that kind of revs so I would say up to 7500rpm you won't have a problem as long as its well balanced and tuftrided.

What is the cranks history? As if it has taken a pasting in several other engines the fatigue life will obviously be reduced.

Also what is the planned usage,, for example if it will do only track days then clearly the crank is gonna be working hard.

Edited by minimole23 on 4th Nov, 2012.

I doubt youll fatigue the crank anywhere near breaking point on a street engine.

Balance is important, and good tight bearing clearances. Make sure you use a crank damper that is in good condition and if you can afford it, a viscous damper. But, in the grand scheme of things, you're worring too much about it. The early cranks used a higher specification steel than the later A+ cranks, so wether its a rolled fillet or a ground fillet, its not really anything of concern

The cranks history is unknown but it will be used in a track/occasional weekend drive car. So when i use it, it won't be under anything other than ardous use really.

Am i to believe that the 12g1505 manufactured from EN16 is an identical material to that of the cam6232 cranks?

As above. But I would reccomend you get it ballance with flywheel, backplate and damper,

Also makes for a very smooth! Motor