LS2 427 Bearing Clearances?
Teching In
Joined: Apr 2005
Posts: 27
Likes: 0
Perhaps. A better finish and geometry would certainly help. However the iron does deflect more under higher loads and this deflection could cause some uneven loading in the bearings that may exceed the materials capabilities. I'm not saying the stock LS crank is limited to 500-550 hp, I am just saying that is a general rule of thumb based on most of the applications I have been involved with. I've had some turbo Buick engine builders tell me they still use the aluminum bearings and stock iron crank in 650+ hp V6s. Keep in mind the guys at GM decided to go with a hardened steel crank for the LS7...
Yeah the LS7 needed it with the higher piston G's that the longer stroke gave it. I normally am dropping the bobweight significantly then the loading can go way down but we are still putting power and RPM thru the setup, all though the RPM is just linked to piston G's and with lower mass the F will be lower overall. We also could do a nitriding or hard chrome plating to the journals but the stock crank has none of this. I'd rather do nitriding over the plating, but it's not cheap and a lot of extra machine work. We can get the Ra down into the 4 or lower area with polsihing and put a 90 deg radius in the corners of the rod journals when going to smaller journals there. That's where my issue is, the mains are the same and will stay the same but when the rod journal geometry changes from the undercut radius to the 90deg we have to use a chamfered bearing and those are normally the copper/lead type. That still leaves the issue with the elasticity of the parent metal, normally I just run a slightly larger bearing clearance with the aftermarket cast cranks in this situation but you are the bearing guy so your thoughts on this would be interesting.
Bret
Bret
Teching In
Joined: Apr 2005
Posts: 27
Likes: 0
Yeah nitriding is good stuff. I know what you mean about the fillets. I don't know a good way to get around that. I don't think we would ever carry a chamfered aluminum bearing because I don't think there would be much demand for it. What surface finish are you getting on the crank (i.e. 4 - what units)? What is the Rz and Tp? If the geometry and polish is good enough I wouldn't worry too much about running the copper lead bearings.
Thanks, next time I run the profolometer over the journals I will check the Rz and Ra as well. If I can figure out how to do nitriting with our local (and very good heat treater) economically I will.
Good discussion either way.
Bret
Good discussion either way.
Bret
