FireHead Posted July 24, 2009 Report Share Posted July 24, 2009 Thermal conductivity properties and cost are the primary reasons for OEMs using Nikasil. It is really a PITA for the back yard rebuild though. Heat soak is really a fact of life in an engine cylinder. Thermal conduction is much better in Al, than Iron and allows for lower operating temps. There are many advantages of Al blocks but rebuilding can be a bitch. I am not sure why sled OEMs are running wider piston clearances. A plated bore cylinder typically expands faster with the piston and has natural lubricity properties thus allows tighter tolerancing. That being said, forged pistons create big problem there. The lower silica content in forged pistons and poorly aligned molecules from forging makes then grow in strange ways. B I think the piston growing all depends on the specific piston for a specific manufacturer. It is not fair to say all forged pistons grow in strange ways. Just as it is not fair to say all cast pistons expand uniformly. For instance, a piston made from a chunk of billet (that is not hammer forged) and goes through a proper heat process, will be far superior, while having a much more uniform expansion rate in all directions. You really don't see many performance small gas engines with open deck cast iron liners any more for good reason. :geek: Quote Link to comment Share on other sites More sharing options...
blowit Posted July 24, 2009 Report Share Posted July 24, 2009 I think the piston growing all depends on the specific piston for a specific manufacturer. It is not fair to say all forged pistons grow in strange ways. Just as it is not fair to say all cast pistons expand uniformly. For instance, a piston made from a chunk of billet (that is not hammer forged) and goes through a proper heat process, will be far superior, while having a much more uniform expansion rate in all directions. You really don't see many performance small gas engines with open deck cast iron liners any more for good reason. :geek: I thought all the big diesels were still running iron liners for speed of repairs???? By the way, how would we call a "billet" piston a "forged" piston? We looked a while back at making some low production pistons on the lathe from some forged slugged solids but decided that they would probably deform all over the place from the forging. Also would probably have a hell of time oval turning them without a camturn lathe. I would be VERY curious to see how cryo work affects forged pistons as well. We have a freezer here that we want to use for cryo work at some point, just no time for it right now..... B Quote Link to comment Share on other sites More sharing options...
FireHead Posted July 24, 2009 Report Share Posted July 24, 2009 I thought all the big diesels were still running iron liners for speed of repairs???? By the way, how would we call a "billet" piston a "forged" piston? We looked a while back at making some low production pistons on the lathe from some forged slugged solids but decided that they would probably deform all over the place from the forging. Also would probably have a hell of time oval turning them without a camturn lathe. I would be VERY curious to see how cryo work affects forged pistons as well. We have a freezer here that we want to use for cryo work at some point, just no time for it right now..... B Big diesels are running liners, but not in a open deck format. A billet piston is technically made out of a forging, since that is basically all a billet is................ All you need to make pistons is a 5-7 axis WFL mill-turn machine and you'll be all set to make pistons, cranks, transparts, etc. :biggrin: Quote Link to comment Share on other sites More sharing options...
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