Workinprogress Posted March 18, 2006 Share Posted March 18, 2006 I have a set of Arias forged pistons, I had them sent back to Arias due to the wrist pin holes being too small, by 2.5 thousanths. Anyway, I asked them about the proper piston to bore clearance and they guy (Elmer) asked one of his co-workers and they said for a piston size of 3.412" I should have the bore taken to 3.416". That seems very tight to me. I looked in the "How to modify" book and they dont say much about forged clearances, other than to follow the manufacture's reccomendations. This seems wrong. Quote Link to comment Share on other sites More sharing options...
dapiper Posted March 19, 2006 Share Posted March 19, 2006 Thats tight at 0.004" clearance for an Arias forging. I run the 7000 series alloy Arias forgings popular 10 years ago at 0.0055 minimum and at that time they recommended 0.006", since the later forgings can be run tighter. Depends on the application, more clearancefor turbo, high boost. Go by mfrs recommendation, since they know their alloys thermal expansivity. OBTW, recently inquired Arias during my rebuild as to clearance and they refused to say, unless I had invoice number they could not trace exact alloy used. You need to mic them on the skirts just below the pins. They may be 0.030 over forgings for a 3.416 bore which would explain Arias response. They should measure 0.006 less or 3.410" approx. Quote Link to comment Share on other sites More sharing options...
Workinprogress Posted March 19, 2006 Author Share Posted March 19, 2006 These pistons are a pain in the A$$, it turns out they are 12-15 yrs old and never have been installed. The rings are old style and I cant seem to find anyone to make good premium rings for me in this size. Either way, once they get put in I should be good to go for a strong NA motor. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted March 19, 2006 Share Posted March 19, 2006 dapiper, mfrs? What is this? I have 2nd hand arias forgies that measure around 85.8mm on my verniers. Funny though, the same verniers measured my F54 bore also at around 85.8mm. :S I need a proper dial guage, would also be nice to check roundness while I'm there. I don't care overmuch about the `correctness' of this combo, just want it to work while I save for a proper rebuild. So you run your arias at 0.0055, any idea what a rough upper bound for say, the turbo high boost applications you mention? I really have no clue. Dave Quote Link to comment Share on other sites More sharing options...
dapiper Posted March 20, 2006 Share Posted March 20, 2006 Mfrs my abbreviation for manufacture's. Older Arias were even worse with recommended clearance of 0.007". Slap city and shorter ring life. Never had an Arias fail, although evidence of moderate detonation.....frosties (erosion pitting) on head land opposite plug. They had less ring land bellmouthing wear than other brands also.......not cheap at $150 a pop and somewhat heavy, since I spec'd thicker dome, around 3/8" and 1/4" head land. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted March 21, 2006 Share Posted March 21, 2006 Cool. I have nfi how old my Arias pistons are. I believe they have 338 cast into the underside? So between 0.055 and 0.06 should be laughing? Dave Quote Link to comment Share on other sites More sharing options...
1 fast z Posted March 21, 2006 Share Posted March 21, 2006 With our bore size you should be between 4 and 5 though, UNLESS your boosted then make it 5-7 thou. Remember its the HEAT and EXPANSION rate that determines the clearence. Ive seen motors with as much as NINE thou. Remember, .0005" too tight will NEVER work, as will result in scuffing. but .002" clearence will ALWAYS work. Keep that in mind. On my last NA stroker, I ran .0045 on all bores. Quote Link to comment Share on other sites More sharing options...
jeffp Posted March 25, 2006 Share Posted March 25, 2006 There are two forgings, the high silicone cont and low silicone content forging. I am running the high silicone content forging and typically for a N/A application you can run 2.5-3 thousands, but keep in mind, if you run hot you will want to give the piston a little more clearance say .004 The low silicone content pistons will require 5-6 thousands clearance. Boosted applications give yourself .001 more clearance. Sucks, but piston expansion is a killer, some call it the black death when it scuffs. Take a look at my web page and see what happened to my cylinders. I got the engine very hot one time, really didn't have any choice in the matter, so I ran it until it cooled off. That instance did not hurt the piston, and at the time I believe it was about .004 clearance as opposed to 2.5 This new build is .005-.0055 and that should take care of my problems. The thing is the heat, you can run closer tolerances, but if you ever overheat, you will run into problems. Better to run a little lose when cold, and let the piston expand under operating temps then to be to tight any day. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted March 27, 2006 Share Posted March 27, 2006 Awesome. Thanks Jeff. I have serious oil pressure issues atm and this time tomorrow will be on my way to California so everything is on hold for a while. Lots of copper shavings in my sump. Stupid 30yo design oil pumps. Dry sump for me. Dave Quote Link to comment Share on other sites More sharing options...
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