Piston to cylinder clearance

Hi, just putting together a 4.125 bore, billet block hemi with darton sleeves, the sleeves measure up spot on but the piston are telling me I have 8-9 thou clearance, 4.126 on the sleeve and 4.117 piston, seems a little excessive to what I have ran on my old Sbc. This is my first blown alcohol engine, what clearance are guys running? Appreciate any help even if it is ( buy new pistons )

 

pistons

If they are new that is a little loose, if they are used that sounds like what happens after they are ran. What mfg. are the pistons ?

 

Who's pistons are they ? Where and exactly how are you measuring the piston ? With what tools and at what location on the piston ?

 

.005 on new builds. Everything works smoothly at that. Even seen some as tight as .0035 from big engine name builders. However it's done with coatings. Line to line coatings in Michigan is leading the way on the nicest stuff out there with awesome results. Ask Janis , all his motors run it. Takes the scuffing right out of the picture and ring seals lasts a lot longer without a piston beating the walls to death

 

they are venoila pistons, i measured them 90 degrees to the pin and about 1/2 up from the bottom of the skirt...., i was going to have them coated from a reputable coater here in Australia, that has also had some great results, the pistons were used and have the lightest about of scuffing you can still see the machining marks im thinking the pistons could possibly be an old style that ran more clearance?

 

Thats about the same clearance I run, no problems. Better than being tight.

 

clearance

Thats is about right for used racing pistons Check and make sure there no cracks in the pin boss area look good the cracks usually very small on each side of the boss

 

The fact that they are USED changes all this. Piston skirts tend to collapse and cause more clearance with use------- they probably were close to .005 for a Alky application when new --------------they should be fine , I don't know how you can coat them after the fact if they weren't cut to be coated in the beginning ???

 

just to confirm im understanding what you mean by cut to be coated in the beginning, if you are talking about when the pistons were originally made and having them machined .001 under to allow for coating, i am told that that is the wrong wway to do it and that you should not allow for the piston coating in your clearances, words for a few builders and the coater,
if your talking about adhesion of coating the pistons prior to coating recieve some sort of etch, before coating is applied, thanks