[DeTomaso] Max bore for 351C

[JDeRyke at aol.com]

In a message dated 12/14/07 12:22:45 PM, kjetfinn at online.no writes:


> With other words what is the normally recommended piston to cylinder wall 
> clearance. (forged pistons, and Cleveland block) The pistons has no markings, 
> or brand names on them.
> 
All piston mfgrs will tell you what clearances work with their pistons. I 
have personally found that a forged TRW piston can run at a max clearance of 
0.004" and still support the rings well enough to seal. This is why I say to 
carefully inspect a candidate block especially up near the top of the bores. If the 
eroded area above the ring travel is whats pushing you to overbore, you can 
basically disregard that part of the bore since it never get the rings on it so 
it need not be perfectly smooth. If the remaining part of the bore is within 
0.004", you need not bore at all; hone smooth (except for the eroded part)   
and use (in your case) 0.030-over pistons with new rings. Note this will cause 
start-up emissions to increase and the pistons will rattle for a minute before 
the piston expands into the bore. If an engine with 004"-oversized bores must 
pass start-up emission tests, it will likely fail. FWIW, I built my present 
engine this way in 1990 and it still seals well.
You can check your piston size with a 4" micrometer on the skirts below the 
piston pin and 90 degrees to the pin bore to get its size. Used forged pistons 
in hard working engines may change diameters a little over the years so you 
might not get an even number to your measurements. To figure out if they're 
forged or cast, look carefully inside the piston: a cast piston will have ribs and 
buttresses in there that could not possibly be made by a forging ram coming 
in from the bottom. All the ribs etc in a forged piston will be oriented 
vertically. Also, many cast pistons have steel struts inside to help resist 
deformation and make the piston stronger. This type may be magnetic, which is another 
tip-off. Good luck- J DeRyke



**************************************
See AOL's top rated recipes 
(http://food.aol.com/top-rated-recipes?NCID=aoltop00030000000004)