October 19, 2021, 05:56 PM
GoobPiston to Deck Clearance
My concern would be the position of the top ring, probably wouldn't want to spray it.
I put together a bracket 565 that ended up .003" out of the hole, .041" gasket, no issues.
Certain combustion chambers like really, really tight quench area for max HP.
I strive to keep mine under .040" and I'm comfortable with most at .035"
October 19, 2021, 07:45 PM
BP758I was told by a World Champ, lay two thin pieces of solder on the deck and across the dome , roll it over no gasket and measure. Adjust from there.
October 21, 2021, 12:25 AM
FootlooseI ran one 2 out the whole and 28 head gasket. Was many years ago, Don't do it. Glad I did not run it long. Almost made witness marks on the piston. Lets just say there was no carbon on the piston.
October 21, 2021, 12:02 PM
TD3550Don't forget another issue when using the thin one
Hitting the plug. Pending on the reach. Are the pistons notched for the plug and the flame travel?
Run the thick gasket and still clay it up. Most critical is 10*BTDC and 10*ATDC.
October 21, 2021, 02:46 PM
imakehpquote:
Most critical is 10*BTDC and 10*ATDC.
If checking piston to valve clearance. You still need to check it several degrees each way if advancing or retarding the camshaft.
October 21, 2021, 07:46 PM
MasRacingquote:
Originally posted by "The Bender":
You say the pistons are .011 out of the hole, but what you don't know is how much piston dome to head clearance there will be. Don't assume that the flat portion of the piston will be the closest part of the piston to the head.
You could put a .060 gasket on it and have .049 clearance on the flat portion of the piston, but .000 (or less) at some point of the dome. Lot of variables there with piston dome/chamber design.
The way I was taught to check this by an old Comp Eliminator engine builder/racer was to scribe the head to the bore. Then put a piston upside down with the dome in the chamber. If you can move the piston out past the scribe line in all directions then you know that the dome clears the chamber with the flat of the piston in contact with the head. Meaning the flat is your closest point.
I also agree that piston skirt and clearance is a big factor in what you can get away with.
As a side note Steve Morris recently posted a really good video about piston to head and quench area especially in regards to an engine running any kind of power adder.
October 25, 2021, 12:15 PM
Triple NickelHave run 4.560 bore 555 with 0.041 gasket, zero deck, 6.535" rod, 4.250" stroke, 9.800" deck. Yes showed evidence of piston rubbing/touching the head on back side of the dome spark plug side of the piston. Swapped to 0.051" head and no longer had issues.
The 0.041" gasket combo didn't "cause" any real issues that i could tell, but it was evident that there was some contact, minimal but there was contact. No damage to pistons but you could see the carbon knocked off of the piston and it was rubbed a tad in the area mentioned.
With the 0.051" gasket i didn't see that on future rebuilds. Its all about piston rock, as mentioned before piston design plays a factor with longer rods and longer strokes wrist pin has to move upwards in the piston effectively shortening the skirt and thus ability to resist rock at the top and bottom of the bore.
Someone said it already, with piston 0.010" out the hole, i'd throw a 0.061" on it and be happy.
October 27, 2021, 09:58 PM
rustyquote:
posted October 25, 2021 12:15 PM Hide Post
Have run 4.560 bore 555 with 0.041 gasket, zero deck, 6.535" rod, 4.250" stroke, 9.800" deck. Yes showed evidence of piston rubbing/touching the head on back side of the dome spark plug side of the piston. Swapped to 0.051" head and no longer had issues.
The 0.041" gasket combo didn't "cause" any real issues that i could tell, but it was evident that there was some contact, minimal but there was contact. No damage to pistons but you could see the carbon knocked off of the piston and it was rubbed a tad in the area mentioned.
With the 0.051" gasket i didn't see that on future rebuilds. Its all about piston rock, as mentioned before piston design plays a factor with longer rods and longer strokes wrist pin has to move upwards in the piston effectively shortening the skirt and thus ability to resist rock at the top and bottom of the bore.
Someone said it already, with piston 0.010" out the hole, i'd throw a 0.061" on it and be happy.
x2