Piston height concern
Thread Starter
Drifting
Joined: Jun 2006
Posts: 1,912
Likes: 12
From: Schaumburg (Chicago) Illinois
Piston height concern
I borrowed some tools from work in order to check how high my pistons are in the
cylinders. Here is how I did it and the attached pictures follow along
I moved each cylinder to TDC. Pretty easy to get within .0005!
Confirmed my timing mark is right.
I then measured each piston height at 2 places: Inboard toward center line and
outboard.
The inboard ones are actually higher than the deck height. So I measured them by
laying the depth gauge against the piston and measuring down to the deck.
I recorded the data.
The data tells me that the pistons are above the deck on both inboard sides by
as much as 12 thousandths. and below the deck on the outboard side by as much as 6.2 thousandth. I
guess it means the cylinders are not machined perpendicular to the decks or that
the pistons tops are not perpendicular to the piston side walls, or both.
IS THIS A CONCERN!!!!!!!!!!!!!
Or is it a normal compromise that the machine shop had to make?
HELP!!
#1 at TDC
Timing mark at TDC #1
Measuring outboard side of piston #1
Measuring inboard side of piston #1
Heres the data
cylinders. Here is how I did it and the attached pictures follow along
I moved each cylinder to TDC. Pretty easy to get within .0005!
Confirmed my timing mark is right.
I then measured each piston height at 2 places: Inboard toward center line and
outboard.
The inboard ones are actually higher than the deck height. So I measured them by
laying the depth gauge against the piston and measuring down to the deck.
I recorded the data.
The data tells me that the pistons are above the deck on both inboard sides by
as much as 12 thousandths. and below the deck on the outboard side by as much as 6.2 thousandth. I
guess it means the cylinders are not machined perpendicular to the decks or that
the pistons tops are not perpendicular to the piston side walls, or both.
IS THIS A CONCERN!!!!!!!!!!!!!
Or is it a normal compromise that the machine shop had to make?
HELP!!
#1 at TDC
Timing mark at TDC #1
Measuring outboard side of piston #1
Measuring inboard side of piston #1
Heres the data
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
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I'm assuming you are pushing down on the piston as you measure?
Measure one side as you push down on the piston. Then push down the piston on the other side to *rock* it the other way. Then measure again. Split the difference and you have true deckheight. Or measure above the wristpin where rock doesn't affect it as much.
Having it above the deck isn't a bad thing...just pick the right gaskets.
Mine is .009 above the deck.
JIM
Measure one side as you push down on the piston. Then push down the piston on the other side to *rock* it the other way. Then measure again. Split the difference and you have true deckheight. Or measure above the wristpin where rock doesn't affect it as much.
Having it above the deck isn't a bad thing...just pick the right gaskets.
Mine is .009 above the deck.
JIM
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You are measuring in the wrong place, like stated above measure above the pin on both sides, you really should use a bridge, this Moroso bridge has three holes, the ones on the outside are used for dished pistons.
The easiest is a flat top, you zero the bridge on the deck then you put the bridge over the hole and center it on the flat top and your done, domes and dished pistons require a little finesse
http://www.jegs.com/p/Moroso/764235/10002/-1/10783
The easiest is a flat top, you zero the bridge on the deck then you put the bridge over the hole and center it on the flat top and your done, domes and dished pistons require a little finesse
http://www.jegs.com/p/Moroso/764235/10002/-1/10783
Thread Starter
Drifting
Joined: Jun 2006
Posts: 1,912
Likes: 12
From: Schaumburg (Chicago) Illinois
Boy I feel stupid. Now that I am measuring in the right place, the difference between the highest and lowest pistons is only .0035. Could be measuring errors too. So I have no problems.
Heres the data:
-.00165 lowest in the hole
-.0007
+.0019 highest, and the only one above the hole at TDC
-.0010
-.0004
-.0004
-.0007
-.0001
Well, I guess I will confirm my head cc's next!!
Thanks guys!!
Heres the data:
-.00165 lowest in the hole
-.0007
+.0019 highest, and the only one above the hole at TDC
-.0010
-.0004
-.0004
-.0007
-.0001
Well, I guess I will confirm my head cc's next!!
Thanks guys!!
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Piston Height Concern...
The most important thing is to ensure that you have enough clearance with the bottom of the head - this is called quench height. Your piston height is essentially zero deck, so you need to run a gasket with a compressed thickness of .038 to .040. Quench height should be 35 or 40 thousandths for good turbulence and anti-knock properties (assuming steel rods).
Cheers,
Larry
Cheers,
Larry
Thread Starter
Drifting
Joined: Jun 2006
Posts: 1,912
Likes: 12
From: Schaumburg (Chicago) Illinois
The most important thing is to ensure that you have enough clearance with the bottom of the head - this is called quench height. Your piston height is essentially zero deck, so you need to run a gasket with a compressed thickness of .038 to .040. Quench height should be 35 or 40 thousandths for good turbulence and anti-knock properties (assuming steel rods).
Cheers,
Larry
Cheers,
Larry
This I knew but thanks. My gasket is .040. So I have a nice quench! Heads are bolted down!
Next, pushrod length detemination.
