Engine Building -Quench distance
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 810
Likes: 4
From: Austria
Engine Building -Quench distance
Hi all
i´m bulding a 396 engine, and received my block today from machine work...
i noticed the pistons are down about 0.02" (?)in the bore, although i ordered the block 0-decked
my question now...IS this 0 decked?
how do you measure quench distance correctly?
also, i have to say, when you rock the piston, the outer margin is level with the bore..thats the clearance you need piston to bore
should i go with .040 or .030 gaskets??
i trust this shop, they are very exactly on their work normally...
please respond
thank you
i´m bulding a 396 engine, and received my block today from machine work...
i noticed the pistons are down about 0.02" (?)in the bore, although i ordered the block 0-decked
my question now...IS this 0 decked?
how do you measure quench distance correctly?
also, i have to say, when you rock the piston, the outer margin is level with the bore..thats the clearance you need piston to bore
should i go with .040 or .030 gaskets??
i trust this shop, they are very exactly on their work normally...
please respond
thank you
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
I'm going to assume you meant 2 thou, not 2 tenths.......
A true zero decked motor would technically involve flycutting the pistons, for perfect tolerance as there's always going to be a slight variance in the assembled heights of the components........I think you're close eough for Government work. Use an .039 head gasket if your P/V clearance allows and you're good to go.
A true zero decked motor would technically involve flycutting the pistons, for perfect tolerance as there's always going to be a slight variance in the assembled heights of the components........I think you're close eough for Government work. Use an .039 head gasket if your P/V clearance allows and you're good to go.
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 810
Likes: 4
From: Austria
hi
no i meant 0.5mm thats about 0.02"
i dont know what to think, fact is, the block was decked, there are the cutting marks visible...
where and how do i measure exactly?
no i meant 0.5mm thats about 0.02"
i dont know what to think, fact is, the block was decked, there are the cutting marks visible...
where and how do i measure exactly?
Last edited by corvette90; Dec 23, 2005 at 12:03 PM.
Safety Car
Joined: Sep 2001
Posts: 4,150
Likes: 551
From: Glenbeulah Wi
What he is saying is .020 or (20 thousands). You want to acheive .040 to .045 quench distance and this is measured over the pin (front to back on the block not side to side). You have .020 and you need to find a head gasket that has .020 to .025 compressed thickness.
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Originally Posted by bjankuski
What he is saying is .020 or (20 thousands). You want to acheive .040 to .045 quench distance and this is measured over the pin (front to back on the block not side to side). You have .020 and you need to find a head gasket that has .020 to .025 compressed thickness.
Sorry corvette90, I hadn't had my morning coffee
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Burning Brakes
Joined: Nov 2004
Posts: 781
Likes: 0
350 SBCs generally have a stock deck height of 9.020"-9.025". Most aftermarket piston manufacturers set their compression height assuming a 'zero' deck height of 9.000". Your measurement reflects very little was removed from your deck, OR casting/machining tolerance differences in your crank, crank bore, connecting rods, or pistons (or any combination of these). When shooting for an exact zero deck for your finished shortblock, you should have your crank, rods, and pistons onhand and measured by the machinists performing the decking of the block. I would use a .029" headgasket to get back some quench, or have the block re-machined. Stock cranks are commonly off slightly from the 3.48" stroke spec.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Some of the confusion may come from the use of and understanding of definitions and/or terms. To ME (and a good many of us). DECK as in zero deck, is the "piston to (block) deck height" (a valid term). The convention for measuring that distance is from the top of the block to the top of the piston, AT the pin. Taking the measurement at the pin eliminates any variation due to the piston rocking in the bore. The "blueprint" deck height of the SBC, block is, 9.025" from the centerline of the crankshaft to the top of the block. Most blocks are taller than that. Someone MAY have interpreted "zero deck the block" to mean, surface the block to it's blueprint dimension. A blueprint block with blueprint, crankshaft, rods, and pistons will result in a deck height of -.025", or the piston twenty five thousandths of an inch, down the hole. I had a block with a piston to deck clearance of -.007". I sent it to the machine shop to be"fixed".
The quench distance is simply the piston to head distance. It is the piston deck height plus the head gasket, compressed thickness.
RACE ON!!!
The quench distance is simply the piston to head distance. It is the piston deck height plus the head gasket, compressed thickness.
RACE ON!!!
Former Vendor
Joined: Jun 2001
Posts: 7,204
Likes: 6
From: St Marys PA
As CFI explained, the proper terminology very well or the aspects of the confusion.
I would say you want the block cut down more. Leaving the piston .020" (referred to as twenty thousands of an inch) in machine shop talk - not two tenths
two tenths in a machine shop would have someone thinking .0002 - which is really short for two ten thousands of an inch. . This will leave the piston at a distance that it will not be easy to find a gasket to give you the correct quench. Quench being the distance from the piston face to the bottom of the head, with gasket in place. You want to shoot for around .045" for a good quench. As stated if your piston is .020 in the hole, you will need to get a gasket with a compressed thickness of .025". Cometic can probable make you one.
The easier route to go, would be to have the machine shop take about .018 more off the block, if your absolutely sure its .020 in the hole. This will let you use a standard thickness (compressed) gasket of .039, which will put you within a few thousands of .045 quench.
I would say you want the block cut down more. Leaving the piston .020" (referred to as twenty thousands of an inch) in machine shop talk - not two tenths
two tenths in a machine shop would have someone thinking .0002 - which is really short for two ten thousands of an inch. . This will leave the piston at a distance that it will not be easy to find a gasket to give you the correct quench. Quench being the distance from the piston face to the bottom of the head, with gasket in place. You want to shoot for around .045" for a good quench. As stated if your piston is .020 in the hole, you will need to get a gasket with a compressed thickness of .025". Cometic can probable make you one. The easier route to go, would be to have the machine shop take about .018 more off the block, if your absolutely sure its .020 in the hole. This will let you use a standard thickness (compressed) gasket of .039, which will put you within a few thousands of .045 quench.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by ski_dwn_it
The easier route to go, would be to have the machine shop take about .018 more off the block, if your absolutely sure its .020 in the hole. This will let you use a standard thickness (compressed) gasket of .039, which will put you within a few thousands of .045 quench.
RACE ON!!!
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
or you could just use a 0.015" steel shim gasket, have a .040" quench distance and not even bother with machining the block further.
You just want to make DAMN sure that you've measured the "in the hole" distance acurately AND in each cylinder. If you've got a shallow piston somewhere due to tolerance stacking or some other issue, then you need to consider that. Also, use clay on the shallowest piston and verify enough valve-piston clearance to avoid bending or breaking something later on.
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 810
Likes: 4
From: Austria
hi
thank you for your answers!!
i think i will have to find a thin head gasket, i had to send the block to germany to get it machined...nobody do this in our area (even country)
i also dont know, why it came out, that the block isnt machined to 0
i called the machine shop, they said, that the measured it and it is correct machined...
but i can measure any way i want, the piston is down 0.02" in the bore...
where can i find this gaskets?
Regards
thank you for your answers!!
i think i will have to find a thin head gasket, i had to send the block to germany to get it machined...nobody do this in our area (even country)
i also dont know, why it came out, that the block isnt machined to 0
i called the machine shop, they said, that the measured it and it is correct machined...
but i can measure any way i want, the piston is down 0.02" in the bore...
where can i find this gaskets?
Regards
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Did they have the crank, and the piston, rod, and bearings for at least 1 cylinder? "Correct machined...", based on what? The 9.025" block height I mentioned earlier? Or the ZERO deck, you asked for?
RACE ON!!!
RACE ON!!!
(I better not jump into this, but I'm learning a lot!)
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 810
Likes: 4
From: Austria
they had everything, crank rod pistons....
also, the owner of the machine shop insured me that they verified ZERO Deck with a hair lineal, where the light barely shined through the resulting gap (piston-ruler)
ok, here´s the Update:
i put the dial indicator on the block, and turned pistons to TDC...
by measuring with a straigth ruler and feeler gauges i came up to exactly to 0.025 in the bore....no change by rocking pistons back and forth..0.025 in the bore...
i dont know how and why this happened, but i will use 0.015 head gaskets and i will be ok
also, the owner of the machine shop insured me that they verified ZERO Deck with a hair lineal, where the light barely shined through the resulting gap (piston-ruler)
ok, here´s the Update:
i put the dial indicator on the block, and turned pistons to TDC...
by measuring with a straigth ruler and feeler gauges i came up to exactly to 0.025 in the bore....no change by rocking pistons back and forth..0.025 in the bore...
i dont know how and why this happened, but i will use 0.015 head gaskets and i will be ok
Last edited by corvette90; Dec 24, 2005 at 08:54 AM. Reason: Update
Large Impressive Member
Joined: Jul 2003
Posts: 65,811
Likes: 71
From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by corvette90
they had everything, crank rod pistons....
also, the owner of the machine shop insured me that they verified ZERO Deck with a hair lineal, where the light barely shined through the resulting gap (piston-ruler)
ok, here´s the Update:
i put the dial indicator on the block, and turned pistons to TDC...
by measuring with a straigth ruler and feeler gauges i came up to exactly to 0.025 in the bore....no change by rocking pistons back and forth..0.025 in the bore...
i dont know how and why this happened, but i will use 0.015 head gaskets and i will be ok
also, the owner of the machine shop insured me that they verified ZERO Deck with a hair lineal, where the light barely shined through the resulting gap (piston-ruler)
ok, here´s the Update:
i put the dial indicator on the block, and turned pistons to TDC...
by measuring with a straigth ruler and feeler gauges i came up to exactly to 0.025 in the bore....no change by rocking pistons back and forth..0.025 in the bore...
i dont know how and why this happened, but i will use 0.015 head gaskets and i will be ok
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 810
Likes: 4
From: Austria
Clearance was set to 0.0023"
JE recommend 0.0020-0.0025
actually, you can barely rock the piston in the bore...you feel, theres some clearance, but no obviously movement..just a bit...difficult to describe
JE recommend 0.0020-0.0025
actually, you can barely rock the piston in the bore...you feel, theres some clearance, but no obviously movement..just a bit...difficult to describe
Large Impressive Member
Joined: Jul 2003
Posts: 65,811
Likes: 71
From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by corvette90
Clearance was set to 0.0023"
JE recommend 0.0020-0.0025
actually, you can barely rock the piston in the bore...you feel, theres some clearance, but no obviously movement..just a bit...difficult to describe
JE recommend 0.0020-0.0025
actually, you can barely rock the piston in the bore...you feel, theres some clearance, but no obviously movement..just a bit...difficult to describe