I need piston rings for 1991 7.3 IDI. What do they mean bore size Std., .020, .030, .040?

Question edited for clarity.

AI Chat GPT4 answer by Shwet Kashyap deleted.

When the vehicle standard size rings are used and this will be mentioned in the Service Manual. If the cylinders are rebored, oversize rings are used and there is normally 2 larger sizes. If you are replacing rings, you should always use an internal micrometer to measure the bores because the bores can wear oval across the bore. This is caused by the lateral force of the connecting rods. If the bore is within limits they should be honed. This removes the glaze and makes the bore slightly rough so that the new rings and bore polish themselves together to make a good fit.

Pistons, piston rings, circlips and gudgeon pins in this link.

https://www.google.com/search?q=1999+Daewoo+Lanos+1.4+piston+rings

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When you remove the cylinder, you should have the bore checked by a machine shop. The bore wears on the front and rear of the bore and can wear slightly oval. In which case it should be rebored and an oversize piston and rings used. The cylinder should also be honed so that the new rings and the bore wear in together and make a good seal. The standard is 56mm.

https://www.google.com/search?q=2004+DT125re.+What+are+piston+and+ring+sizes

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we are USA
no KB here, not a one., sorry why ask Yankee's this./..??
your machine shop would not ask that question.
a real overhaul (if measurements prove the case, all parts are MIKED)
1: measure bores. top/bottom and 90 degrees.
2: then bore and hone it to next oversize.
3: then new pistons and rings. and all new bearings

any thing, less is a DIY, trash build.
shade tree , hack.
(the Bernard Lawrence Madoff" ) way. (dig?)
there is one more way, if measurements warrant. IT.
light hone,.
new rings, std, size or what's there, now.
then keep old pistons if lands measure ok. (inspections here are many )

I guess you don't have the micrometer sets to do this right?
inside bore gauge. etc.?
what we do is take the block to a real machine shop
the mic it for a fee. (some do it for free)
then they tell you what is best, and is always the best answer.
why not let a pro rebuild your engine.
for max future life, not lowest cost and shortest life.

ask how to clean a block after honing
its not easy and must NOT BE SKIPPED.

the size of the ring will be determined by the bore size
so if it is a 3"(75mm) bore the ring will be that size if placed in the bore separate to the piston and pushed square and to the bottom of the bore the ring gap will denote if standard , worn or oversize to standard
new rings in new bores will have a ring gap of around .010"
worn rings will have a larger gap up to .040" and will have sharp edges where the ring lands wear the rings
over size rings in standard bore probably won't even fit in the bore to start with
ring sets are bought in standard size , .010" over size,.020" oversize,.030" oversize,.040" oversize with the oversize equalling the final hone of a machine bore
so if the machine shop bores the cylinder out to .020" oversize then you need .020" oversize rings to maintain the correct ring gap
from experience I have found that if I follow that rule , on measuring the ring gap at the bottom of the bore the ring gap is about .015" or half worn out
I counter this by getting the next size ring .030" and filing the ends of the rings at the gap to obtain the .010" gap This has produced better longer lasting repairs

Three sizes of pistons are available:
1. Std.
2. Over size 0.010 in (0.25 mm).
3. Over size 0.020 in (0.50 mm).
Over sized pistons and rings are widely used in all automobiles with no trouble at all. They last for more than 200,000 km, provided if the engine oil, oil filter and air filters are replaced at the recommended intervals.
The most important point to consider here is to maintain the oil clearances between the various parts during the machining process.
For example piston to cylinder clearance, crankshaft to main journals and big ends clearance, valve to guide clearance, at room temperature. Then comes cleaning process and the engine assembling process.

General Specifications Item Specification
Displacement L (CID) 4.6 (281)
Number of Cylinders 8
Bore and Stroke mm 90.2 x 90.0
Firing Order 1-3-7-2-6-5-4-8
Oil Pressure (HOT @ 1500 rpm) kPa 138-310
Drive Belt Tension a
Cylinder Head and Valve Train
Combustion Chamber Volume cm 52?±.5
Valve Seats Width?€"Intake mm 1.9-2.1
Valve Seats Width?€"Exhaust mm 1.9-2.1
Valve Seats Angle 44.51-45.01 degrees
Valve Seats Runout (T.I.R.) Max mm 0.025
Valve Arrangement (Front-to-Rear) (Left Hand) E-I-E-I-E-I-E-I
(Right Hand)
I-E-I-E-I-E-I-E
Valve Stem to Guide Clearance?€"Intake mm (Inch) 0.020-0.069
(0.00078-0.00272)
Valve Stem to Guide Clearance?€"Exhaust mm (Inch) 0.045-0.095 (0.0018-0.0037)
Valve Head Diameter?€"Intake mm (Inch) 44.5- (1.75)
Valve Head Diameter?€"Exhaust mm (Inch) 34.0 (1.34)
Valve Head Diameter?€"Gauge Diameters mm (Inch) 42.5- and 32.0
(1.67 and 1.26)
Valve Face Runout Limit mm (Inch) 0.05 (0.002)
Valve Face Angle 45.25-45.75 degrees
Valve Stem Diameter (STD)
?€"Intake mm (Inch) 6.995-6.975 (0.275-0.2746)
Valve Stem Diameter (Std)
?€"Exhaust mm (Inch) 6.970-6.949 (0.274-0.2736)
Valve Springs?€"
Compression Pressure N @
Spec. Length?€"Intake 587.14 N @ 28.02 mm
Valve Springs?€"
Compression Pressure N @
Spec. Length?€"Exhaust 587.14 N @
28.02 mm
Valve Springs?€"Free
Length ( Approximate)?€"
Intake mm (Inch) 49.55 (1.951)
Valve Springs?€"Free
Length (Approximate)?€"
Exhaust mm (Inch) 49.55 (1.951)
Valve Springs?€"Installed
Pressure N @ Spec. Length
?€"Intake 244.64 N @ 40.0 mm
Valve Spring?€"Installed
Pressure N @ Spec. Length
?€"Exhaust 244.64 N @ 40.0 mm
Valve Springs?€"Installed
Pressure N @ Spec. Length
?€"Service Limit 10 % Pressure Less @ 28.02 mm
Valve Springs?€"Installed
Pressure N @ Spec. Length
?€"Out of Square Limit 2 degrees
Valve Guide Inner
Diameter mm (Inch) 7.015-7.044 (0.2761-0.2773)
Rocker Arm?€"Ratio 1.75:1
Valve Tappet?€"Diameter
(STD) mm (Inch) 16.000-15.988 (0.66-0.629)
Valve Tappet?€"Clearance
to Bore mm (Inch) 0.018-0.069
(0.00071-0.00272)
Valve Tappet?€"Service
Limit mm (Inch) 0.016 (0.00063)
Valve Tappet?€"Hydraulic
Leakdown Rate b 5-25 seconds
Valve Tappet?€"Collapsed
Valve Tappet Gap?€"
Desired mm (Inch) 0.085-0.45 (0.0033-0.0177)
Camshaft
Lobe Lift?€"Intake
mm (Inch) 6.58939 (0.2594)
Lobe Lift?€"Exhaust
mm (Inch) 6.58939 (0.2594)
Lobe Lift?€"Allowable
Lobe Lift Loss mm (Inch) 0 (0)
Theoretical Valve Lift @
Zero Lash?€"Intake
mm (Inch) 12.0 (0.472)
Theoretical Valve Lift @
Zero Lash?€"Exhaust
mm (Inch) 12.0 (0.472)
End Play mm (Inch) 0.025-0.165
(0.00098-0.0065)
Journal to Bearing
Clearance mm (Inch) 0.025-0.076
(0.00098-0.003
Journal to Bearing
Clearance?€"Service Limit
mm (Inch) 0.021 (0.0048)
Journal Diameter (All)
mm (Inch) 26.962-26.936
(1.061-1.060)
Journal Diameter (All)?€"
Bearing Inside Diameter
(All) mm (Inch) 27.012-26.987
(1.063-1.0625)
Camshaft Runout
mm (Inch) 0.05 (0.002)
Cylinder Bore
Diameter?€"Surface Finish
(RMS) 0.2-0.6 Microns
Diameter?€"Out-of-Round
Limit mm (Inch) 0.015 (0.0006)
Diameter?€"Out-of-Round
Service Limit mm (Inch) 0.020 (0.00079)
Diameter?€"Taper Service
Limit mm (Inch) 0.006 (0.00023)
Piston
Piston?€"Diameter?€"
Coded Red 1 mm (Inch) 90.177-90.197
(3.550-3.551)
Piston?€"Diameter?€"
Coded Blue 2 mm (Inch) 90.190-90.210
(3.5507-3.5515)
Piston?€"Diameter?€"
Coded Yellow 3 mm (Inch) 90.203-90.223
(3.513-3.5521)
Piston-to-Bore-Clearance
mm (Inch) -0.015 + 0.031 (0.0005-0.0012)
Pin Bore Diameter
mm (Inch) 22.0015-22.004
(0.866-0.8663)
Ring Groove Width?€"
Compression (Top)
mm (Inch) 1.520-1.550 (0.06-0.610)
Ring Groove Width?€"
Compression (Bottom)
mm (Inch) 1.520-1.530 (0.060-0.0602)
Ring Groove Width?€"Oil
Ring mm (Inch) 6.996-7.224 (0.275-0.2844)
Piston Pin?€"Length
mm (Inch) 61.93-62.05 (2.44-2.443)
Diameter mm (Inch) 21.994-21.999
(0.866-0.8661)
Pin to Piston Clearance
mm (Inch) 0.005-0.010
(0.0002-0.0004)
Pin to Rod Clearance
mm (Inch) 0.015-0.040
(0.0006-0.00157)
Piston Rings?€"Ring Gap
?€"Compression (Top)
mm (Inch) 1.0 MAX (0.0394)
Piston Rings?€"Ring Gap
?€"Compression (Top)
mm (Inch) 1.0 MAX (0.0394)
Oil Ring?€"Side Clearance
mm (Inch) 1.25 MAX (0.05)
Oil Ring?€"Compression
(Top) mm (Inch) 0.040-0.090
(0.0016-0.0031)
Oil Ring?€"Compression
(Top) mm (Inch) 0.030-0.080
(0.0012-0.00031)
Oil Ring Snug Fit
Oil Ring?€"Service Limit
mm (Inch) 0.015 MAX (0.0006)
Ring Gap?€"Compression
(Top) mm (Inch) 0.23-0.49
(0.01-0.02)
Ring Gap?€"Compression
(Bottom) mm (Inch) 0.23-0.49
(0.01-0.02)
Ring Gap?€"Oil Ring (Steel
Rail) mm (Inch) 0.05-0.66 (0.006-0.026)
Lubrication System
Oil Capacity?€"Automatic
Transmission (Quarts U.S.) 6.675?±0.125
Oil Capacity?€"Manual
Transmission (Quarts U.S.) 6.425?±0.125
Cylinder Block
Main Bearing Bore
Diameter mm (Inch) 72.401-72.422 (2.85-2.851)
Crankshaft and Flywheel
Main Bearing Journal
Diameter mm (Inch) 67.483-67-503 (2.65-2.657)
Connecting Rod Journal?€"
Diameter mm (Inch) 52.988-53.003
(2.0861-2.0867)
Crankshaft Free End Play
mm (Inch) 0.130-0.301 (0.0051-0.012)
Crankshaft Runout to Rear
Face of Block mm (Inch) 0.050 MAX (0.002)
Connecting Rod Bearings
Clearance to Crankshaft?€"
Desired mm (Inch) 0.027-0.069 (0.001-0.0027)
Clearance to Crankshaft?€"
Allowable mm (Inch) 0.027-0/069 (0.001-0.0027)
Bearing Wall Thickness
(STD) mm (Inch) 2.44-2.452 (0.096-0.0965)
Main Bearings
Clearance to Crankshaft?€"
Desired mm (Inch) 0027-0.065
(0.0011-0.0026)
Clearance to Crankshaft?€"
Allowable mm (Inch) 0.027-0.065
(0.0011-0.0026)
Bearing Wall Thickness
(STD) mm (Inch) 1.920-1.928 (0.075-0.076)
Connecting Rod, Piston and Rings
Connecting Rod?€"Piston
Pin Bore Diameter
mm (Inch) 21.959-21.979
(0.864-0.865)
Connecting Rod?€"
Crankshaft Bearing Bore
Diameter mm (Inch) 56.756-56.876 (2.234-2.24)
Connecting Rod?€"Length
(Center-to-Center)
mm (Inch) 150.7 (5.93)
Alignment (Bore-to-Bore
Max. Diff.) c ?€"Twist
mm (Inch) 0.050 per 25 (0.0015-0.984)
Alignment (Bore-to-Bore
Max. Diff.)?€"Bend
mm (Inch) 0.038 per 25 (0.0015-0.984)
Side Clearance (Assembled
to Crank)?€"Standard
mm (Inch) 0.015-0.45 (0.0006-0.0177)
Side Clearance (Assembled
to Crank)?€"Service Limit
mm (Inch) 0.05 MAX (0.02)
Crankshaft Main Bearing
Journal Taper mm (Inch) 0.020 (0.0007)
Crankshaft Main Bearing
Journal Runout mm (Inch) 0.05 (0.002)
Crankshaft Connecting Rod
Journal Taper mm (Inch) 0.015 (0.0006)

The end gap is derived from the bore size. For the 2.91" (74mm) Geo 3 cyl bore, the top ring end gap is .004" divided by bore, so that is 2.91" / .004 = .012". The second ring and oil ring should be bore divided by .005", so that is 2.91" / .005 = .015". Don't file the springy part of the oil ring, as it is designed to compress and fit snuggly; just file the top and bottom ring that sandwich the springy part.

The std bore is 54mm and some available piston sizes are (Vertex Pistons)

53.93
53.94
53.95
53.96
53.97

It depends on how deep the gouge is. Having it bored and a new oversized piston may set you back more than a new stock piston and cylinder.

First, be sure they actually do fit the bore. Take a ring and insert it in the bore. push the ring halfway into the bore using the piston. There should be about a 1/32" gap in the ring. Anything more than 1/16" and you need rings the next size up. If the ring won't go into the cylinder because the gap fully closes, the rings need to be a smaller size.

With the correct size rings, put them on the piston. Some pistons have an index pin in the ring groove Fit the gap to the pin. Put the piston mid-stroke and place the cylinder over the top of the piston. Squeeze the rings closed as you gently tap the cylinder downward and over the rings.

Please rate this solution. Thanks garethholleb!