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GEO Metro Engine Information
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The following technical bulletins were published by AERA.
 REVISED CAMSHAFT SPROCKET ON 1994 ENGINES
                                        Revised Camshaft Sprocket On
                                                1994 1.0L GM Engines

AERA member machine shops should notice a timing sprocket design change on 1994 1.0L GM engines used in the Geo Metro.  The revised timing sprocket is part of ongoing production changes and may not be reflected in the current service manual.  While service procedures remain unchanged for engines prior to 1994, an added precaution must be used when a spoked sprocket is
encountered. 

There are two camshaft sprockets used, one with a semi-solid interior and the other with a spoked design (see illustrations below).  One element that may be confusing on the later spoked design is that it has two slots in which the camshaft timing pin could fit.  However, only one of those slots is correct.  The
slot marked 5 must be used to correctly position the sprocket on the camshaft (See Figure 1).  If the sprocket is installed incorrectly, valve timing will be off and the will valves bend on engine start.

See Figure 2 for additional information on timing mark alignment for this engine.

                                                                         The AERA Technical Committee
 LACK OF POWER/REVISED LIFTER
                                                      Lack Of Power On
                                           1989-92 GM 1.0L Geo Engines

AERA members report lack of power or stalling shortly after start-up on some 1989-92 GM 1.0L Geo Metro vehicles.  Revving the engine shortly after starting or continued high RPM aggravates the problem.  This condition occurs on an existing engine or immediately after cylinder head installation.

If all other valve train components meet specifications and the problem still exists, the valves may not be closing completely.  This may be due to high pressure building up in the hydraulic lifter assemblies caused by the lifter's inability to bleed oil quickly enough.

To correct this problem, replace the hydraulic lifter assembly with revised lifter Part #17106263 with a faster bleed down rate.  Varnish build up within a used lifter may also prevent the lifter to bleed down, thus holding valves open.  To prevent this from occurring replace all lifters previous to VIN breakpoints N6761709 and NK211827.

                                                                         The AERA Technical Committee
 REVISED CAMSHAFT SPROCKET
                                       Revised Camshaft Sprocket On
                                       1993-95 GM 1.0L VIN 6 Engines

AERA members have reported a timing sprocket design change on 1993-95 GM 1.0L VIN 6 engines. These engines are used in the Geo Metro and Firefly cars. Previously AERA published TB-1095 on this subject. This bulletin offers additional information to aid in the installation of the revised sprocket.

There are two camshaft sprockets used on this engine. One has a semi-solid interior and the other sprocket has a spoked design as shown below. The later spoked design has two slots in which the camshaft-timing pin could fit.  However, only one of those slots is correct, the slot marked with the number 5 as shown in Figure 1.  The slot (5) must be used to correctly position the cam sprocket pin (7) on the camshaft. When correctly timed the number one piston should be at top dead center while the reference mark ?A" is at approximately the eight o?clock position and the reference mark ?B" is aligned with the ?V" mark (3) on the front cover.

If the sprocket is installed using the slot indicated by the number 6, the valve timing will be off and piston to valve contact will occur when the engine is turned over.

The first design solid sprocket installation is straightforward and should be installed as shown in Figure 2.

                                                                       The AERA Technical Committee
 INTERFERENCE ENGINES
                                          Interference Engines

The AERA Technical Committee would like to offer the following information on engines that present the possibility of interference between pistons and valves. The interference or contact may bend valve(s) when the timing between the camshaft and crankshaft is interrupted. This is generally the result of a timing belt or chain breaking or slipping.

The following list are engines that AERA is currently aware of that have exhibited interference. There may be other engines that are not listed below that have the possibility of piston to valve contact. If the engine you are working on is not listed, do not assume that it is a freewheeling design. It is suggested to add to this listing as additional information is obtained.

ACURA
1986-89 1.6L Integra
1991-95 1.7L Integra
1990-95 1.8L Integra 
1986-89 2.5L Legend
1992-94 2.5L Vigor
1986-89 2.7L Legend
1990      2.7L Legend
1991-95 3.0L NSX
1991-95 3.2L Legend

AUDI
1970-93 All Except 1970-77 
1.9L & 1970-73 1.8L

BMW
1987-95 2.5L 325I 525I
1994-95 4.0L 740I

CHRYSLER
1993-95 1.5L Colt 
1987-88 1.5L Colt	
1992-95 1.5L Eagle Summit
1987-88 1.6L Colt	
1989-92 1.6L Eagle Summit
1994-98 2.0L Neon Stratus
1990-95 2.0L Eagle Talon

DAIHATSU
1988-92 1.0L Charade
1988-92 1.3L Charade
1990-92 1.6L Rocky

FIAT
1974-79 1.3L 128 Series
1979-82 1.5L Stranda
1974-78 1.6L 124 Series
1974-78 1.8L 124 Series
1974-78 1.8L 131 Series, Brava
1979-82 2.0L Brava, Spider 

FORD
1981-85 1.6L Escort, EXP
1981-83 1.6L LN7, Lynx
1984-85 2.0L Escort, Tempo
1993-95 2.0L Probe
1986-88 2.0L Ranger
1984-87 2.0L Lynx, Topaz Diesel
1985    2.2L Ranger
1989-92 2.2L Probe
1986-88 2.3L Ranger
1986-87 2.3L Diesel Ranger
1991-98 4.6L Crown Victoria

GM
1986-95 1.0L Geo Metro
1989-91 1.0L Firefly (CANADA)
1985-88 1.5L Sunburst (CANADA)
1985-89 1.5L Spectrum
1990-93 1.6L Prizm, Storm
1981-84 1.8L Diesel (CANADA)
1982-86 1.8L Buick Skyhawk
1990-98 1.9L Saturn
1987-88 2.0L Buick Skyhawk
1988-95 2.3L Quad Four
1985-87 3.0L Buick
1979-95 3.8L Buick

HONDA
1986-87 1.0L Prelude
1973-78 1.2L All
1973-78 1.3L All
1980-84 1.3L All
1973-78 1.5L All
1985-89 1.5L Civic
1988-95 1.5L Civic, CRX
1993-95 1.5L Civic Del Sol
1979-84 1.5L All
1985-87 1.5L CRX
1993-95 1.6L Civic Del Sol
1973-78 1.6L All
1980-82 1.6L All
1988-95 1.6L Civic, CRX
1984-87 1.8L Prelude, Accord
1979-83 1.8L All
1986-91 2.0L Prelude
1990-91 2.1L Prelude
1990-95 2.2L Prelude, Accord
1992-95 2.2L Prelude
1995      2.7L Accord

HYUNDAI
1984-95 1.5L Excel Scoupe
1995-98 1.5L Accent
1992-95 1.6L Elantra
1993-95 1.8L Elantra
1992-95 2.0L Sonata
1989-91 2.4L Sonata
1990-95 3.0L Sonata

INFINITI
1990-92 3.0L M30

ISUZU
1987-89 1.5L I-Mark
1990-93 1.6L Stylus Impulse
1987-89 2.0L Impulse
1981-87 2.2L Diesel Truck
1986-95 2.3L Truck Trooper
1988-95 2.6L Truck Rodeo Amigo
1991-96 3.2L Trooper Rodeo Amigo

KIA
1995      2.0L Sportage

MAZDA
1984-85 2.0L 626 
1988-92 2.2L 626 MX6
1989-93 2.2L Pickup
1988-95 3.0L 929 MPV

MITSUBISHI
1985-95 1.5L Mirage Precise
1990-92 1.6L Mirage
1989-95 2.0L Galant Eclipse
1983-86 2.3L Diesel Pickup
1994-95 2.4L Galant

NISSAN
1982      1.5L Centra
1983-88 1.6L Sentra Pulsar
1987-89 1.8L Pulsar
1982-89 2.0L Stanza 300ZX
1984-95 3.0L Maxima 300ZX Pathfinder

PORSCHE
1976-83 2.0L 924
1976-89 2.5L 944 Series
1989      2.7L 944 Series
1989-91 3.0L 944 Series
1976-83 4.5L 928
1984      4.7L 928
1985-91 5.0L 928
1992-95 5.4L 928

SUZUKI
1985-94 1.3L Samurai Sidekick
1989-94 1.3L Swift

TOYOTA
1986-95 1.5L Tercel
1981-83 2.2L Pickup
1984-87 2.4L Pickup
1982-88 2.8L Celica Cressida
1987-94 3.0L 4-Runner

VOLKSWAGEN
1976-91 All Except 1.9 2.1L Engine
1990-92 1.6L Golf (CANADA) Jetta
1990-95 2.0L GTI Jetta GLI Passat

VOLVO
1991      2.3L Coupe 940
1986-94 2.3L 240 740 940 

                                                                              The AERA Technical Committee
 CYLINDER HEAD BOLT REUSE
                                          Cylinder Head Bolt Reuse On
                                           GM 1.0L & 1.6L Geo Engines

The AERA Technical Committee recommends replacing head bolts on Geo 1.0L & 1.6L engines any time the bolts have been removed.  There are two different length bolts used, which carry the GM part numbers of 96061591 and 96059992.  AERA is unaware of an aftermarket supplier of head bolts for GM 1.0L & 1.6L engines as of this writing.

     Vehicle                       Engine

     1985-1989 Sprint        1.0L, 3 cyl.*
     1989-1992 Metro        1.0L, 3 cyl.*
     1989-1992 Tracker    1.6L, 4 cyl.*

* Engine manufactured by Suzuki for Geo

AERA members are advised to use the following illustrations when installing cylinder heads on General Motors Geo 1.0L & 1.6L engines.  Torque the head bolts in sequence to 51-54 ft. lbs. In two steps.

                                                                                 The AERA Technical Committee
 BURNED EXHAUST VALVES
                                          Burned Exhaust Valves On
                                             GM 1.0L Geo Engines

The AERA Technical Committee has received calls concerning repeated exhaust valve burning on GM 1.0L engines used in the Geo Metro.  One reason for this type of failure may be caused by a restriction in the exhaust system.  

After repairing a cylinder head with a burned exhaust valve, instruct your customer to perform an exhaust system backpressure check.  After the engine has reached normal operating temperatures, this test should be performed at 2,500 rpm.  A value of 2.8 psi or higher indicates a restricted exhaust condition.

An exhaust restriction may be due to a collapsed header pipe, internal center pipe failure, internal muffler failure, a damaged tailpipe or a plugged catalytic converter.
                                    
                                                                          The AERA Technical Committee