| General Specifications |
| Model |
U20 |
| Cylinder arrangement |
4 Inline |
| Displacement |
1982 cc |
120.9 ci |
| Bore and Stroke |
87.2 x 83 mm |
3.4331 x 3.2667 in |
| Valve arrangement |
SOHC |
| Max HP |
Solex - 150 @ 6000 rpm
SU - 135 @ 6000 rpm |
| Max Torque |
Solex - 138 @ 4800 rpm
SU - 132 @ 4400 rpm |
| Firing order |
1-3-4-2 |
| Engine idle rpm |
700 rpm |
| Compression ratio |
9.5:1 |
| Manifold vacuum at idle (inches of mercury) |
Solex - 23.0-26.0
SU - 46.0-48.0 |
| Oil pressure - hot at 2000 rpm |
28.38 psi |
| Fuel pressure |
3.55 psi |
| Cylinder Block |
| Bore out of round |
0.015 mm |
0.0006 in |
| Bore taper |
0.02 mm |
0.0006 in |
| Block head surface flatness |
less than 0.1 mm |
less than 0.0039 in |
| Cylinder Head |
| Head thickness stock |
115.0-115.062 mm |
4.528-4.530 in |
| Head surface flatness |
less than 0.1 mm |
less than 0.0039 in |
| Valve Mechanism |
| Valve clearances (hot) |
Intake - 0.2 mm
Exhaust - 0.3 mm |
Intake - 0.0079 in
Exhaust - 0.0118 in |
| Valve clearance wear limit |
0.35 mm |
0.0138 in |
| Valve head diameter - Intake |
46 mm (+0.2/-0.0) |
1.81 in (+0.0079/-0.0) |
| Valve head diameter - Exhaust |
36 mm (+0.2/-0.0) |
1.42 in (+0.0079/-0.0) |
| Valve stem diameter - Intake |
8.7 mm (+0.043/-0.030) |
0.343 in (+0.0017/-0.0012) |
| Valve stem diameter - Exhaust |
8.7 mm (+0.073/-0.060) |
0.343 in (+0.0029/-0.0024) |
| Valve length |
120.8 mm |
4.76 in |
| Valve lift |
Solex - 11.6 mm
SU - 11.2 mm |
Solex - 0.46 in
SU - 0.44 in |
| Valve spring free length |
Outer - 49.7 mm
Inner - 48.4 mm |
Outer - 1.96 in
Inner - 1.91 in |
| Valve spring loaded length |
Outer - 29.6 mm / 76.4 kg (+2.0/-4.0)
Inner - 27.6 mm / 29.9 kg (+1.8/-1.8) |
Outer - 1.17 in / 168.1 lb (+4.41/-8.82)
Inner - 1.09 in / 65.8 lb (+3.96/-3.96) |
| Valve spring assembled height |
Outer - 41.2 mm / 32.3 kg
Inner - 39.2 mm / 13.3 kg |
Outer - 1.62 in / 71.1 lb
Inner - 1.54 in / 29.3 lb |
| Valve spring effective turns |
Outer - 4.25
Inner - 5.5 |
| Valve spring wire diameter |
Outer - 4.6 mm
Inner - 2.95 mm |
Outer - 0.18 in
Inner - 0.116 in |
| Valve spring coil diameter |
Outer - 35.0 mm
Inner - 24.2 mm |
Outer - 1.38 in
Inner - 0.95 in |
| Valve guide length |
55 mm |
2.17 in |
| Valve guide height from head surface |
13.0 mm (+0.1/-0.1) |
0.512 in (+0.004/-0.004) |
| Valve guide inner diameter |
8.685-8.700 mm |
0.3419-0.3425 in |
| Valve guide outer diameter |
14.313-14.326 mm |
0.5635-0.5640 in |
| Valve guide to stem clearance |
Intake - 0.015-0.043 mm
Exhaust - 0.045-0.073 mm |
Intake - 0.0006-0.0017 in
Exhaust - 0.0018-0.0029 in |
| Valve seat width |
Intake - 1.40 mm
Exhaust - 1.77 mm |
Intake - 0.055 in
Exhaust - 0.069 in |
| Valve seat angle |
45 deg. |
| Valve seat interference fit |
Intake - 0.081-0.113 mm
Exhaust - 0.064-0.096 mm |
Intake - 0.0032-0.0044 in
Exhaust - 0.0025-0.0038 in |
| Valve guide interference fit |
Intake - 0.022-0.050 mm
Exhaust - 0.022-0.050 mm |
Intake - 0.0009-0.0020 in
Exhaust - 0.0009-0.0020 in |
| Camshaft and Timing Chain |
| Camshaft end play |
0.1-0.3 mm |
0.0039-0.0118 in |
| Camshaft lobe lift |
Solex - 8.3 mm
SU - 8.0 mm |
Solex - 0.327 in
SU - 0.315 in |
| Camshaft journal diameter |
1 thru 4 - 29.964-29.997 mm
5 - 24.966-24.979 mm |
1 thru 4 - 1.1800-1.1802 in
5 - 0.9830-0.9834 in |
| Camshaft bend |
less than 0.01 mm |
less than 0.0004 in |
| Camshaft journal to bearing claerance |
1 thru 4 - 0.023-0.052 mm
5 - 0.021-0.047 mm |
1 thru 4 - 0.0009-0.0020 in
5 - 0.0008-0.0019 in |
| Camshaft bearing inner diameter |
1 thru 4 - 30.0 mm (+0.016/-0.0)
5 - 25.0 mm (+0.013/-0.0) |
1 thru 4 - 1.18 in (+0.0006/-0.0)
5 - 0.98 in (+0.0005/-0.0) |
| Rocker Arm Ratio |
~1.4:1 |
| Connecting Rod |
| Center-to-center length |
144.0 mm (+0.03/-0.03) |
5.67 in (+0.001/-0.001) |
| Bearing length |
24.0 mm (+0.1/-0.1) |
0.94 in (+0.001/-0.001) |
| Bearing thickness |
Std - 1.493-1.506 mm |
Std - 0.0588-0.0593 in |
| Big end side clearance |
0.2-0.3 mm |
0.008-0.012 in |
| Bearing clearance |
0.034-0.086 mm |
0.0013-0.0034 in |
| Connecting rod bend |
less than 0.04 mm
per 100 mm length |
less than 0.0016 in
per 3.94 in length |
| Crankshaft and Main Bearings |
| Journal diameter |
62.942-62.995 mm |
2.4780-2.4785 in |
| Journal taper |
less than 0.005 mm |
less than 0.0002 in |
| Crankshaft end play |
0.05-0.18 mm |
0.002-0.007 in |
| Wear limit of end play |
0.3 mm |
0.012 in |
| Crank pin diameter |
51.941-51.954 mm |
2.0449-2.0454 in |
| Crank pin taper and out-of-round |
less than 0.005 mm |
less than 0.0002 in |
| Main bearing thickness |
Std - 1.822-1.835 mm |
Std - 0.0717-0.0722 in |
| Main bearing clearance |
0.020-0.072 mm |
0.0008-0.0028 in |
| Main bearing clearance wear limit |
0.12 mm |
0.0047 in |
| Crankshaft bend |
less than 0.03 mm |
less than 0.0012 in |
| Jackshaft |
| Journal diameter |
1 - 45.434-45.447 mm
2 - 43.877-43.910 mm
3 - 41.218-41.231 mm |
1 - 1.7887-1.7892 in
2 - 1.7274-1.7287 in
3 - 1.6228-1.6233 in |
| Jackshaft end play |
0.08-0.28 mm |
0.0031-0.0110 in |
| Pistons |
Piston diameter
Note: the oversizes referred to here are the production
oversizes (look for a number in a diamond stamped into the top of the piston), not the overbore sizes used when boring an engine.
Overbore replacement pistons are normally stamped with a "0.5", "1.0" or "1.5" to indicate 0.5, 1.0 or 1.5 mm oversize. |
Std - 87.180-87.230 mm
Oversize 1 - 87.410-87.460 mm
Oversize 2 - 87.660-87.710 mm
Oversize 3 - 87.910-87.960 mm
Oversize 4 - 88.160-88.210 mm
Oversize 5 - 88.660-87.710 mm |
Std - 3.4323-3.4342 in
Oversize 1 - 3.4413-3.4433 in
Oversize 2 - 3.4512-3.4531 in
Oversize 3 - 3.4610-3.4630 in
Oversize 4 - 3.4709-3.4728 in
Oversize 5 - 3.4905-3.4925 in |
| Piston out-of-round |
0.39-0.42 mm |
0.0154-0.0165 in |
| Ring groove width |
Top - 2.0 mm (+0.050/-0.030)
Second - 2.0 mm (+0.040/-0.020)
Oil - 4.0 mm (+0.040/-0.015) |
Top - 0.079 in (+0.0020/-0.0012)
Second - 0.079 in (+0.0157/-0.0008)
Oil - 0.157 in (+0.0157/-0.0006) |
| Piston to bore clearance |
0.030-0.050 mm |
0.0012-0.0020 in |
| Piston pin hole offset |
1.0 mm (+0.05/-0.05) |
0.03937 in (+0.002/-0.002) |
| Piston Pin |
| Piston pin diameter |
22.0 mm (+0.0/-0.013) |
0.866 in (+0.0/-0.0005) |
| Pin length |
72.6 mm (+0.0/-0.1) |
2.858 in (+0.0/-0.0039) |
| Piston pin to piston clearance |
0.006-0.012 mm |
0.0002-0.0005 in |
| Piston pin to connecting rod bushing clearance |
0.025-0.035 mm |
0.0010-0.0014 in |
| Piston Rings |
| Ring height (thickness) |
Top - 2.0 mm (+0.023/-0.010)
Second - 2.0 mm (+0.023/-0.010)
Oil - 4.0 mm (+0.0/-0.010) |
Top - 0.079 in (+0.0009/-0.00039)
Second - 0.079 in (+0.0009/-0.00039)
Oil - 0.157 in (+0.0/-0.0009) |
| Side clearance |
Top - 0.040-0.073 mm
Second - 0.030-0.063 mm
Oil - 0.025-0.063 mm |
Top - 0.0016-0.0029 in
Second - 0.0012-0.0025 in
Oil - 0.0010-0.0025 in |
| Ring end gap |
Top - 0.25-0.40 mm
Second - 0.015-0.030 mm
Oil - 0.014-0.029 mm |
Top - 0.0098-0.016 in
Second - 0.0060-0.0118 in
Oil - 0.0055-0.0114 in |
