Manual - Chapter 1 Engine

Specifications

Engine
Bore 67 mm (2.64 in)
Stroke 70 mm (2.76 in)
  75 models 100 models
Number of cylinders 3 4
Capacity 740 cc 
(45 cu in)
987 cc 
(60 cu in)
  UK 75, 
early US 75 models*
Late US 75 models* 100 models
compression ratio 11,0 : 1 10,5 : 1 10,2 : 1
Maximum power - DIN
(kw/bhp @ rpm) 
55/75 @ 8500 51/70 @ 8200 66/90 @ 8000
Maximum torque - DIN
(Nm/lbf ft @ rpm)
68/50 @ 6750 65/48 @ 6500 86/63 @ 6000
* Changeover date approximately mid - 1986 
Cylinder identification Numbered consecutively front to rear.
Number 1 cylinder at front (cam chain) end.
Firing order
75 models 3 - 1 - 2
100 models 1 - 3 - 4 - 2
Direction of rotation Anticlockwise, looking at ignition trigger from front of machine.
Compression pressure - see Section 2
Good Over 10,0 bar (145 psi)
Normal 8,5 - 10,0 bar (123 - 145 psi)
Poor Below 8,5 bar (123 psi)
Valve timing - at 5/100 preload and 3 mm (0.12 in) lift
UK models US models
Intake opens 5° BTDC 5° ATDC
Intake closes 27° ABDC 27° ABDC
Exhaust opens 28° BBDC 28° BBDC
Exhaust closes 5° BTDC 5° BTDC
Valves clearances - engines cold ( max. coolant temperature 20°C / 68°F)
Intake 0,15 - 0,20 mm (0.006 - 0.008 in)
Exhaust 0,25 - 0,30 mm (0.010 - 0.012 in)
Camshafts and cam followers
Camshaft bearing journal OD:
At front (thrust) bearing 29,980 - 29,993 mm (1.1803 - 1.1808 in)
At all other bearing 23,980 - 23,993 mm (0.9441 - 0.9446 in)
Cylinder head bearing ID:
At front (thrust) bearing 30,020 - 30,041 mm (1.1819 - 1.1827 in)
At all other bearing 24,020 - 24,041 mm (0.9457 - 0.9465 in)
Camshaft radial clearance 0,027 - 0,061 mm (0.0011 - 0.0024 in)
Camshaft base circle 30,000 mm (1.1811 in)
Cam lift:
Intake 9,3927 mm (0.3698 in)
Exhaust 9,3819 mm (0.3694 in)
Cam follower OD 33,475 - 33,491 mm (1.3179 - 1.3185 in)
Cylinder head bore ID 33,500 - 33,525 mm (1.3189 - 1.3199 in)
Cam follower/cylinder head clearance 0,009 - 0,050 mm (0.0004 - 0.0020 in)
Valves, guides and springs
Valve head diameter:
Intake 34 mm  (1.3386 in)
Exhaust 30 mm  (1.1811 in)
Valve head rim thickness:
Standard 1,350 - 1,650 mm  (0.0532 - 0.0650 in)
Service limit 1,000 mm  (0.0394 in)
Valve head maximum runout 0,030 mm  (0.0012 in)
Valve overall length:
Intake 111,000 mm  (4.3701 in)
Exhaust 110,610 - 110,810 mm  (4.3547 - 4.3626 in)
Valve stem OD:
Intake 6,960 - 6,975 mm (0.2740 - 0.2746 in)
Exhaust 6,945 - 6,960 mm (0.2734 - 0.2740 in)
Valve guide ID: 7,000 - 7,015 mm (0.2756 - 0.2762 in)
Valve stem/guide clearance:
Intake - standard 0,025 - 0,055 mm (0.0010 - 0.0022 in)
Exhaust - standard 0,040 - 0,070 mm (0.0016 - 0.0028 in)
Intake & Exhaust
Service limit 0,150 mm (0.0059 in)
Valve guide overall length 45,0 mm (1.7717 in)
Valve guide OD 12,964 - 13,044 mm (0.5104 - 0.5135 in)
Cylinder head bore ID 13,000 - 13,018 mm (0.5118 - 0.5125 in)
Valve guide oversize available + 0,2 mm (+ 0.0079 in)
Valve seat angle 44° 10' - 44° 30'
Valve seat width 1,5 mm (0.0591 in)
Valve seat oversize available + 0,2 mm (+ 0.0079 in)
Valve spring standard free length 44,500 mm (1.7520 in)
Spring force at 29 mm (1.14 in) test length 740 - 800 N (166.36 - 179.85 lbf)
Cylinder block
Bore ID 66,995 - 67,005 mm (2.6376 - 2.6380 in)
Piston/cylinder clearance
Standard 0,030 - 0,040 mm (0.00012 - 0.00016 in)
Service limit 0,080 mm (0.0032 in)
Pistons and gudgeon pins
Piston standard OD: At size code A At size code B
Mahle - nominal 66,970 mm (2.6366 in) 66,980 mm (2.6370 in)
Mahle - actual 66,963 - 66,977 mm 66,973 - 66,987 mm
(2.6363 - 2.6369 in) (2.6367 - 2.6373 in)
KS - nominal 66,973 mm (2.6367 in) 66,983 mm (2.6371 in)
KS - actual 66,966 - 66,980 mm 66,976 - 66,990 mm
(2.6365 - 2.6370 in) (2.6368 - 2.6374 in)
Piston weigth group + or - stamped in piston crown. All pistons must be of same weight group, ie carry the same marking
Gudgeon pin OD 17,996 - 18,000 mm (0.7085 - 0.7087 in)
Piston bore and small-end bearing bush ID 18,002 - 18,006 mm (0.7088 - 0.7089 in)
Piston/gudgeon pin clearance 0,002 - 0,010 mm (0.0001 - 0.0004 in)
Piston rings
Top compression ring:
Thickness 1,178 - 1,190 mm (0.0464 - 0.0469 in)
End gap - installed 0,250 - 0,450 mm (0.0098 - 0.0177 in)
Ring/groove side clearance
75 models (Mahle)
0,050 - 0,082 mm (0.0020 - 0.0032 in)
Ring/groove side clearance
75 models (KS)
0,040 - 0,072 mm (0.0016 - 0.0028 in)
Ring/groove side clearance
100 models
0,013 - 0,027 mm (0.0005 - 0.0011 in)
Second compression ring:
Thickness 1,478 - 1,490 mm (0.0582 - 0.0587 in)
End gap - installed 0,250 - 0,450 mm (0.0098 - 0.0177 in)
Ring/groove side clearance
75 models (Mahle)
0,040 - 0,072 mm (0.0016 - 0.0028 in)
Ring/groove side clearance
75 models (KS)
0,030 - 0,062 mm (0.0012 - 0.0024 in)
Ring/groove side clearance
100 models
0,012 - 0,026 mm (0.0004 - 0.0010 in)
Oil scraper ring:
Thickness 2,975 - 2,990 mm (0.1171 - 0.1177 in)
End gap - installed 0,200 - 0,450 mm (0.0079 - 0.0177 in)
Ring/groove side clearance 0,020 - 0,055 mm (0.0008 - 0.0022 in)
Connecting rods and bearings
Maximum permissible weigth
difference between connecting rods - without bearing shells
± 4 grams (0.1411 oz)
Note: all rods must always be of same weight category, ie carry the same color coding
Small-end bearings bore ID - less bush 20,000 - 20,021 mm (0.7874 - 0.7882 in)
Big-end bearing bore ID 41,000 - 41,016 mm (1.6142 - 1.6148 in)
Big-end bearing width 21,883 - 21,935 mm (0.8615 - 0.8636 in)
Crankshaft big-end journal width 22.065 - 22,195 mm (0.8687 - 0.8738 in)
Connecting rod axial play (endfloat) - at big-end 0,130 - 0,312 mm (0.0051 - 0.0123 in)
Crankpin standard OD 37,976 - 38,000 mm (1.4951 - 1.4961 in)
Size groups:
White 37,976 - 37,984 mm (1.4951 - 1.4954 in)
Green 37,984 - 37,992 mm (1.4954 - 1.4957 in)
Yellow 37,992 - 38,000 mm (1.4957 - 1.4961 in)
Big-end bearing radial clearance 0,030 - 0,066 mm (0.0012 - 0.0026 in)
Undersize bearing shells available:
1st stage (1 paint mark) -0,25 mm (-0.0098 in)
2nd stage (2 paint mark) -0,50 mm (-0.0197 in)
Crankshaft and main bearings
Crankcase bearing bore ID 49,000 - 49,016 mm (1.9291 - 1.9298 in)
Crankshaft endfloat 0,080 - 0,183 mm (0.0032 - 0.0072 in)
Thrust bearing width:
Standard 23,000 mm (0.9055 in)
At 1st stage undersize crankshaft reground by 
- 0,25 mm (- 0.01 in) 23,200 mm (0.9134 in)
At 2nd stage undersize crankshaft reground by
- 0,50 mm (- 0.02 in) 23,400 mm (0.9213 in)
Main bearing journal standard OD 44,976 - 45,000 mm (1.7707 - 1.7717 in)
Size groups:
White 44,976 - 44,984 mm (1.7707 - 1.7710 in)
Green 44,984 - 44,992 mm (1.7710 - 1.7713 in)
Yellow 44,992 - 45,000 mm (1.7713 - 1.7717 in)
Main bearing radial clearance 0,020 - 0,056 mm (0.0008 - 0.0022 in)
Undersize bearing shells available:
1st stage (1 paint mark) -0,25 mm (-0.0098 in)
2nd stage (2 paint marks) -0,50 mm (-0.0197 in)
Primary drive
Reduction ratio - crankshaft to output/balancer shaft 1:1
Torque wrench settings

75 models

100 models

Component Nm lbf ft Nm lbf ft
Cylinder head cover drain plugs - early models only N/App N/App 7 5
Cylinder head cover bolts 8 6 ± 0.5 6 4.5
Crankshaft (engine right-hand) cover bolts 8 ± 1 6 ± 0.5 N/Av N/Av
Cam chain (engine front) cover screws 7 ± 1 5 ± 0.5 6 4.5
Cam chain top guide rail Torx screws 9 ± 1 6.5 ± 0.5 N/Av N/Av
Camshaft bearing cap nuts 9 ± 1 6.5 ± 0.5 8,8 6.5
Camshaft sprocket bolts 54 ± 6 40 ± 4.5 54 40
Cam chain tensioner mounting screws 9 ± 1 6.5 ± 0.5 N/Av N/Av
Crankshaft sprocket and ignition rotor flange retaining bolt 50 ± 6 37 ± 4.5 50 37
Cylinder head bolts - bolt threads lightly oiled:
1st stage 30 ± 4 22 ± 3 30 22
2nd stage - after 20 minute wait 45 ± 5 33 ± 4 45 33
Connecting rod big-end bearing cap retaining nuts:
1st stage - to preload shells 30 ± 3 22 ± 2 30 22
2nd stage - applies to all models Tighten (rotate) nuts through an angle of 80°
Crankshaft main bearing cap bolts 50 ± 6 37 ± 4.5 50 37
Crankcase lower section to cylinder block:
10 mm bolt - output shaft rear 40 ± 5 29.5 ± 4 40 29.5
8 mm bolt or screw - output shaft front 18 ± 2 13 ± 1.5 21 15.5
6 mm bolt or screw 7 ± 1 5 ± 0.5 6 4.5
Oil/water pump assembly mounting screws 7 ± 1 5 ± 0.5 N/Av N/Av
Auxiliary drive shaft bearing retainer screws 9 ± 1 6.5 ± 0.5 N/Av N/Av
Bellhousing Torx screws 9 ± 1 6.5 ± 0.5 N/Av N/Av
Starter clutch body/auxiliary drive shaft:
Early 100 models - 8 mm screws N/App N/App 24 18
Late models - 6 mm bolts 9 ± 1 6.5 ± 0.5 9 ± 1 6.5 ± 0.5
Alternator drive flange/auxiliary drive shaft retaining bolt 33 ± 4 24 ± 3 33 24
Engine and transmission unit/frame mountings:
Early (1984, 1985) 100 models N/App N/App 32 23.5
Late (1986 on) 100 and 75 models 40,5 ± 4 30 ± 3 40,5 ± 4 30 ± 3

 

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