Cubic Capacity 248 c.c.
Stroke 77 mm
Bore Nominal 64 mm
Actual 63.970 mm/2.5185 in.
(Rebore to .020 in. when wear exceeds 005 in. and
again to .040 in. after a further .005 in. wear.)
Compression Ratio 6.5 to 1
Piston Diameter-
Bottom of Skirt Fore and Aft. 63.926/63.901mm
Top Lands 63.50/63.45 mm
Piston Rings-
Width-Plain Rings (Two) .0625/.0615 in.
Scraper Ring (One) .15625/.15525 in.
Radial Thickness 2.612/2.460 mm
Clearance in Grooves .0035/.0015 in.
Renew Piston Rings when gap exceeds
1
/
16
in.
Oversize Pistons and Rings available .020 and .040 in.
Piston Boss Internal Diameter .7500/.7498 in.
Gudgeon Pin Diameter .7498/.7495 in.
Con. Rod Small End Diameter .7510/.75025 in.
Con. Rod Big End Diameter 1.6257/1.6252in.
Floating Bush Ext. Diameter 1.6235/1.6230 in.
Floating Bush Int. Diameter 1.2502/1.2498 in.
Floating Bush Width .739/.736 in.
Crank Pin Diameter 1.24900/1.24875in.
Engine Shaft Diameter 1.0000/.9997 in.
Driving Side Main Roller Bearing
Outside Diameter 1.876/1.875 in.
Inside Diameter 1.5002/1.4998 in.
Width 1.437/1.432 in.
No. of Rollers 24 (2 rows)
Timing Side Main Roller Bearings-
Outside Diameter 1.8772/1.8770 in.
Inside Diameter 1.5004/1.5002 in.
Width .4425/4405 in.
No. of Rollers 12 (1 row)
Size of Rollers
Diameter .2500/.2490 in.
Length .328/.327in.
Graded Rollers are available in steps of .0001 in. from
.2490 in.-.2500 in.
Rocker Bearing Inside Diameter .626/.625 in.
Rocker Spindle Diameter .624/.6235 in.
Inlet Valve Stem Diameter .34275/.34175 in.
Exhaust Valve Stem Diameter .34175/.34075 in.
Valve Guide Internal Diameter .3452/.3437 in.
Valve Guide External Diameter .624/623 in.
Guide Hole in Cylinder Head .623/622 in.
Tappet Stem Diameter .375/.374 in.
Tappet Guide Internal Diameter .3765/.3750 in.
Tappet Guide External Diameter .875/.874 in.
Guide Hole in Crankcase .875/.874 in.
Tappet Clearance with cold engine-
Inlet .002 in.
Exhaust. .004 in.
Valve Spring Free Length
Inner 1
13
/
16
in.
Outer 1
27
/
32
in.
(Renew when reduced by
3
/
16
in.).
Valve Timing with .012 in. clearance-
Exhaust Opens 75° before B.D.C.
Exhaust Closes 35° after T.D.C.
Inlet Opens 30° before T.D.C.
Inlet Closes 60° after B.D.C.
Cam Spindle External Diameter .6245/.6235 in.
Cam Bush Internal Diameter .6255/.6250 in.
Cam Lift . .3125 in.
Valve Lift (approximately) .3125 in.
Contact Breaker-
Speed Half Engine Speed
Points .015/.018 in.
Timing
3
/
8
in. before T.D.C.
advanced
1
/
64
in. before T.D.C.
retarded
Engine Sprocket 17 Teeth.
Clutch Sprocket 42 Teeth.
Final Drive Sprocket 15 Teeth.
Primary Chain
Type 110046 Renold
Length 66 Pitches.
Width .305 in.
Pitch .500 in.
Feed Oil Pump
Speed
1
/
12
Engine Speed.
Piston Diameter .25 in. (nominal)
Stroke .375 in.
Return Oil Pump-
Speed
1
/
12
Engine Speed.
Piston Diameter .375 in. (nominal)
Stroke .375 in.
Sparking Plug
Type Lodge H 14.
K.L.G.F70.
Champion L10S.
Diameter 14 mm
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