Vespa GTS Super 300 ie - Service manual > Overhaul data

Assembly clearances

Cylinder - piston assy.

CYLINDER - PISTON

COUPLING CATEGORIES

N.B.

THE PISTON MUST BE INSTALLED WITH THE ARROW FACING TOWARDS THE EXHAUST SIDE, THE PISTON RINGS MUST BE INSTALLED WITH THE WORD "TOP" OR THE STAMPED MARK FACING UPWARDS.

• Measure the outer diameter of the gudgeon pin.

Characteristic

Pin outside diameter
16 +0 -0.004 mm

• Measure the diameter of the bearings on the piston.

Characteristic

Standard diameter
16 +0.006 +0.001 mm

• Calculate the piston pin coupling clearance.

N.B.

THE PIN HOUSINGS HAVE 2 LUBRICATION CHANNELS. FOR THIS REASON, MEASUREMENT MUST BE MADE ACCORDING TO THE PISTON AXIS

Characteristic

Standard clearance:
0.001 - 0.010 mm

• Carefully clean the seal housings.
• Measure the coupling clearance between the sealing rings and the piston grooves using suitable sensors, as shown in the diagram.
• If the clearance is greater than that indicated in the table, replace the piston.

N.B.

MEASURE THE CLEARANCE BY INSERTING THE BLADE OF THE FEELER GAUGE FROM THE SECOND SEAL RING SIDE.

Fitting clearance

Top piston ring - standard coupling clearance 0.015 - 0.06 mm Top piston ring - maximum clearance allowed after use 0.07 mm Middle piston ring - standard coupling clearance 0.015 - 0.06 mm Middle piston ring - maximum clearance allowed after use 0.07 mm oil scraper ring - standard coupling clearance 0.015 - 0.06 mm oil scraper ring - maximum clearance allowed after use 0.07 mm

• Check that the head coupling surface is not worn or misshapen.
• Pistons and cylinders are classified according to their diameter. The coupling must be made with those of the same type (M-M, N-N, O-O, P-P).

Characteristic

Maximum allowable run-out:
0.001 over 0.05 mm

Piston rings

Sealing rings

• Alternately insert the three sealing rings into the cylinder, in the area where it retains its original diameter.

  Using the piston, insert the rings perpendicularly to the cylinder axis.

• Measure the opening (see figure) of the sealing rings using a feeler gauge.
• If any measurements are greater than specified, replace the piston rings.

N.B.

BEFORE REPLACING ONLY THE PISTON RINGS, ENSURE THAT THE CLEARANCE BETWEEN THE PISTON RINGS AND THE PISTON RING GROOVES, AND BETWEEN THE PISTON AND THE CYLINDER, IS AS SPECIFIED. IN ANY CASE, NEW PISTON RINGS USED IN COMBINATION WITH A USED CYLINDER MAY HAVE DIFFERENT BEDDING CONDITIONS THAN THE STANDARD.

Characteristic

Top piston ring
Standard opening: 0.15 to 0.30 mm
Middle piston ring
Standard opening: 0.20 ÷ 0.40 mm
scraper ring
Standard opening: 0.20 ÷ 0.40 mm

Crankcase - crankshaft - connecting rod

CRANKSHAFT

Axial clearance between crankshaft and connecting rod

AXIAL CLEARANCE BETWEEN CRANKSHAFT AND CONNECTING ROD

Diameter of crankshaft bearings.

Measure the bearings on both axes x-y.

CRANKSHAFT

MAX. ADMISSIBLE DISPLACEMENT

Characteristic

Crankshaft-crankcase axial clearance (H)
0.15 ÷ 0.43 mm

• Using a bore gauge, measure the connecting rod small end diameter.

N.B.

IF THE CONNECTING ROD SMALL END DIAMETER EXCEEDS THE STANDARD DIAMETER, EXHIBITS WEAR OR OVERHEATING, PROCEED TO REPLACE THE CRANKSHAFT AS DESCRIBED IN THE CRANKCASE AND CRANKSHAFT CHAPTER.

Characteristic

Standard diameter
16 +0.025 +0.015 mm

• To obtain a good bushing lubrication it is necessary to have both an optimal lubricating pressure and a good oil flow rate; the bushings must be correctly positioned so as not to obstruct the oil supply channels.
• The main bushings are comprised of two half-bearings, one with holes and channels for lubrication whereas the other is solid.
• The solid half-bearing is intended to stand the thrusts caused by combustion, and for this reason it is arranged opposite the cylinder.
• To prevent shutters in the oil feeding channels, the matching surface of the two half-bearings must be perfectly orthogonal to the cylinder axis, as shown in the figure.
• The oil feeding channel section is also affected by the bushings driving depth compared with the crankshaft axial clearance of the limiting surface.
• Check the inside diameter of the main bushings in the three directions indicated in the diagram.
• Repeat the measurements for the other bushing half. see diagram.
• There are three crankcase versions: with BLUE bushings, with YELLOW bushings and with GREEN bushings.
• There is only one type of main bushing housing hole in the crankcase. The standard bushing diameter after driving is variable on the basis of a coupling selection.
• The bushing housings in the crankcase are classified into 2 categories - Cat. 1 and Cat. 2 - just like those for the crankshaft.
• The main bushings are available in three thickness categories, identified by colour markings, as shown in the table below.

BUSHINGS

COUPLINGS

Combine the shaft with two category 1 crankwebs with the category 1 crankcase (or cat. 2 with cat. 2).

Furthermore a spare crankcase cannot be matched with a crankshaft with mixed categories. The spare crankshaft has half-shafts of the same category.

CATEGORIES

N.B.

DO NOT TAKE THE MEASUREMENT ON THE TWO HALFSHELL COUPLING SURFACE SINCE THE ENDS ARE RELIEVED TO ALLOW BENDING DURING THE DRIVING OPERATION.

N.B.

CRANKCASES FOR REPLACEMENTS ARE SELECTED WITH CRANKCASE HALVES OF THE SAME CATEGORY AND ARE FITTED WITH CATEGORY C BUSHINGS (YELLOW)

Characteristic

Crankshaft-bushing maximum clearance admitted:
0.08 mm
Diameter of crankcase without bushing
CAT. 1: 32.959 ÷ 32.965 mm
CAT. 2: 32.953 ÷ 32.959 mm

Cylinder Head

Before performing head service operations, thoroughly clean all coupling surfaces. Note the position of the springs and the valves so as not to change the original position during refitting

• Using a trued bar and a feeler gauge check that the cylinder head surface is not worn or distorted.

Characteristic

Maximum allowable run-out:
0.1 mm

• In case of faults, replace the head.
• Check the sealing surfaces for the intake and exhaust manifold.
• Check that the camshaft and the rocking lever pin capacities exhibit no wear.
• Check that the head cover surface is not worn.
• Check that the coolant seal plug exhibits no oxidation.

 

• Insert the valves into the cylinder head.
• Alternatively check the intake and exhaust valves.
• The test is carried out by filling the manifold with petrol and checking that the head does not ooze through the valves when these are just pressed with the fingers.

Measure the camshaft bearing seats and rocking lever support pins with a bore meter

HEAD BEARINGS

Measure the unloaded spring length

Characteristic

Standard length
40.2 mm
Allowable limit after use:
38.2 mm

• Remove any carbon deposits from the valve seats.
• Check the width of the mark on the valve seat "V" with Prussian blue.

Characteristic

Standard value:
1 - 1.3 mm
Admissible limit:
1.6 mm

• If the width of the mark on the valve seat is larger than the prescribed limits, true the seats with a 45º milling cutter and then grind.
• In case of excessive wear or damage, replace the head.

STANDARD VALVE LENGTH

• Measure the diameter of the valve stems in the three positions indicated in the diagram.

STANDARD DIAMETER

MINIMUM ADMISSIBLE DIAMETER

• Calculate the clearance between valve and valve guide.

 

• Check the deviation of the valve stem by resting it on a "V" shaped support and measuring the extent of the deformation using a dial gauge.

Characteristic

Limit values admitted:
0.1 mm

• Check the concentricity of the valve head by placing a dial gauge at right angles to the valve head and rotating it on the "V" shaped support.

Characteristic

Admissible limit:
0.03 mm

Measure the valve guide.

Characteristic

Valve guide:
5 +0.012 mm

• After measuring the valve guide diameter and the valve stem diameter, check clearance between guide and stem.

INTAKE

EXHAUST

• Check that there are no signs of wear on the mating surface with the set screw articulated terminal.

• If no faults are found during the above checks, you can use the same valves. To obtain better sealing performance, grind the valve seats. Grind the valves gently with a fine-grained lapping compound.

  During the grinding, keep the cylinder head with the valve axes in a horizontal position. This will prevent the lapping compound residues from penetrating between the valve stem and the guide (see figure).

CAUTION

TO AVOID SCORING THE FAYING SURFACE, DO NOT KEEP ROTATING THE VALVE WHEN NO LAPPING COMPOUND IS LEFT. CAREFULLY WASH THE CYLINDER HEAD AND THE VALVES WITH A SUITABLE PRODUCT FOR THE TYPE OF LAPPING COMPOUND BEING USED.

CAUTION

DO NOT REVERSE THE FITTING POSITIONS OF THE VALVES (RIGHT - LEFT).

• Check that the camshaft bearings exhibit no scores or abnormal wear.
• Using a micrometer, measure the camshaft bearings.

STANDARD DIAMETER

MINIMUM ADMISSIBLE DIAMETER

• Using a gauge, measure the height of the cams.

STANDARD HEIGHT

Check the axial clearance of the camshaft

CAMSHAFT AXIAL CLEARANCE

• Measure the outside diameter of the rocking lever pins
• Check the rocking lever pins do not show signs of wear or scoring.
• Measure the internal diameter of each rocker.

Check there are no signs of wear on the slider from contact with the cam and on the jointed adjustment plate.

ROCKING LEVERS AND PIN DIAMETER:

Slot packing system

Characteristic

Compression ratio
10.5 ÷ 11.5 : 1

Measurement "A" to be taken is a value of piston re-entry, it indicates by how much the plane formed by the piston crown falls below the plane formed by the top of the cylinder. The further the piston falls inside the cylinder, the less the base gasket to be applied (to recover the compression ratio) and vice versa.

N.B.

MEASUREMENT "A" MUST BE TAKEN WITHOUT ANY GASKET FITTED BETWEEN THE CRANKCASE AND CYLINDER AND AFTER RESETTING THE DIAL GAUGE, EQUIPPED WITH A SUPPORT, ON A GROUND PLANE

ENGINE 300 SHIMMING

Products

RECOMMENDED PRODUCTS TABLE

Tooling

SPECIFIC TOOLS

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