To Remove Pistons and Connecting Rod Assemblies
1. Remove the cylinder head (Page E.1).
2. Drain and remove the lubricating oil sump. (T4.236 engines. To prevent damage to the piston cooling jets they should be removed).
3. Remove the nuts from the big end bolts.
F1
4. Remove the big end caps, bearing shells and bolts (Fig. F.1).
NOTE: If the bearing shells removed are serviceable, refit them in their original positions.
F2
5. Push pistons and connecting rods out of the top of the cylinders (Fig. F.2).
NOTE: Keep each piston and connecting rod assembly separate, each to each as marked
To Remove Pistons and Rings from Connecting Rods
1. Remove the rings from each piston.
2. Remove the circlips and withdraw the gudgeon pin. If the gudgeon pin is tight in the piston bore, warm the piston in clean liquid to a temperature of 100/120°F (38/49°C).
Inspection
1. Examine the pistons for scoring and clean carbon from the ring grooves. Check the clearance of the new piston rings in their respective grooves and if, with a new ring fitted the vertical groove clearance exceeds 0.008 in (0,20 mm) fit new piston.
2. Check the fitted gap of the rings in the unworn portion at top of cylinder bore. For details of ring gap dimensions see "Technical Data", Pages B.6 to B.7. Ring gaps for conformable rings are with spring fitted.
3. Check the fit of the gudgeon pin in the piston bore and in the small end bush. For details of piston bore, gudgeon pin and small end bush bore diameters see "Technical Data", Page B.7. When renewing a small end bush, ensure that the oil hole in the bush aligns with the hole in the connecting rod. Ream out to suit the gudgeon pin and check the connecting rod for parallelism see "Technical Data", Page B.8. The small end of the connecting rod on T4.236 engines is wedge shaped and the small end bush should be machined to suit the contours of the wedge. The earlier T4.236 connecting rod is also drilled from the big end to the small end to provide piston cooling by a feed of lubricating oil. Later T4.236 engines have piston cooling jets fitted in the cylinder block wall.
4. Examine the big end bearings for wear and scoring. Also examine the crankpins for wear and ovality. For crankshaft details see page B.8.
F3
To Assemble the Pistons to the Connecting Rods
If the original pistons are being used they must be assembled to the original connecting rods. For markings of pistons and connecting rods see Figs. F.8 and F.9.
1. The cavity in the piston crown is off-set towards one side of the piston. Place the piston on the connecting rod with the cavity towards the side of the rod which carries the rod and cap identification numbers. Insert the gudgeon pin and fit new circlips, warming the piston, if necessary.
2. Fit the rings in the following order, ensuring that the ring gaps are equally spaced around the piston.
(a) 4.2482 Engines (see Fig. F.4)
F4
- Chrome Faced Spring Loaded Conformable Scraper - above gudgeon pin.Internally Stepped Taper Faced Compression - second groove.Molybdenum Faced Internally Stepped Barrel Faced Compression - top groove.
When fitting the spring loaded conformable scraper ring, ensure that the latch pin enters both ends of the spring. With the ring gap diametrically opposite to the latch pin, position the oil control ring over spring correctly located in annular groove of ring, i.e., between the oil control ring and the bottom of the ring groove in the piston.
When fitting the internally stepped taper faced compression ring, ensure that the "step" is towards the piston crown.
When fitting the top compression ring, ensure that the manufacturers mark is towards the piston crown.
(b) 4.248 Engines (4 Ring)
**Spring Loaded Conformable Scraper - above gudgeon pin.
Internally Stepped Compression - third groove.
*Internally Stepped Compression - second groove.
Chrome Insert Barrel Faced Compression - top groove.
When fitting sealed power rings, ensure that the ends of the spring loaded segment butt together and do not overlap.
**Some earlier A4.248 engines had a sealed power scraper ring fitted in the 4th groove.
*On some earlier A4.248 engines rated up to 2,000 rev/min, the second compression ring is plain cast iron.
Some later engines, rated up to 2,000 rev/min, have internally stepped chrome faced rings in both 2nd and 3rd grooves.
When fitting internally stepped compression rings, ensure that the step is towards the piston crown.
When fitting the spring loaded conformable scraper ring, ensure that the latch pin enters both ends of the spring. With the ring gap diametrically opposite to the latch pin, position the oil control ring over spring correctly located in annular groove of ring, i.e., between the oil control ring and the bottom of the ring groove in the piston.
(c) 4.248 Engines (3 Ring)
- Chrome Faced Spring Loaded ConformableScraper - above gudgeon pin.Internally Stepped Taper Faced Compression - second groove.Molybdenum Faced Internally Stepped Barrel Faced Compression - top groove.
When fitting the spring loaded conformable scraper ring, ensure that the latch pin enters both ends of the spring. With the ring gap diametrically opposite to the latch pin, position the oil control ring over the spring correctly located in the annular groove of ring, i.e., between the oil control ring and the bottom of the ring groove in the piston.
When fitting the internally stepped compression rings in the second and top grooves, ensure that the "step" is towards the piston crown.
(d) T4.236 Engines (see Fig. F.6)
F6
- Chrome Faced Spring Loaded Conformable Scraper - above gudgeon pin.Cast Iron Taper Faced Compression - second groove.Molybdenum Faced Wedge Compression - top groove.
When fitting the spring loaded conformable scraper ring, ensure that the latch pin enters both ends of the spring. With the ring gap diametrically opposite to the latch pin, position the oil control ring over spring correctly located in annular groove, i.e., between the oil control ring and the bottom of the ring groove in the piston.
When fitting the compression rings, ensure that the manufacturers mark is towards the piston crown.
(e) 4.236 Engines fitted with cast iron liners
- Slotted Scraper - below gudgeon pin.Slotted Scraper - above gudgeon pin.Internally Stepped Compression - third groove.Internally Stepped Compression - second groove.*Chrome Faced Compression - top groove
*With later combine engines, a plain cast iron ring is fitted in the top groove. This plain ring is completely interchangeable with the earlier chrome faced ring. When overhauling combine engines, the later plain ring should always be fitted (in engine sets).
NOTE: From Engine No. 236U68569 fitted to combine applications, some piston ring packs have been altered from five to four rings. The two slotted scraper rings fitted in the forth and fifth grooves have been replaced by one conformable chrome faced ring in the fourth groove only, leaving the fifth groove empty.
On later engines, the slotted scraper fitted above the gudgeon pin has been replaced by a conformable scraper ring and on combine engines having an empty bottom groove has been fitted with a slotted scraper. Fit "step of internally stepped compression rings towards piston crown.
(f) 4.236 Engines fitted with chrome liners
- Slotted Scraper - below gudgeon pin.Slotted Scraper - above gudgeon pin.Laminated Compression - third groove.Internally Stepped Compression - second groove.Cast Iron Compression - top groove.
NOTE: When fitting internally stepped compression rings, ensure that the "step" is towards the piston crown. Never fit chrome faced rings to engines having chrome plated liners.
Fit the laminated compression ring to the piston as follows: (ensure piston is positioned with the crown uppermost).
F5
1. Fit the first segment to the piston so that when held horizontally between the thumb and fingers and radially compressed, the ring ends point downwards (see Fig. F.5). Place this ring on the bottom face of the groove and position gap over the gudgeon pin bore.
2. Fit the second segment on top of the first so that when held and compressed as described in (1) above, the ring ends point upwards (see Fig. F.5). Position the gap at 180° to that of the first segment.
3. The third segment should be fitted on top of the second, so that when held and compressed as described, the ring ends point upwards (see Fig. F.5). Position the gap immediately above that of the first segment.
If all the segments have been fitted in the groove correctly, they will be positioned as shown in the right hand illustration of Fig. F.5.
(g) 4.236 Engines (3 ring)
Chrome face, spring loaded conformable scraper above the gudgeon pin.
Chrome taper face compression, second groove.
Chrome barrel face, internally stepped compression, top groove.
NOTE: When fitting the internally stepped compression ring, ensure that the step is towards the piston crown, When fitting the spring loaded conformable scraper ring, ensure that both ends of the latch pin enter the spring and position the ring so that the gap is diametrically opposite the latch pin.
(h) 4.212 Engines
High Compression Piston
- Spring Loaded Conformable Scraper- above the gudgeon pinInternally Stepped Compression- second grooveChrome Faced Compression- top groove
Low Compression Piston
- *Spring Loaded Conformable Scraper- above the gudgeon pinInternally Stepped Compression- third grooveCast Iron Plain Compression- second grooveChrome Faced Compression- top groove
*From engine no. 212UA147672 onwards a revised piston ring pack became effective which changed the Sealed Power Scraper to a Chrome Faced, Spring Loaded Conformable Scraper. The remaining rings stay unchanged. Earlier engines fitted with different piston and ring assemblies may be changed to the latest assembly.
NOTE: When fitting the internally stepped compression ring, ensure that the "step" is towards the piston crown.
When fitting the Spring Loaded Conformable Scraper ring ensure that both ends of the latch pin enter the spring and position the ring so that the gap is diametrically opposite the latch pin.
To Fit the Pistons and Connecting Rods to the Cylinder Bore
1. Before fitting the piston and connecting rod assemblies to their respective cylinder bores, liberally coat each bore and piston with clean engine oil.
F7
F9
2. Using a ring guide (Fig. F.7), insert the pistons and connecting rod into the top of their respective cylinder bores. The piston and rod number must relate to the cylinder into which it is being fitted and the rod identification number must be on the fuel injection pump side of engine. The word "Front" or arrow marked on the piston crown must be towards the front of the engine (Fig. F.9). (T4.236 engines, refit piston cooling jets).
F8
3. Fit the bearing shells and cap with the numbers on the same side of the rod and cap (Fig. F.8).
4. Refit the two connecting rod bolts so that the flat on the head of each bolt is located against the shoulder of the rod. Secure with two new nuts. See Page B.2 for Recommended Torque Tensions.
5. Refit the lubricating oil sump.
6. Refit the cylinder head (Page E.7).
Fitting New Pistons
The piston height can be checked by means of a straight edge and feeler gauges.
Correct piston heights above the cylinder block top face are as follows:-
**4.2482 ... 0.016/0.023 in(0,41/0,59 mm)
4.248 ... 0.003/0.010 in(0,08/0,25 mm)
T4.236 ... 0.016/0.024 in(0,41/0,61 mm)
*4.236 ... 0.003/0.010 in(0,08/0,25 mm)
4.212 ... 0.015/0.021 in(0,38/0,53 mm)
*Where 4.236 engines have to conform with the smoke density regulations B.S.AU 141a:1971, then the piston height must be 0.016/0.024 in (0,41/0,61 mm) and the pistons topped accordingly.
**The pistons have hard anodised crowns and must not be topped. To achieve this tolerance in production three grades of piston are used, H, M and L but for service use, only the L grade is available which can be below the tolerance figure given.