Thermal clearance of piston rings on the diesel engine of a power tiller

1-047 Piston Rings

NOTE : Signs of scuffs and scuffs are deep scratches, discoloration of the metal, and bumps (B).

Possible causes of galling and scuffing:

  • The engine is overheating
  • Liquefaction of oil
  • Poor maintenance of the lubrication system
  • Piston cooling nozzle failure
  • The engine oil pressure gauge is not designed for this purpose

If the engine is running too hot, the piston rod may be scraped and the liner may be damaged.

Possible Causes of a Plugged Wiper Ring

  • Low engine operating temperature due to prolonged idling or faulty cooling system.
  • Oil change intervals not met
  • Use of improper grade of engine oil
  • Use of poor quality engine oil

NOTE : Before performing the test, verify that the cylinder itself meets the specifications. See. Procedure 001-026 in Section 1.

Measure the piston ring lock clearance by installing them in the cylinder in which they will work. Install the rings 50 mm (2 inches) from the top surface of the cylinder block (A) so that the ring plane is perpendicular to the cylinder surface, using the piston.

The type and location of the ring can be determined by the ring profile.

Use a feeler gauge to measure piston ring lock clearance.

mm in
Top view 0.26 MIN 0.010
0.36 MAX 0.014
Second compression ring 0.50 MIN 0.020
0.75 MAX 0.030
Oil 0.25 MIN 0.010
0.50 MAX 0.020

If the ring lock clearance is not normal:

  • Check the type of ring used and its catalog number
  • Check compliance with the norm cylinder. See. Procedure 001-026 in Section 1).
  • Be sure to measure ring gap at 50 mm (2 inches) from the top surface of the cylinder block.
  • Try a different set of rings.

Maintenance of the Mole Cultivator

8.5. Adjusting the V-belt drive. Proper adjustment of the V-belt drive will ensure reliable operation of the clutch and the necessary longevity of the V-belt. The main tension of the V-belt perform with the clutch off by moving the engine 10 along the frame 25 (arrow D). Pre-unscrew the screws 21, 24 with washers 20, 22, 23, remove the housing 19 and loosen the four nuts 26 fixing the engine to the frames. Tension should be maximum, but should not cause rotation of the rotors. Adjustment checks can be made by slowly cranking the engine with the starter motor. Additional tensioning is done with the tensioning pulley by changing the position of screw 4. Before setting, screw 4 must be screwed in as far as it will go. In this position, with the engine running, engage the clutch and check the full load operation of the MC. If the belt slips, increase the tension of the pulley by unscrewing screw 4. Tighten the screw 4 using the nut 3. Adjust the position of the end stop 13. Loosen the fastening nut. The end stop should not touch the outer surface of the V-belt. Allowable clearance AND must be within 1. Adjust the stop position 13. 3 mm. It is allowed to use V-belt with cracks on inner diameter. WARNING! When fixing the drive shafts check position of the belt pulleys (11,15) and the V-belt drive (15). Pulleys must be in one plane. Allowable deviation max. 1 mm. When installing the housing 19 limiting bracket G (on the inner surface of the housing) should not touch the outer surface of the V-belt when fixing the lever 1 with clamps 2. The allowable gap B must be within 1. 3 mm.

To inspect the magneto 7 remove the helical cover 6. cup 2, unscrew the flywheel nut. Place the flywheel puller on the flywheel, fasten with three screws. Screw in the bolt Ml0x20 (from the spare parts list) into puller and remove the flywheel. Carry out a visual inspection of magneto, in case of loosening the screws fastening magneto and mismatch marks “a” and “b” on the magneto 7 and the crankcase 8 to combine them, fix the screws. If necessary to disassemble the magneto unplug the electrical connector 3, using a screwdriver to free the wire lugs from the socket magneto plug, unscrew the tip of the candle 5 from the wire 4. Remove magneto 7 with wires from a place in the crankcase seat 8 by first removing the fastening screws (2 pcs.).). Unscrew high-voltage wire from magneto transformer. Reassemble the dismantled parts in reverse order. ATTENTION! When mounting the flywheel, align the keyways on the flywheel hub and the crankshaft journal with a segmented key. Tighten the flywheel nut with the torque 3. 4 kGsm. in order to avoid breakage of the high-voltage transformer screw, screw the high-voltage wire into the magneto transformer screw 7 for a length of 8. 10 mm. Visually inspect the button “Stop” 1, low-voltage wires 2, electrical connector 3, high-voltage wire 4, suppressor resistance 5. If the insulation is disturbed, repair the defect with an insulating tape. To inspect the spark plug 6 remove it on the cooled down engine with the hood removed. use the tool enclosed in the spare parts list. In case of presence of oil, soot or carbon deposits clean the electrodes and the plug cone, wash the electrodes and the cone in petrol, dry and blow out the spark plug. Measure the gap between the center and side electrodes. The gap must be within 0.4. 0.6 mm. WARNING! If it is necessary to adjust the gap, do not allow pressure on the center electrode this could cause it or the ceramic thermal cone to break. Before installing the spark plug, install the o-ring and turn it in by hand as far as it will go, using a spark plug wrench. Do not apply excessive force when tightening. it can lead to tearing off the thread of the cylinder head.

8.9. Cleaning of soot from cylinder, cylinder head, piston, MC units, lubrication of control cables. To perform these operations, it is necessary to partially disassemble the engine: remove the hood with the bracket; the tip of the high-voltage wire from the spark plug; unscrew the spark plug; remove the fuel tank by removing the screw 21 in the carburetor cap and releasing the carburetor cable termination from the slot of the air damper, unscrew the four nuts and remove the cylinder head with washers and gasket; install the piston in the bottom dead center and, raising the cylinder up, remove it from the studs; disconnect the muffler and carburetor; remove piston rings, for which to enter under the rings steel or brass plates of thickness 0.2. 0.3 mm and a width of 4. 5 mm. Flush with fuel mixture cylinder, cylinder head, muffler, carburetor, clean cylinder channels and combustion chamber of the head from sludge. If there is a ledge in the upper part of the cylinder bore (at the boundary of the upper piston ring) remove the ledge with a sickle-shaped scraper or an abrasive tool, making sure not to damage the cylinder bore below the ledge. If necessary, clean up risks, scuffing of the cylinder surface with fine emery cloth, rubbed with chalk and coated with oil. Do not remove small dings. Clean off sludge under the piston and piston ring grooves by first covering the crankcase bore with a clean cloth. The piston grooves are easy to clean with an old, broken piston ring. Thoroughly wash the cleaned parts with fuel mixture. Check thermal clearance at the joints of piston rings inserted in the cylinder, quality of fit of piston rings to the mirror of the cylinder. Insert the piston rings alternately into the cylinder to a depth of 8. 10 mm by pushing them through with the bottom of the piston. Piston ring gap should be 1 mm, max. At a gap of more than 1 mm piston rings must be replaced with new ones. Assemble dismantled parts and components of engine and MC in reverse order. Fit the piston so that the arrow on the bottom faces the cylinder exhaust port, i.e. е. to the muffler. Lubricate cylinder bore with engine oil before mounting. Cylinder head fastening nuts tighten evenly crosswise. If necessary, replace the gaskets. ATTENTION! Assemble: parts and assemblies of selective assembly: piston, cylinder, piston pin must be assembled together considering identical color markings on parts surfaces (see Pic. Appendix 4). Lubricate throttle control cable with grease.

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After assembling the MC make adjustments to the carburetor controls (Section 8.4.)

8.12. disassembly and assembly of the starter. If it is necessary to replace the coil spring 6 or the starter cord 2, carry out a complete disassembly. To remove the starter from the engine and clean from dust and dirt. Disassembly should be carried out in the following order: Pressing the disk 13. remove the lock 15, then sequentially remove parts 8, 14, 13, 9, 11, 12, 10, 9, 8. Then remove, turning counterclockwise, the coil 7 fixed in her spiral spring 6, with particular care due to the possible sudden unwinding of the spring. If the starter cord 2 is broken, free the cord parts from the reel 7 and cord holder 4. remembering the ways of fixing the cord in the coil and in the holder. Replace the cord. Before assembly, lubricate all rubbing surfaces with one of the applicable oils. When replacing the coil spring 6, carefully insert it into the coil 7, catching the hook of the spring on a ledge in the coil or loop the spring on a tooth in the wall of the coil. Release the spring from the assembly wire. Check the position of the centre of the pit of the hook of the inner coil with respect to the axis of the central hole of the coil. There should be 18 mm distance between them. If necessary, bend the annealed end of the internal coil of the spring. place the cord 2 clockwise in the groove of the coil 7 not more than one turn and pull it out of the housing 1 through the slot in the flange of the coil. Then drag it through the holes in the housing toward the starter handle, leaving a loop inside the housing about 200 mm long. Place the coil with the spring and the cord on the axis of the housing 1. by aligning the hook of the inner coil of the spring with the flanging of the housing bottom. Fixation of the spring with the body should be checked by turning the coil clockwise by hand within 1/4 of the circle. the spring resistance should appear. Put parts 8 in series on the axle of case 1. 9, 10, 12, 11, 9, with the hook of the long end of the spring 11 inserted into the hole of the coil. Hook the short end of the spring into the hole disk 13, put the disk on the axis and turn it clockwise to the coincidence of the 2 slots with a dog 12. Pressing on disc 13. set details 14, 8, 15. Axial clearance between disc 13 and washer 14 should be 0. 1. 0.3 mm. is provided by means of selection of washers 14. having fixed the body, take hold of the cord by hand at a distance of 40. 60 mm from the spool groove and, rotating the spool clockwise by the cord, make a 6. 7 turns, thus winding up the spring 7. having fixed the spool and the body, pull the cord completely towards the handle 3. Braking the cord and at the same time releasing the spool, allow the cord to slowly wind onto the spool. If the bobbin is not fully retracted, it is necessary to wind the spring one more turn. In a properly assembled starter pawls 12 when pulling the cord should easily slide out from under the disc 13, when you release the cord to retract.

8.13. Adjusting the reversing device. The reversing mechanism on all rotary cultivators is set at the factory. While doing this measure the stroke of the lever shaft 4 or the difference in the distance between the end of the screw 13 and the tip of the backstroke cable with the backstroke engaged and disengaged. On a new cultivator with a correctly adjusted device, the stroke of the roller should be 22.6 mm, size difference. 12 to 13 mm. If necessary, adjust the reversing device as follows. Screw the adjusting screw 13 into the handle bar over its entire length;. set the bracket 16 in the first pair of holes (from the lever mounting axis 17);. start the engine, set the minimum steady revolutions;. Perform reverse gear engagement. If the reverse gear does not engage, achieve its activation by unscrewing the adjusting screw 13. If necessary, repeat this method by successive repositioning of the bracket 16 in the 2nd and 3rd pairs of holes, with the preliminary return of the adjusting screw 13 to the initial position. Adjustment is correct if gears in the gearbox mesh when reverse gear engages and the output shaft changes direction under load. No grinding of gears, no spontaneous shifting. Note. Backstroke may not be available due to mismatch of gear teeth. In this case, stop the engine and turn the gears by slow cranking the engine by the starter, simultaneously pressing the “Stop” button. Start the engine and reverse again.

Piston Ring Gaps.

Measuring piston ring clearances is often a misunderstood and misguided part of the job of replacing them. You can allocate a minimum and maximum ring gap, which should be taken into account for the best result when installing a new set. The minimum ring gap should be considered as a must to prevent the ends from being docked while the ring expands when the motor is brought to operating temperature. Piston Ring Pattern. Ring gap recommendations differ for each thermal condition and engine type. City, utility vehicles not subjected to high temperature loads (such as drag racing or nitrous oxide engines) on average set the clearances at a factor of 0.0045 x Cylinder diameter for single-ring pistons (two-stroke engines) as well as 0.003 x DR upper ring / 0.0038 x DR lower ring for twin-ring pistons (two-stroke engines). This includes mopeds, mini bikes, scooters, road bikes, dirt bikes, ATVs and jet skis powered by two-stroke engines. For four-stroke engines the recommended clearance for the first ring is 0.004 x DC, second 0.005 x DC and liners (both) minimum 0.015 x DC. This also includes cross-country utility bikes, ATVs and snowmobiles. 2. Racing, sports equipment, usually operating under high thermal loads, requires minimum ring gaps slightly more than utilitarian equipment: Two strokes. for one ring 0.005 x DC, for two 0.0045/0.0055 x DC Four Stroke. Upper Ring 0.005 x DC, second ring 0.0055 mm x DC and a minimum of 0.015 x DC

For example: The cylinder diameter on a Yamaha Jog moped is 40 mm The standard piston on this moped has two rings, so the first ring is 400.003, which means the recommended clearance is 0.12 mm. Second ring 400.0038 which means recommended clearance 0.15 mm.

Example : Cylinder diameter on a Yamaha Tricker 74mm. Recommended top ring clearance 740.004, and second ring 740.005. What does clearance 0 mean?29 mm first, 0.37 mm second and 1.11mm wipers. Manufacturer’s stated value: 0.19-0.31 minimum/maximum for the top ring, 0.30-0.45 minimum/maximum for second ring. DC stands for Cylinder Diameter.

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Profile types. To measure the ring gap you need a set of gauges of appropriate size and the operating cylinder on which the rings were or will be installed. Using a cylinder that is not new, measurements should be taken at the lowest part of the cylinder as this part is not worn, which is what the rings are designed for. Measurement of piston ring gaps in the worn portion of the cylinder will show an increase in the gap in direct correlation to the degree of wear. The illustration below shows this. The effect of the taper of a worn cylinder on the piston ring gap is depicted. If the cylinder is excessively worn, it must be reamed. Maximum piston ring gaps are no small component of decreased compression, loss of power, and catastrophically poor oil control. This diagram shows the specifications for piston ring gaps laid out by SAE (Society of Automotive Engineers) as standards for piston ring manufacturers. It is important to remember that the manufacturer strictly adheres to these tolerances and the ring gaps are checked by the sensors with an accuracy of 0.0025 mm per DC. Any increase in cylinder diameter used in the case, anything over the designed size results in about 0.076 mm increase in ring gap for every 0.025 mm increase in DC. Manufacturers recommend a maximum of 0.076 mm of wear for every inch of DC, but not to reach 0.30 mm in any case for successful and timely replacement of piston rings. If the cylinder is worn beyond this point, re-bore the diameter to match the larger rings. Checking ring gaps can give information about approaching cylinder wear just as well as help avoid mistakes when installing the wrong rings. It is recommended that the rings be installed in the correct order and position: Do not place the rings in clearance coincident with the piston rod and piston pin bore.

Do not try to close the oil ring expander, its ends must fit loosely. Unfortunately, different manufacturers have different recommendations for setting the rings. How you install the rings is up to you.

Part of the information you may need when repairing a power tiller, see the text of the article The construction of a power tiller.

the engine malfunction

If we are talking about a gasoline engine, when searching for a fault, it is necessary to consistently check all possible causes of malfunction, namely:

thermal, clearance, piston, rings, diesel

The entry of fuel into the engine cylinder can be evidenced by the condition of the spark plug, which in any case should be checked when searching for faults in the ignition system. The candle is unscrewed from the cylinder cover, having previously disconnected the wire, and inspected. If it is dry, it means that the fuel mixture is not being fed into the cylinder. And if before it was found that the carburetor receives gasoline, then the cause of the failure to start the engine may be in the carburetor. If you have an engine problem, such as a dirty strainer, a clogged nozzle, or some other problem. Whatever it is, the carburetor needs to be removed, disassembled and cleaned, but this device is very complicated and before repairing it, you should at least look at the carburetor diagram.

A wet spark plug shows that fuel is getting into the cylinder. Sometimes the single axle tractor does not start because of an excess of fuel mixture, so if the spark plug has too much gasoline, you need to dry the cylinder by giving the engine a good “pumping” with the hand starter with the spark plug turned out. Before doing so turn off the fuel supply.

if the spark plug is clogged, it should be cleaned with gasoline and a fine sandpaper. You must also check the gap between the electrodes and if necessary adjust it according to the requirements of the manual. The spark plug gap should normally be about 0.8 mm.

After that it is necessary to check the spark. connect a wire to the spark plug, press its metal part to the cylinder head and imitate starting the engine with the starter. If the spark plug is good, there will be a spark between the electrodes. Sometimes there is a spark but it is so weak that it is not enough to ignite the fuel. If there are doubts in the strength of the spark, it is necessary to check the engine operation with a new spark plug.

Lack of spark can mean a faulty spark plug, lack of contact in the electrical circuit, a gap between the ignition coil and the ignition coil, a faulty electronic ignition coil. All of these elements should be checked. Defective spark plugs and coil should be replaced.

If a single axle tractor is equipped with an electric starter the engine may not start due to low battery, blown fuse, defective starter. Check battery charge, replace fuse, repair or replace starter.

If your power tiller engine starts but does not develop power (works intermittently, stops or does not pick up speed under load) the possible reasons of unsatisfactory work are the following malfunctions.

The air filter is clogged, causing insufficient air flow into the carburettor and creating an over-enriched fuel mixture. A correct maintenance of your power tiller requires periodic cleaning of the air filter, but very dusty work may require more frequent cleaning. Check the condition of the air filter and clean it by a suitable method depending on the filter material. The paper filter is cleaned by lightly tapping on something hard and blowing with a vacuum cleaner, the foam filter is washed in water with detergent and dried, the mesh filter is blown with a vacuum cleaner, etc.д. At the end of their working life the filters must be replaced.

Diesel pistons

At the subassembly area the pistons are matched to the liners and the piston rings are installed.

Maximum difference in weight of pistons mounted on one diesel engine shall not exceed 10 g. At big deviations in piston weight the dynamic equilibrium of high-speed diesels such as B2-300 and D6 is impaired.

Diesel pistons (Fig. 199 ) are assembled according to two criteria: weight and clearance in the block liners.

The clearance between the piston in the lower part and the liner block is permitted in the range of 0.45-0.7 mm. If the clearance is less than 0.45 mm, there is a risk of the piston sticking in the cylinder.

Pistons of diesel engines made of aluminum alloy noticeably expand when heated, so the clearance in the upper part increases to 1,20-1,50 mm.

Increase in the clearance in the skirt of over 0.7 mm causes knocking of the piston on the cylinder walls and, consequently, premature wear of the liners and piston group parts.

Pistons of nominal diameter are selected for liners of diameter 150-150.20 mm (on the mirror) (149.55-0.05 mm). Casing sizes 150.20-150.40 mm complete the pistons repair diameter (149.75-0.05 mm)- Pistons for liners 150.40-150.50 mm select the following repair diameters: 149.95-0.05 or 150.05-0.05 mm.

The diametrical clearance between the parts shall be measured with a 100 mm feeler gauge.

The piston should rotate easily around its axis when a 0.35 mm dipstick is inserted between its skirt and the liner.

When a piston set is selected, the diesel engine number and cylinder group (R. right-hand or L. left-hand) are stamped on the headstock.

Piston pins are assembled to match the piston head bores and connecting rod upper head holes. The pin must be pressed into the piston to interference of 0.028-0.001 mm. If piston head bore has wear to within tolerance, piston pin may be set to 0.02 mm clearance. The clearance of the pin in the head hole of the connecting rod should be 0.05-0.10 mm. The difference in weight of a set of piston pins must not exceed 5 g.

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When selecting a plug for the piston pin bore, the clearance must be within 0.025-0.2 mm. Selected parts and the tag with the number of the diesel engine are placed in the kit box.

Piston rings are matched to the block liners and pistons. At the overhaul of the diesel engine install new piston rings. Due to the difference in diameters of repaired liners, as well as the height of grooves in pistons, piston rings of nominal and repair dimensions are used during repair.

According to the outside diameter piston rings are made in three sizes: 150, 150.2 and 150.4 mm. In terms of height, the rings are manufactured in two sizes: 2.38 and 2.68 mm. Thus, there are six kinds of piston rings in all: rings of one nominal size and five repair sizes P1, P2, P3, etc. д. Piston rings may only be fitted in one group per diesel engine. Thus, for the liner with a diameter of 150-150.08 mm select piston rings rated size of diameter by 150 mm and the nominal or repair size of the height.

Casing with a diameter of 150.08-150.30 mm completed with rings with a diameter of 150.20 mm and a height of 2.38 or 2.08 mm.

Rings with a diameter of 150,30-150,50 mm are selected for sleeves with a diameter of 150,40 mm.

Piston rings are matched to the liner pressed into the block; clearance and joint lock determined by feeler. For rings with the cut at an angle of 45 ° this gap is 0.5-0.7 mm, and for rings with the cut at an angle of 60 ° clearance equal to 0.78-1.02 mm. If these clearances are increased, it is possible that gases may enter the crankcase.

Piston rings are then matched to the height of the grooves in the pistons. Due to the different temperature conditions, different clearances are allowed for the first and second compression rings, as well as for the liner ring.

kamco power tiller piston rings replacement

The following ring gaps in mm are set for new pistons and pistons with regrooved grooves:

What is the allowable thermal clearance in the piston ring lock?

Note that there are very high quality requirements for piston parts. This is because they are subject to inertial forces, gas forces and high temperatures. The design of the complete set, its dimensions and required dimensions, compliance with the selected material, the exact implementation of the production technology. all this is necessary for long-term service. But here we didn’t take into account the clearance in the piston rings. Let’s take a look at what it is.

What is the clearance for??

What is thermal clearance? Every car engine part that is exposed to high temperatures has the property of expanding. Many people have known this since high school. So, when the part expands, its parameters change. Thus, a change in the size of the part can lead to deterioration or damage to other parts of the mechanism that are tightly packed together.

When the thermal expansion looses thermal space, the butt joints are pressed against each other, with unpleasant consequences for both the rings and the piston.

Thermal clearance in the piston ring lock is a very important design feature that ensures the normal operation of piston rings. The main condition for normal functioning, is the possibility of its free rotation in the groove. When it gets stuck in a ditch, it will not be able to provide a seal as well as heat dissipation.

How big should it be??

The piston has two kinds of rings: compression rings (keep out burnt gases) and lube rings (remove excess oil from the cylinder walls). They are not all continuous in construction, but have a slit in the design to prevent the rim from sticking when heated. The cut also promotes elastic pressure against the walls of the cylinder. A very important role in the functioning of the rings and cylinder is the thermal space in the locks. Its permissible range is from 0.3 to 0.6 millimeters. Not following the range can lead to missing and more damage in the cylinder.

The bevel cut is much more valued. Since the pressure on the walls is more uniform due to the fact that its edges are slightly thinner.

Useful to know about the gaps in the locks. Sometimes mechanics try to make the thermal space in the locks as small as 0.2 millimeters. This not infrequently results in ring and cylinder scoring. And this is natural, because when the part heats up, the space in the lock becomes smaller (or completely absent) and it cuts into the cylinder walls.

The simplest straight cut lock has one disadvantage. its ends have high pressure on the cylinder, or rather on its walls. This leads, above all, to oil leaks and premature wear of the walls.

To summarize the above, let’s list the characteristics of piston rings and what should be the thermal clearance of piston rings:

  • Temperature regulation. This is one of the most important features, since a large mass of heat that is absorbed by the piston during combustion will be dissipated. If there is no heat dissipation, the piston melts in seconds.
  • Pressure. The main function is to compact. And full realization of this characteristic is only possible at the appropriate pressure. When pressure builds up, it affects the piston rings, which in turn press against the cylinder walls. In order for the compression to be uniform. you need a uniform distribution and proper clearance in the piston rings.
  • Reliability and oil supply. oilers. They have two oil bridges, which are responsible for the necessary amount of oil flow of 1-2 microns. If oil supply is correct. then its consumption is not high, as well as fuel consumption. The wear rule will be followed as much as possible and the service life will be increased.

As a result, I would like to wish every motorist and driver, regardless of whether he has a diesel or gasoline, to check on their own or to contact the experts in this matter. Especially when it comes to cars with high mileage and more than 5 years of constant driving.

The result of gaps

As the gap increases, and usually it is also associated with ring deterioration, more and more oil begins to penetrate into the combustion chamber and is consumed for burnout.

Theoretically the compression should decrease, but more often it increases, because of the abundance of oil on the compression rings, sealing their gaps. But it will not last long, the rings will get coked, they will get stuck and the compression will be gone for good.

thermal, clearance, piston, rings, diesel

Pistons with increased clearances can no longer work properly and start knocking. The knock of the piston can be clearly heard in the overlapping, that is in the upper position, when the lower connecting rod head changes its direction of movement and the piston passes the dead center.

The skirt moves away from one wall of the cylinder and strikes the opposite wall with force. You can not drive with such a bell, the piston can collapse, what will lead to the disaster of the whole engine.

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