1. Connecting rod bolt bears great alternating impact load during engine operation. It is an important part of small mixer engine. It is made of high-quality alloy steel through quenching and tempering treatment and precision machining. It has high strength and impact toughness. It can not be replaced by ordinary bolts or low-quality parts. If the bolt material, heat treatment and machining accuracy do not meet the technical requirements, it will lead to insufficient mechanical strength and deformation and fracture accidents.
2. Check carefully before assembly. If the bolt is found to be scratched, buckled, cracked, dented, necked or cracked (inspected by oil immersion method or magnetic flaw detection), or the bolt and nut fit is loose, or the bolt cannot fit closely with the bolt hole, or the bolt length is 2% longer than the new standard bolt length by comparison method, it shall be replaced.
3. Check the fit clearance between connecting rod bearing and connecting rod journal. If the clearance is too large, it is easy to cause the fracture accident of connecting rod bolt. At this time, the connecting rod bearing shall be replaced with a new one or enlarged one, and shall be selected or scraped.
4. Check the fit between the connecting rod bolt or nut and the shoulder bearing surface of the connecting rod end cap. If there is burr or unevenness, it shall be polished, otherwise the connecting rod bolt is easy to break under the action of additional torque.
5. During assembly, the connecting rod bolts shall be tightened to the specified torque with a torque wrench in alternating times (generally 3-4 times). If the tightening button torque is insufficient, there is a gap on the connecting rod joint surface during operation, and the bolt is easy to be pulled or cut off when subjected to impact force; If it is tightened too tightly, the bolt will stretch and deform, the strength will be reduced, and it is easy to break and damage after being stressed. The specified torque of connecting rod bolts of various engines is different. In the absence of technical data, the safety torque range can be estimated according to the bolt diameter. For example, the safety torque of Mu connecting rod bolt is 60-80nm; M12 bolt, with torque of 80-100nm; M14 bolt with torque of 100-120nmo.
6. If it is found that the torque of a bolt on the same connecting rod exceeds the specified value too much during bolt driving, loosen all the two connecting rod bolts on the connecting rod and tighten them alternately in several times, and make the tightness of the two bolts consistent. It is not allowed to only loosen the over tightened bolt, otherwise the bolt will produce additional bending stress and be prone to fatigue fracture.
7. During tightening the connecting rod bolts, try to rotate the crankshaft to check whether it rotates freely. If it is difficult for the crankshaft to rotate after the bolts are tightened, find out the reason. Do not loosen the connecting rod bolts to rotate the crankshaft.
8. In order to prevent the connecting rod bolts or nuts of small mixer from loosening during operation, new locking devices such as cotter pin, iron wire or locking plate shall be used for locking; If the notch on the nut is aligned with the end of the hole on the bolt, in principle, it can only be screwed inward for alignment; Used cotter pins, wires or locking tabs shall not be reused.
9. During use, the tightening and lying of connecting rod bolts shall be checked regularly. When it is found that the connecting rod bolts are loosened, the cause shall be found, the bolts shall be checked for damage, and then the power wrench shall be used to screw them to the specified value according to the specified button torque.
10. During operation, when the connecting rod bolt is loosened or stretched, before it is completely loosened and broken, there will be a large knocking sound and vibration due to the looseness of the connecting rod bearing. At this time, stop immediately to avoid greater accidents.
11. When a connecting rod bolt is buckled, cracked or broken, the two connecting rod bolts on the same connecting rod shall be replaced in pairs, and the old and new shall not be used together.
12. When the engine burns the Bush for many times or once, the connecting rod bolt material is subject to high-temperature annealing, the metallographic structure changes, the mechanical strength decreases and the bearing capacity decreases, so it should be replaced.
13. In case of flying, cylinder biting or rollover accidents of the engine, the careful inspection of the connecting rod bolts must not be ignored. When the bolts are found to be deformed and cracked, they should be replaced in time.
14. In order to prevent fatigue fracture and damage of connecting rod bolts, even if the bolt surface is obviously damaged after 6000-7000 hours of operation of small mixer engine, it shall be replaced.