7.15. Survey of radical and conrod bearings


Typical defects of bearings

Even while radical and conrod bearings are subject to replacement at capital repairs of the engine, they need to be examined carefully as they can give valuable information concerning a condition of the engine.

Failure of the bearing can happen because of a lack of lubricant, presence of dirt or other foreign debris, an overload of the engine or corrosion (see rice. Typical defects of bearings). Irrespective of the reason of failure of the bearing the cause which caused a bearing exit out of operation before the engine repeatedly gathers has to be removed.

At survey of bearings remove them and spread out in the same order as they were established on the engine. It will allow to define the corresponding neck of a bent shaft and will facilitate search of malfunctions.

Foreign debris can get to the engine in various ways. Metal particles can be in engine oil as a result of normal wear of the engine. Small particles together with engine oil can get to bearings and easily take root into soft material of the bearing. Big particles, getting to the bearing, will scratch the bearing or a neck of a bent shaft. The best prevention of failure of the bearing for this reason, carefully clear all internal surfaces of the engine and you keep them clean at assembly of the engine. Also frequent and regular replacement of oil with the filter is recommended.

Insufficient lubricant of necks of a bent shaft can be caused by many different reasons, such as high temperature of oil, an overload of the engine and leak of oil.

The driving manner the car also exerts impact on durability of the bearing. Completely open butterfly valve at low turns of the engine creates high load of bearings and expression from a zone of contact of an oil film. These loadings lead to emergence of cracks in a working part of the bearing that weakens the bearing and can lead to a separation of an antifrictional layer from a steel basis.

The movement on short distances leads to corrosion of bearings as a result the engine does not come to the stabilized working temperature at which water vapor and corrosion gases are removed. These couples and gases, being condensed in engine oil, form acid and a deposit. Acid together with engine oil gets to bearings and corrosion of bearings begins.

The wrong selection of bearings at assembly of the engine also leads to failure of bearings. The bearings installed with a preliminary tightness leave an insufficient working gap of the bearing therefore there is no butter layer for lubricant.

Bolts of fastening of covers of radical bearings

Measurement of length of a bolt of fastening of a cover of the radical bearing

On 6-cylinder petrol DOHC engines it is necessary to measure length of bolts of fastening of covers of radical bearings. On other engines it is recommended to use new bolts for fastening of covers of radical bearings.

PERFORMANCE ORDER
1. Measure length of each bolt from the head basis until the end of a carving part of a bolt (see rice. Measurement of length of a bolt of fastening of a cover of the radical bearing). If length at least of one bolt exceeds admissible limits, it is necessary to replace all bolts in a set.

Bolts of fastening of covers of conrod bearings

Place of measurement of the minimum diameter of a bolt of fastening of a cover of the conrod bearing of the 4-cylinder petrol engine

PERFORMANCE ORDER
1. Measure length of bolts of fastening of covers of conrod bearings. However at assembly of the engine it is desirable to replace bolts with new always.
2. Vypressuyte bolts from rods.
3. On 4-cylinder petrol engines measure diameter of a bolt in the narrowest part (see rice. Place of measurement of the minimum diameter of a bolt of fastening of a cover of the conrod bearing of the 4-cylinder petrol engine). If diameter of a bolt is less than admissible, replace bolts in a set.
4. On other engines measure bolt length from the head basis until the end of a carving part. If length of a bolt exceeds admissible limits, bolts need to be replaced in a set.