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Main bearing cap bolts are critical fasteners used to secure the main bearing caps to ensure proper operation of the crankshaft.

They keep the engine main-bearing, or the “cover” holding the crankshaft, secure.

By using main bearing cap bolts, different components of the bottom part of the engine are tightened. This type of fastener constitutes about half of the main bearings (main bearing caps, half-blocks, complete main bearings).

Mechanical strength

Use of more superior materials

Surface coating

Very stable friction

Strength class

10.9 and 12.9


Main bearing cap bolts keep the engine main-bearing, or the “cover” holding the crankshaft, secure.


Brugola OEB main bearing cap bolts must be tightened twice, so the double tightening strategy is perfectly integrated into their design.

#Brugola OEB

The Brugola OEB main bearing cap bolts are the result of many years of experience and the utmost attention paid to the unique needs of every customer.
Every fastener we produce comes up to the Total Quality and Zero Defect principles.
Brugola OEB main bearing cap bolts originate from a comprehensive consultancy service.

The Brugola OEB main bearing cap bolts are born from an attentive consultancy service.

The main characteristics of main bearing cap bolts

Depending on the architecture of the engine and the dimensions contemplated, the main bearing cap bolts may be available in different solutions in terms of the shape of the head but rarely have a washer.
They usually have a threading that may vary depending on the applications.
Compared to the cylinder head bolts, they are usually shorter and smaller. Located in the cold part of the engine, they are not subject to the considerable thermal stresses that the cylinder head bolts instead have to sustain.
Despite this, the main bearing cap bolts fall into the category of critical bolts since they have a special characteristic: they have to be tightened not once, but twice.

The double tightening strategy (when the engine block is being machined and during the installation of the crankshaft) must be perfectly integrated into their design. 
The purpose of the double tightening of the main bearing cap bolts is to guarantee a more constant distribution of the axial load.
Every time that the bolts are tightened, they slightly become longer than the initial measurement and never return as before. Considering the double tightness, the main bearing cap bolt sizing is crucial.
It is necessary to carefully assess how they behave during both the first tightening and the second, bearing in mind that at that point they will already be slightly stretched compared to the beginning.
The physiological lengthening of the bolts must comply with the dimensions contemplated and must in no way jeopardize their proper functioning.

Technical data

Main bearing cap bolts work in a plastic field and usually are tightened to torque + angle.
Moreover, to achieve their task they must have very stable friction and a restricted strength class.
They are usually made in strength class 10.9 and 12.9; more rarely in class 8.8.
Although usually made of steel, changes in the choice of material are possible depending on the strength class.
For class 12.9, for example, the use of superior materials, and lower quantities, is contemplated.
Furthermore, today it is not infrequent to design main bearing cap bolts having customized strength classes.

 Every customer has its application requirements. Thanks to the experience, knowledge of the sector, and the upstream consulting service that we provide, we can make 100% customized and top-quality main-bearing cap bolts, saving the customer time and work.

Why choose
Brugola OEB main bearing cap bolts

Brugola OEB main bearing cap bolts originate from a comprehensive consultancy service with the customer.
Our expertise allows us to design fully customized products suitable for specific applications.

The process is simple:

  1. Starting from the specifications, we conduct a study to establish the characteristics of the main bearing cap bolts necessary for the engine.
  2. If the project is accepted, we create the prototype and sampling for the customer.
  3. Once the necessary tests on the sampling are performed, mass production can start.

Depending on the application requirements, we use different coatings for the main bearing cap bolts. They are usually greased and phosphatized, but we evaluate which products to use case by case, and how to implement the coating to achieve the best result required.

Thanks to the coating, precise characteristics are obtained, such as corrosion resistance and the coefficient of friction, which may vary case by case.

By always aiming at Total Quality and Zero Defects, we select 100% of the bolts we produce.

Like for all of our bolts, we perform tests to check the behavior of the main bearing cap bolts.

Considering the double tightening, an exhaustive analysis of how they behave is of vital importance. This is attainable thanks to a software program developed in-house by Brugola OEB, which performs real simulations in a given application and therefore obtains concrete and reliable data.