Developments in cylinder head bolts can sometimes cause confusion and problems after assembly. In this blog, we discuss the different types of bolts and give tips on how best to install them including a step-by-step plan.

Cylinder head bolts are available in various sizes and brands, but the correct installation of these bolts is often the success behind a well-functioning engine. We point out to our customers that cylinder head bolts, also known as 'torque to yield' bolts or angular tightening bolts, can only be used once. However, not all wrenchers follow this rule.

Back in the 1980s, there was a development in head bolts that no longer needed to be torqued, meaning that once the engine was warm, the bolts did not need to be torqued again. Today, engines have increasing requirements and demand a good fit and perfect seal. Thus, cylinder head bolts are very important as they are the connector in the engine block.

In this blog, we discuss various types of cylinder head bolts and installation tips from our specialists to make your overhaul or repair with these bolts perfect.

Angular tightening bolts or not?

Normal head bolts (torque tightening bolts)

These head bolts can only be used in elastic zones. When tightening, tension occurs, head friction and thread friction, so the pressure is not equal across the entire seal. In addition, the corresponding gaskets are often thinner and of softer material.

The bolts should be retightened after the engine warms up to avoid problems, however, this cannot prevent the problem with bolt tension. Torque tightening bolts, in good condition, can be reused again.

Angular tightening bolts

Angular tightening bolts do not require tightening and can be found in most common engines today. These bolts easily adapt to the manufacturer's technical specifications because they are designed to be stretched plastically.

When fitted, a small torque (Kpm) is applied gradually to all bolts and the tension is therefore the same over the entire seal.

Because the angular tightening bolts are used in the elastic area, they are permanently deformed after disassembly. When reusing these bolts, the same and correct tightening torque cannot be achieved and the bolts may even break. Therefore, these bolts must absolutely not be reused.

Points of attention 

New bolts

Our specialists point out never to reuse angular tightening bolts. Wilmink Engine Parts sells a wide range of head bolts from various brands, such as Elring and Victor Reinz, and offers great availability. Our private label also has a range of head bolts with an excellent price-quality ratio. Like head bolts, reusing a head gasket is not possible.

Manufacturer’s instructions

For cylinder head bolts to work properly, it is very important to follow the instructions and specifications for tightening and fitting cylinder head bolts exactly. If this is not followed, larger sealing problems such as leakage may occur. Over-tightening of bolts can also lead to damage and incorrect sealing.

Tightening sequence

When fitting cylinder head bolts with angle tensioning, it is important to fit the bolts in a specific order prescribed by the manufacturer. Failure to follow this and the tightening specifications may cause unwanted stress, deformation, premature head gasket failure, leakage or cracking in the cylinder head or cylinder block.

Mounting material

When tightening normal head bolts, a torque spanner is applicable, but for angular tightening bolts, an angular rotation gauge should be used.

Performance

Various normal head bolts are also available for performance. For instance, the brand ARP has a large range, including their well-known 'head-studs, which feature a loose threaded end with nut. The brand uses a special type of metal that is very strong in the elastic area. For advice or more information, you can also contact our performance specialists.

Tightening the cylinder head bolt

Below, supplier Victor Reinz and our specialists provide a handy step-by-step guide for installing cylinder head bolts. Also, always read the manufacturer's instructions before tightening cylinder head bolts.

Installation steps for cylinder head bolts

1. Thoroughly clean the surface of the cylinder head and adjacent parts. Make sure gasket and dirt residues have been removed to avoid problems;
   
2. Use a ruler or row to check the flatness of the surface in length and width;
   
3. Ensure that grooves, scratches, deformations or other uneven areas have been eliminated in a specialised workshop.
   
4. Check the dimensions of the engine block and cylinder head and the thickness of the gasket and whether they match the manufacturer's specifications.
   
5. Remove oil, water or other contamination in the threads of the bolt holes with e.g. compressed air.
   
6. Place the head gasket on the engine block without sealants, grease or oil.
   (Read our blog on installing cylinder head gaskets for more information).
   
7. Then carefully install the cylinder head without damaging the gasket.
   
8. Always use a set of new head bolts.
   
9. Using an oiled cloth, lubricate the threads of the bolt and the bottom of the head with a small amount of oil by turning it around.
   
10. If a washer is used by the manufacturer, it should also be lightly lubricated on the sides.
    
11. Before tightening the bolts, always read the manufacturer's instructions. This is because they may vary from manufacturer to manufacturer, but also from engine type to engine type.
    
12. Use only approved and recommended antifreeze and corrosion inhibitors.
    

If this step-by-step plan is followed, bolts will be fitted correctly. You will find a wide range of cylinder head bolts through our webshop. Do you have specific questions about your application or project? Then contact our specialists and they will be happy to help you.