Valves and valve accessories

Temperature-resistant precision

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Valves are primarily used in four-stroke engines, to control the charge exchange process. The valve head seals off the inlet or outlet duct of the closed valve from the valve seat in the cylinder head. Valves feature a diverse range of additional equipment, depending on the engine load and type of use, such as hardening and armouring for the valve heads and valve stem faces. This ensures reliable engine running and durability, even under extreme conditions. 

Motorservice has a constantly growing product range with over 1,100 valves designed for more than 8,000 applications.


Valve guides

The valve guide has the task of absorbing the lateral forces acting on the valve stem. The valve guide centres the valve on the valve seat insert, and conveys some of the heat from the valve head through the valve stem to the cylinder head. 

Motorservice has a wide range of over 800 valve guide types for more than 3,500 applications.


Valve cotters

Valve cotters are employed as retaining and locking components. They connect the valve-spring retainer to the valve by friction locking, and thus keep the valvespring preloaded. Valve cotters are wear parts, and must always be replaced at the same time as valves. Motorservice has the right cotters in its range for all common valve stem faces.


Valve seat inserts

Together with the valves, valve seat inserts seal off the combustion chamber of the cylinder head. The valve seat inserts are made from grey cast iron or sintered metal and prevent the valve from knocking/burying into the cylinder head. They also convey the heat from the valve. 

Valve seat inserts are not selected on the basis of engine type, but by their dimensions. With over 400 different dimensions available, Motorservice offers virtually unlimited use in all conventional engines.


Valve control elements

In order to ensure valve train reconditioning is carried out flawlessly, the control elements such as rocker arms, tappets or hydraulic tappets or valve push rods often also need to be replaced. All valve control elements are available separately from Motorservice.


Further information

Valve guides are made of materials with good gliding and thermal conductivity properties. Grey cast iron and brass materials with selected alloy components have been particularly proven.


Grey cast iron with pearlitic structure. This material is characterised by good wear resistance and is suited to guides under normal strains.


Grey cast iron with pearlitic basic structure and increased phosphorus proportion. The reticular formation of the phosphor provides higher wear resistance and better emergency run properties. For usage in engines under medium strain.


Grey cast iron with pearlitic basic structure and increased phosphorus proportion as well as increased chromium content. For usage in highly supercharged engines.


CuZnAl alloy. This material is characterised by good wear resistance with high sliding properties. The guide is suited to usage in engines under normal and medium strain.

D = external diameter
d1 = flange diameter
d = bore diameter
L = total length


Technical background

The valve guide in the cylinder head is kept in its position by a press fit. The valve guide is radially constricted when pressed into the housing bore of the cylinder head. The housing bore however is expanded. The extent of this deformation depends on the one hand on the ratio of housing bore diameter and external diameter of the guide and on the other hand on the rigidity of the two components. If there are strong diff erences in the rigidity of the housing wall, the radial distortion can differ quite significantly along its length.


When installing and removing the valve guides, ensure correct warming up of the cylinder head (specified by engine manufacturer). Use suitable mounting mandrels for installation and deinstallation. An additional cooling off of the valve guides facilitates assembly significantly.

After assembly

Before installing a valve in the valve guide, it is measured whether the borehole of the valve guide is still cylindrical, i.e. it has the required diameter in all places. Motorservice generally recommends correcting the diameter and shape of the borehole by reaming it with a reamer.


Standard values for the clearance between valve guide and valve stem:

Stem diameter Clearance: Intake valves Clearance: Exhaust valves
6 to 7 mm 10 - 40 μm 25 - 55 μm
8 to 9 mm 20 - 50 μm 35 - 65 μm
10 to 12 mm 40 - 70 μm 55 - 85 μm

In the most recent engine generations of renowned car manufacturers, valve seat inserts made of sintered material (powder metallurgical procedure) are used. The increasingly high, thermal strain of the seat insert in the combustion chamber can hardly be met anymore by materials from conventional casting processes. For this reason, Motorservice offers sintered valve seat inserts amongst others from two different material combinations, which covers the entire application range of future engines.

Sintered metal seat inserts

HM series semi finished

(high machinability)
This material combination is characterised by its excellent machinability. The sintered HM valve seat insert has a composition of tungsten carbide precisely adapted to the strain, embedded in alloy steel. This way, so far impossible combinations of material properties like high hardness and very good machinability can be combined. Furthermore, the HM series has good wear resistance and good heat resistance. The HM series was developed for naturally aspirated and turbocharged engines from the bottom to top performance segment.

HT series semi finished

(high temperature resistance)
This material combination is characterised by its high wear resistance, which also withstands extremely high temperatures. The sintered HT valve seat insert corresponds to ceramic tool steel made of tungsten carbide, with respectively adapted, high temperature resistant additives embedded into its matrix. Due to the large amounts of permanently embedded lubricants, these rings are especially suitable for high performance, highly charged, highly strained Otto and diesel engines. Despite the high strain on these engines, "micro-welding" of the valve seat insert and the valve is prevented. The field of application of the HT valve seat insert includes especially highly strained engines.This material was developed fro dry fuels like CNG, LPG and Flex Fuel.

HT+ series semi finished

(high temperature and high wear resistance - very high temperature and wear resistance)
This material combination is characterized by a very high wear resistance even at extremely high temperatures. The material composition of the HT+ valve seat inserts shows an average strain of the cutting material and simplified machining properties despite increased wear resistance. The combination of ceramic tool steel made of tungsten carbide and the large amounts of permanently embedded lubricants is especially suited for dry combustion occurring in gas utilizations such as LPG, CNG, propane gas and Flex Fuel. Another application for high performance Otto and diesel engines, for example, is also possible. In addition, the HT+ valve seat insert shows excellent thermal conductivity properties. Despite the high strain on these engines, "micro-welding" of the valve seat insert and the valve is prevented.

Cast iron seat inserts

G1 series finished

(highly heat resistant)
The G1 series consists of a highly heat resistant grey cast iron alloy with the additives chromium and molybdenum. The G1 series has been developed for a large application area and is mainly used for utility vehicles. This valve seat insert has a composition of annealed martensite precisely adapted to the strain, with a distinct carbide network. This valve seat insert thus has good wear resistance and is highly heat resistant.

G2 series finished

(highly wear resistant)
The G2 series consists of a highly wear resistant grey cast iron alloy with a high proportion of the additives molybdenum and vanadium. This material combination is characterised by its high wear resistance, which also withstands very high temperatures. It is a high-alloy material with a distinctive, closed network of composite or special carbides respectively in a martensitic matrix and evenly distributed proportions of solid lubricant.

  High Machinability High Temperature Resistance High Temperature Resistance Highly Wear Resistance High Temperature
and High Wear
Type of fuel/ 
Petrol (unleaded),
Petrol (unleaded),
CNG, LPG, flex fuel, petrol (unleaded), Diesel Otto (unleaded), diesel, CNG, LPG, propane gas, Flex Fuel
Materials cylinder head Aluminium, 
grey cast iron
grey cast iron
grey cast iron
grey cast iron
grey cast iron
Engines Low performance Otto and diesel engines with low to normal strain High performance, highly charged, highly strained Otto and diesel engines Naturally aspirated engines, turbocharged engines Highly strained engines, performance enhanced engines, all above mentioned gas engines Gas utilization such as LPG, CNG, propane gas, Flex Fuel; high performance Otto and diesel engines


Extreme operating conditions as well as high strains of the respective engine must be taken into consideration and are the responsibility of the engine repairer.

The selection of the specification of engine parts must be carefully checked by the engine repairer.

Intake Valve

  • Mono-metallic valve
  • Mono-metallic valve with hardened seat
  • Mono-metallic valve with valve seat armouring 
  • Bimetallic valve
  • Bimetallic valve with seat armouring

Exhaust Valve 

  • Mono-metallic valve 
  • Mono-metallic valve with valve seat armouring
  • Bimetallic valve 
  • Bimetallic valve with seat armouring

Mono-Metallic Valve

Mono-metallic valves are only made from one material. For this, one material is chosen that is suited to both requirement profiles, namely high heat resistance and good sliding properties.

Bimetallic valve

Bimetallic valves enable material combination of a highly heat resistant agent (headpiece) with a skirt material which can be hardened on the one hand (skirt end) and also has good sliding properties for valve guidance. The materials are combined through friction welding.

Hollow valves

Hollow outlet valves are mainly used for lowering the temperature in the particularly vulnerable fillet area and are additionally filled with sodium. A desired and positive side effect is a reduction in weight. Hollow, unfilled inlet valves are only used for this reason of mass reduction. In order to achieve a temperature decrease for valves, the skirt that is drilled hollow is filled with sodium by approx. 60 % of the volume and closed by a friction welding procedure. Sodium melts at 97.5 °C, has a density of 0.97 g/cm³ and is a very good heat conductor. During engine operation the sodium becomes liquid and is moved backwards and forwards in the skirt by the inertial forces. This is also called “shaker effect” in this context. In this process, the sodium transports a proportion of the heat generated during combustion from the valve head to the skirt area. Here, the heat is dissipated via the valve guide. Temperatures on the valve head can thus be decreased between 80° C and 150° C.


Handling sodium-filled hollow valves

The machining and cutting open of sodium filled hollow valves requires respective care. It must be ensured that the cavity is not opened my mistake, as sodium reacts strongly with water or drilling and grinding emulsion. When sodium reacts with water, hydrogen and caustic soda is produced.

Examination and disposal

Small quantities of hollow valves can be scrapped in the usual way. No special regulations are to be observed. If sodium-filled valves are to be examined or larger quantities are to be disposed of, the cavity is to be opened either by drilling holes in two different places without using coolant, or through splitting the valve open in the middle. The valves that are prepared in this way are individually thrown into a bucket with water to render the sodium harmless. Once the reaction has run its course, the valves can be scrapped as normal. Disposal of the remaining caustic soda occurs according to the respective local regulations.

Safety instructions

Due to the sometimes strong reaction and release of hydrogen during reaction of sodium with water, the neutralization of the valves should only occur in well ventilated rooms or outside. Contact with skin or eyes must be avoided. For this reason, sodium must only be handled by respectively trained personnel wearing corresponding protective clothing (gloves, safety goggles etc.). The usual safety provisions when dealing with aggressive and caustic materials and explosive gases are to be observed.

Seat armouring and hardened seats

Special outlet valves are highly strained thermally as well as with regard to wear. For this reason, these valve seats are often armoured. Inlet valves for highly strained engines are mostly hardened inductively. The impact and the wear of the valve seat inserts are avoided with these measures.


The valve stem face

The valve stem face is heavily used by the valve actuation (tilting lever, finger type rocker arm, tappet). To avoid wear and tear here, valve stem faces are hardened from curable steel. Valve stem faces from noncurable steel get stellite armouring or have a hardened platelet welded on.

1 Total length = L
2 Total valve head thickness
3 Seat height
4 Height of valve seat face
5 Seat armouring (optional)
6 Valve head
7 Skirt diameter = d
8 Valve stem
9 Groove area
10 End face of stem (hardened)
11 Grinding length
12 Throat
13 Valve seat angle = α
14 Head surface
15 Head diameter = D
16 Calotte


The service life of the valves and thus effectiveness of the engine strongly depends on correct assembly. During assembly, always observe the fitting guidelines and adjustment values of the engine manufacturers.

Careful Handling

Valves are to be handled with care. Valves must neither be treated with abrasive paper nor marked with centre punch or punch numbers on the base.


A suitable tool must be used for installing the valve into the cylinder head. When installing new valves, new cotters must also be used. The internal cone of the valve-spring retainer is to be checked for wear and tear and damage. The valve-spring tension is to be checked for the limit values of the engine manufacturer.


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Room 302, Building E

201106 Shanghai


Phone: +86 (0)21 3405 6800



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