Introduction.

As we operate on the market for internal combustion engine (ICE) parts machining services, we deal with a certain set of questions on cylinder head (CH) machining from our Customers. We are pleased to describe the main operations for CH recovery machining.
ICE technical and economic features, i. e. power, torque, fuel and oil consumption etc., mainly depend on the efficiency of processes provided by correct operation of cylinder head components.
Cylinder head in the ICE has several important functions.

CH is an ICE component that takes part in:

• ICE cooling system;
• ICE gas distribution system where such elements of the valve train as the“bushing-seat-valve” system on the inlet and on the outlet camshaft (or camshafts) with clearance adjustment components and mechanisms; nozzles, ignition plugs and other non-components are mechanically placed.
  

This complex system of ICE components mechanisms requires careful inspection and measuring before defining the repair and machining methods.
Before inspection, all attachable equipment shall be removed from the ICE, the ICE shall be washed, cleaned from carbon deposits, any deposits in combustion chambers, collector channels, water jacket space, oil channels, and shall be inspected for fractions, chips, or cavitation air pockets.
The most common cylinder head defects are:

• poor tightness of water jacket space, nozzle bonnets and expansion plugs;
• valve bushing wear;
• valve seat wear;
• valve disc and valve stem faces wear;
• valve spring flexibility loss;
• cracks in valve seat bridges, fractures between valve seats and injection nozzle holes, cracks in ignition plug holes, or cavitation damage of combustion chamber planes;

Process Operations Summary

We present to you the ICE repair and machining standard operations procedure as applicable throughout our «ProMotor»shop network.
The Customer may order process operations from the list of works that we provide. We provide operations as follows:

CH measuring;

CH cooling system space leakage test;

CH valve guides replacement;

valve guides repair by installation of a bronze bush into the valve guide inside diameter using the K-Line technology (USA);

valve seat replacement on the inlet and outlet sides;

machining of CH plane for cylinder block gasket and planes for inlet and outlet collectors;

grinding of valve disc working faces;

shaping of valve seat working faces.

Upon application to any of our shops, according to our Internal Combustion Engine (ICE) Machining and Repair Acceptance and Performance Regulations the Customer ICE repairman shall perform CH dimensioning and provide parameters according to which the machining shall be performed. If the Customer does not have the measuring instruments, we may offer measuring according to the parameters accepted at our facility, so that the Customer selects the proper CH machining procedure. If the Customer does not have the CH parameters, our specialists may provide references available at our facility or average parameters accepted and recommended by the world's leading ICE manufacturers.

Summary of the main CH machining operations

CH measuring (according to our parameters).
The specialist visually inspects the component, registers any damages, air pockets, cracks, or chips.

Step 1: measuring of valve guides (v.g.) on the inlet side and measuring of valve guides on the outlet side. Measuring of the inside diameter is performed using a bore gauge. Diameter and surface geometry perturbation is measured accurate to within 0.01 mm.
The installation height, the v.g. height above the plane are measured

The measuring results are registered in the Works Performed Sheet.

According to the measuring results the valve guide repair procedure is selected.

Step 2: measuring of valves on the inlet side and measuring of valves on the outlet side. The measuring is performed for each valve bank alone.
The following parameters are measured:

• overall valve length (height gauge readable to 0.01 mm);
• valve disc diameter (beam caliper readable to 0.05 mm);
• valve disc parallel height (beam caliper readable to 0.05 mm);
• valve disc working face angle (special gauge or universal protractor UN-127);
• valve stem diameter (micrometer 0-25 mm readable to 0.01 mm);
• wedge lock groove parameters (beam caliper readable to 0.05 mm);
• measuring of radial runout of the valve disc working face against radial runout of the valve stem (special instrument PBK007, dial gauge ICh-10 readable to 0.01 mm)

Step 3: measuring of valve stem overhang value of the valve bank on the inlet and outlet side This parameter is very important for CH with clearance adjustment by hydraulic compensators (hydraulic compensator working height out of tolerance) and adjustment cups with the measuring bottom thickness or with measuring orifices (with manufacturer's commercial set of package heights).

Step 4: Measuring of valve disk sticking value of the valve bank on the inlet and outlet side. This parameter is generally measured for diesel ICE CH, but it can also be measured for petrol ICE.

Valve seat wear is defined by measuring parameters according to Item 3 and 4. Valve seat ring replacement decision is taken according to the results.

Step 5: CH height value measuring.
The CH height value is of critical importance for ICE. This is due to raised nozzles (diesel ICE CH) as well as to the limited size of the combustion chamber which is formed mostly by means of the piston structure, gasket width and camera shape inside the CH; it is also important to preserve the centre-to-centre valve train gear alignment.

The measuring is important for petrol ICE. CH height change (reduction) leads to changes in the combustion chamber space, parameter affecting the camshaft drive chain tensioning mechanism and other design features. In CH with non-parallel plane structure the limitation usually affects the combustion chamber space.

Step 6: CH plane deformation value measuring

This parameter has a significant impact on ICE performance and correct compression of the gasket between CH and CB.
In CH on ICE of heavy vehicles, the plane for fastening of inlet and, in particular, outlet collectors must be inspected for wear and deformation. In case of poor tightness of the collector to CH connection contaminated air is drawn inside the working ICE. When air impurities get on valve stems, the valve stem delivers them onto the guide inside diameter surface. This significantly reduces the v.g. service life, especially on the outlet side (it is usually only 15,000-30,000 km), after CH repair.
Following measuring, CH plane machining procedures are discussed with the Customer.

CH cooling system space leakage test.

CH cooling space defects (water jacket space) are divided into two subgroups.

• Subgroup 1 — visible defects. These are cracks, cavitation air pockets, metal porosity, mechanical defects that can be visually detected.
• Subgroup 2 — invisible defects. These are defects located inside the CH cooling space that were formed under valve seats, within valve guide installation points, within collector spaces on the inlet and on the outlet sides, and in other CH areas.

Step 1:
CH water jacket space shall be put in order by an engine mechanic or the Customer. (We don't perform such operations!) This means that the water jacket space shall be cleaned mechanically and chemically of deposits developed during continuous ICE service. All damper plugs must be released, all spaces cleaned and inspected, and then all damper plugs must be reinstalled. Engine mechanic (or the Customer) shall perform this work. This is the first step of CH body inspection

Step 2:
CH cooling system space test
CH cooling system space test is performed using the following units: Piccinotti PMD PTM, Serdi SPT 1501 or UMD 1200 ProMotor, under simulated actual conditions during CH operation on ICE, as follows:

• CH test fluid temperature — 70 ºС;
• compressed air pressure — 2–4 atm abs. (applied to space). These are technical CH testing conditions for test bath.

Technical capabilities of these units allow raising the compressed air pressure up to 10 atm abs.; however, such pressure induced load can damage the CH, e. g. damage the damper plugs, nozzle bonnets and other components. Such pressure rise is not safe and is performed only at the insistence of the Customer using increased labour safety protective measures.
Technical capabilities allow to increase the test bath water solution temperature up to 90 ºС. This, however, is not done in practice for water jacket space testing safety reasons, and it is forbidden to apply such conditions! Water solution with the temperature above 70 ºС is a damage effect that can cause serious burns to personnel.
These equipment specifications are used to detect faulty sealing of the water jacket in most cases, but not in 100 % cases.
We detect only those sealing defects that manifest themselves in these test conditions visually by compressed air bubbles leaking out of the defect area.
From practical experience we know that it is difficult, for example, to detect sealing defects in CH with chemical sealing additives used in the cooling system (these function when the ICE is heated; in other words, if the CH has faulty sealing when cooled, this cannot be detected when the CH is heated). There are other reasons why defects cannot be detected, such as carbon deposits that were not removed properly, or strong requests of the Customer to perform the CH leakage test with assembled valves, etc. For this reason the CH water jacket space leakage test results are about 90-95 % accurate

If the water jacket space test results are positive, i. e. the water jacket cooling space sealing is defect-free at the time of testing under described conditions (t = 70 ºС, compressed air pressure = 2–4 atm abs.), further CH machining operations can be performed. Otherwise CH body defect areas shall be repaired or the CH shall be replaced.

CH valve guide replacement

Valve guides (v.g.) wear over the inside diameter during CH operation. As a rule, the inside diameter wears off and the geometry of the inside surface forming the inside guide diameter is perturbed. This usually occurs in the axis transverse to the camshaft rotation axis. Both defects influence the ICE operation. For example: excess unspecified oil consumption and related smokiness, excess noise during CH operation, formation of tar deposits between the valve disc and the valve stem bottom on the inlet side and carbon deposits on the outlet side, which narrows the geometrical sections of collector channels, the engine loses power etc.

We offer two methods of handling valve guides wear:

Method 1 — replace worn out valve guides (both according to the diameter and to geometrical parameters) with new ones.
Benefits of this repair method:

• A guide made of manufacturer's material with warranted machining quality (size, geometry, surface roughness) is installed.

Drawbacks of this repair method. As the end result service consumer, you should be prepared for the following:

• when removing worn out valve guides (especially in aluminium CH), tears and other defects of the valve guide well usually occur, which requires additional machining or special anaerobic sealant application to eliminate negative effects after the removal;
• v.g. axis and seat assembly axis bend which leads to excess metal removal from the seat during valve seat angle shaping;
• If valve guides are moulded together with the CH body, v.g. removal is impossible. In this case a new valve bank with increased valve stem oversize diameter and v.g. inside diameter oversize machining or complex mechanical boring of replacement v.g. wells must be ordered. As a result, the repair of such CH structure leads to delayed repair and/or installation of replacement v.g.;
  

There is an alternative v.g. repair operation.

V.g. repair using K-Line technology (USA).

Method 2 — repair of worn out inside diameter of the valve guide by installation of a special bronze bush into the prepared guide inside diameter using the K-Line technology (USA).

Benefits of this guide repair method:

• the original valve guides are not removed from the CH body, subsequently the above-mentioned drawbacks are technologically eliminated.
• the bush installed inside the guide is made of special bronze and has rolled concentric grooves inside and a special section for motor oil containment, and the material offers a low friction coefficient and good heat transmission.
• v.g. service life increases by up to 30 % under correct ICE operation modes;
• valve gear operation noise is reduced.
• repeat v.g. repair is simplified. The worn-out bush is replaced with a new one preserving the v.g. inside diameter size and geometry.
• low repair cost.

Drawbacks of this method:

• excess wear of the valve guide inside diameter of over 0.40 mm.
• physical fatigue of the guide material around the sealing gland housing. Crack formation is possible which requires replacement with a new valve guide. We also recommend to install a bronze bush into the new v.g. in order to guarantee similar service life for all valve guides.
  

K-Line technology summary.

The valve guide repair technology developed by K-Line (USA) involves five process steps:

Preparation for the operation:

• We select v.g. repair tool set. The valve stem diameter is the tool selection criterion.
• We select the base aligning bar according to the valve seat diameter.

Step 1:
Valve guide bore counterboring
The valve guide inside diameter is increased to size with a special counterboring tool (supplied), to match the mounting bronze bush.

The inside dimension machining result is checked with a plug go/no-go measuring instrument
«Проход»/«Не проход». Измерительный инструмент входит в набор.

Step 2: Bronze bush installation Install the adapter from the set into a pneumatic hammer with 3,000–4,500 double strikes per minute. The bronze bush of a required size (the size is measured taking into account the expansion gap, with control of the required size overlapping, or “interference”) is placed into the adapter with the bush lead-in face towards the v.g. The pneumatic hammer is used to clinch the bronze bush into the valve guide (on the valve seat side) with increased inside diameter, so it comes out from the valve guide to the same length on both sides.

Step 3: «Обработка н.в.к. под требуемый размер» Установленная бронзовая втулка, путем прошивки, набором гладких прошивок (увеличивающихся по диаметру с шагом 0.02мм, от меньшего размера к большему), уплотняется по толщине стенки втулки и разравнивается по всей поверхности внутреннего диаметра н.в.к.. Этим переходом мы выполняем два очень важных технологических требования. Во первых, we ensure size overlapping (interference) between the bronze bush and the body of the prepared original valve guide. This provides for reliable fixing of the bush inside the guide body keeping the correct heat exchange mode.
Second, we form correct geometry and required gap between the valve stem and the repaired valve guide inside diameter established by the manufacturer.
Attention:
It is forbidden to adjust the size of the valve guide with a bronze bush installed using reamers!
This operation with bush metal removal reduces the interference size which leads to bush offset during the CH operation.

Step 4: Bronze bush facing cut. Installed and inside-diameter formed bronze bush is smoothly cut on both sides. The operation is performed using a special trim with a guide pin (the trim is supplied as part of the tool package).

Step 5:  inside diameter finishing. The inside diameter of the installed bronze bush is finished with a special tool, a flex-hone. This is a finishing operation. After flex-hone finishing only the valve guide-stem assembly operation may be performed. No other items shall be installed to preserve roughness of the flex-honed surface:

• the bronze bush inside diameter shall be free from machining by-products;
• • an additional hone profile is applied to contain the additional motor oil, which guarantees correct valve stem working conditions (the inside diameter during this operation does not change; the amount of bush metal removal is 0.001–0.002 mm). Finishing is performed in one drill movement with down-up rotations!

This way we repair the valve guides using one of the offered methods. We shave provided a basis for valve seat machining. The inside diameter of the:

• valve guide with a bronze bush is inspected;

Valve seat replacement. This operation is performed when necessary.

After extended operation of the CH the valve guide/valve/seat assembly wears out

We have analysed valve guide repair methods. Now we are going to discuss the valve seat ring replacement operation.
The valve seat ensures correct and long-term operation of the CH and shall meet certain quality requirements to perform its functions. These include:

• high thermal conductivity;
• physical durability;
• chemical durability.
  

Original valve seats supplied by the manufacturer, provided that the CH supports the installation of these seats (the slot size provides for required interference), as well as own-produced valve seats shall be installed. We carefully inspect each batch of valve seats supplied for serviceability.
The following parameters are inspected for defects: geometrical dimensions, machinability, hardness, chemical composition. Inspection for cracks, pores, metal structure homogeneity defects is performed with by dye penetrant testing.
We use the following seat installation technology:

• djustment of the CH valve seat housing (except for original seats where the oversize is not provided), which allows restoring the necessary cooling and provides for v.g. and valve seat axiality to ensure the correct service life of the valve seat/valve assembly. Bore diameter size, alignment of support angle seat for a seat ring and valve seat ring installation height are monitored; the aluminium CH is heated up to 90 to 100 °C. Cast iron CH are not heated due to their heavy weight and massive body; the material strength capacity of cast iron CH is sufficient for the installation of seat rings with the required interference value
• the valve seat is cooled down in liquid nitrogen up to -190 °C. The seat is easily mounted into its housing on the CH using special aligning bars. When the CH temperature reaches the normal range (time lag is provided), the recommended interference between the seat and the seat housing is provided by means of physical uniform wrapping of the seat body by the CH body. The less is the installation effort, the lower the possibility of the seat ring base hole damage. The correct geometry and roughness of the valve seat ring and valve seat housing surface guarantee full ring wrap and proper heat exchange.
  The fitting of the valve seat ring against the housing support angle are inspected visually and using a set of feeler gauges.

CH plane machining.

This operation is performed when necessary.



CH jointing plane machining for a cylinder block gasket. This machining operation is performed using special universal equipment.

 This equipment is intended for CH jointing plane machining according to a special cutting pattern.The cutting pattern provides plane parameters within 0.01–0.02 mm and surface roughness parameters during CH machining within Ra 0.8 µm and Rz 6.3 µm;, which matches the requirements of the world's leading manufacturers of CH gaskets of different materials. The accuracy and precision of this cutting pattern are based on rotation of the fixed cutting plane over the revolving table crosswise of the ICE crankshaft, which provides transverse arrangement of cutting traces. This arrangement ensures correct operation of the gasket between CH and CB with maximum tightness under installation force. The equipment universality is provided by the possibility of CH machining according to the structure of all commercial ICEs (we also have a separate equipment line for special machinery). Industrial CHs have structurally parallel planes and non-parallel planes. Special universal accessories supplied together with the equipment provide for fast and reliable CH clamping without deforming the plane.
The high-technology cutting plate installation diagram provides two conditions during the operation. Condition 1 is metal layer removal. Condition 2 is that in the cutting mode, the plate geometry provides for the required surface roughness by way of smoothing by the cutting plate back surface.
To perform the operation the following parameters must be known:

• CH height;
• CH minimum permissible height;
• CH bending.
  

Grinding of valve disc working faces.
This operation is performed when necessary.

After measuring, a decision on further valve operation is taken. If the valve disc or valve stem is worn to the limit, it is recommended to replace the valve. In case of minor wear of the valve stem diameter (not more than 0.015 mm), where a valve disc parallel of a specific size is available, valve disc machining is performed, which includes the following process steps:

• valve stem face removal, valve facing — valve height-wise machining to obtain the same size and providing a basis for further machining;

• valve disk working face grinding at a recommended angle.

The valve disc working face repair is performed by means of valve disc parallel height h up to the acceptable value (ICE manufacturers' recommendations).
Valve disc face runout value after machining shall be within 0.01–0.02 mm. Valve runout is checked using a special device with two indicators, one indicating valve stem radial runout, and the other indicating valve disc working face runout.
The operation results are recorded into the work performed sheet for the order.

Shaping of valve seat working faces.

Shaping of valve seat working faces is performed after installation of the seats or if the valve stem overhang/valve disc sticking value is within the limit and the machining stock is not above the value of this limit.
This operation is performed using high-accuracy Newen GII, Newen Contour BB, and Newen Epoc machines produced in the USA. The following parameters from ICE manufacturers are required for shaping:

• valve stem overhang and/or valve disc sticking;
• valve seat angle combination;
• valve seat working face width.

When machining and shaping the valve seats using our equipment, profiles of virtually any complexity and angle combination may be maintained, with the perfect alignment with the guide bush achieved due to self-centring of the “floating spindle” on an air pad, which allows for machining of the working and auxiliary valve seat faces with the displacement of 0.010 mm and less.
After shaping, no additional machining or reseating is required. The seating tightness of a new or machined valve to a machined seat is inspected using a vacuum tester. The machining results are recorded into the order accompanying document, work performed sheet.
The machining data is recorded into the work performed sheet that is given to the customer together with the component part. Work performed sheet contains machining data reported or approved by the Customer (before machining) and output data (after machining). After the order is complete, the Customer shall carry out total quality control of the work performed. Out tools can be used for this purpose. In our work we take responsibility for agreed parameters of machined surfaces:

• part surface size;
• part surface geometry;
• part surface roughness.
  

The article contains the list of the main CH machining operations. See the list of operations in the Work Cost Estimator section on our website or get the list at your local «ProMotor» network division.