Mira VGX-21 User manual

Instruction manual
English (EN)
Precision valve seat
refacing device

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
1
Table of contents
Safety Regulations...................................................................................................................................2
Elementary safety-advices.......................................................................................................................3
Copyright ©...............................................................................................................................................7
Non-liability...............................................................................................................................................8
Warranty....................................................................................................................................................8
Declaration of conformity........................................................................................................................9
1 Device parts VGX-21........................................................................................................................11
1.1 Device parts AV-Mobile .................................................................................................................12
2 Installation of the cylinderhead support AV-Mobile......................................................................13
3 Clamping of the cylinderheads.......................................................................................................14
4 Processing of valve seats...............................................................................................................15
5 Processing of insert counterbores (ring seats).............................................................................24
5.1 Processing the Counterbores.........................................................................................................25
6 Changing tool-heads.......................................................................................................................26
7 Maintenance of the VGX-21.............................................................................................................27
7.1 Advancing device (Feed nut) .........................................................................................................27
7.2 Hydraulic oil clamping system........................................................................................................28
8 Spare parts list.................................................................................................................................29
9 Assembly drawing of the VGX-21 (with crank handle)..................................................................31
10 Schematic diagram..........................................................................................................................32
11 Special accessories ........................................................................................................................33

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
2
Safety Regulations
For the eletronic installation activity, please pay attention to the local directives.
We would like to draw your attention to some dangers, which may occur. You should therefore read the following instructions carefully
and proceed accordingly.
It is not allowed to use the device in a dusty, humid or explosive environment => Danger of shortcircuit!
The VGX-21 must not be used with a opened chassis!
To bypass or paste-over the handgrip-switch as well, can be very dangerous!
During processing the valve seats, there must be worn safety goggles! There must be worn a hairnet for long hair as well!
Risk of injury by the formtool of the rotating spindle!
Avoid to suck in any dirt or dust while the vacuum pump is running!
The filter and the suction cable should be controlled in constant intervalls!
Clean the suction cable if it is polluted and exchange the filter!
Before working on electronic elements and repairs, the device must be fully isolated from the current electric circuits!
Repairs are only allowed by the local MIRA-dealer or the manufacturer (MINELLI Corporation) in every case!
Only use genuine MIRA spare parts, which are registered in the respective instruction manual!
Do not touch the electric circuits of the device = Contact with these circuits are dangerous to life!
Modifying of the electronical elements could cause severe aftermath!
Repairs of the VGX-21 must be basically accomplished ONLY by authorised personnel or the MINELLI Corporation.
Safety advices for the VGX-21 valve seat refacing unit
The following safety advices must be observed in every phase of the launching, during processing valve seats and the maintenance or
repairs. Disregarding of these assignments is a incorrect use of the device.
Earthing of the device
To reach an optimum touch protection, the device must be earthed. Therefore the earth-clamp must be connected with the earthing
of the main circuit.
Do not use in explosive environment!
The use of the device in explosive environment (flammable gases, vapours or dust) may induce the lightning of these materials and are
strictly forbidden.
ATTENTION!
1. To avoid the risk of partial overheating, the device must not be used in dusty or steamy atmossphere.
2. The device must not be used in wet environment, respectively the device must not be exposured to rain or dew. This may induce an
electric connection between electonic elements in the devices.
3. The User of this device must accomplish access, launching, setting and service by authorised personnel. Operations by the
electronic elements of the device are dangerous because of the electric tension, that can be a high risk of an electric shock. The
electric tension can even exist for a short time if the device is already switched off. Before starting service-operations on the
device, make sure that the capacitors of the device do not carry electric tension.
4. The device builds no physical separation. It is prohibited to work on the connectors of the device if the electric tension is running.
Running of the device without mechanical switch or fuse in the power supply is forbidden.
5. Service and adjusting operations must always be done by a minimum of 2 people. In an emergency, there must be a person that
can cut off the electric circuit to execute first aid.
6. This device must not be used for emergency- and safety tests. A failure or damage of the connected VGX-21 by the running electric
tension can be induced.
7. Every contact with the electric circuits must be avoid. During the operation, every contact with these circuits are dangerous to life.
Therefore added, the device can be damaged by careless contact of sensitive elements.
8. To avoid further risks, you must gain the agreement of the manufacturer MINELLI Corporation, if you want to add, change, replace
and/or manipulate some parts of the device by yourself.
9. If there are some repairs or replacing works to do, the VGX-21 must always becompletely disconnectec from the electric circuits.
By Repairs and replacing works read carefully the certain chapters in the Instruction manual. (See “Maintenance of the VGX-
21“on Page 27)

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
3
Elementary safety-advices
Advices in the instruction manual
•The knowledge of the Basic safety advices and safety regulation are basic conditions for the
design to security using of this device in cooperation with the “Safety Regulations”on page 2.
•The instruction manual contains the core of the importants advices, to use this device in a safety
condition.
•The instruction manual, especially the safety advices, must be consider by all users, who work
with this device.
•Beyond that it must be paid attention to the valid location regulation and the provisions of the
accident control.
Responsibility of the operator
The operator are committed to let only user working, if they
•will be intimate to the basic advices for working safety and accident control. They must also be
instructed to the device application.
•have read, understood and signed the safety advices and warning notices in the instruction
manual.
The safety-conscious work from the users will be controlled in constand intevalls.
Responsibility of the employees
The employees who work on the device have to commit, before beginning the work:
•that they pay attention to the basic safety advices of work safety and accident control.
•that they have read, understood and signed the safety advices and warning notices in the
instruction manual.
Risk in using the device
The device VGX-21 has been developed based on the newest state of technology and was
constructed by the accepted safety-related regulation. However, it is possible by using the device,
that there appear some risks for the user or third persons, especially if the device is misused and
operated not accordingly to the MIRA operation manual. Only utilise the device:
•for designated use.
•in safety-related good condition.
Breakdowns are to correct immediately, if they become some vitiations to the safety-advices.
Conventional utilisation
The MIRA VGX-21 device is exclusively designed for refacing and cutting valve seats and insert-
counterbores of the cylinder heads for combustion engines. Another- or beyond going utilisation are
not intended. The Minelli Corporation will not be liable for damages which evolved herefrom. To the
intended utilisation also belongs:
•to pay attention of every advice from the instruction manual and
•to keep on the control- and service work.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
4
Warranty and liability
Warranty matters are described in MIRA‘s terms of sales and return policy conditions and are a
integral part of any sales contract between MIRA an the customer. Warranty- and liability by people
and material assets are void, if they had one or more of the following causations:
➢Non-designated use of the device
➢Incorrect mounting, launching, using and servicing of the device
➢Operating of the device with damaged safety-apparates or incorrect and missing mounting of the
safety- and protection apparates
➢Non-observance of the advices in the instruction manual with regard to the transport, storage,
assembling, launching, operating and servicing of the device
➢Independent constructive manipulating of the device
➢Independent manipulation of the VGX-21 (for example: magnetic plate or switches, protection and
earthing against dangerous currents)
➢Bad monitoring of the device components, which are wearout
➢Incorrect executed repairs
➢Emergencies by external-material influence and force majeure
Symbol- and advice description
Following descriptions and icons will be used for risks in this instruction manual:
Warning notice –Generally danger: Shows a potentially dangerous situation, which can
induce low to severe injuries up to death, if they will be ignored.
Warning notice –Danger of an electric shock: Shows a dangerous situation, which can
induce an electric shock and severe burns up to death, if they will be ignored.
Warning notice –Danger of squeezing: Shows a potentially dangerous situation, which can
induce low to severe constant injuries, if they will be ignored.
Info –notice: Shows Information and/or additions, which are important for theappropriate use
of the machine and its functionality.
Application –notice: Shows accessories and further application features of the machine.
Organisational provisions
•The operator must prepare the required safety-equipment.
•All safety-devices must be checked by constant intervalls.
Protection-apparates
•Before launching the device, all protection-apparates must be correct installed and functioning.
•Protection-devices maybe only removed
- after shutdown and
- coverage against re-launching of the VGX-21
•By delivering of part-components, the protection-devices must be installed agreeable to the
regulation by the operator.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
5
Informative safety provisions
•The instruction manual must be always kept by the location of the device.
•Additional to the instruction manual, there must be paid attention to the generally and local
regulation of the accident control and pollution control. They must be prepared.
•All safety- and warning advices on the device must be kept in a readable condition
Training of the users
•Only introduced and trained users may work on the device.
•The user competence must be clearly appointed for the mounting, launching, handling, servicing
and repairing of the device.
•Beginners may only work on the device under the attendance of an experienced user.
Device- and apparate electrics
•Do not manipulate the magnetic plate and do not modificate the switches in any circumstances.
•Only introduced users are be able, to apply the VGX-21 device.
Safety provisions in the standard mode
•All protection-apparates must be absolute functioning, if the device is in operation.
•Before switching-on the device, there must be paid attention that nobody is exposed to the risks
by starting the device.
•The device should be checked for external damages and safety device functioning in minimum
one time by every shift.
Risks by electrical energy
•The works on the electrical supply must be done by an expert (Certified Electrician, etc.)
•The electrical equipment of the device must be checked in constant intevalls. Lose connections
and damaged cables/wires must be removed immediately.
•If it is essential to do work on energised components, there must be a second person/user that
guards the work and can remove the power cord from the main socket in case of an emergency.
Especially danger areas
•The VGX-21 valve seat refacing unit contains rotating machine parts, which are an upper risk for
(long) hair, hands and fingers. Wear suitable safety equipment (e.g. hairnet etc.).
•The magnetic base of the VGX-21 may be a risk of squeezing fingers and hands by clamping
down the device on a handling plate. The device must be clamped carefully and thoughtful.
•The mounted formtools maybe have very sharply and spiky turnings, which can induces severe
lacerations or others injures. It must be worked careful and thoughtful by refacing and recutting
the valve seats!
Leaking of hazardous dust and vapours
•During the refacing of the valve seats, metal dust, particles and vapour from the cutting oil can
occur. They can irritate and injure the lungs and the eyes. Wear suitable safety equipment (e.g.
protection goggles, mask etc.). Ensure enough ventilation during processing valve seats. Special
safety precaution, for example: eyeflushing device.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
6
Service and repairs, trouble shooting
•Arrange the prescribed setting-, servicing- and checking works to the limit date.
•The users must be informed about imminent servicing and repairs of the device.
•All of the device pre- or after switched machine parts and operating mediums, e.g. electricity,
must be ensured against accidentally launching.
•By all servicing-, checking- andrepairing works, the devicemust be switched off from main supply
and the mainswitch must be locked against unexpectet restarting
- Lock and strip of the key from the main switch, if it is possible.
- Add Add a shield or Information on to the device, which the device may not be able to be
switched on.
•Greater devices must be carefully mounted and ensured on lifting gears, by the replacing.
•Check loosened screw connections for a compact seat.
•After finishing the service work, the saftey apparates of the device must be checked and verified.
Constructive modifications on the device
•Without written authorisation by the manufacturer Minelli Corp. (MIRA), theres no right to add
some components and/or making some modifications on the device. This is also valid for welding
wearing components.
•All constructive modifications requires a written affirmation from the Minelli Corp. (MIRA)
•Faulty device parts must be replaced by original replacements only.
•Only use original genuine mira replacement parts.
- By replacements of externals, there are no guarantee, that they are constructed for the required
operational demands and the required safety functions.
Cleaning of the device and disposal of wastes
•Used stuff and materials must be correct removed and handled, especially:
- by works on greasing systems- and devices
- by cleaning with dissolvers
•The device must be cleaned external in constant intevalls, with a flannel and less of machine- or
industry cleaner.
•Further cleaning per grade of using and grade of pollution of the device.
•The packaging material of the VGX-21, after delivering, must be correct disposed in the respective
waste container and/or according to local envirement legislations!
Noise emission of the device
•The noise pressure level going out from the VGX-21, behave to 0dB(A)
•In combinated use with the Vario Drive System, there is a noise pressure level up to 70dB(A)
going out from the Vario Drive.
•Based on the local environment, there is a possibility of a higher noise pressure level. This can
cause noise deafness. In this case, the users must be wearing protection devices (e.g. hearing
protection, Oro-pax etc.)
Safety advices for carrying
•For transport, the VGX-21 must be carried in the storage box (in the same as it was delivered
from the Minelli Corporation).
•Ensure all moving parts from the device against loosening, by the transport.
•The device must be protected against damages by the transport. If essential, the device can be
fully packed in.
•The MINELLI Corporation will not take liability for ignoring and not paying attention of the safety
regulations by shipment.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
7
Copyright ©
The exclusive copyright of this instruction manual remains in the hands of the MINELLI Corporation. (MIRA)
This instruction manual is appointed for the operator and his personal.
Minelli Corporation
MIRA Division
Mattenstrasse 3
CH-8330 Pfäffikon ZH
Switzerland CH
For the provided technical documentation see the assigned person at chapter “Declaration of conformity”
on page 9.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
8
Non-liability
The valve seat refacing device VGX-21 may only be operated according to the Operating Instructions. The
manufacturer refuses to accept any liability for accidents and damages caused by incorrect operation. He
also refuses any liability for alienated use of the device.
Warranty
In case of manufacturing or material defects Minelli Corporation will replace the defective part or parts at no
charge within 12 months after the date of final purchase. No further claims can be covered under the
warranty. Defective parts must be returned along with proof of purchase. The warranty does not cover any
subsequent damage caused by these defective parts. The warranty does not cover unprofessional handling,
the use of incorrect electronic parts or deliberate damage, nor does it cover shipping and packing costs.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
9
Declaration of conformity

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
10
VGX-21 Valve seat refacing unit
We congratulate you for your purchase of the VGX-21 valve seat refacing unit with hydraulic clamping
system. The VGX-21 allows to process extremely precise valve seats in a very efficient way. This device is
the product of many years of experience in valve seat recutting.
The simplicity of handling and simultaneous processing of the three angles (seat with correction angles) are
the outstanding features of the VGX-21.
We are sure that this device will serve you well in your workshop and we recommend you to follow the
suggestions for preparation and starting to operate it.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
11
1 Device parts VGX-21
1 Disconnect power, first, if there are any
work to do at the electrical components in
the VGX-21.
It is recommended to disengage the
magnetic base, when not in use.
Handle
1 Tumbler switch
(Magnet On/Off)
Adapter for
crank handle or
Vario Drive
Clamping
lever (Pivot
arm)
Advancing
device
Spindle
guide
Pivot arm
Bleeding
screw
Adjusting screw
1 Magnet base
(230V/110V)
Hexagon screw
Star grip
Pivot arm guide
Clamping lever
of the stopping
ring
1Power cord
(230V/110V)

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
12
1.1 Device parts AV-Mobile
Star grip handle
Vertical guide
Steel plate
Tensioning unit
Steel plate mount
Inclining plate
Stop brackets
Wall support with
socket
Star grip handles
Carry arm
The AV-Mobile should be installed,
with the help of two employees, on a
solid wall side!

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
13
2 Installation of the cylinderhead support AV-Mobile
The universal cylinderhead support requires a clean, proper installation on a solid wall in order to ensure
best results with the Mira VGX-21 Valve seat refacing device. The carry arms are installed, approximately
90cm, above the floor. Fig. 1
When you place the steel plate, ensure that the milled
side is on top, because of the slightly bended (convexed)
steel plate. The steel plate becomes straight when it is
tightened.
(See also “Processing of valve seats”on page
15)
Installation of the wall support:
(1)To mount the support base,
there must be drilled 4 bores in
the footprint. (2) The included
expansion bolts (1N0307M08)
can be inserted into the bores and
the wall support can be mounted
on the footprint against a solid
wall. (3) Use the included
hexagonal screws
(1N0056M08x030) to fastening
the wall support. Tighten the
screws firmly.
The carrier arms, the steel plate and the steel plate
mount, can now be fixed on the wall support.
The standard AV-Mobile cylinderhead-support includes
inclining plates.
The inclining plates for cylinderheads with inclined valve
seats, allows processing of the valve seats in an
appropriate position (Fig. 2).
See also page 14 and 33 for “Clamping of the
cylinderheads”and “Special accessories”.
Fig. 1
Fig. 2
To avoid damages and
injuries, there are two
employees required to
mount the wall support!

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
14
3 Clamping of the cylinderheads
There are different possibilities for clamping cylinderheads. When fixing cylinderheads, attention must be
paid that the magnet base and the clamping plate are in a clean condition and placed at level.
At Fig. 3, the cylinderhead is fixed upright on to the MIRA
cylinderhead support AV. This situation shows the
standard position for straight valve seat processing.
If the cylinderhead includes inclined valve seats, like Fig.
4, the cylinderhead support must be equipped with the
inclination plates (SH).
The inclination plates are delivered with 2 pairs of screws,
nuts and a pair of stop brackets. See also “Special
accessories” on page 33.
The plates can be mounted easily and accommodate a
safe and solid base for the valve seat refacing with the
VGX-21. Fig. 4
Fig. 3
Fig. 4
PLEASE PAY ATTENTION!
The clamping of the cylinderheads
and the processing of the valve
seats must be done careful! To
avoid injuries by squeezing or by
cuts of sharp formtool edges, wear
safety equipment (E.g.: Safety
shoes, goggles etc.)!

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
15
4 Processing of valve seats
1. The cylinderhead must be clamped down on the
MIRA cylinderheadsupport AV (Fig. 5). The clamping
plate should be positioned parallel and nearly even
to the valve seats. For inclined valve seats mount the
inclination plates SH, for further informations see
pages 12, 14 and 33.
2. Clean the guidances of the valves with a flex-hone
brush. Note: We always recommend using a brush
in a clean condition. Dip in the brush into industrial
cleaner before using. Fig. 6
3. Clamp the VGX-21 on the storage table (AT) or on a
clean workbench surface by activating the magnet
base (Pos.1), clamp the pivot arm and lock the star
grip. Select a suitable tool-head (see the MIRA
formtool catalogue) for optimal valve seat
processing. Insert the tool-head firmly into the
spindle. Control that the markpoint of the tool-head
and the setscrew of the spindle guide are aligned
(Fig. 7). For further informations see “Changing tool-
heads”on page 26.
Fig. 5
Fig. 6
Fig. 7
Use the stop
brackets from
the inclining
plates, to secure
the cylinderhead
from slipping.

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
16
4. Select the biggest possible pilot. For high precision
processing a pilot must be inserted in the guidance
with a maximum clearance of 0.01mm, against the
inner guide-diameter. The Pilot should be moveable
without resistance. (Fig. 8) See formtool and pilot
catalogue.
5. Insert the correct pilot into the tool-head and secure
the lower setscrew, by using the enclosed inhex key.
Turn the advancing device to the upper position.
Fig. 9
Fig. 8
Fig. 9

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
17
6. Select the formtool, considering of the prescriptions
of the factory, or based on your own experience. See
also the formtool catalogue. Fig. 10
Description on the formtool:
Example, 115A 1,5/45°
115 = Number of the formtool
A= Type of tool-holder
1,5 = Seat width in mm
45° = Seat angle in °degrees
7. The formtool must be tightened slightly. It must
remain moveable for the following adjusting works.
Fig. 11
8. The grinded valve can be inserted in the formtool
setting gauge and the knurled head screw can be
slightly tightened. In this position the valve stem must
remain moveable. Fig. 12
Fig. 10
Fig. 11
Fig. 12
PLEASE PAY ATTENTION!
The formtools may have some
sharp edges and angles! Avoid cut-
injuries by careful handling of the
formtools!

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
18
9. The tip of the adjusting tongue must now be placed
in the upper quarter of the valve head just like Fig.
13. Carefully but firmly fix and tighten the valve with
the knurled head screw as well as the adjusting
tongue with the star grip handle.
10. The knurled head screw must be loosened slightlyby
a ¼ rotation in order to check the adjusting through
moving the valve. Make sure that you are not
loosening the star grip handle! After checking the
setting, the knurled head screw can be released and
the valve can be removed from the formtool setting
gauge. Fig. 14
11. Fit the formtool setting gauge on the pilot and fix the
gauge slightly by the knurled head screw. Adjust the
formtool in the way that the adjusting tongue will
match with the corner (line) of the upper correction
angle (Fig. 15). Tighten the formtool in following and
remove the formtool setting gauge.
Fig. 13
Fig. 14
Fig. 15
Correct final
adjustment
Check if the
adjusting tongue
is placed as in
Fig. 13 showed

18 July 2023/ v1.6 VGX-21 |Serial-No. 963 © (All rights reserved)
19
12. Unlock the clamping lever handle and place the pivot
arm at the upper position by means of the adjusting
screw and the stopper ring (the stopper ring is below
the pivot arm and is fixed by a clamping lever).
Loosen the star grip until the spindle is free moving.
Fig. 16
13. Disengage the magnetic base by pushing against
Position 2 of the tumbler switch. Remove the device
from the clamping plate. Insert the pilot carefully into
the first valve guide. Fig. 17
Please keep the contact area on the steel
table and magnet base always clean!
14. Place the magnet base careful and flat onto the clean
steel table. Push on Position 1 of the tumbler switch
=> magnet base activated. Turn the spindle
clockwise 2-3 rotations for self-centering the pilot in
the valve guide. Fig. 17
Place one hand on the magnetic base, when you
clamping down the VGX-21 on the steel table. By
activating the magnetic base, you can feel any
uneveness on your finger tips. Fig. 18
If unevenness on the magnet base occurs, repeat
step 13-14.
Fig. 16
Fig. 17
Fig. 18