MIRA BB-86 Precision Counterbore Machining of Cylinder Liner Seats
The MIRA BB-86 is the portable counterbore tool for refacing the seats of flanged cylinder liners in diesel engine blocks. Electromagnetic base, automatic centering and maximum tolerance of 0.02 mm, even with the engine still in the vehicle.
DESCRIPTION
Recutting the seating surface of a flanged liner is one of the most critical operations in the overhaul of a diesel engine with wet liners. Through wear or in case of leaks, the counterbore seat loses flatness, compromising the seal of the head gasket fire ring until it burns through. Refacing the seats at every overhaul ensures correct liner protrusion and a perfect seal between engine block and liners.
The MIRA BB-86 counterbore cutter for cylinder liner seats, designed and built in Switzerland, carries out this operation quickly and precisely. The machine clamps directly onto the head gasket surface by means of a powerful electromagnetic base: since it rests on the sealing surface itself, the refaced seats are automatically parallel to the gasket plane, with a maximum tolerance of 0.02 mm. Centering is automatic, in a few seconds, via the guide roller behind the cutting tool.
The cutting depth is set on a vernier with 0.01 mm scale: once the first measurement is set, all following seats are machined to the same depth, keeping within the tight liner protrusion tolerance between adjacent cylinders. The radial tool feed, 0.15 mm per revolution through a planetary gear, produces a perfectly flat, vibration-free surface.
Compared with face mills and boring machines, the BB-86 uses a single machine body for the entire diameter range, changing only the carbide MB cutting tool.
Counterboring can be carried out on removed blocks, installed engines and even underfloor engines: weighing 5.8 kg in the Standard version, the BB-86 is easy to transport and suitable for work directly on the vehicle. With the dedicated accessories it is possible to machine a seat without removing the adjacent liners, work on tilted gasket surfaces, and recut deep-seated counterbores down to 200 mm with the BB-EXT extension.
The BB-86 is used on the wet liner seats of diesel engines for trucks, earthmoving, agricultural, industrial and marine applications. The MB tool range covers diameters from Ø 73 to 240 mm and includes dedicated tools for specific applications: Volvo FL6, PACCAR/DAF MX11 and MX13, Cummins, Scania, Volvo, Mercedes Actros, plus the MB-136/139 series for CAT engines with interrupted counterbore walls (CAT 3304/06, D343, D379/D398, 3500 series). For seats larger than the magnetic base, a steel plate is used; 45° and 75° chamfering tools are available for seat chamfering.
Available Versions
- MINI MD: Ø 154÷197 mm magnetic base and Ø 73÷182 mm working range
- STANDARD: Ø 170÷212 mm base and Ø 73÷198 mm working range
- GIANT: Ø 198÷239 mm base and Ø 85÷225 mm working range
TECHNICAL DATA
| MINI MD | STANDARD | GIANT | |
|---|---|---|---|
| Magnetic base diameter inside/outside | Ø 154÷197 mm | Ø 170÷212 mm | Ø 198÷239 mm |
| Min. – Max. working range | Ø 73÷182 mm | Ø 73÷198 mm | Ø 85÷225 mm |
| Max. tolerance | 0.02 mm | ||
| Tool feed | Rack type | ||
| Radial feed | 0.15 mm/rev (planetary gear) | ||
| Depth measurement | Vernier, 0.01 mm scale (1 revolution = 1 mm) | ||
| Max. working depth | 35 mm (up to 200 mm with BB-EXT extension) | ||
| Clamping | Electromagnetic base, 3-position switch (ON / OFF / reversed polarity) | ||
| Electrical requirements | 230/115 V | ||
| Weight | 5.5 kg | 5.8 kg | 6.2 kg |
FAQ
Is a shim-type counterbore tool the same as the MIRA BB-86?
No. Shim-based tools compensate a worn counterbore by adding a shim under the liner – a temporary fix. The MIRA BB-86 re-machines the counterbore seat itself, restoring the original geometry to 0.02 mm tolerance: a permanent repair, not a workaround.
STANDARD EQUIPMENT
- BB-86 counterboring unit in the chosen version: Mini (magnet inside Ø 154 mm), Standard (Ø 170 mm) or Giant (Ø 198 mm), without cutting tools
- Rotation drive crank handle
- Service wrenches
- Instruction manual
- Wooden case
OPTIONALS AND ACCESSORIES
- MIRA MB counterbore cutting tools: MB85 (73.00÷86.00 mm), MB86 (85.00÷104.00 mm), MB87 (97.00÷126.00 mm), MB88 (122.00÷162.00 mm), MB88AD (130.00÷170.00 mm), MB88DAF (123.00÷162.00 mm), MB89 (158.00÷198.00 mm)
- Tools for engines with interrupted counterbore walls: MB136 (105.00÷130.00 mm), MB137 (130.00÷160.00 mm), MB138 (160.00÷190.00 mm), MB139 (190.00÷220.00 mm)
- BB-86 Extension: extends the vertical working range up to 200 mm for deep-seated counterbores
- 45° and 75° chamfering tools for seat chamfering
- RR flux transmitter ring: counterbore machining without removing the adjacent liners
- Voltage regulator: centering on engine blocks with tilted gasket surface, also on the vehicle
- Short crank handle for work in confined spaces
- Custom-made MB special tools on request
