ARP 81.5mm Ring Compressor

This ARP performance fastener, stud, bolt, tool, or assembly is the 81.5mm Ring Compressor. Confirm the exact engine or vehicle application, thread size, length, material, strength series, included quantity, installation lubricant, tightening sequence, and current ARP torque specification before ordering.

Key Features

• Exact 81.5mm Fit: Matches oversized pistons in popular 81mm bore engines for seamless compatibility.
• 6061-T6 Aluminum Build: Lightweight yet tough construction handles repeated professional use.
• ARP Engineering: Application-matched design ensures reliable clamp load every time.
• Specifically for 81.5mm diameter pistons common in rebuilt VW/Audi 1.8T, Honda B18, BMW M42 engines.
• Precision Tapered Profile: Gradually squeezes rings evenly to avoid distortion or breakage during piston insertion.
• Knurled Grip Surface: Provides firm hold in oily conditions for controlled placement.

Fitment

Specifications

What’s Included

One new ARP tool in the exact configuration and quantity identified by this listing. Brackets, wiring, air lines, fittings, switches, fasteners, fitting kits, fluids, covers, and accessories are included only when expressly stated for this exact part.

About ARP

Automotive Racing Products manufactures high-performance studs, bolts, nuts, washers, wheel hardware, assembly tools, and installation lubricants for engine, drivetrain, chassis, and racing applications. Thread dimensions, material, preload method, lubricant, torque, and included quantity remain exact-part specific.

Important Disclosures

• California Proposition 65 warning applies. Review the current manufacturer warning before handling or installation.

Related Parts

• Shop all ARP products
• ARP 4.055in Ring Compressor
• ARP 4.110in Ring Compressor
• ARP 4.2125in Ring Compressor

Frequently Asked Questions

How do I confirm the 81.5mm Ring Compressor fits my application?
Match the exact engine family or vehicle, component location, thread diameter and pitch, under-head length, material, strength series, and every current ARP application note.

Can I reuse the factory torque value with this ARP hardware?
Not automatically. Use ARP’s current instructions for the exact part, material, lubricant, tightening sequence, and preload method. Factory torque values may be based on different hardware and friction.

What is included with this ARP kit?
Only the studs, bolts, nuts, washers, lubricant, and tools expressly listed for this exact part number are included. Verify the required quantity before disassembly.

Installation Instructions

1. Confirm ARP part number 901-8150, the complete application, and every required supporting component before beginning work.
2. Clean and inspect all mating threads and components, then verify thread engagement, length, washers, nuts, lubricant, and required preparation before assembly.
3. Follow ARP’s current tightening sequence, lubricant instructions, torque or stretch method, and any retorque procedure for this exact part.
4. Verify clearance, preload, fastener seating, and normal component operation before returning the vehicle or engine to service.