ARP Tools

Most of ARP’s assembly tools serve two jobs that shape an engine build: fitting pistons without damaging the rings, and cleaning threads so that torque readings can be trusted. Bore-specific ring compressors make up the bulk of the section, alongside thread chasers, a ring squaring tool and a rod vice.

A tapered ring compressor is a sleeve whose bore narrows to the size of the cylinder. As the piston is pushed through, the rings close evenly into their grooves and pass into the bore without a step. An adjustable band compressor can let a ring edge catch on the top of the bore, which can break the ring or score the cylinder wall.

Thread chasers clean and re-form existing threads without cutting new metal, so they do not oversize a thread the way a cutting tap can. Dirt, rust and old sealant in a thread add friction, and the torque wrench then clicks before the fastener reaches its clamp load.

Choose by your engine’s measurements:

• Ring compressors: match the finished bore, not the nominal size. Sizes are listed in inches, such as 3.630, 4.020 or 4.750, and in millimetres, such as 75.5, 87.25 or 100.0.
• Thread chasers: sold singly, such as M6 x 1.00 or M12 x 1.50, or as kits. The pitch must match, as one diameter can come in several pitches, for example M12 x 1.25, 1.50 or 1.75.
• Ring squaring tool: two-sided, with a 108 mm side and a 115 mm side. It sets a ring square in the bore so that the end gap can be measured with feeler gauges.
• Rod vice: holds a connecting rod securely on the bench while its bolts are tightened or stretched.
• Other items: a 14 mm spark plug indexer, a hex-key socket and a cabinet of stainless 12-point accessory bolts.

Oil the rings, the piston skirt and the compressor bore with assembly oil, then push the piston through with steady hand pressure. If it stops, find out why before pushing harder, as a ring caught at the edge of the bore will break. Turn chasers by hand, and blow out blind holes afterwards to clear loosened dirt and old sealant.

A chaser is for cleaning, not for repairing stripped threads, which usually need a thread insert. Store compressors where the tapered bore cannot be knocked, because a nick in it marks every ring that passes through. Keep chasers lightly oiled.