This piston assembly set of 4 is built to the high-compression specification of the Austin Healey 100M. Supplied in +020 oversize, they deliver an approximate 8.6:1 compression ratio and are designed for engines rebored by 0.020 inch.
Correct for the following engines when rebored by 0.020 inch:
Exclusions: Not suitable for early BN1 3-bearing engines prior to chassis 221536, or for standard low-compression 100/4 engines unless converted to 100M specification.
Professional installation is strongly recommended. Verify bore diameter after machining, set ring gaps precisely, and check piston-to-bore clearance. To prevent ring damage and ease assembly, use a piston ring compressor tool (TOL111).
Purpose-made for Healey 100M engines, these +020 pistons provide the correct compression and crown shape post-rebore, ensuring reliable sealing, performance, and authenticity.
Yes. These are for engines rebored by 0.020 inch. If your block is still within standard tolerance, use the standard size set.
It indicates the piston diameter is 0.020 inch larger than stock, to match a cylinder rebored by the same amount.
Yes, each piston includes its ring set, plus gudgeon pin and circlips.
8.6:1 HIGH COMPRESSION
