Unless requested not to we will supply the nearest oversize piston available. Do not bore your barrel before obtaining a piston, as the size you require may not be available. In any case a barrel should always be bored to suit a piston. If when boring the barrel you find that a larger oversize than that which you have obtained is required we will exchange it.
If you are not sure whether your piston, bore or rings are worn then your local automotive machine shop will normally check them for you without charge. Piston ring gaps are frequently quoted as a method of ascertaining bore or ring wear. When using this method, the ring gap should be measured near the top of the bore and compared with the gap obtained in the unworn section of the cylinder at the bottom. Divide the difference by Pi (3.142) to obtain the amount of wear on the cylinder. The difference between the gap measured at the unworn section and the originally fitted gap will indicate the amount of ring wear; however you do need to know what the gap was originally. The figures that are given for ring gaps are the minimum in order to prevent the rings closing up when they expand, a larger gap, within reasonable limits, is not detrimental. Some of the re-manufactured rings do have a larger gap than would normally be expected. The piston clearances are listed below. All pistons are complete with rings, gudgeon pins and circlips. 1.0 mm is equivalent to .040″.
Standard bore is 60mm 1954-58 (200cc) Piston to bore clearance .003″-.005″
|Piston c.r. 7.5:1 – STD||1||1954-58|
|Piston c.r. 7.5:1 – 15||1||1954-58|
|Piston c.r. 7.5:1 – 20||1||1954-58|
|Piston c.r. 7.5:1 – 30||1||1954-58|
|Piston c.r. 7.5:1 – 40||1||1954-58|
|Piston c.r. 7.5:1 – 60||1||1954-58|
|Piston ring, set of 3 – STD/20/30/40/60||1||1954-58|
|Piston ring, set of 3 – 20||1||1954-58|
|Piston ring, set of 3 – 30||1||1954-58|
|Piston ring, set of 3 – 40||1||1954-58|
|Piston ring, set of 3 – 60||1||1954-58|
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