We currently have 98 different types of pistons, 16 liners and 40 ring sets in stock. For this reason it is not possible to list them all here. Before enquiring whether we have a particular ring set or piston for your model, find out as much as you can about it, as there are many variations. Original VH and VB rings, for instance, vary in depth by as little as .005” so please measure them or quote the piston number which is to be found inside the skirt. If the piston is not an Ariel or Hepolite one we will need to know all 3 dimensions of the rings. There is a table on our web site listing the dimensions of all known Ariel pistons, rings and gudgeon pins. Click here
Most replacement pistons are a little heavier than the original but despite rumours, are of very good quality no matter what part of world they come from, Italy, Australia or Taiwan. We have enquired about reducing the weight but the tooling costs involved make this prohibitive.
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. Do not despair if your cylinder has run out of space for a rebore, we have liners available for most models. A liner is a sleeve that is fitted inside the cylinder that reduces the bore back to standard size.
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 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″.
All prices for pistons and rings are now each and unless stated otherwise are available singly.
Some GPM ring sets have a stepped ring; this goes in the 2nd groove, thicker part to the top.
250cc Colts
Part No.
Description (c.r. = Compression Ratio) Oversizes
Model
Years
Standard bore:- 1929-32 65mm; 1933-40 61mm. Piston to bore clearance:- .003”-.005”
Standard bore: – 1928-31 81.8mm; 1931-34 86.4mm; 1935-58 81.8mm.
Piston to bore clearance:- solid skirt pistons in cast iron cylinders .005”- .007”; solid skirt pistons in alloy cylinders, .002”-.004”; split skirt pistons in iron cylinders, .002”-.004”; split skirt pistons in alloy cylinders, .002”-.004”.
Piston clearance:- ohc .004-.006″ (recommend .004″ on front and .006″ on rear); ohv iron cylinder .002-.004″ (recommend .002′ on front and .004″ on rear to prevent seizure of the rear cylinders and the perpetration of the ‘old wife’s tale’), alloy cylinders .001-.003″
