Pistons – All models

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”
DO NOT FORGET TO STATE SIZE REQUIRED.
1948 Piston, std / 20 / 30 / 40 LB 1929-32
1950 Piston c.r. 5.4:1 – std / 30 / 40 LF 1929-32
4489 Piston c.r. 7:1 – std / 20 / 30 / 60 LH/OH 1933-40
5613 Piston c.r. 6:1 – std / 20 / 30 / 40 LH/OH 1933-40
1717-31 Piston circlip L/M 1931-32

350cc Models

Standard bore 72mm. Piston to bore clearance: – solid skirt .003”-.005″; split skirt .001”-.0025″.
DO NOT FORGET TO STATE SIZE REQUIRED.
3081 Piston- std / 30 / 40 MB/MF 1931-32
4104 Piston low c.r. – std / 10 / 20 / 30 NH/NG 1933-58
11210 Piston c.r. 6.2:1 – std / 10 20 / 30 / 40 / 60 / 80 / 106 NH/NG 1933-58
10431 Piston c.r. 7.5:1 – std / 20 / 30 40 / 60  NH/NG 1933-58
12745 Piston c.r. 8.5:1 – std NH/NG 1933-58
R3560 Piston rings Standard / 20 / 40 / 60 NH/NG 1933-58
1064 Liner 72mm bore NH/NG 1933-58
1064A Liner and 12745/STD piston for about £35 off list NH/NG 1933-58
1064B Liner and 11120/STD 6.2:1 piston for about £21 off list NH/NG 1933-58
1711-33 Gudgeon pin NH/NG 1933-58
1716-31 Circlip Sing 1931-58

500cc Single Cylinder Models

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”.
DO NOT FORGET TO STATE SIZE REQUIRED
1111 Piston 1” gudgeon pin – std / 40 C/D/F/G/VF 1928-31
10503 Piston cr. 7.5:1 – std / 20 / 40 / 60 / 80 VH 1935-58
10793 Piston cr. 6.3:1 – 20 / 40 VH 1935-58
12488 Piston c.r. 9:1 – STD / 20 / 30 / 40 60 / 80 HS 1955-58
18400 Piston c.r. 7.5:1 – -10 / -30, yes minus VH 1947-58
R3600 Ring set for pistons 5045, 5056, 5627, 10503, 11497 STD / 20 / 40 / 60 VH 1935-58
R8550 Ring set .131” deep, Piston 13246, 13316, 13339 STD / 20 / 40 / 60 VH 1935-58
R10850 Ring set for piston 12488 (Use R8550) HS 1954-58
R12488 Ring set – std/0.5/1.0/1.4 mm (PHC pistons only) HS 1954-58
R17830 Ring set .110” deep for Piston 10793 STD / 20 / 3040 / 60 VH 1935-58
R22336 Ring set for 18400 piston VH 1947-58
677 Liner 86.4mm bore VH/Fleet 1933-34
755 Liner 81.8mm bore iron cylinder VH/VG 1935-58
32-50 Liner 81.8 bore alloy cylinder VCH/VHA/HS/HT 1949-58
1705-35 Gudgeon pin All 500 1935-58
1716-31 Circlip Sing 1931-58

550cc / 600cc Side Valve Models

Standard bore: – 86.4mm. Piston clearance:- .0045-.0065”
DO NOT FORGET TO STATE SIZE REQUIRED.
1109 Piston suitable for models with 1” gudgeon pins STD / 20 / 40 / 60 A/B 1928-31
11327 Piston c.r. 7.0:1 – STD / 20 / 30 40 / 60 / 80 VB 1931-58
R3580 Ring set, all sizes, 3 compression (.120 deep) STD /20 / 40 / 60 VB 1931-58
R3590 Ring set, all sizes, 2 compression, 1 oil ring (.120 deep) STD / 20 / 40 VB 1931-58
2083 Liner 86.4mm bore VB dot-58
1700-31 Gudgeon pin VB 1931-58
1716-31 Circlip Sing 1931-58

500cc Twin Fieldmaster

Standard bore: – 63mm. Piston clearance: – .0028”-.0043”.
DO NOT FORGET TO STATE SIZE REQUIRED
10930 Piston c.r. 6.8:1 – STD / 20 / 40 / 60 KG/KH 1948-57
11563 Piston c.r. 7.5:1 – STD / 20 / 40 / 60 KG/KH 1948-57
R3570 Ring set, please enquire STD / 20 / 40 / 60 KG/KH 1948-57
2489 Liner, iron barrels KG/KH 1948-57
1719-37 Circlip KG/KH 1948-57
1704-37 Gudgeon Pin KG/KH 1948-57

650cc Twin Huntmaster

Standard bore: – 70mm. Solid skirt piston clearance is .003”-.0045”; split skirt .0025”-.0045”.
DO NOT FORGET TO STATE SIZE REQUIRED.
11016 Piston, 6.5:1, STD / 20 / 40 / 60 / 80 FH 1954-58
11062 Piston, 7.25:1, STD / 20 / 30 40 / 60 FH 1954-58
11431 Piston, 8:1, STD / 20 / 40 / 60 / 80 FH 1954-58
11787 Piston, 8.25:1, std / 20 / 40 / 60 / 80 FH 1954-58
67-1370 Piston, 8.26:1 STD available only FH 1954-58
11412 Piston, 9:1, STD / 20 / 40 / 60 / 80 FH 1954-58
15638 Piston, 10.5:1, +30 available only FH 1954-58
R3650 Ring set STD / 20 / 40 / 60 FH 1954-58
2131 Liner 70mm bore FH 1954-58
10507-54 Gudgeon pin FH 1954-58
10508-54 Circlip for Hepolite pistons FH 1954-58
67-101A Circlip for GPM pistons FH 1954-58

Square Four

Standard bore: – 1931-32 4F5 50.8mm; 1932-36 4F6 (ohc) 55.8mm; 1937-40 4F (ohv) 50.4mm; 1937-58 4G 65mm.
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″
DO NOT FORGET TO STATE SIZE REQUIRED.
3094 Piston – 30 / 40 / 50 / 60 (sets of 4 only) 4F5 1931-32
4162 Piston c.r. 5.8:1 – STD 20 / 30 / 40 / 60, (sets of 4 only) 4F6 ohc 1932-36
‘Bore to .0055” and relieve an area the size of a thumb print by .004 just below the bottom ring land on the front and rear faces.’
8167 Piston STD / 20 / 30 / 40 / 60 (only available in sets of 4) 4F 1939-40
7188 Piston c.r. 5.8:1, – STD / 20 / 40 / 60 / 80 4G/MK I 1937-52
12487 Piston c.r. 7.2:1, – STD / 20 / 40 / 60 MK II 1953-58
R3610 Piston ring set, original and Hepolite pistons, all sizes STD / 20 / 40 / 60 4G/MK I 1937-52
R6030 Ring set for 7188 pistons marked “GPM” STD / 20 / 40 / 60 4G/MK I 1937-52
R6030 Ring set (per piston) STD / 20 / 40 / 60 MK II 1953-58
1700 Liner 50.4mm bore 4F ohv 1937-39
1773 Liner 65mm bore 4G 1937-48
32-49 Liner MK I/II 1949-58
1704-37 Gudgeon Pin SQ 4 1937-58
1719-37 Circlip SQ 4 1937-58
1719-91 Circlip for ‘GPM’ pistons SQ 4 1937-58

Tools that you may need

TOOL-18 Piston ring clamp 60-65 mm LH, KH
TOOL-19 Piston ring clamp 65-70 mm SQ4
TOOL-20 Piston ring clamp 70-75 mm NH, FH
TOOL-21 Piston ring clamp 75-80 mm
TOOL-22 Piston ring clamp 80-85 mm VH
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