RM Pistons

The following table contains basic information for pistons used in RMs. It is based on old data and does not relate to replacement pistons although it does provide a useful comparison.

Model RMA
CR 6.8:1
RMA (HC)                        
CR 8:1
RMB/F        
CR 6.8:1/6.6:1
RMH
CR 7.25:1
Material Low Expansion Silicon Alloy Aluminium Silcon Alloy Tin Plated Silcon Alloy Tin Plated
Cylinder Bore
69 mm
2.7165 in.
69 mm
2.7165 in.
80.5 mm
3.1693 in.
80.5 mm
3.1693 in.
Ref.No. RS11654 5669 S9361 RSW1770
Compression Height 50.7 mm 57 mm 57.2 mm 2.25 in.
Length 90.7 mm 97 mm 95.2 mm 95.2 mm
Head Shape Flat Bevelled Dome Cone Flat Bevelled
Piston Rings




2 x 2.5 mm
P.8665
1 x 4.5 mm D0.8666
1 x 4.5 mm
D0.8667M
2 x 1.5 mm
P.1175
2 x 3 mm
D0.314

2 x 3/32
TP.11212
2 x 4 mm
ED0.9966


2 x 3/32
TP.11212
1 x 4 mm
D0.7589
1 x 4 mm
D0.11208
Original Sets
Regular
Oilmaster


2560/V
2564/V


-
-

2520/V
2524/V

6660/V
6664/V

Replacement Sets
Regular
Oilmaster


6332/V
6335/V


-
-

2520/V
2525/V

6662/V
6665/V
Pins
Diameter
Type

Ref. No.

19mm
Seeger
Circlip
SC
1862A

19mm
Seeger
Circlip
SC
1862A

22 mm
Seeger
Circlip
SC
2378A

22 mm
Seeger
Circlip
SC
2621A