Bottom trunnion pin cup - fit into thick arm
Posted: Sat May 23, 2026 5:27 pm
Having had discussion on MMOC face book page about the fit of the cup into the thick suspension arm I put these notes forward for consideration.
The the cup forward face should be around 2mm from the forward face of the thick arm when assembled. It is the thin arm that holds the pin and cup in place laterally. There is no securing of the cup in the thick arm (other than nip fit) therefore it can move outwards relative to the thick arm recess. The cup and pin should be nipped between the bottom of the cup recess in the thick arm and the front shoulder of the pin against the rear face of the thin arm. If the thin arm is distorted at its inner end it can mean that the cup is not fully entered or nipped in the thick arm. The inner end of the thin arm is prone to distortion and this was recognised by BL when introducing the Ital. To eliminate any distortion the outer end of the Ital thin arm the arm was reinforced and the flanges at the inner end enlarged. It should be noted that the Marina/Ital thin suspension arms are similar to the Minor thin arm and can be fitted to the minor with slight modification dependent on the type of eye bush used..
It is important that the inner end of the Minor thin arm is parallel to its centre part. If it is distorted it can be straightened and brought back parallel.
Having the inner end of the thin arm parallel ensures that the cup is fully entered into the thick arm recess and nipped between the thick and thin arms.
Below is how the cup should be when fitted into the thick arm and assembled correctly.
Below is the Ital strengthened thin suspension arm. In due course these strengthened arms will be fitted to my Minor.
The the cup forward face should be around 2mm from the forward face of the thick arm when assembled. It is the thin arm that holds the pin and cup in place laterally. There is no securing of the cup in the thick arm (other than nip fit) therefore it can move outwards relative to the thick arm recess. The cup and pin should be nipped between the bottom of the cup recess in the thick arm and the front shoulder of the pin against the rear face of the thin arm. If the thin arm is distorted at its inner end it can mean that the cup is not fully entered or nipped in the thick arm. The inner end of the thin arm is prone to distortion and this was recognised by BL when introducing the Ital. To eliminate any distortion the outer end of the Ital thin arm the arm was reinforced and the flanges at the inner end enlarged. It should be noted that the Marina/Ital thin suspension arms are similar to the Minor thin arm and can be fitted to the minor with slight modification dependent on the type of eye bush used..
It is important that the inner end of the Minor thin arm is parallel to its centre part. If it is distorted it can be straightened and brought back parallel.
Having the inner end of the thin arm parallel ensures that the cup is fully entered into the thick arm recess and nipped between the thick and thin arms.
Below is how the cup should be when fitted into the thick arm and assembled correctly.
- eye pin cap.jpeg (59.15 KiB) Viewed 3266 times
- Strengthened Marina arm.jpeg (62.8 KiB) Viewed 3268 times