Engine Rebuilding : Engine machining>Clean pistons and fit new pins

Clean pistons and fit new pins

Part 1. Preparation and safety

Objective

• Clean pistons and fit new pins.

Personal safety
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection - such as rubber gloves and barrier cream
• Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.
Safety check

• Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.

Points to note

• Rod ends need to be heated to allow the tight fitting pin to be pushed home. This process needs to occur quickly to avoid the pin getting stuck part way.

---

Part 2: Step-by-step instruction

1. Clean pistons
   If the pistons are reusable, they have to be cleaned. Cleaning them by hand is laborious and not as effective as masking of the skirts with tape and sand blasting old carbon deposits off in a blast cabinet.
   Often, the best thing to do is to buy an engine kit that will be complete with a new set of pistons of the correct size and everything else you'll need for reassembly.
2. Install new piston pins
   To fit the pistons to their connecting rods the pin bores are lubricated and the pins are set in one side ready to be pushed through. The piston and pin are set in a fixture and a rod is set in a rod heater.
   With semi-floating pins the small end of the rod is too tight for the piston pin to pass through, if the metal is at room temperature. But when the end of the rod is heated up, the opening will expand. Then the rod is held is place and the pin can pass through the temporarily larger opening in the rod. This stopper on the back of the piston holding fixture makes sure the piston pin stops in the right position.
   This is not a simple procedure, the rod must be facing the right way on half of the pistons and the other way on the other half and if the pin is not passed through quickly enough, the rod could cool just a bit and the pin would be pinched too early and they'd have to go back and press out the pin and try again.