Part 1. Preparation and safety
Objective
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
- Put some protection sleeves on the connecting rod bolts to prevent the bolts from marking the bore as they are removed.
- Pistons and their associated parts are a matched set and must be reassembled together as a matched set. Mark and organize all parts.
Part 2: Step-by-step instruction
- Remove rod caps
Start by removing the nuts for the connecting rod cap on the number one piston. Then, remove the rod cap by hitting the end of the rod bolts that are pressed into the rod body with a punch, or you can hit them directly with a softer brass hammer.
When the cap separates, you can pull it off by working it back and forth. Inside the cap, there should a flat piece of curved metal with a soft metal coating. This is an engine bearing. If the bearing shell is not in the cap, it will be stuck to the rod journal of the crank, so remove it from there.
- Prepare to remove pistons
Put some protecting sleeves onto the rod bolts so they cannot scratch the crankshaft or cylinder walls as the pistons are pushed out.
To prevent the piston from falling out of the block and onto the ground when you push them out of the cylinders, thread two long bolts a short way into the block either side of the cylinder and then stretch some rubber bands or a twist a piece of wire between them to catch the piston.
While a motor is running the piston rings slowly wear away part of the cylinder wall and create what is called a ridge. Higher mileage and harder worked engines develop more severe ridges than other motors. Carbon buildup also adds thickness to the ridge of a cylinder, but this can be removed with a razor blade. A thick ridge will make it more difficult to push the piston out.
It is possible to use a ridge reaming tool to cut this ridge to make piston removal easier, but this tool is not very accurate, can be difficult to use, and it can permanently damage the block. The most reliable way to remove pistons from a well-used engine is the careful application of the right kind of force.
- Remove the pistons
Use a wooden dowel about as thick as a broomstick and around two feet long. Move the rod journal of the crank to the centerline of the cylinder bore and place the dowel at this point on the piston.
Several hits to the dowel in the right spot should cause the pistons to slide out. In extreme cases where the pistons might be frozen in their bores by corrosion a wooden dowel might not be strong enough. In that case switch to a metal rod of some sort and then apply more force with the hammer.
It is not uncommon for a piston ring or even a piston skirt to break while worn pistons are being banged out, but this is not necessarily a problem. The cylinders will probably need to be rebored anyway, so new pistons will be needed to fit the larger bore cylinders.
The rubber bands or wire will stop the piston from dropping and causing damage. Be careful not to scratch the cylinder walls with the edges of the connecting rod as you slide the piston out.
Treat the other pistons in the same way. Sometimes it helps to lightly tap the cap on the side to loosen it, and you may have to hit the rod bolt quite hard to get it to separate. Line up the rod journal with the bore centerline again and hit the dowel until the piston pops out.
If you have to hit the piston hard enough to break the rings to get it past the ridge, the rubber bands might break too, so in that case have someone else there to catch it for you so you don't cause more damage than necessary.
- Keep pistons organized
As the pistons come out, keep them in the same order that they were installed in the engine.
A soft-drink bottle rack from a local convenience store makes a perfect container for 4, 6 and 8 cylinder engines. Put some labels of the side of the container that match the cylinder numbering of your engine as it's listed in your manual.
- Look for engine problem evidence
This is a close-up of one of the rod journals and the damage that was caused by running an engine with a broken rod bearing. The crank had been machined undersize in a previous rebuild and the damage is so severe that this crank can't be saved by machining it again.
