Part 1. Preparation and safety
Objective
- Inspect and measure engine components.
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
- Be careful of sharp edges on components when you handle them.
- 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
- Make sure all parts are kept in organizer trays and in the correct order.
Part 2: Step-by-step instruction
- Check for cracks in block and heads
After a visual once-over, the block and heads need to be checked for hard to see hairline fractures or cracks. Cracks in cast iron parts can be detected by a process called Magnaflux. In this process an electromagnet is attached to the part which is then sprayed with a special powder that will stick to cracks and make them very visible. Aluminum parts are not magnetic, so for these parts there is a die process to make cracks visible.
- Measure the cylinders
Once you know that the parts are still good and not cracked, measure the tolerances to see what machining is necessary. If the visual inspection showed that there were obvious scratches or damage to the cylinder walls in the block, then the pistons could not be reused and the block would need to be bored out. If they are not cracked or scratched, use a dial bore gauge to check the cylinders and see if they are out of round or if there is a taper from the bottom to the top of the cylinder.
The dial bore gauge will reveal whether the cylinder has to be re-bored and then honed to straighten it out, or if a honing is all that's needed to clean up the cylinder walls. In either case the you need to measure the pistons.
- Measure the pistons
If new pistons are required they don't have to be on hand for the boring process but they do have to be physically measured to determine the size of the final hone.
Pistons cannot be machined, so the cylinder must be made to fit the size of the piston.
With the piston inverted, measure the skirt just above the pin bore with a micrometer. This will determine if a used piston will be able to be reinstalled in the block after it has been honed.
If the pistons are new, this diameter measurement will tell the machinist what dimension to hone the block to, so that the pistons will have proper clearance in the cylinders.
If a piston is measured and found to be worn too far, it is considered a collapsed piston and cannot be reused.
- Inspect and measure valves stems and guides
Both cast iron and aluminum heads will get a close visual inspection. Some machine shops have a vacuum fixture that can test how well the valve seats are sealing.
The valve guide is the hole in the head where the valve slides. Check this for excessive play and if wear is found, check the valve stem with a micrometer to make sure the valve can be reused.
- Check camshaft and lifters for wear
With the valve train, examine the camshaft and lifters. Any signs of wear will indicate that all the lifters and the cam will need to be replaced. This will nearly always be the case.
- Check the pushrods are straight
Any pushrods that don't roll smoothly on a piece of glass should be replaced as well as any keepers or retainers or rocker arms with signs of damage. Remember to keep everything in order if you're gonna re-use the same parts.
- Inspect and measure the crankshaft
Inspect and measure the crankshaft. If there are serious scratches or gouges in any of the journals they will need to be ground undersize and oversized bearings will have to be used when the engine is reassembled.
Bearing manufacturers usually make oversized bearings in size increments of ten thousands of an inch, or point two five of a millimeter, depending on where the engine and bearings are made.
This crank needed to be cut one size under on the main journal and two sizes under on the rod journals. Then it received a final polish to make the journals as smooth as glass.
Sometimes the final polish is all that's necessary to return an old crankshaft to a usable status.
- Inspect the connecting rods
Inspect the big and small ends of the connecting rods and the rod bodies to make sure they are not bent or twisted.
