The objective of this procedure is to show you how to test install the pistons. The objective of this procedure is to show you how to test install the pistons. A pre-assembly check of the piston bearing clearance is quicker if you don't install the piston rings.
Part 1. Preparation and safety
- Test install the pistons.
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.
- 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
- For test assembly don’t install the piston rings.
- Use clean paper towel to wipe down components prior to fitting it won’t leave any cloth residue.
Part 2: Step-by-step instruction
- Prepare to install pistons
A pre-assembly check of the piston bearing clearance is quicker if you don't install the piston rings. That also makes it easier to rotate the crank for the rest of the checks.
Make sure everything is clean. Wipe any dust off the rod journals of the crank, then wipe out the cylinder bores with a clean dry paper towel. Don't use a shop rag, they leave cloth fibers on the cylinder walls. When the bores are clean, wipe an even coat of some fresh engine oil all over the insides of the bores. Do this for both sides of the block.
Spin the crank so the furthest forward rod journals are facing up, and disable the rotation of the crank. Pinch the rear flange of the crank shaft with some vice grips and then tie or tape the pliers to the engine stand, or install the flywheel or flexplate and disable its rotation in a similar way.
This locks the crank in place so it cannot spin and ruin the plastic gauge when you install it in the connecting rods. When the crank is set, get the pistons together. It is a good idea to label the tops with the numbers of the cylinders and an arrow that points towards the front of the engine. All pistons have some type of notch or marking that indicates which side of the piston is meant to face toward the front of the engine.
- Install wrist pins
There are two types of wrist pins that could hold the pistons to the rods. With full floating wrist pins, wipe out the connecting rods, lubricate the pins and then fit it together. Make sure to check the engine manual to make sure you install the rod in the correct direction. There's no need to use any snap rings right now.
Most engines have semi-floating wrist pins in which case the machine shop would have already attached the pistons to the rods. This next inspection will verify that the machine shop has installed them correctly.
With either type of wrist pin, you need to remove the caps from the rods. If they were machined, they'll be torqued in place. Hold the rod steady in a vice and loosen the nuts. The caps are usually stuck in place so you'll need to hammer them off gently with a brass hammer.
- Install rod bearings
With the caps separated from the rods, install the new rod bearings.
First verify the part numbers to be sure that they match the sizes on your crankshaft. If the crankshaft was cut undersize on the rod journals, the bearings should have an indicator in the part number to tell you that the bearings are a similar amount oversized. The bearing set may appear to match the machined crankshaft, but you need to check to make sure.
- Install pistons
Stick the plastic clearance gauge in place with petroleum jelly. Put a gauge in both the number one and two rods and then install protector boots. If you use long pieces of fuel hose they make it easier to line up the rod bearing to the journal of the crank. Don't let go of the piston, because it will fall right out with no rings to hold it in place. Keep your hand on the rod, and have the cap and bolts nearby so your other hand can install the cap. Don't forget to line up the tangs in the rod and the cap on the same side as each other. When you have at least one bolt threaded on you can let go and cinch up the bolts hand tight.
With the crank in this position, you can also put in the number two piston with a piece of plastic gauge material on the bearing. Again, don't let go of the rod until the cap is on properly and there is at least one bolt tightened. Now two rods are in place, the crank is locked and you have access to all four rod bolts.
- Torque the rod bolts
Check the rod bolt torque specification. Set the wrench to one third of the final torque setting for all four of the bolts, Then torque them at two thirds, and then finish tightening them all at full torque.
Immediately afterwards, loosen all four of the bolts. The most important thing is to make sure not to rotate the crank at all when you are tightening and removing the caps.
- Remove pistons and check bearing clearance
Sometimes the caps can be worked off by hand. Usually, you have to hit the bolts to break the caps loose. That is the reason why you put the gauge in the rod and not the cap.
As before, keep a hand on the piston or the rod because when the piston breaks loose, it wants to fall right out of the cylinder with no rings to hold it. Install the protector boots and take it out to be checked.
If the clearance is correct, clean the plastic off the bearing or the crank. Now we can lubricate the first bearing and slip the piston back into its cylinder and make the bolts hand tight. Then, pull the other rod and check its clearance. Again, if it is correct, oil it, put some bolt protectors on and put it back in.
- Check rotation clearances
When both caps are back on you, torque them again in three increments and then unlock the crank. Now rotate the crank at least twice, slowly. This will mean the camshaft will have gone around one full turn. Look at the cam lobes as they rotate to make sure that none of the piston skirts interfere with the camshaft lobes.
Also check to make sure that the rod bolt heads don't contact the block or a piston skirt or a cam lobe.
If everything is clear, rotate the crankshaft so that the next set of rod journals are facing up. Lock the crank again and continue installing the rest of the pistons. When all the pistons are installed check they are rotating smoothly.