How to hone an engine cylinder
Tom Vondrasek | 29th Feb 2024 | 5 minutes to read
Honing an engine cylinder ensures a proper seal between the piston rings and cylinder walls. This procedure can be used when giving an engine a freshen-up, or when rebuilding an older engine that has not been used for a long time. If the cylinder bores are too worn, then the engine block will need to be machined.
The wear is caused by the pistons going up and down in the cylinders and it will eventually cause the cylinders to lose their nice round shape. This then makes the seal of the piston rings worse causing a loss of power and an engine that starts to blow smoke from the exhaust. It is a gradual process and doesn’t suddenly happen overnight.
Before any honing can commence the engine is normally stripped down so you have a bare engine block. It is worth taking measurements to see how bad the wear and taper in the cylinders are. If the wear is too great, they will need machining. If not, honing will do the trick. It can also work for that engine or block you have had sitting in a shed corner. The hone will remove light surface rust, scratches, and marks from the bores.
Below is the general procedure for honing an engine block:
Tools & Materials
Honing tool
Hand-held electric drill
Accurate measuring tools
Honing oil or lubricant
Safety goggles
Gloves
Rags
Notes About the Tools
There are some important things to consider when gathering the above tools and there are specific ways to utilise them during the process of honing your engine block.
Honing Tool
It is recommended to use a hone with the 3 x stones on it rather than a Flex or Ball-Hone. The reason is the stones sit flat across the surface of the bore so you can see any imperfections in the bore, such as raises or dips.
The ball types follow the contour of the bore and are best used for a quick clean up when you know the bore is round. They are adjustable for different bore sizes and have a different grade of stones based on the piston rings you are going to use.
Electric Drill
When using the electric drill, you are aiming at a 45-degree cross hatch pattern so you will need to play with drill speed and how fast or slow you move the tool through the bores.
Measuring Tools
You need accurate measuring tools as bore variations are measured in thousandth of an inch; 1 one thousandth of an inch = 0.0254mm. They are the sort of specs you can’t gauge by looking at them. A bore dial gauge and outside micrometre are needed for this process.
Honing Oil
Make sure to use honing or cutting oil when using the stone. A good lightweight 10W-30 mineral engine oil will also work.
Safety Gear
Wear safety goggles and gloves to protect against any debris or particles that may be generated during the honing process.
Cleaning Supplies
Have rags or towels, detergent, degreaser, and water on hand to clean the block and surrounding area before and after honing.
It is very important to get the bores nice and clean after honing. So clean that if you ran a white glove over the surface, it would stay white. If you don’t clean it thoroughly, premature piston ring wear can occur.
Pistons and Piston Rings
Based on measurements and by electing to hone the block, fitting new piston rings to your old pistons is an important part of the process. Check with manufacturers to make sure you can get the new rings in the size you need before starting the process.
Prepare the Engine Block
It needs to be a bare block and supported so you can run the hone through it without it moving. You also need to be able to clean it thoroughly so allow for this when picking a suitable location for the job. Ensure the engine block and surrounding area are clean and free from any debris or contaminants.
Inspect the Cylinder
Visually inspect the cylinder for any signs of damage, scoring or wear. Check for scratches, ridges, or other irregularities on the cylinder walls. Measure the bores and check the manufacturers tolerances to see if honing or reboring is required. You need about 6 measurements per bore. Top, middle, bottom on the thrust and non-thrust sides of the bore.
Select the Correct Honing Tool
Choose the appropriate tool size that matches the cylinder bore diameter. Select the grade of stones you need to match the piston rings. Ensure the hone tool is compatible with the type of engine cylinder being honed.
Apply Lubricant
Liberally apply honing oil or lubricant to the cylinder walls to facilitate smooth movement during the honing process. Ensure even distribution of the lubricant.
Honing Process
Insert the honing tool into the cylinder and attach to a drill or hone driver. Start the drill at a low speed and move the hone tool up and down the cylinder. Experiment with the drill speed and movement in and out of the bore to get the crosshatch pattern correct. The trick is being consistent with this technique across all the bores.
Check Progress Regularly
Periodically inspect the cylinder walls to monitor the honing progress. Stop honing once the desired surface finish is achieved, ensuring the cylinder walls are smooth and free from imperfections.
Clean the Cylinder
After honing, thoroughly clean the cylinder walls using clean rags or towels and a suitable solvent or cleaning solution to remove any honing residue or debris. Use the ‘white glove’ test with a rag or paper towel to prove they are clean.
Inspect and Measure
Inspect the honed cylinder walls to ensure they are uniform, and the cross hatching is consistent. Measure the cylinder bore diameter using the precision measuring tools to confirm it meets the engine specifications.
Prepare for Reassembly
Clean the surrounding areas and components thoroughly before reassembling the pistons in the bores. Check gaps on the new piston rings in the bores before reassembly. Ensure all parts are properly cleaned, lubricated, and dimensioned before reinstallation.
Honing an engine block is a meticulous process that requires attention to detail and precision. This goes for rebuilding engines in general. By following these step-by-step instructions and using the right tools and materials, you can effectively hone an engine block. Once the new piston rings are fitted, it will bring back the engines performance to factory specs and give the vehicle a new lease of life.
