Understanding Head Resurfacing Tools
Head resurfacing tools are an important piece of equipment for engine rebuilding shops and automotive machine shops. As engines accumulate wear and tear over hundreds of thousands of miles, the cylinder heads can become warped or damaged. Resurfacing the cylinder heads is often required to restore proper sealing and compression before reassembling the engine.
What is Cylinder Head Resurfacing?
Cylinder head resurfacing, also known as milling, is a machining process to remove a very thin layer of material from the head gasket surface to restore a smooth, flat sealing surface. This allows the rebuilt engine to have the proper compression and performance.
The amount of material removed during resurfacing is usually only a few thousandths of an inch, just enough to clean up any warpage or imperfections. Taking off too much material can reduce the compression ratio and combustion chamber volumes beyond acceptable tolerances.
Why Cylinder Head Resurfacing is Necessary
There are a few main reasons why cylinders heads become warped or damaged and require resurfacing:
- Normal engine wear over time
- Overheating events which can warp the heads
- Corrosion from coolant leaks which damage the surface
- Physical damage from foreign objects or debris getting sucked into the engine
Resurfacing the cylinder heads is much more economical than replacing them entirely. It also allows the rebuild shop to restore the engine to like-new condition and performance specifications.
Head Resurfacing Process
The cylinder head resurfacing process consists of several key steps:
- Securely mounting the cylinder head to the resurfacing machine
- Indicating the head to determine amount of material needed to remove
- Setting up and preparing the tooling
- Making finishing passes across the head gasket surface
- Checking the surface finish quality and flatness
- Cleaning and preparing head for reassembly
This process requires specialized machining equipment and experienced technicians to properly set up and operate. The tooling consists of extremely sharp cutting tools mounted to a precision spinning arbor. Most shops will resurface the heads multiple times during the rebuilding process to achieve the tightest tolerances.
Key Components of Head Resurfacing Machines
Head resurfacing equipment features heavy duty components to withstand tough shop use. The main sections of the machine include:
Rigid Base and Frame
The base and column provide a solid foundation to keep the head perfectly stationary while the cutter arbor spins at high speeds. This allows for smooth, vibration-free cuts and precision accuracy.
Head Fixture Mounts
Dedicated head fixture mounts properly secure different engine cylinder heads to the table. Multi-angle mounts allow tilting the head for the optimum cutting angle.
Precision Spindle and Bearings
The precision spindle assembly supports and spins the cutter arbor smoothly thanks to high quality bearings. Powerful motors provide ample torque for the cutting operation.
Digital Readout Displays
Digital readouts show the vertical position of the spinning cutter arbor as it is slowly lowered to make finishing passes across the head surface. Operators can set precise cut depths down to 0.001”.
Cutting Tool Arbors
The arbors hold a range of interchangeable cutting tool bits specially designed for aluminum or cast iron heads. Carbide inserts with precision ground geometries provide a smooth cutting action.
Safety Shields
Safety shields fully enclose the spinning arbor and cutters to contain sparks, debris, and coolant spray.
Coolant Systems
High pressure coolant nozzles flood the cutter and head surface with lubricating fluid to control heat, flush away metal debris, and extend cutting tool life.
Types of Head Resurfacing Tools
The tooling arbors used for resurfacing cylinder heads come in two main styles:
Milling Cutters
Milling cutters feature inserted carbide or CBN tips arranged in a helical pattern around the arbor. This allows taking deeper cuts without overload. The inserts cut on the periphery as well as the face for high material removal rates. Indexable carbide inserts are economical and easy to replace as they wear.
Fly Cutters
Fly cutter style arbors support a single, larger cutting insert and rely on speed to achieve the material removal rate instead of multiple teeth. The insert angles down to cut mostly on the leading edge. Fly cutters require rigidity to prevent chatter and vibration.
Both milling cutter and fly cutter arbors have advantages and are widely used for successful head resurfacing. The choice depends on shop preferences and types of heads being machined.
Quality Control Checks for Resurfaced Heads
Once the head resurfacing process is complete, the head surface should be checked to ensure it meetsrebuild specifications. Quality control checks include:
Surface Finish Measurement
A surface finish gauge verifies the surface has the proper smoothness and flatness. Typical target Ra surface finish measurement is around 60 Ra microinches.
Flatness Checks
Precision straight edges combined with feeler gauges check across several areas to confirm the deck surface is flat within 0.003" or less. The head may need to be indicated and recut if out of spec.
Cleaning and Visually Inspecting
Finally, the head deck should be thoroughly cleaned to remove all metal debris and coolant residue before the final visual inspection. Any remaining scratches or surface defects require additional spot machining.
Maintaining and Care of Head Resurfacing Equipment
To sustain precision resurfacing results over many years of use while minimizing downtime, a comprehensive preventative maintenance program should include:
- Replacing worn spindle bearings on schedule
- Inspecting gibs and ways for tightness
- Checking tramming/indication of the arbor
- Sharpening or replacing worn cutting tool inserts
- Cleaning under safety shields to prevent build up
- Greasing zerks on slides and screws
A well-cared for head resurfacing machine is an invaluable piece of equipment for any engine rebuild shop. With quality tooling and proper usage, technicians can reliably resurface thousands of heads to OEM specifications.
FAQs
How much material is removed when resurfacing a cylinder head?
Typically only a few thousandths of an inch (a few microns) are removed from the head gasket surface during resurfacing. This is just enough to clean up warpage and surface irregularities. Removing too much material can reduce combustion chamber volumes and compression ratios.
What surface finish should be targeted when resurfacing heads?
The recommended surface finish is approximately 60 Ra microinches. This provides the proper seal between the head and engine block without retaining too much oil.
What checks are made to verify proper head resurfacing quality?
Three main checks made are: surface finish measurement with a gauge, flatness checked along the deck using a precision straight edge and feeler gauges, and thorough visual inspection after cleaning.
How often should head resurfacing machine maintenance be performed?
Preventative maintenance including spindle bearing replacement, gib adjustment, tramming checks, tool sharpening and more should be performed on a regular basis. Every few months is recommended for shops with frequent use.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.
Add Comment