How Much Does It Cost to Rebore an Engine?

Last Updated on March 11, 2024
Written by CPA Alec Pow | Content Reviewed by CFA Alexander Popinker

If you have an older vehicle with high mileage, chances are the cylinders in your engine are worn out. This causes loss of compression and reduces engine performance.

Reboring the engine cylinders is a cost-effective way to restore compression and power. But how much does it cost to rebore an engine? Let’s take a look.

How Much Does It Cost to Rebore an Engine?

Reboring an engine involves machining the cylinder bores to a larger diameter to remove damage and wear. Then, oversized pistons and rings are installed to match the new bore size. This restores the seal between the piston and cylinder bore, increasing compression.

The average cost for reboring a standard 4-cylinder engine is $300 to $800. For a V6 or V8 engine, expect to pay $450 to $1,200. However, costs vary widely based on the specific engine, bore size, parts needed, and machine shop rates. Luxury makes like BMW and Mercedes tend to cost more.

For example, reboring a small 4-cylinder Honda Civic engine may run around $400. While boring the cylinders on a Chevy 350 V8 could be $800 to $1,000. Higher-performance boring jobs with larger oversizes cost more as well.

Additional expenses like new pistons, rings, bearings, gaskets, and a full rebuild kit can add $500 to $2,000 or more to the total engine reboring price. The make, model, bore size, and parts needed impact costs significantly.

Why Rebore an Engine?

Engine cylinders become worn and out-of-round from friction over tens of thousands of miles. Reboring restores roundness and the proper clearances. This brings compression back up and reduces blow-by gases.

Reboring an engine enables installing larger pistons and rings for increased displacement and horsepower. This affordable upgrade boosts performance.

For high-mileage engines, reboring can restore power and efficiency while being much cheaper than replacing the engine. It extends engine life at a fraction of replacement cost.

The Engine Reboring Process Step-by-Step

Reboring an engine is a precision machining job best left to professional engine builders and machine shops. Here is the general process:

• The engine block is cleaned and secured in a fixture in the boring machine.
• The bore diameters are precisely measured to determine the rebore size needed.
• A cutting head on a rotating bar is inserted in each cylinder and bores out material to the new diameter. Coolant keeps the cutter and cylinder cool.
• Torque plates simulate engine assembly so bores are machined in proper alignment.
• After boring, the cylinders are honed with abrasive stones to achieve the desired surface finish and roundness. This ensures optimal piston ring seal.
• The bores are test fitted with new oversize pistons and measured with precision gauges. More honing may be needed for a perfect fit.
• For performance builds, the block undergoes additional machining steps like decking, align boring, or surfacing.
• Finally, the block is carefully cleaned and assembled with new parts.

Precision boring bars, micrometers, honing equipment, and specialty fixtures are required. This professional equipment is very expensive. Proper setup, measurements, and experience are crucial for accuracy.

What Impacts the Cost of Reboring an Engine?

Several key factors affect what you will pay:

• Engine size – Larger V6 and V8 blocks cost more to bore than smaller 4-cylinders. More cylinders means more machining time and parts.
• Bore size – The oversize of the bore increases the price. A 0.020″ oversize is cheaper than a 0.060″. Maxing out the bore size costs more.
• Damage amount – Severely scored cylinders take longer to rebore and may need additional repairs, increasing labor and parts costs.
• Machine shop rates – Prices vary between small local shops versus high-end builders. Engine specialists typically charge more.
• Replacement parts – The more new parts needed, the higher the total expense. Pistons, rings, bearings all add up.
• Performance modifications – Upgrades like porting the heads, blueprinting, or balancing raise the price but can dramatically boost horsepower.

You might also like our articles about the cost of valve cover gasket replacement, engine rebuilding, or full engine swap.

Choosing a Shop for Reboring

Finding the right shop ensures a quality job at a fair price:

• Lookup local engine machine shops online and compare Google reviews. Shops with 4+ stars and expertise in your engine type are preferable.
• Ask trusted mechanics and car enthusiasts for referrals to the best local bore shops.
• Call the shops and describe your specific engine – ask if they have experience reboring it. Inquire about their machining capabilities.
• Ask lots of questions: Do they offer a warranty? What is the typical turnaround time? What will the estimated total price be?
• Get quotes from multiple shops. Compare the prices, experience levels, and services included to choose the one that best fits your needs and budget.
• For performance builds, look for a shop experienced in maximizing horsepower gains during boring/honing.

How to Reduce Reboring Costs

Here are some tips to lower the costs of your engine boring job:

• Supply any usable core parts from your existing engine like heads, oil pan, etc. This reduces the shop’s markup on parts.
• For minor oversizes (0.010-0.030″), reuse the bearings if still in spec. Check with machinist first.
• Supply your own performance parts if you want upgraded pistons, rods, etc. The shop markup is less.
• Negotiate shop rates, price match quotes, offer to supply your own parts – most will work with you.
• Only bore as much as needed – avoid maxing out the cylinders.
• Skip unnecessary machining steps like surfacing or alignment boring if the block is undamaged.

The typical price for reboring a standard engine ranges from $300 to $1,200 depending on the motor size, machining needed, and parts required.

Additional performance upgrades or repairs increase costs further. With research and negotiating, you can find an experienced shop to rebore your engine affordably. The restored engine performance will be worth the investment.

Can you bore out an engine at home?

While some DIYers attempt to rebore their own engine, this is not recommended. Reboring is not a home DIY job for several reasons.

Reboring requires professional boring and honing machines for proper cylinder finish. These boring bars cost thousands of dollars and are not something you will find in most home toolboxes.

It also demands precision measurements and careful setup for accurate bore alignment with the block and crankshaft. Without precision equipment, an improper bore angle will lead to serious issues down the road.

Reboring requires extensive experience in specific engines and bore oversizing to ensure proper ring to wall clearances. Mistakes here will result in lower compression later. This is something home mechanics are not equipped to handle.

Lastly, there is no cost savings in DIY engine reboring. Purchasing the necessary tools, training, and parts will cost more than paying a shop. For inconvenience, risk of costly mistakes, and lack of experience, reboring at home is not recommended. Trust this important engine project to an expert shop instead.

Does boring an engine increase horsepower?

Yes, bored out and stroked engines can produce significant horsepower gains. Here is how boring increases engine power:

• Larger cylinder bores allow installing bigger pistons and rings. The extra piston displacement boosts torque and horsepower potential.
• More air/fuel mix can be drawn into larger cylinders. This maximizes volumetric efficiency for increased power output.
• Lower friction from tight new bores reduces parasitic losses that restrict output.
• Higher compression ratios can be run with thick cylinder walls and lower combustion chamber volumes.
• When combined with a longer stroke crankshaft, larger bores enable bigger total displacement and power.
• Oversized engines provide more room for performance upgrades like ported heads or camshafts with extra lift and duration. This adds even more potential hp.

For a street performance engine, boring 0.030 to 0.060 inches over stock size can reliably add 20-50 horsepower or more when combined with supporting mods like intake, heads, cam, and tune. This makes affordable boring one of the best bang-for-buck upgrades available.

How long does a rebored engine last?

With proper maintenance, a professionally rebored engine can easily last over 100,000 miles or more. Here are some key factors in maximizing rebored engine longevity:

• Use the best quality parts like forged pistons and rings when rebuilding the engine. Quality components last.
• Stick with the recommended bore oversizes and avoid excessively overboring the block. This maintains cylinder wall integrity.
• Break in the new engine properly with conservative RPMs to seat the rings. Follow break-in oil recommendations.
• Maintain regular oil changes, tune ups, and service intervals after install. This keeps the engine running like new.