Engine rebuilding and the techniques utilised within an engine shop are highly specialised and perhaps undervalued in general. If a mechanic is akin to a doctor on farm machinery, then the engine rebuilder is a surgeon.

It is certainly a unique craft where attention to detail is critical and one that requires a mind-boggling store of knowledge to fix all the various makes and models of engines from old to new.

The machining and engineering skills of the people involved are extraordinary considering the multitude of issues that arise. Tolerances in places like these are measured in thousands of a millimetre, so the room for error is tiny.

Inside the engine shop, a host of highly sophisticated machines are needed to perform a vast array of complex machining tasks on various engine components.

McCarthy Engine Reconditioning, based outside Castle island in Kerry, is a business known for its ability to transform worn metal and bring it back to life.

Jerry McCarthy and his wife Sheila started the business from humble beginnings in 1997.


Jerry McCarthy and his wife Sheila started the business from humble beginnings in 1997 in a shed at the back of their family home and have since gone from strength to strength.

Engines come here from far and wide as the McCarthys have built a large customer base due to their hard work and professionalism.

“The original business was grinding crankshafts and sleeving blocks and over the years it just spiralled from there,” says Jerry.

The business now can only be described as a state-of-the-art modern workshop where the cleanliness is something to behold.

“We currently have six staff along with Sheila and myself and we offer a full suite of engine services such as pressure testing heads, skimming, refacing valves, fitting valve seats and guides, boring and honing blocks, surfacing blocks, line boring as well as grinding and polishing crankshafts.”

Maintenance is key

Jerry says the business currently is about 80% diesel engines, and the rest petrol with the odd gas engine.

Jerry says the business currently is about 80% diesel engines, and the rest petrol with the odd gas engine here and there. Automotive and agri/plant breakdown is close to a 50/50 split, with the odd mixer engine, motorbike, generator, etc. making up the rest.

Massey/Perkins, Ford, Fiat, New Holland, Deutz, Zetor, John Deere and Case IH make up the bulk of the agricultural work.

Massey/Perkins, Ford, Fiat, New Holland, Deutz, Zetor, John Deere and Case IH account for the bulk of the agricultural work.

Jerry highlights the importance of maintenance for engine longevity. “The simple stuff certainly matters to get longevity, such as air filters, fuel filters, good quality oil, service on time and as per the manufacturer’s guidelines. Keep an eye on the cooling system, thermostat and radiator.”

On the main changes he has seen since he started the business, he says: “Where do I start, skilled labour is definitely an issue nowadays, as we have much more complete engines to tear down rather than just components to machine.”

Dealerships don’t have enough skilled staff so engine work tends to be contracted out. Also, these days “emissions devices like EGR and DPFs are great in theory but once they clog up and block the inlet manifold or exhaust, they prevent the engine breathing properly,” he says.

The knock-on effects are harmful to the engine and can be very costly to rectify. Jerry points out that modern engines work at greater loads and temperatures for their cubic capacity (cc) compared to years ago: “Today’s engine and cooling packages are so refined that there is no room for error so the head/block can overheat more easily if not serviced properly.”

Jerry emphasises that a young or inexperienced mechanic doing a job for a customer “must remove and flush all coolers as a new reconditioned engine will run hotter and the cooling packages are designed to work – but not if the performance is down due to scaling or partial blockages”.

Thorough cleaning and flushing of the engine ancillaries left on the machine are so important as otherwise the freshly rebuilt engine may give trouble down the road.

Customer expectation is something Jerry also notes has changed, as some people would drop an engine in the morning and expect to collect it at teatime that day. This kind of turnaround time is impossible with the number of processes involved.

“They might have little concept of the time to strip, properly clean, assess the job, order parts, set up the machine and reassemble,” he says.

It was different in the past. “Thirty years ago customers would be very grateful and thankful that you saved them from buying a new engine altogether, even if it took a few days.”

And he believes the car, tractor and truck industries aren’t helping themselves either and the designers clearly don’t think about the product when it has 5,000 plus hours on it. Without electronics and software, it is impossible to start the modern engine before leaving the shop.

“Clearly the engine shop isn’t considered by the manufacturers and it’s letting us down as we have to rely on others to make sure sensors are reset correctly, components tightened and sealed correctly,” he says.

Manufacturers are saving weight with “flimsy plastic components which are harder to seal to metal parts due to varying expansion rates” compared to older engines.

A dying trade

Is engine rebuilding a dying trade? “Yes, most definitely,” replies Jerry. The reasons he outlines are many but it is not because there is a lack of engine work out there, quite the opposite.

“The Government needs to wake up here as the cost to run a business today is skyrocketing with no let-up in sight,” he says.

Like all small businesses right across Ireland, rising costs are the main issue with rates, wages, insurance, and bank charges to name a few at an all-time high. For this particular type of business, the electricity to heat the water for pressure testing and running the engine washers is critical as it is for machinery to perform related tasks – electricity costs have gone through the roof.

Jerry says he couldn’t possibly see how anyone would start into this business today due to high set-up and running costs and the difficulty in sourcing staff. “The staff are key here and without them we would be in big trouble. We are blessed with the team we have, and I simply wouldn’t be able to cope without them, but the whole country is crying out for mechanics, machinists and fitters.”

In the engine trade it is a unique skillset as there is the machining side and a rebuilding side. Attention to detail is critical. “Schools and teachers aren’t putting any value on these hand skills, a software engineer isn’t going to be able to set a liner to flange height correctly or centre a crankshaft properly for regrinding,” he says.


However, he is up to speed with technology and highlights the investment in his Computer Numerical Control (CNC) machine as an example of moving with the times, but he stresses you need to understand the methodology in situ, the tolerances and so forth prior to setting up the machine to perform the task.

Once set up, the CNC machine will free up the operator to carry out other tasks as it performs the machining operation, which increases the workshop’s overall efficiency.

Ultrasonic cleaning is something that Jerry feels could certainly increase in the future as it gets into all those impossible-to-reach places and does a fantastic job on carbon removal.

He says that more garages need to utilise the service to clean manifolds, EGR coolers, pipes, etc. that are coked up with carbon.

‘Upcycling’ is a new buzzword used by large corporations and government bodies when talking about green and sustainability goals. It means taking something no longer in use and giving it a second life and new function. It’s worth remembering that the McCarthys’ engine shop and diesel shops up and down the country are doing this all day everyday for the farming community.

Fergal O’Sullivan is a lecturer in the agricultural engineering department at Munster Technological University (MTU) Kerry.

Case study and costs

We sampled the rebuilding process in the McCarthy workshop of a vintage MF 135, and two common farm workhorses – a more modern John Deere 6-cylinder 30 Series and New Holland TM150. From this, readers will appreciate the expertise of these dedicated engine rebuilders.

2010 JOHN DEERE - 6930 6-cylinder 24 Valve Head

  • Decarbonise, wash, inspect and strip down to bare head.
  • Machine valve guides for phosphor bronze guide inserts.
  • Supply and fit 24 valve Guides.
  • Supply 12 new exhaust valves.
  • Supply 12 new inlet valves.
  • Cut 24 valve seats for inlet and exhaust.
  • Skim head.
  • Rewash engine head to remove debris.
  • Supply and fit 24 valve stem seals.
  • Lap in valves.
  • Reassemble 24 valve head, collets, caps, springs.
  • Suction test valve seating.
  • Ultrasonic cleaning.
  • Approx. €900-1050 plus VAT. When asked about pricing, Jerry said that “no job is ever the exact same, even for the same make and model”. The factors he considers include:
  • Is the head properly clean?
  • Are all components removed or only some?
  • Are the injectors removed or are they stuck in the head?
  • Is the exhaust manifold properly removed, or studs left, or some sheared off and stuck in the head? In this example, John Deere 30 series 24V heads don’t come with guides but are a complete casting. The creativity and innovation here is what separates a professional job from a botch job. Jerry and his team machine out the guide casting and press in a new phosphor bronze guide sleeve supplied by the manufacturer so the valve stem to guide clearance is back within specifications. It’s this ingenuity along with ultrasonic cleaning that sets places like this apart.
  • 2002 - NEW HOLLAND - TM150 - 6-cylinder 12 Valve Head

  • Decarbonise, wash, inspect and strip down.
  • Remove worn valve guides.
  • Supply and fFit 12 valve guides.
  • Supply 6 new exhaust valves.
  • Supply 6 new inlet valves.
  • Cut 12 valve seats.
  • Skim head.
  • Rewash head to remove debris.
  • Supply and fit valve stem seals.
  • New valve collets.
  • 12 New valve caps.
  • Skim exhaust manifold side of the head.
  • Approx. €730-850 plus VAT
  • Jerry advises that along with conventional head face skimming and current valve set-up, he recommends to customers that New Holland TM heads need to have both the exhaust manifold side of the head and the exhaust manifold surface machined.

    “Due to the heat and various expansion rates of different components and the added weight and leverage effect of the corner post exhaust, the silencer box and turbo, it’s hard to get good sealing,” he says.

    If this process is not performed after a full engine rebuild, the engine when hot might not boost adequately due to leakage. By advising customers on this additional process Jerry helps them eliminate lots of potential issues and customers are delighted as it makes sealing the manifold and the head a lot easier.


  • Dismantle engine, decarbonise, wash and inspect three liners, and three pistons with rings.
  • Regrind crankshaft and supply main bearings.
  • Re-sleeve block and skim block.
  • Big end bearings and thrust washers.
  • Supply bushings and bush conrods.
  • Recondition cylinder head.
  • New oil pump, water pump, and thermostat.
  • Full set of gaskets and seals.
  • Cam seal, drain tap etc.
  • Skim pistons, oil suction pipe kit, core plugs.
  • Recondition injector pump and injectors.
  • Reassemble engine.
  • Approx €2750 - €3200 plus VAT.
  • “The Massey Ferguson 135 was our bread and butter one time, and they are still coming in the door today despite all the larger tractors around,” says Jerry.

    McCarthys have rebuilt a lot of them and while they are straightforward it is still time-consuming work to rebuild them properly. Quality parts like oil pumps and setting piston height are critical.

    “To set correct piston height the pistons have to be fitted, measured, removed, machined and then refitted, which all takes time,” says Jerry. If not, he explains that compression won’t be consistent in the cylinders, and it is this type of attention to detail that demonstrates the knowhow at work here.