In-situ Machining the World’s Largest Four-Stroke Diesel Engines

Ø 64 cm bore, 90 cm stroke, 2’150 kW (2’880 hp) power per cylinder: The world’s largest four-stroke engines are very mighty machines indeed!

These powerful engines were built during the late 1990’s, mostly in a 6-cylinder configuration. With a nominal power output of 12’900 kW, they found popular application as single propulsion engines in multi-purpose cargo vessel of about 20’000 DWT size.

During 20 – 25 years of operation until now, these engines have accumulated more than 120’000 running hours each. In terms of number of engine revolutions, this is equivalent to a car driving for 1.8 million kilometers (1 million miles)!

In-situ crankpin polishing
In-situ crankpin polishing

It is therefore hardly surprising, that after that many running hours signs of wear were found on the crankpins of these engines. As is often the case on medium-speed, four-stroke engines, the crankpins were suffering from what is called “cam effect” or “ridge wear”.

Has your four-stroke engine accumulated around 60,000 running hours or more?

Although the crankpins might appear to be in good condition, it is very likely that they suffer from the cam effect (also known as ridge wear) and are in need of machine polishing. If this is not done, then you might face a failure soon!

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Usually, then the cam effect will manifest itself in two ways:

  1. Through uneven wear in horizontal direction, with nearly no wear at the centre of the pin and at the edges, but with easily noticeable wear to the left and right of the oil bore.
  2. The pin is not affected evenly throughout its circumference. The cam effect is usually most pronounced at about 30 – 45 degrees after Bottom Dead Centre (BDC). For this reason it is called “cam effect” – the pin is not perfectly circular anymore.

QuantiServ appeals to owners and operators of medium-speed four-stroke engines to sensitize the crew about the cam effect. We highly recommend that the pins are carefully checked whenever an engine overhaul or bearing replacement is carried out. If any uneven wear patterns are detected, then the pin must be machine-polished to restore its proper geometry before any new bearings are installed and the engine is restarted.

If the cam effect is detected in good time, then machine polishing of the pins is usually sufficient to correct the problem. After machine polishing, the crankshaft will be ready again for several years of continuing operation. Whether standard bearings or undersize bearings will have to be installed after polishing will depend on the actual situation.

If, on the other hand, the cam effect goes undetected for too long, then a crankpin failure is almost inevitable. Such was also the case here on the first engine. Heat treatment and machining was therefore necessary and was swiftly carried out by our Swedish specialists. Having seen the excellent result and now aware of the cam effect, the customer tasked us to machine polish all pins on this engine and on the sister vessels, which is why we eventually polished about 70 pins in quick succession but in different ports.

In-situ heat treatment
In-situ heat treatment (annealing)
Crankpin machining
Crankpin machining
Completed crank pin
Completed crank pin

All work described above was carried out on board by our Swedish in-situ specialists. They were supported by our reconditioning experts that meanwhile worked on those engine components that were removed from the vessel for an intervention ashore. These components were sent to our reconditioning centre in Kruiningen, The Netherlands, where they underwent  thorough overhauling and machining works.

By the time of writing in August 2022, we have overhauled around 70 cylinder heads and have re-bored a similar quantity of big end bearing housings. Machining the big end bearing housings became a necessity due to excessive ovality in the bore.

Newly overhauled cylinder heads in our workshop
Newly overhauled cylinder heads in our workshop
Big end bearing bore machining
Big end bearing bore machining

More Than 1,000 QS50K Pistons Delivered – And Counting!

In 2019, following an extensive research and testing period, we have introduced the first QS50K pistons into the market. It was the beginning of a lasting success story: Ever since, we have produced and delivered more than 1’000 pieces, to many different customers.

These pistons are now installed all around the world, in ocean going vessels and in power plants. They are performing extremely well and achieve time between overhauls (TBO) that hitherto were unthinkable. The earliest QS50K pistons have accumulated well over 30,000 running hours and are still in service!

Rebuilding the piston ring grooves
Rebuilding the piston ring grooves

Benefits of the QS50K technology

With the introduction of the QS50K coating technology, QuantiServ has redefined the piston reconditioning process. This proprietary technology was developed by QuantiServ and offers the following important advantages:

    • Extremely durable, wear resistant coating, resulting in very long life-time / time between overhauls (TBO)
    • Fully automated process carried out by a robot, resulting in a top-quality product due to the robot’s very high accuracy, repeatability and consistency.
    • Faster than chromium plating, therefore shorter turnaround times
    • Less heat input into the piston, eliminating any residual stresses that over time could develop into cracks
    • Environmentally sound, non-toxic process

Availability

We offer the QS50K technology for any engine brand and for any cylinder bore above ø 48 cm. The QS50K pistons that we have delivered so far covered the bore range, from ø 48 cm to ø 98 cm. They were destined for engines manufactured by the big three OEMs, in an approximately 45%/45%/10% ratio.

At this moment, our recon centres in Kruiningen (The Netherlands) and Suzhou (China) are equipped with the required machinery to offer this product. Our large recon centre in Singapore will follow very soon.

24,000 Hour Ring Groove Life Time. Guaranteed!

The quality of our QS50K coated ring grooves is so good that we now offer a 24,000 hour* warranty on fully reconditioned, QS50K coated two-stroke pistons!

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*pro-rata, 24,000 running hours or three years after delivery, whichever comes first

To give maximum flexibility to our customers, we offer three different ways of working to chose from:

  1. Reconditioning on exchange. The customer gets a newly reconditioned component delivered from one of our four reconditioning centres. Once he has installed the component into his engine, he returns his old part to us.
  2. Reconditioning of the customer’s own part. The customer sends the component to be reconditioned to a QuantiServ reconditioning centre, where it undergoes professional reconditioning after which it is returned to the customer.
  3. Straight sale. The customer purchases a reconditioned piston from us, without returning an old one.

We can apply the QS50K coating to pistons that are undergoing full or partial reconditioning.

Full reconditioning

The entire top surface and ring groove area is first machined off and then rebuilt by robotic MIG or SAW welding. Thereafter, the piston undergoes final machining before the QS50K coating is applied to the ring grooves. The last step is grinding of the ring grooves, which completes the full reconditioning process.

If it is requested by the customer, then we can coat the top of the piston by a protective layer of Inconel. This can be a good solution for engines that suffer from excessive hot corrosion at the piston top.

Partial reconditioning

If only the ring grooves are worn and if a piston is in otherwise good condition, then partial reconditioning is possible. A precondition is, however, that none of the ring grooves has worn so much that not only the chromium layer but the steel substrate itself has worn. In this case, partial reconditioning is not possible and full reconditioning is the only remedy.

During partial reconditioning, any remaining chromium is removed before the QS50K layer is applied to the ring grooves. All mating surfaces will be skimmed, to remove any signs of fretting corrosion and if there are small internal cracks, then these will be repaired too.

 

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Our reconditioning centres

We operate four reconditioning centres that are strategically located along major shipping routes: Singapore, Kruiningen (The Netherlands), Suzhou (China), Dubai. Each of the four centres carries a large inventory, so it can offer components on exchange in addition to reconditioning the customer’s own part. Both ways of working are available, it is entirely the customer’s choice.

Our reconditioning centres are the most modern ones within our industry. Welding and QS50K coating is typically performed by robots and machining is done on numerically controlled (NC) machines.

QuantiServ Reconditioning Centres
We operate four reconditioning centres globally.

This enables us to provide consistently high quality and short turn-around times at attractive prices.

 

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QuantiServ Suzhou Workshop
The QuantiServ reconditioning workshop in Suzhou, China. The others are in Singapore, Dubai and Kruiningen (The Netherlands).