cam effect Archives - QuantiServ

Very Extensive Crankshaft and Block Repair on a Passenger Ferry

5th November 2024

Overview

QuantiServ recently completed a large-scale repair assignment on a passenger ferry. The ferry was built in the year 2000 and is equipped with four 12-cylinder, 46-bore main engines, with a nominal power output of 12.6 MW each.

In early 2024, two of these engines required extensive repairs, having each accumulated over 120,000 running hours and having suffered a recent failure.

QuantiServ was contracted to carry out the repair of both engines. As additional defects were found during the repair, the work turned into a sizeable project that took almost four months to complete.

Our in-situ machining specialists from Sweden carried out all work during the winter months of 2023/2024, while the vessel was out of operation during the low season.

One of the two crankshafts was removed from the engine and underwent repair on the vessel's car deck.

Damage

The following damages were found. They were all addressed by our specialists during the repair.

Engine Number 1

Crankpin bearing failure
As a consequence: Multiple cracks, excessive surface hardness of 600 – 680 HB

Engine Number 2

Failure of four crankpin bearings
Crankshaft bent
Failure of one adjacent main bearing
A collapsed main bearing saddle, as a consequence of the heat generated
Poor fitting of another bearing saddle
Severe cam effect on all other crankpins

Multitude of cracks in the crankpin journal — After cutting off some material from the crankpin, a multitude of cracks became visible. They were caused by the rapid temperature raise and fall during the bearing failure.

In-process hardness measurement during machining. The areas with increased hardness are easily visible. — In-process hardness measurement during machining. The dramatic temperature changes resulted in changes in the local microstructure that are easily visible.

Surface hardness of up to 680 HB following the failure. The acceptable limit is 300 HB. — Due to excessive heat generated by the failed bearing, the surface hardness had increased to 600 - 680 HB. The acceptable upper limit is 300 HB.

Detailed Work Performed

All repair works was done while the vessel was berthed during low season.

Engine Number 1

Crankshaft Repairs:

Heat Treatment and Machining: One crankpin was machined to an undersize of -3.00 mm.
Polishing: Two main bearings were polished to ensure smooth operation.

Engine Number 2

Due to damage found on the engine block, the crankshaft was removed so that line boring on the block could be carried out. Heat treatment and in-situ machining on the crankshaft was carried out on the vessel’s car deck.

Crankshaft Repairs:

Heat Treatment: Four crankpins and one main journal underwent heat treatment.
Machining: The treated components were machined to undersize diameters ranging from -2.00 to -5.00 mm, depending on their condition.
Straightening: The crankshaft, found bent with a run-out of 1.50 mm, required peening (in-situ straightening).
Polishing: All main journals and crankpins, exhibiting strong indications of the “cam effect,” were polished.

Engine Block Repairs:

Bearing Saddle Realignment: The overheating of one main bearing caused misalignment, necessitating the replacement of the bearing cap and subsequent line boring.
Bearing Cap Adjustment: Another main bearing cap showing a gap with the cylinder block was corrected.

Additional Improvements

In addition to the primary repair tasks, QuantiServ addressed machining work previously carried out by another company on some of the crankpins. The fillets were not nicely cut, and the radius around the oil hole needed improvement. Our specialists refined these areas, ensuring optimal performance and longevity of the crankshafts.

Summary Table of Work Done

Engine	Work done
# 1	Heat treatment and machining to -3.00 mm undersize of one crankpin
	Polishing of two main bearings
# 2	Removal of the crankshaft for external heat treatment and in-situ machining
	Machining to undersize diameters of -2.00 to -5.00 mm
	Peening (in-situ straighening) to correct a bent crankshaft with 1.50 mm run-out
	Polishing of all main journals and crankpins
	Replacement of a bearing cap and line boring due to misalignment
	Adjustment of a main bearing cap gap with the cylinder block

One of totally five crankpins that our specialists machined to under-size

The mirror-like finishing on one of the crankpins. — Impressive, mirror-like finishing after polishing of the crankpins.

Conclusion

This extensive in-situ repair project on a passenger ferry highlights QuantiServ’s expertise and ability to perform critical repairs without interrupting service.

The phenomena known as “cam effect” or “ridge wear” could be identified as reason for the bearing failures and the ensuing, rather extensive and therefore costly, repairs. It is therefore very important that ship owners and operators are sensitive to this issue and regularly check the condition of the crankpins once their engines have surpassed aproximately 60,000 running hours.

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!

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

12th August 2022

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)!

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?

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

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.
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.

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

Be Aware of Cam Effect/Ridge Wear that Affects Four-Stroke Crankshafts!

1st December 2017

Whenever a four-stroke engine has accumulated around 60,000 running hours or more, then its crank pins are in all likelihood affected by what is called the “cam effect” or “ridge wear”.

This phenomenon develops over time and manifests itself in an uneven wear pattern that is, with the right tools, easily detectable as a protruding band (“cam”) that goes around the circumference of the crank pin. It usually only develops on engines equipped with grooved bearing shells and its development is a function of time. The more impurities (abrasive particles) the lubricating oil contains, the faster the cam effect develops.

The two major makers of medium-speed diesel engines, MAN Diesel & Turbo and Wärtsilä, have booth issued Service Letters to make their customers aware.

The following pictures are typical and exemplify well how the cam effect develops and what damage it can cause. The pictures were taken during an attendance on a German-owned small tanker, where QuantiServ’s specialists machined one crank pin and polished all the others on the vessel’s single 50/54 main engine. The damage was in fact so severe that in-situ heat treatment (annealing) had to be performed too in order to reduce the crankpin’s hardness, which had increased as a result of the failure.

QuantiServ very much recommends to all owners and operators of medium-speed four-stroke engines to keep a close eye on the condition of the crankpins and to regularly inspect them once they have surpassed around 60,000 running hours. The cost of rectifying the pin geometry in good time pales in comparison to the cost of a repairing a failed crankpin bearing. And fail they will, if no action is taken.