used for propulsion 2 stroke engines are as follows:
Lead Bronze Bearing: These bearings consist of the following layers
• Flash layer: It is the top most layer with thickness of 0.035mm and made up of tin and lead. It is used to protect the bearing from corrosion and dust when not in use. This layer flashes off when bearing is under running-in.
• Nickel Barrier: It is the second layer made up of nickel with thickness of 0.02mm. Its main function is to
prevent corrosion and avoid diffusion of tin into bearing metal.
• Lead Bronze: The third layer composed of lead bronze has
excellent anti seizing property and is
A Guide to Two Stroke Marine Engine Components
the principle component, which acts as the bearing.
• Steel back: Steel back is the last and backing part of the bearing used for shape and support, over which all the layers are bonded together.
Flash
Nickel Barrier
Lead Bronze
Steel Back
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Bi-metal Bearing: This bearing consists of following layers
• Aluminium Tin: The first layer of bi- metal consists of Al and Sn with thickness of 0.5 to 1.3 mm. It is the main layer of this type of bearings.
• Bonding Layer: The bonding layer is made of aluminum and has 0.1mm thickness. The main function of the bonding layer is to obtain a good bond between the shell and the top layer.
• Steel Back: The steel back part is used for shape and support.
Tri Metal Bearing: These bearings are called tri metal bearing because they consist of three main layers (excluding flash layer as it flashes off) and a steel back. It consists of:
• Flash Layer: It is the top most layer with thickness of 1 micron and is made up of tin and lead. It is used to protect the bearing from corrosion and dust when not in use. This layer
flashes off when bearing is in running-
Aluminium tin
Bonding Layer
Steel Back
in period.
• Overlay: The second layer is made up of white metal, (Tin Antimony Copper) which is the main component in this type of bearing. Its thickness is 20 microns.
• Interlay: It is the third layer used as anti corrosive layer for overlay. It is of 5 microns thickness.
• Lining: It is the lining layer between interlay and steel back with thickness of 1 mm and is made up of lead and bronze.
• Steel Back: The backing part used for shape and support.
A Guide to Two Stroke Marine Engine Components
Overlay
Flash
Interlay
Lining Steel Back
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Measuring Main Bearing Clearance:
A marine engine comprises of several types of bearings, which support the rotating and reciprocating crankshaft, camshaft, and crosshead of the engine.
It is extremely important to maintain good quality and quantity of lubricating oil to all these bearings in order to avoid
breakdown of the engine.
The main bearing of a marine engine supports the long running crankshaft
throughout the engine length. This makes it imperative to check the condition of the bearing at regular intervals of time.
The clearance measurement of the main bearing determines the amount of wear down, which the bearing has been
subjected to. There are various types of
methods adopted by different marine engine manufacturers to measure the clearances of the main bearing of marine engine. Following are some of the most prominent methods used onboard ships to measure the clearance of main
bearing:
1) Bridge with Depth Gauge
This method is used in SULZER 2 stroke marine engines where the bearing‘s shell is removed along with the keep (the
bearing shell is lined with the keep). After that a bridge is fitted over the top of the journal pin, from port to starboard,
making a bridge over the crankshaft with two ends supported on the cross girder.
A simple vernier type depth gauge is then inserted in the hole provided on the
bridge and the scale of depth gauge is
rested on the crankshaft pin. The total depth on the scale is measured and
compared with the previous reading and the reading in the manual for calculating the wear down of the bearing.
A Guide to Two Stroke Marine Engine Components
In old model SULZER engines, a collar is provided in the bearing shell along with a small hole. Thus, without removing the keep, the bridge is fitted adjacent to the keep and the depth gauge is used from the hole provided in the shell to measure the shell wear down.
2) Bridge With Feeler Gauge: In some engines, after removing the shell and the keep, the bridge is installed as explained in the above point.
Also, in place of depth gauge, a feeler gauge is used to measure the clearance between the journal pin top and the
bridge bottom.
The bridge used here is different in terms of height and the gap between pin and the bridge is very less compared to that of the bridge used in the earlier method.
Bridge Gauge
Depth Gauge
Shaft
Bearing Shell
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3) Telescopic or Swedish Feeler Gauge
In engines like MAN B&W, this is the most common method used to measure the bearing clearance of the top shell. In this method there is no need to remove any connection or bearing keep for
measuring the clearance.
The telescopic gauge is inserted
between the gap of the crank web and the bearing keep.
When the tip reaches the shell top, the feeler is inserted between the shell and the pin to check the clearance
4) Dial type Depth Gauge: This method is used in new MAN B&W engines (SMC- C), which does not require the top keep to be removed.
The lube oil pipe connection screw hole is in the bearing keep, which can
be accessed from the hole on the bearing shell.
The dial gauge is inserted in this screw hole and the reading is taken as the clearance for upper shell.
Dial Gauge
shell Bearing Keep
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A Guide to Two Stroke Marine Engine Components