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Service Letter SL12-562/JAP
Action code:
WHEN CONVENIENT
POP Piston Ring Pack
New standard for piston top ring
SL12-562/JAP
June 2012
Concerns
Owners and operators of 26-50 small
bore MAN B&W two-stroke marine die-
sel engines.
Type: MC/MC-C, ME/ME-C/ME-B and
ME-GI
Dear Sirs
Recently, we have seen a number of incidents with high top ring wear
on our small bore engine types 26 to 50. For this reason, we have
successfully tested a new piston top ring, which we now introduce as
part of the standard ring pack coniguration for our two-stroke MAN
B&W 26-50 bore engines.
Summary
New POP ring pack coniguration stand-
ard for 26-50 bore two-stroke diesel
engines.
On our small bore engines, the smaller depth of the controlled leak-
age (CL) grooves reduces the wear potential of the piston top ring
compared to the large bore engine types.
In the cases observed, premature wear out of the controlled leak-
age (CL) grooves on the top ring running surface can be seen. As
a result, the pressure drop over the top ring increased further and
caused increased wear on the top ring, as well as a high liner wear
rate and an increased ring groove wear.
To remove the negative inluence from worn out (CL) grooves, we
have tested an alternative ring type to replace the CPR-CL ring. The
new ting type is called CPR-POP (Port-On-Plane).
Yours faithfully
Mikael C Jensen
Vice President, Engineering
Stig B Jakobsen
Senior Manager, Operation
Head ofice (& postal address)
MAN Diesel & Turbo
Teglholmsgade 41
2450 Copenhagen SV
Denmark
Phone: +45 33 85 11 00
Fax: +45 33 85 10 30
info-cph@mandieselturbo.com
www.mandieselturbo.com
PrimeServ
Teglholmsgade 41
2450 Copenhagen SV
Denmark
Phone: +45 33 85 11 00
Fax: +45 33 85 10 49
PrimeServ-cph@mandieselturbo.com
Production
Teglholmsgade 35
2450 Copenhagen SV
Denmark
Phone: +45 33 85 11 00
Fax: +45 33 85 10 17
manufacturing-dk@mandieselturbo.com
Forwarding & Receiving
Teglholmsgade 35
2450 Copenhagen SV
Denmark
Phone: +45 33 85 11 00
Fax: +45 33 85 10 16
shipping-cph@mandieselturbo.com
MAN Diesel & Turbo
Branch of MAN Diesel & Turbo SE,
Germany
CVR No.: 31611792
Head ofice: Teglholmsgade 41
2450 Copenhagen SV, Denmark
German Reg.No.: HRB 22056
Amtsgericht Augsburg
Service Letter SL12-562/JAP
On our small bore engines, the smaller depth of the con-
trolled leakage (CL) grooves reduces the wear potential of the
piston top ring compared with the large bore engine types.
These passages have been conigured with a 90 degree
narrowing, causing the ring to increase the bypass area as
the ring wears, instead of reducing it when the minimum
depth is reached, as is the case with the CL grooves.
Thereby, the pressure drop decreases instead of increases.
We have observed areas with premature wear out of the
controlled leakage (CL) grooves on the top ring running
surface. As a result, the pressure drop over the top ring in-
creased further, resulting in increased wear on the top ring,
high liner wear rate and increased ring groove wear.
To measure the wear of the ring, the width of the leak-
age passage can be measured using a feeler-gauge-type
measuring tool, see Fig. 2. The opening is 3 mm from the
beginning, and the milled passage is designed in such a
way that for every 1 mm the ring is worn radially, the gap
opens 2 mm. Table 1 lists the maximum allowable width of
the leakage gap for our small bore engines.
To eliminate the negative inluence from worn-out (CL)
grooves, we have tested an alternative ring type to replace
the CPR-CL ring. This new ring type is called CPR-POP
(Port-On-Plane).
The main coniguration with the double S-lock and gas relief
grooves remains unchanged. The CL grooves on the run-
ing side have been omitted and replaced with a number of
ports milled into the lower side of the piston ring, see Fig. 1.
Milled Passage
Fig. 2: Feeler-gauge-type measuring tool
Bore
size
[mm]
Max. radial
ring wear
[mm]
Max. width of leakage
groove (measured with
feeler gauge)
260
1.8
6.6
350
2.2
7.4
400
2.2
7.4
420
2.2
7.4
460
2.2
7.4
500
3
9
Table 1: Ring wear
Double S-Lock
Fig. 1: CPR-POP piston ring
POP Piston Ring Pack. Page 2 of 3 pages
Service Letter SL12-562/JAP
If the oil ilm between the cylinder liner and the piston rings is
damaged, adhesive contact will occur, followed by temporary
high temperatures on the surface and, subsequently, cooling,
with hardening of the running surfaces as the result.
All ring packs from 26 to 50 bore with the new CPR-POP
top ring have alu-coat on the running surface, see Table 2.
26 to 50 Bore
These areas of hardened surface must be removed to facili-
tate the running-in of new piston rings.
1st ring
Controlled Leakage
Port-On-Plane (POP)
To place an order, or for further advice or clariication, you
are welcome to contact MAN Diesel & Turbo PrimeServ in
Copenhagen (email: Primeserv-cph@mandieselturbo.com).
Base material:
Vermicular cast iron, CV1
Running-in coating:
Alu coating
Questions regarding this service letter can be directed to our
Operation department in Copenhagen (email: Operation-
cph@mandieselturbo.com).
2nd ring – left cut
Base material:
Grey cast iron, CF5
Running-in coating:
Alu coating
3rd ring – right cut
Base material:
Grey cast iron, CF5
Running-in coating
Alu coating
4th ring – left cut
Base material:
Grey cast iron, CF5
Running-in coating:
Alu coating
Table 2: New CPR-POP piston ring coniguration
The new piston top ring has been tested on the various
engine types. The test results have shown improved TBO
in all cases, compared with the previous CPR-CL piston
top ring.
Therefore, we now feel conident in introducing the CPR-
POP ring as the new standard on our small bore engine
types 26-50.
Liner hardening
It is important that operators experiencing worn-out top rings
of the CPR-CL type on small bore engines note that there is
a risk of liner surface hardening when running with a worn-
out top ring.
In a number of cases, we have seen a high increase in liner
and ring wear rates after installing new rings in a liner suffer-
ing from a hardened surface due to running with worn-out
piston rings.
To ensure normal wear rates and eliminate surface hardening,
the liner surface must be machined by honing or grinding.
POP Piston Ring Pack. Page 3 of 3 pages
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