956980 Volvo.Penta Fitting nut

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PRIORITY:REPLACE PISTON COOLING JETS AND INSPECT RECENTLY OVERHAULED ENGINES - 3406B, 3408, 3412 TRUCK, MARINE, AND IND USTRIAL ENGINES AND GENERATOR SETS; 637D TRACTORS - PI3096
  The information supplied in this service letter may not be valid after the termination date of this program.   Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.
REPLACE PISTON COOLING JETS AND INSPECT RECENTLY OVERHAULED ENGINES 3406B, 3408, 3412 Truck, Marine, And Industrial Engines And Generator Sets; 637D Tractors, 1214, 1307 PI3096 (Revised May 1985) U-13 A-9 AU-11 B-3 C-11 E-11 O-10 TT-2 TA-1 TM-1 priority parts stock action needed In response to dealer input we will attempt to replace pages or completely revise the Service Letter when a correction is needed. Replace Pages 1 and 2 of Service Letter (PI3096) dated January 30, 1985 with this revision. See the changes denoted by (right arrow).
Problem
The above engines use oil cooling jets for piston cooling and piston pin lubrication. Recently, improved pistons became effective in all these engines, but the first quantity of these pistons can contact and break the piston cooling jets. A broken cooling jet will cause piston seizure and engine failure. This could be a problem with the pistons shown in the chart. Pistons with a box date code of 2-85 or later can be used and do not need to be checked (SEE ILLUSTRATION) (right arrow) Piston-to-jet clearance should be measured whenever pistons are installed. If you have a piston seizure always measure the piston-to-jet clearance on all pistons before they are removed to help determine the cause of failure. If the clearance is less than 0.64 mm (.025"), install a new cooling jet at this location. The cooling jet may have already been bent by the piston, or during piston installation. In production, the interference has been eliminated by machining a groove in the piston skirt. The same cooling jet (4N9881 Tube Assembly) continues to be used and it is not stamped "U8". Engines already assembled at the factory and OEM factories are being modified with a 7W7496 Tube Assembly. This tube is bent to eliminate interference and "U8" is stamped on the bottom of the tube block. These cooling jets may not meet the spray location specifications on a bench test, but they will provide adequate piston cooling. Affected Models And Parts Required 3408 Truck Engines 28V4734, 4735, 4737, 4739, 4742, 4744, 4746 3408 Marine Engines 99U4654-99U4659, 4661, 4662 3408 Industrial Engines 67U11108-67U11118, 11122 3408 Generator Set Engines 78Z1374-78Z1378, 1381, 1384-1387, 1389, 1390, 1393, 1398, 1400, 1402, 1403 637D Tractors 27W1754, 1804 3412 Marine Engines 60M2381-60M2383 3412 Generator Set Engines 81Z4167, 4169-4171, 4175, 4178, 4179, 4181, 4185-4188, 4190, 4191, 4193, 4195, 4199, 4204 3406B Marine Engines 4TB501, 502, 505 3406B Industrial 6TB1961, 1963, 1964, 1967, 1969, 1973, 1980, 1982, 1984 3406B Generator Set 2WB1955-2WB1973, 1975, 1976, 1978-1982, 1984, 1985, 1987, 1988, 1991-1993, 1995-1999, 2001, 2003-2004, 2006-2009, 2011, 2015, 2016, 2018, 2020-2023, 2026-2029, 2033 3406B Truck Engines 7FB25414-7FB25423, 25425-25431, 25433-25436, 25438-25448, 25450-25461, 25463-25469, 25471, 25474-25481, 25483-25488, 25490-25516, 25518-25525, 25527-25533, 25535-25538, 25540-25555, 25557-25572, 25574, 25576-25610, 25612-25615, 25617-25620, 25622-25637, 25639-25642, 25644-25654, 25656-25666, 25670, 25672-25675, 25677-25694, 25696, 25697, 25699-25701, 25703-25706, 25708, 25709, 25711-25713, 25715-25718, 25720-25734, 25736, 25739-25741, 25743-25751, 25753-25755, 25757-25763, 25765, 25766, 25768, 25769, 25771-25773, 25776-25792, 25795-25804, 25806-25816, 25818-25832, 25834-25839, 25841-25861, 25863-25867, 25870, 25871, 25874-25877, 25879-25891, 25894, 25896-25903, 25905-25917, 25919, 25921-25932, 25934-25939, 25941-25953, 25955-25961, 25963, 25966, 25968-25970, 25973-25990, 25992-26001, 26003-26013, 26016, 26017, 26019-26030, 26032, 26034-26037, 26039-26042, 26044-26052, 26054-26056, 26058-26060, 26062-260269, 26073-26076, 26079-26082, 26084, 26086-26090, 26093-26096, 26098, 26099, 26101, 26102, 26104-26109, 26112-26115, 26117, 26120-26125, 26127-26131, 26134-26137, 26139-26141, 26143-26145, 26147-26149, 26151, 26152, 26154-26156, 26158-26160, 26162, 26163, 26165, 26166, 26169, 26170, 26172, 26173, 26176, 26177, 26180, 26183, 26184, 26186-26188, 26190, 26191, 26194, 26197, 26200, 26202, 26204, 26206-26209, 26211, 26212, 26214, 26215, 26218, 26219, 26221, 26222, 26225, 26226, 26228, 26229, 26232, 26233, 26236, 26239, 26241, 26242, 26243, 26245, 26246, 26248, 26249, 26253, 26255-26257, 26259, 26260, 26264, 26267, 26269, 26271, 26273, 26274, 26276-26278, 26281, 26286-26288 26290-26292, 26294, 26295, 26299, 26302, 26304, 26308, 26309-26311, 26313, 26314, 26316, 26319, 26321, 26323, 26326, 26330, 26331, 26333, 26334, 26337, 26338, 26342, 26344, 26345, 26347-26349, 26351, 26352, 26354-26359, 26361-26363, 26365, 26366, 26369, 26370, 26372-26374, 26376, 26377, 26379, 26380-26385, 26387, 26388, 26391, 26394-26402, 26404, 26405, 26408, 26410, 26411, 26413, 26414, 26416-26422, 26424, 26425, 26429-26435, 26438-26440, 26442, 26443, 26445, 26446, 26448, 26451, 26454-26462, 26464, 26465, 26467-26471, 26475-26479, 26482, 26484-26487, 26490, 26492-26494, 26496, 26499, 26500, 26502-26505, 26507, 26509, 26510, 26514-26516, 26518-26524, 26526, 26527, 26529, 26531, 26533, 26535, 26536, 26538, 26539, 26542-26545, 26547, 26549, 26551, 26552, 26554, 26556, 26557, 26560-26567, 26570, 26571, 26573-26577, 26582-26586, 26588-26594, 26597, 26600, 26601, 26604, 26607-26611, 26613-26615, 26618, 26621, 26624, 26626-26628, 26632, 26635, 26637, 26639, 26640, 26643, 26644, 26647, 26650, 26653, 26655-26657, 26659, 26666, 26669, 26670, 26672, 26673, 26675, 26679, 26682, 26683, 26686, 26690, 26691, 26693, 26695, 26696, 26701, 26702, 26706, 26708, 26710, 26716, 26717, 26719, 26721, 26723, 26724, 26727, 26730, 26732, 26733, 26735, 26739, 26743, 26744, 26746, 26747, 26749, 26752, 26753, 26756, 26759, 26760, 26762, 26763, 26766, 26767, 26770, 26772, 26774, 26777-26780, 26784, 26787, 26790, 26791, 26794, 26798, 26799, 26801, 26803, 26805-26807, 26809, 26810, 26812, 26814, 26816, 26819, 26820, 26822, 26823, 26827,