Front Timing Cover and Rear Crankshaft Seal Housing: Fixing Oil Leaks with Caterpillar 232-3657 and Cummins X3.3 Housing 0104-2116

Oil on the bilge under a generator set or a propulsion engine is one of the most common faults an engineer is asked to fix, and many of those leaks come from the two ends of the crankshaft. At the front, the timing gear train is closed by a cover that carries the front crankshaft seal. At the back, a seal housing carries the rear crankshaft seal behind the flywheel. Both parts are simple, but both need the right gasket, seal and fitting method, or the leak comes back within weeks. Two of these parts are now approved in the Sea Keepers catalogue: Caterpillar front housing cover assembly 232-3657 as SK-00028 and Cummins (Onan) crankshaft rear oil seal housing 0104-2116 as SK-00029.

SK-00028: Caterpillar front housing cover assembly 232-3657

SK-00028 is genuine Caterpillar part 232-3657, Front Housing Cover Assembly, for the Caterpillar C4.4, C6.6, C7.1 and 3054 family of engines, including the C3.3 and C3.4 front housing groups. The Cat Parts Store describes it as the front gear housing cover that protects the inner engine mechanisms. In the front housing group it sits with gasket 277-3012, front crankshaft seal 288-0422 and front housing 294-0288. Aftermarket suppliers list the Perkins-style interchange number 4142A503, which is useful because these Caterpillar engines share their design with Perkins industrial engines, and an old spares list may carry either number. No supersession was found in the sources reviewed.

SK-00029: Cummins X3.3 / X2.5 crankshaft rear oil seal housing 0104-2116

SK-00029 is genuine Onan (Cummins) part 0104-2116, Crankshaft Rear Oil Seal Housing Assembly, which Cummins describes as the housing crankshaft rear end oil seal assembly with joint. It bolts to the back of the cylinder block behind the flywheel housing on Cummins X3.3 and X2.5 diesel engines, as used in Cummins C22 D5, C33 D5, C38 D5, C30 D6 and C35 D6 generator sets. It holds rear-end seal 0509-0494 in rear oil housing 0130-8002. Related parts are joint 0101-0861, dowels 0516-2127 and flywheel housing 0104-2117. No supersession was found in the sources reviewed.

Finding where the oil is really coming from

Oil runs downhill and is blown backwards by the cooling fan, so the wet spot is often not the leak. Before ordering a cover or a housing, clean the engine, run it to temperature and look again, or add a UV dye to the oil and check with a lamp. At the front, look at the joint between the cover and the front housing, the crankshaft seal behind the pulley or damper, and the timing cover bolts. At the back, oil dripping from the bottom of the flywheel housing may be the rear crankshaft seal, but it can also be a leaking oil gallery plug, a rocker cover gasket running down the back of the block, or a sump gasket. A crankcase breather that is blocked raises crankcase pressure and pushes oil past both seals, so the breather should always be checked first; see the crankcase breather guide linked below.

When the cover or housing has to be replaced, not just the seal

Many leaks are cured with a new lip seal alone. The cover or housing is replaced when the seal bore is damaged or out of round, when the cover is cracked or bent after a timing gear job, when the mounting face is corroded or pitted so that a new gasket cannot seal, or when a previous fitter has driven a seal in crooked and scored the bore. On the Cummins X3.3 the 0104-2116 assembly comes with its joint, which saves a separate line on the order. On the Caterpillar C4.4 to C7.1 front cover, the gasket 277-3012 and the seal 288-0422 are separate lines and should be ordered with the cover.

Check the crankshaft surface as well

A lip seal runs on a polished band of the crankshaft or the damper hub. After years of running, the lip wears a groove into that band, and a new seal on an old groove will leak again. Run a fingernail across the seal track: if it catches, the surface needs a wear sleeve or the seal has to be fitted at a different depth where the manual allows it. At the front, also check the crankshaft gear and timing gears while the cover is off. On the C6.6 and C7.1 the approved catalogue carries the 34-tooth crankshaft gear 276-7391 (SK-00064-AV). At the back, check the flywheel housing face and the crankshaft flange; the flywheel and damper guide linked below covers the rear end of larger engines.

Fitting the cover and seal housing correctly

Both faces must be clean, dry and free of old gasket and sealant. Use the gasket or joint specified in the parts book rather than cutting one from sheet, because the thickness sets the position of the seal. Fit the dowels first, so the cover or housing is centred on the crankshaft before the bolts are tightened; a housing that is off-centre wears the seal on one side and leaks. Lightly oil the seal lip, use a seal protector or tape over the keyway, and press the seal in square with the correct driver. Tighten the bolts in a cross pattern to the torque in the Caterpillar or Cummins service manual. Run the engine and check again once it is hot.

Parts to order for a seal job

For the Caterpillar front end: front housing cover 232-3657 (SK-00028), gasket 277-3012, front crankshaft seal 288-0422, a wear sleeve if needed and new bolts if the manual calls for them. For larger Caterpillar C15 and C18 engines, the catalogue also carries the front housing 248-2607 (SK-00072). For the Cummins X3.3 or X2.5 rear end: rear oil seal housing 0104-2116 (SK-00029), rear seal 0509-0494 if the housing is being re-sealed, joint 0101-0861 and dowels 0516-2127. If the flywheel housing is damaged, flywheel housing 0104-2117 is listed with it.

What to send with an enquiry

Send the engine model and serial number (for example C4.4, C7.1, X3.3 or X2.5), the generator set model if it is a genset (for example C33 D5), the part number on the old cover or housing if it can be read, and whether you want the cover only or the full kit with gasket, seal, sleeve and dowels. Add the delivery port and any certificates the buyer needs. Sea Keepers will confirm the numbers against the serial number and quote the complete set.

For the business buyer

Confirm the intended vessel or facility, operating environment, quantity and required approval before requesting a quotation. Capacity, coverage and service interval should be matched to the risk rather than selected by headline price.

For technical experts

Verify the delivered model against the maker reference, rating, dimensions, materials, operating limits and certification scope. Record the serial or batch number and retain the manufacturer datasheet, declaration, test report and maintenance instructions in the vessel file.

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