Mercruiser 3.0 liter / litre timing cover replacement


If you have recently discovered a leak from under the front of your GM 4 cyl Mercruiser, Volvo Penta or OMC inboard you are possibly suspecting the front crankshaft seal (and it may well be) however in our experience the main cause of this problem is a corroded timing cover, caused by a previously leaking water circulation pump, the only cure for this is to fit a replacement cover.

The correct way to do this is to remove the engine from the boat, draw the front pulley off the crankshaft (DO NOT GRAB THE OUTSIDE WITH A 2 OR 3 LEGGED PULLER) The front pulley is also a harmonic balancer with a rubber insert and will be ruined if you try to remove it any other way but with the tapped holes in the center casting and a tool similar to (for the Brits reading) a classic Mini (car) flywheel puller,
The pulley is an interference fit on the end of the crank and has no other means of retaining.

It Is important the the Sump/Oil Pan is either removed completely (the correct way) before refitting the timing cover, or at the very least is unbolted most of the way to the back of the engine and the front prised away from the block by a few millimeters, (obviously if the gasket gets damaged there is a risk of oil leakage) once the new cover has been fitted the sump can be refitted or bolted back up.

If This step is not carried out the Timing cover will NEVER locate correctly and will be pushed up 2 or 3 mm, the seal will leak at the top, and the bottom of the seal will be pushed up so far that the steel part of the seal will cut into the crank pulley

After the pulley is removed and Sump/Oil pan lowered the timing cover can be unbolted and removed taking care to clean any flaky rust and belt debris off the block first so as not to allow it to drop in the Sump/Oil Pan,(if it is still attached)
Once the cover is removed the face can be cleaned and the new cover fitted (taking care not to allow debris to enter the Sump whilst cleaning) when fitting the new cover it is important to get the oil seal located centrally around the crankshaft, and as the seal runs on the pulley and not the crank, a "dummy" needs to be made (any small machine shop could do this) to slide over the end of the crank to recreate the back of the pulley and locate the cover, then the cover can be tightened up, the dummy removed and the pulley re-fitted. (Note : the "dummy" can be made from any material as long as the Inside and outside diameters are concentric) also the actual pulley can be used but it would need drawing off with the puller again and only a couple of bolts are accessable with the pulley on.

If The owner chooses to not to remove to Sump / Oil Pan completely but just to lower the front away quite often the proces can be carried out with the engine still left in the boat, and supported (hung) suitably from above,

These operations should only be carried out by suitably qualified persons using the correct equipment and safety procedures.



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