Opel Manta with crankcase pressurisation issues

One of my regular email correspondents reported recently that he has been having an odd problem with his Opel Manta A series blowing its dipstick out of its hole. In the past I have heard of similar tales involving the oil filler cap popping off unexpectedly. Both are bad news, apart from the mess it will make of the engine bay, if you are on the motorway and don't notice what has happened your engine could run dry and seize up.

In my opinion, the most likely cause is the build up of crankcase pressure due to a blocked breather gauze. Sadly, it is synonymous with a vehicle that has been neglected or otherwise unloved. When the oil isn't changed regularly and / or is poor quality it becomes thick and tar like, clinging to surfaces and not flowing as it should.

The majority of Opel Manta A series models are fitted with the cam in head or C.I.H. engine. The breather gauze is made of a metallic mesh located inside the top of the rocker cover and  held in place by a steel plate spot welded to the inside the cover at the time of manufacture.

As I see it there are a number of servicing options available:

Option 1 - Flush through with white spirit, engine degreaser or a full can of carb/injection cleaner. This can be sprayed or poured through the breather hole at the top of the rocker cover and collected with a suitably large solvent resistant bowl placed underneath.

Option 2 - Soak the whole rocket cover in a bucket of strong caustic cleaner. This will probably remove any finish and require you to paint or powder coat afterwards.

Option 3 - Drill out the spot welds, remove and clean the gauze and refit. Replace the spot welds with some pretty stainless steel bolts, not exactly concours standard but very practical.

Furthermore if the engine has covered over 75,000 miles, even if it is still running well, a light engine rebuild is in order. Fitting parts such as new piston rings, bearings and honing the bores, not a cheap option today, but good value in the longer term.

From my past experience with these engines I found that they responded well to either; changing the oil at the recommended 6000 miles intervals with a cheap oil from the motor factors or leaving it for a longer period, providing it was quality semi-synthetic oil.

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