Decarbonizing the engine - according to Rover

[lakesrally]

At Paul Gregory's Cumbria Rally this afternoon we were discussing decoking engines, as you do in a beautiful, nay stunning, location overlooking Coniston Water and the Coniston fells. I was telling him the Rover suggested method as described in the 14/45 and 16/50 owner's handbook. It would not reproduce well by the time it had been scanned and reduced in size for Photobucket so I have reproduced it here word-for-word exactly as it is in the manual, I accept no responsibility for the consequences of anyone trying this, if this was on the TV I would be saying 'Don't try this at home folks'.


DECARBONIZING ENGINE BY OXYGEN PROCESS.
The engine can be decarbonized without removing head by making use of the oxygen process. A cylinder of compressed oxygen is necessary, also a strong flexible tube with a metallic nozzle of suitable length and shape to allow it to be inserted through the sparking plug holes, and to be turned round inside the head so that the stream of oxygen can be directed on to every part of the combustion chamber and piston top. A piece of 1/4 in. external diameter copper pipe, curved about 3 inches from its end, is suitable.

First turn off the tap on Autovac controlling supply of petrol to carburetter, and run engine until carburetter is quite dry. Remove bonnet completely by lifting away from radiator and from clip on dash. Protect wings and dash with suitable coverings, as the carbon leaves the cylinders in the form of burning granules.

Next rotate the engine until the exhaust valve of No. 4 cylinder (farthest from radiator) is just closing. (The position of exhaust valve can be seen through sparking plug hole.) The piston of No. I cylinder will now be approaching top dead centre, and, when exactly at top of stroke, No. 1 cylinder will be ready for decarbonizing.

Now turn on oxygen until a fairly powerful stream emerges from nozzle of pipe, and direct this stream at sparking plug hole for 30 secs. Then touch edge of sparking plug hole with a lighted taper, and the carbon will immediately catch fire. Gradually work the nozzle all round the interior of the combustion chamber, and on to piston head taking great care not to allow it to remain in any one position for more than a moment, until no more carbon emerges. During this process, the operator should stand well out of the path of the burning carbon.

When no more carbon emerges, the oxygen should be turned off, and a stream of compressed air should be directed into the combustion chamber just cleaned to remove any fragments. (A few strokes from a powerful tyre pump will accomplish this. if no compressed air is available).

To prepare No. 2 cylinder for decarbonizing, turn engine until exhaust valve of No. 3 cylinder is just closing, and set piston of No. 2 cylinder on top dead centre, proceeding as before. To prepare No. 3 cylinder, set piston on t.d.c. with exhaust valve of No. 2 cylinder just closing. To prepare No. 4 cylinder, set piston on t.d.c. with exhaust valve of No. 1 cylinder just closing.

The entire operation can be carried out inside of 30 mins.,and a IO ft. cylinder of oxygen should be sufficient for one engine.

[David Bliss]

I still use this method of decarbonising, but not for the engine! This method was mainly used for non-detachable cylinder heads. If there was a large amount of oily carbon in an engine it would have to be done very gently because it produces a considerable amount of heat, and definitely would have to be done with water in the engine. With modern oils and petrol there should not be any significant amount of carbon build-up in the engine. My 1906 Rover ran extremely cool but, in the thousands of miles we did with the car there was absolutely no carbon build-up, even though I ran a certain amount of oil in the petrol.

Where I do find the method useful is for decarbonising the exhaust system. I used this earlier this year on another 6hp Rover, which still had its original tail-pipe. As you can imagine, the amount of oil going through the system over years with a worn-out engine had clogged the pipe. I use oxypropane to start the process, but once you get it going the oxygen can make this a bit aggressive, so I switch to compressed air down the pipe, watching the red glow work its way down the pipe as the carbon burns off. If the colour starts to go past red I reduce the amount of air, but it is essential to keep enough air flowing to keep the carbon going and the technique only comes with practice. You must have the exhaust pipe aimed outside, it can be like a Roman candle when burning properly. The pipe must also be supported in several places to prevent it distorting from the heat.

David