Question: "Although my MG 1,5 Litre runs exceedingly well, I would like to boost up the performance. A supercharger reduces the mpg far too much, so that it is not possible. However I imagine the compression ratio could be raised somewhat, as at present it is quite impossible to make the engine "pink". Will you give your views on same, please?" Answer by MG
"We note your desire for an improved performance without supercharger. Unfortunately it is not possible to raise the compression ratio by skimming the cylinder head, as there is insufficient material to allow this to be carried out. In view of the impossibility of removing metal and raising the compression ratio, there is very little one can do to improve the performance this way". Note: The castings for a VA, Wolseley and Morris 12 cylinder head seem to be identical. The only difference may be in the height of the ready machined casting, and looking at the Abingdon Factory info the cylinder head for a VA was already machined so heavily that skimming afterwards is a hazardous action, because there may not be enough material left. I measured some cylinder heads from the bottom face (where it rests on the head gasket) to the top face (where the gasket for the rocker cover rests). A cylinder head from a genuine VA engine measures usually 89-90 mm. Other heads: A Morris cylinder head (TPBM engine) = 93 mm A Wolseley Taxi engine cylinder head (TPDW-T) = 92,5 mm A standard Wolseley cylinder head (TPBW-3) = 90 mm All these seem to be the same casting so 89 mm is realistically the limit just as MG says in the above article.
BdV
Below pictures show a VA cylinder head which measured 88 mm and had developed a crack starting from the middle water hole. Lots of coolant escaped via the tappet gallery into the sump. It seems proof that going below 89-90 mm weakens the head to much. Remember that the thinner metal has a hard job dealing with the heat and will warp quicker and consequently crack quicker.
This excellent photo made by Gobby shows a valve cap slightly lowered by a valve spring compression tool and is made to note where the rubber oil seal ring on a VA valve stem is supposed to go.
Rocker shaft problems: This is a very serious matter and may ruin your engine if left unattended: Some years back Lex Stibbe from Holland had a broken rocker shaft.
Right in front of the foremost support bracket the shaft had sheared off and in the process it had also knocked off the head of the valve stem, causing the valve to drop with this time luckily not such disastrous effects. The valve did not drop right into the engine for unknown reasons. Lex was very lucky this time. It made me thinking why the valve and the rocker shaft broke at the same time.
While working on the engine of another VA I wanted to check for top end lubrication so I had the engine running with the rocker cover off. This is not very advisable if you have a very neat environment as it can make quite a mess with oil sputtering all over the place. While observing the rocker shaft I noticed that the bit of shaft in front of the foremost support bracket was actually moving every time the valve was pushed open.It was jumping up and down. Because I did not like this happening I took the whole assembly off the engine and inspected all the bits and pieces carefully on my workbench. I found out that there was actually quite a bit off play where the shaft is going through the support bracket, causing the jumping up and down of the shaft. I also saw that through this hammering action the shaft had marks we don’t want and the support bracket is worn to the extend that it is no longer serviceable in this condition.
It is these hammering marks that eventually will make your shaft break with possibly horrible results leading to a badly blown up engine. Looking at other engines in my stock I saw that the front and rear support brackets are more like the design of the middle two brackets, being slotted and carrying a ring to fill the slot. On the front and rear brackets the ring is flat on one side to make way for the shaft. This construction makes it possible to clamp the shaft tight and it no longer hammers into the bracket. Seeing this I studied the parts list to see if it was one of the many modifications which was made during production. Yes, from engine number 2250 the front and rear rocker shaft support brackets are different and have a different part number, also mentioning the different washer. I would strongly advise everybody with a VA to check your engine on this point before disaster struck.
Remember that although your VA carries a guarantee plate I doubt that MG’s in there present situation will positively react on your claim. I do not think that there are enough proper brackets available if every body needs them, but with some tinkering from a good engineering firm a "wrong" bracket can be modified into a proper one.