Iain's 1970 MG BGT

Gas Flowed Cylinder Head

After I had built the new engine I put an unmodified head on as I had no yet cleaned up the gas flowed unleaded cylinder head that I had on the original engine. The following shows a few pics of the refurbishment of the unleaded head.

Cleaning

The first job was to clean the head. This was done with Fairy Power Spray and water, petrol, and then wire brushes on a drill and angle grinder. Click on the picture below for more before and after shots of the cleaning.

The head was then painted green to match the block and all the threads were tapped.

Lapping

A good set of second hand valves were sourced from Ebay. These were tried in the valve guides and checked for excessive wear. There appeared very little movement, so I decided not to replace the valve guides. The valves were marked with number 1 to 8 and then lapped into the respective valve seat, until a continuous matt gray line could be seen on both the valve and the valve seat. Click here to see a couple of photos.

Putting Valves in Place

The valves were then put back into place using a valve spring compressor. This squashes the spring so the collets can be put in place.

The order was to put the valve in place (having oiled the stem with 20W/50 oil), followed by the shim, then valves stem seal, the spring and finally the the top cover. The compressor was then applied so the spring could be moved down and the collets added to lock everything together. The springs used were the single springs that were previously on the head. I measured them and compared them to new springs and there was no difference. The valve stem seals used were the improved umbrella type, as shown in the picture below. These are far better than the original rubber ring seal. I used them on both the inlet and exhaust valves. Many people say they shouldn't be used on the exhaust valves, but as they were listed in the manual I decided to fit them.

Fitting the Head

The face of the cylinder face was then cleaned up and the head was ready to fit. I measured the compression on the current engine as a reference point. The readings were 190, 188, 191, 190psi and the mileage 78883.

Over a couple of mornings off work I removed the old head and fitted the new one. I have had the head off the engine on a couple of occasions so it was pretty straight forward, with getting the non standard exhaust attached the most difficult part. Here's a picture of the head waiting to have the rocker gear added and then be tightened to the correct torque.

I then set the tappet clearances to 12 thous and turned the engine over with the plugs out to pump up oil pressure. When the electrics were reconnected the car started first time and the initial test run showed no leaks.

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