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Chicagoland MG Club: Driveline
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  Chicagoland MG Club:Driveline

Go Brit Baby! - Tech Sessions

We had several tech sessions in March covering a Midget brake system, a cylinder head evaluation, and a Z-S to SU carburetor conversion. Something for everyone!

The cylinder head evaluation was done to my ’58 MGA 1500. This car had extremely low compression on #4 cylinder - just 30 lbs. The other cylinders ranged from 130-140 lbs. I am already in the process of rebuilding and installing a more robust performance oriented 1600 engine for this car. However, I thought it might be fun to tear into this old, tired engine to see what the problem was.

It’s a good idea to do a compression check once and a while. The compression readings can give you an idea of the relative health of your engine. You like to see these numbers within about 10% of each other.

Bad rings, valves, or a head gasket can bring on a low compression reading. A car with low compression will likely to be harder to start and have poor acceleration. Well, my MGA was certainly hard to start and had poor power, particularly on the highway or going up a hill.

We pulled the head off the 1500 and it was immediately clear what the problem was. The exhaust valve on #4 had chunks (British term?) of metal missing out of it. It was really a wonder that it had managed any compression at all. The head wasn’t in much better shape. It had valve recession on several of the valve seats. So, there was no sense in putting this head back on right away. Fortunately, I had a back up head ready to go from an early MGB (I guess two heads really are better than one).

The cylinder walls were in good shape. So, we milled in some relief eyebrows into the top of the block for the larger MGB valves and torqued the new head down onto the 1500 block. The before and after results are below:

'58 MGA 1500 Roadster
Cylinder  1  2  3  4 

The lowest reading was within 9% of the highest reading. So, we achieved the goal of having the numbers within 10% of one another.

We then took the car out for a test run. The change in the car was immediately obvious with a now higher compression engine. It started quite easily and the improvement in acceleration was dramatic.

To me this tech session was a huge success. I bought this car in October of ’99 after it had sat in storage for 14 years. Although I was hopeful for a good outcome, in the back of my mind I thought this engine was just too tired to be brought back without a major rebuild. What a surprise to be able to basically resurrect this engine without much expense. Our MG’s really do have resilient engines.

The cost to bring this engine back from the grave was less than $120. I picked up the spare head for $50 and spent about $70 having the B head milled down to the proper MGA size. This engine is now ready to deliver some more years of top down enjoyment.

On April 22nd we will be having the Spring Tune Up Party at Quality Tire starting from 9 a.m. to 2 p.m. Quality Tire’s address is 6710 Rt 83, Darian, IL. So, throw that car cover off your MG and bring your car in for our annual Spring check up. Start the driving season off right with some new plugs, points, and fluids. Please bring your own parts; lifts will be available for your use. I look forward to seeing everyone there.

Steve Merical

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