1971 MGB GT

MICROMETER

This lesson was learned on an MGBGT that we used to autocross before building the Elan. However, I certainly applied what I had learned when building the engine for the Elan. The story starts in about 1982, when I was restoring the MG for autocrossing and pulled and rebuilt the engine. I asked around about reputable machine shops, picked one associated with a performance parts shop, and took the block in for machine work, including an align bore. My goal was to blueprint the engine to obtain maximum performance and reliability from the engine. At the end of about three months, I had the car back together and commenced driving it daily and autocrossing on occasional weekends. The car ran well, but seemed to have lower oil pressure at idle than I remembered. After about 10,000 miles, on the way to work one morning, terrible noises started emanating from the engine and I was forced to pull over and tow the car home. The engine came out, was taken to a new machine shop who an autocross friend had real good luck with, and the problem was explained. They were asked to check the block and make sure it was good before doing any work. I was assured the block was fine, reinstalled the engine, and about 10,000 miles later, I was on the starting grid at a Pro-Solo in Texas when the engine let go again. Both times, I had spun a rod bearing. I should add here that both times I rebuilt the engine, I used plasti-gauge to verify bearing clearances and nothing seemed amiss. By now, I am quite the unhappy camper, so I decided it was time to take matters into my own hands. I went to the local discount tool place and purchased telescoping gauges, vernier caliper and two sizes of micrometers. I took every reading I could think to take on the block and discovered the front main bearing was .01 inches out of round! Maximum bearing clearance was supposed to be less than .003. The deviation was on the horizontal plane, where plasti-gauge could not detect it. Apparently, the original align bore had been bungled! So, armed with all this information, off I went to a third machine shop with the best reputation in the area for performance engine construction. Everything was explained. I told them I had another block that I could build if need be, but would prefer to build the original, if it could be made a good block. I explained I didn't know how much they could do with machining operations. They called and said the block was fine and I could pick it up, as the machine work was done. I took the block home, miced it again, and it was still way out on the number one main. Needless to say, they machined my other block at no charge. Now, if I am going to have machine work done on a block, it gets measured by me before and after!