Old Fart, been there done that, in some cases may have been the first to do dat.

I have certainly had blocks over the years that were not rebuildable because they were heat warped or severely pounded, but if everything else was o-k, the Mainliner did an excellent job of machining the main bearing seats. There are people in this world who shouldn't pick up a hammer, never mind a line-boring machine. When he machined a case, he only torqued down the six large case nuts and neglected to tighten the two 13 m/m nuts that straddle the small main bearing near the crankshaft pulley. I did know of one person with a mainliner that had problems with it, but the problem was self-inflicted. The only addition I added to the Mainliner was I made my own setting tool for the cutters so I didn't have to bother sending them out to be sharpened. The only problem I had with this tool was after years of use I needed to put some oil in the hydraulic feed unit as some evidently had leaked out. I was always impressed with how accurate the bores were time after time, even when switching between cutters. I always gauged bored cases with a dial bore gage after I bored them. As a machinist who has made precision bearings for virtually all aircraft engines that fly today as well as the bearings for the Space Shuttle I am well trained on making products with tolerances sometimes down to 30 millionths of an inch. I used this tool to line bore dozens of cases over the years and it has always done an excellent job for me. In 1980 I purchased a Mainliner, I READ THE INSTRUCTIONS. I started rebuilding VW motors while I was still in high school. I am 60 years old and have been a machinist/mechanic all my life. I was surprised to see negative postings about the Porta-Tool Mainliner.

Porta tool vw line bore tool