When I had my MG-B one of the forums had a 'DPO (dumb previous owner)/IPO (idiot previous owner)' thread that listed what folks had done thinking they were doing the right thing while making things much more difficult for the next owner to fix. I could not find one here so I will start one.
I am in the process of changing out the engine in my 1951 Plymouth Cambridge. The old engine was tired and I was on the OPEC Christmas card list and Exxon-Mobil was ready to set me up as a dealer for all of the oil it was leaking. We all know that the previous owners mean well with their repairs but sometimes they are not as skilled as they think they are. In the process of changing out the engine here are some of the things that I found were incorrectly done.
First, when the DPO changed out the engine, the head was missing the tapped hole for the throttle bellcrank pin. To compensate they welded a plate to two of the head bolts and welded on a piece of rod for the bellcrank pivot. I needed to grind off the plate to remove the head from the old engine. Both bolts were loose and could not be retorqued with the plate welded between them. I was surprised that it never blew the head gasket.
Second, when I went to reinstall the yoke and radiator support after installing the new engine, things were not lining up. When I removed them, I noticed that the radiator support could easily be installed backwards and that there was a lot of stress on the bolts. I carefully marked the radiator support to make sure it went back in correctly. I had noticed that when removing them there was a lot of shear stress on the bolts. When reinstalling the yoke, I had all kinds of difficulty installing the bolts and that is when I found that the support was installed backwards by the DPO. Once I reversed it, everything lined up and the front end sits about one inch lower. It also explains why they drilled new holes for the radiator bolts.
Third, the previous owner who did the engine work must have liked spending a lot of money buying hardware store quality bolts. I think I broke off at least a dozen on this project. Grade 8 bolts are less than $5 per pound at Tractor Supply and Runnings so you can get a lot of high quality bolts for a lot less money than buying them a couple at a time at the hardware store.
I am sure I will find more as I continue with this project.