What caused this

69_340_GTS said

You absolutely have to put a zinc additive in your oil these days. Or buy oil that already has it. No regular motor oil has enough ZDDP (zinc) in it to properly lubricate flat tappet camshafts & lifters.

Click to expand...

Actually there are quite a few oils that have enough ZDDP in them; you just have to do your home work to see which ones. In the olden days, the ZDDP levels were in the 1300-1500 PPM range. That got reduced to 1200 PPM and cams were not being lost. Then the ZDDP levels were reduced to 900 PPM's for one of the recent service grades, and that is when the problems started.

Those 900 PPM reduced levels are for generally found in the the lighter grade oils, 30W straight and multi-grade, and lower. If the service code is SN, then you have a newer, low ZDDP level oil.