ORIGINAL: downunder
More likely though is that in a converted weed eater type engine the original needle rollers weren't designed to handle the extra loads placed on them by converting to methanol and being run at higher revs. Needle rollers only have a line contact taken by the uppermost couple of needles while a bush spreads the load evenly over the upper half of the bush. This reduces the unit area pressure dramatically.
Nothing to do with lubrication.
Brian,
I am not completely sure... At least some people, even real engineers, do blame it on lubrication...
As I wrote, the difference in power and therefore in load on the con-rod, is quite small, between gas engines used for R/C planes (not for weed whacking, chain-sawing, shrub-trimming, spraying, Etc.) and glow engine versions of the same.
Yet, the difference in rod bearing life is very noticeable.
It could be the more corrosive attribute of glow fuel components and its waste products (with those bearings beginning to go out with rust), but it could also be inferior lubrication supplied by the lubricant solution in methanol.