NP foxy, i know theres a time and place and know to respect others threads.
ORIGINAL: MONAROMAN
So why was I snapping pinion bolts then LW when they weren't overtightened? They were just snug with locktite to keep them from backing out - as you mentioned that star washer is pretty poor, and to boot i wasn't even getting a chance to warm up gears. You seem to have all the answers so i am interested to know.... And as I mentioned, your fave mfg's part wasn't to blame, all I did to fix the situation was increase the bolt's diameter as many others have done. We can't all be wrong, or can we...
Sorry mate, miss interpreted your use of 'rolleyes' to mean something else. Maybe lay off that smiley for a while eh?
Anyway there could be any number of reasons your engine not being one of them. If your clutch is slipping alot and or you have a habit of throttleing in the range where your clutch is barely starting to engage you'll heat the bell up alot, heat from that will also weaken the bolt. As foxy said the rotation of the pinion gear is anti-clockwise meaning the bolt will have a tendency to tighten itself, i don't think the point where it would shear off its own head but along with other factors can be enough to break it.
The fact that it is breaking is a clue to something else being wrong with your setup that you'll have to go through with a fine toothed combe, like a slightly twisted chassis or your gearplate might be warped, sometimes happens after an impact with the alloy one making the SG & pinion mesh at a slight angle - that will put uneven pressure on the pinion and might break the bolt - thats where those alloy rear engine mounts that are out there come in useful.
By replacing the bolt with a stronger 5mm one you've only masked the issue and it probably still needs to be addressed, when you've found the exact cause you can then decide whether its worth fixing or not. I'm not saying you or anyone else is wrong, but the approach is just attacking the symptom not going after the cause, the danger of which is you end up ignoring the signs that somethings wrong only to have the cause bite you later and it normally costs alot more to fix at that point. The most you would ever have to do is switch the stock bolt for a 12.9 grade alloy steel one (cheap as chips) but retapping the CB for 5mm is excessive.
edit: I'm sorry that you feel that i'm someone who seems to have all the answers. I'm not trying to post like i'm some sort of know it all but i do have some experience from maintaining alot of the local guys Baja's along with experience with other R/C's that have very similar setups, again as foxy said issues like this arn't exclusive to the Baja.