John Black wrote:
[quote]I noticed $225 for all new (12) rockers. I broke two at Mid Ohio 2 years ago - really makes for a crappy end of a weekend. Just trying to understand the reason to replace old ones that are not broken. Do they stress (which would make sense) that would make them more likely to break? Is this a "while I have the head open? Is this "there is a new, better design" thing? My mechanic only replaced the 2 broken ones, and told me not to worry about the others (I was thinking, "they are relatively cheap compared to what he was charging for labor, for a bit more, should I replace them all) - they are good right up until they go bad. Just trying to understand, in case I find myself in the same place I was last time (or if I am bored this winter). I know there are some billet ones out there…but WOW on the price - I could get 2 junkyard motors for that jingle!
Thanks![/quote]
IMHO, I would replace ALL 12 rockers if one breaks- unless it’s a POS beater and I was too broke to afford to fix it "right". If it’s a track/race car, then no question- replace all of them.
To answer your question, yes- the rockers fatigue over time and this contributes to their propensity to break. The M20 rockers were updated sometime ago, maybe 8-10 years ago. So, the original rockers are the "old" design and any new rockers will be the new better design- they’re beefier in the center section where they tend to break.
You hit the nail on the head when you said that replacing all rockers is relatively cheap- compared to the labor charge to R&R the head- and there should be -0- additional labor cost to install new rockers vs. the old ones. This could be the difference between a good weekend and one sitting on the sidelines watching others have a good time while you have plenty of time to wish you had replaced all of those rockers… 
Bret
