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"See, we're adding a little something to this month's sales contest. As you all know, first prize is a Cadillac Eldorado. Anyone wanna see second prize? Second prize is a set of steak knives. Third prize is you're fired."
What causes this? Overrev? Or just fatigue? :shock:
Mostly fatigue, they get weaker with age and higher revs just accelerate the process. Chips that raise the redline would accelerate it even further. Still it's alot less of a worry than breaking a timing belt. And, broken rocker arms would be the least of your worries if you ever overreved.
I have seen alot of broken rocker arms on motors with misadjusted valve clearance, and it seems most of them were on motors with very morn cam lobes. I broke one a few months ago on the origional 320i motor from my touring, and drove it with the broken rocker arm for about a month or so-since the motor was going in the trash anyway. It makes a wonderful popping noise out of the AFM when you accelerate! sorry to see you had the problem. All of the BMW tuners in germany say that is why you really cant build the M20 motors to rev higher than 6900rpm. good luck with the fix, and I suggest to buy all new excentrics for all of the rocker arms during the repair phase. at least that is what my machine shop says to do, and it seems to work ok for me, I rev my motor to the 6900rpm redline all the time(cause it sounds so cool bouncing off the rev limiter)j/k, and have had no problems with my new motor.
Hit the rev limiter and the engine floats a valve, the lobe of the cam comes around and cracks the rockerarm. Thats what I'm told anyways and it makes sense cause everytime that I broke a rocker arm was because I got a little carried away and hit the limiter.
I've always believed that rocker arm failure as primarily due to worn or misadjusted parts. If course age and fatigue of parts does come into it but if everything is adjusted correctly, you shouldn't have a problem.
Basically, when you have worn parts, rather than the rocker following the cam lobe, it tends to impact it and this is what stresses the rocker and causes them to break. Therefore, if I had a rocker break on me, I would change the cam, rockers and eccentrics to ensure it didn't happen again.
Click on this link to see what happened to my engine when a rocker broke.... I think you were lucky!
ouch. i'd seen those pics before, but didn't sink in what happened.. I hear what you're saying about worn parts.. the rockers i took out of the motor do have a fair amount of wear on their contact patch. i do not have the interest in spending the money on a new cam, and taking the time to put it in. i need this car to go back together quickly and cheaply. daily driver = transportation to work = how to make more money.
in any event, the cam in the motor looks good. i'm not sure i would be able to tell if it were worn beyond tolerances. i did, however, run a test to check tolerances on my rocker arms (the one where you see if there's any play between rocker and shaft) and they were well within spec. i am changing all rockers, shafts, and eccentrics as well as putting in new eccentric hardware.
New rockers and shafts should do the trick, cam's are pretty hardwearing anyway... it's the wear on the rockers where it contacts the cam that causes the problems.
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