Rocker arms continuously breaking on my SpecE30 motor

[rogerscgreg]

I’m running an M20B25 with factory parts. I didn’t grow up driving manual, so 99% of the manual driving I’ve done has been in this car at speed.

In January, I money shifted at high revs, 3rd to 2nd instead of 3rd to 4th. I got the clutch in quickly, so there were no catastrophic or terminal parts failures at that moment.

Fast forward to June after a few lapping sessions and a full race weekend. Halfway through my 2nd race weekend with it, one of the rocker arms broke mid-race with no obvious over-rev. I replaced it and carried on. The 4th race weekend, a different rocker arm broke, again without any obvious over-rev. Just yesterday, another one gave out, so I’m going to replace all of them.

All 3 failures have been on the intake side, but I believe that’s just coincidence. Valves have been lashed to 0.010” each time. Oil has been changed regularly.

I suspect that there are hairline fractures in most of the rocker arms from the money shift in January and that the failures are now rearing their head one at a time, but I’d like to confirm that suspicion both by running it by the group as well as doing a thorough inspection of the remaining rocker arms from the incident.

My greater concern is that I’m actually causing isolated failures in each of these instances with my driving style. I don’t believe I’m shifting irresponsibly, I heel-toe and try to rev march as best as I can, and I’m not super aggressive with upshifts. I guess I could be more gentle on the clutch release? But even then, I don’t feel like the rocker arms would fail so regularly because of a clumsy upshift once in a while.

Any thoughts would be appreciated.

[zaq123]

what rpm did it rev to when you mis-shifted? Stock rockers don't like to go past 7-7.2k with stock springs. If you shifted from 5k rpm from 3rd to 2nd, the engine was at about 7.8k rpm. 5k was just an example, you can figure it out yourself using this formula: your RPM X [2.20 / 1.40] . Getrag 260, 2.20 is 3rd gear ratio and 1.40 is 3rd, in case you are wondering what those numbers are.

[rogerscgreg]

I was at 6700ish, so it was likely 9-10k

[zaq123]

I was at 6700ish, so it was likely 9-10k

10k rpm is a little bit too much for stock parts.

[TobyB]

It's not coincidence that it's all intakes.

They're heavier, so they float first, and float worst. If you made it to 9k, I'd replace the rest of the intake rockers,
measure the springs for free length and rate at installation and on the nose-
just to make sure they're ok (they almost always are, but soft springs break valves)
and see how it goes.

I'm honestly surprised you made it that high without breaking rockers immediately- when I hit the
spring limit and then go beyond, the first downshift results in a 'pop' and a misfire...

t
uses cheap rockers, too.