Mythbuster: continuing project thread of my 1303 '75

[Wally]

Originally Posted by effvee

Walter, what head work have you done or had done? Very good results, congrats.

These are the 'old' heads from my former 2,7 and have 46x40 valves and some smart porting done to them, mostly based on airspeed, so not very large ports.
They are a 35 year old 914 2.0 casting and no welding was done.
In N/A form they flowed 220 hp...

[Wally]

Today I have broken two (!) original type 4 8mm rockers during a dragrace meet...
Can't figure out how this could have happened, but no further damage was done to the engine: no bend pushrods, no bend valves. The latter really surprised me, as how the heck can these rockers break otherwise??

Whats wrong with this picture?:


The weirdest thing: I exchanged the broken rockers for two 'new' ones and the engine started on 4 cylinders and has the same compression as before...
I am totally puzzeled how this could have happend, but count my blessings as the engine runs fine now again...pffft.

[dub_crazee]

Bizarre!!! Glad there was no damage! Put any decent runs in before the damage?

[Wally]

Originally Posted by dub_crazee

Bizarre!!! Glad there was no damage! Put any decent runs in before the damage?

Not really, it happened on the 2nd run. First run was a track-sensing 12.8/181km/h, but I had hoped for an 11-run this day...

[michael86]

Could it be a age related that the rockers broke.
The material getting brittle over the years.
I've never seen this before.

Glad it was only two rockers and no more damage.

Tiki

[Humble]

That's really strange that it snapped off 2 rockers in the same fashion on the same cylinder. It's amazing there's nothing else wrong, you really lucked out

[Wally]

Originally Posted by Humble

That's really strange that it snapped off 2 rockers in the same fashion on the same cylinder. It's amazing there's nothing else wrong, you really lucked out

Yeah, I did huh?

Might indeed be something like metal fatique Michael, but you would have thought this would have happened to others then too? Never seen it before and especially not at two on the same cylinder...
I am still very much puzzeled by the whole thing.