<VV> Gernade engine autopsy

[Tony Underwood]

At 09:12 hours 07/07/2005, Levair at aol.com wrote:
>all,
>Michael tore down his "Gernade with pin fully pulled" engine today.
>The No 5 and no 6 rods left the crankshaft. There are no big ends left to
>examine.
>Trashed the block and cam also. The heads and valve train are perfect.
>If the MSD rev limiter is reliable ---big, big IF-- the engine never exceded
>6800 rpm.
>   The no 5 main journal is trash but 4 and 6 are perfect. We suspect that 
> the
>big ends of the rods simply let go. The rods were bored (weakened) for
>oversize bolts and had extensive metal removed for balancing. Weakened in the
>interest of speed?
>    Opinions welcomed.



I've not had any personal experience with boring Vair rods for larger 
bolts.   However, I *have* seen other stuff (mostly SBCs) with stock rods 
bored for larger bolts and the engine started shedding rods at 
rpm.    Moral of story seemed to be to leave as much meat on the big end as 
you can and concentrate instead on better attachment hardware and stress 
point relief.   I'd seen people with relatively stock bottom ends on 
built-up SBC engines turn 8000 rpm with uncut factory rods fitted with 
tougher bolts and it stayed together.   I myself have twisted a bigblock 
Chrysler engine with stock rods and stock rod bolts to 7400 rpm and it took 
it.   Maybe I was lucky... or maybe not; if I'd fitted larger type "NASCAR" 
rod bolts to the factory rods I'd likely have never broken a bolt but the 
rod would have gone south.


Vair rods are relatively OK, not all that meaty but then the piston isn't 
that heavy either.   Still, the instincts say to leave the rod alone, don't 
remove anything, use tougher hardware in the existing rod.   Weakening the 
rod for the sake of a stronger bolt kinda seems like going a mile out of 
one's way to take a shortcut.   If a super strong rod was needed, maybe a 
custom aftermarket would be the best way to go...  providing one could 
spare the $$$; such stuff gets damned expensive for my tastes.

Again, this is just a personal opinion, I'm not a machinist nor am I a 
metallurgist nor an authority on the absolute strengths of a factory 164" 
Vair rod.   But I do have a little practical experience in breaking 
stuff.   ;)


Hope the engine issues get resolved and that the woes are put behind 
everyone and onward down the track you go.



tony..