[DeTomaso] Solid roller cam failures
JDeRyke at aol.com
JDeRyke at aol.com
Thu Apr 30 15:05:54 EDT 2009
In a message dated 4/30/09 7:33:51 AM, kirby.schrader at gmail.com writes:
> The lifters now in my GT40 are solid rollers. Clearance set at 0.008.
> They are supposed to last... Crane claimed ramp design and technology
> improvements help them live.
>
KIrby, I was told by Isky's cam expert there are two main failure modes on
solid roller cams. The first and most common on street cars is the roller
wheel skidding at low engine speeds. This wears a flat spot on either the cam
lobe or the lifter wheel, rather than rolling. Happens to full-roller rocker
arms, too. This also coincides with low oil supply since splash-oil is all
the rollers get. The second is impact damage- usually from over-revving with
too light valvesprings. I have a set of solid rollers that not only floated
at moderate rpms, the anti-rotation strap unlatched from one pair,
destroying the block and cam. And in spite of all mfgr efforts, roller lifters are
heavier than flat tappets and absolutely require stiffer springs and maybe
stiffer pushrods. Those racing springs drop their rated pressures pretty fast,
too.... One cure is a rev-kit to keep float away. Hydraulic rollers are
even heavier than solid-rollers. The roller-lifter wheel is really the outer
side of a very hard bearing race and doesn't take impacts at all. Cams dent or
chip and rollers crack, and the great game is about over for those parts.
No known way to check except disassembly followed by a magnifying glass
examination. But Roger Sharp's 392 Cleveland with a radical Comp solid roller cam
in his street-only Pantera, has had zero problems for 9 years now including
two trips to 'Vegas. So failures don't always happen; I suspect they are
infrequent. Cam breakage is even rarer. The last busted cam I heard of was in
a NASCAR flat-tappet engine- and they turn to above 9800 rpms on short
tracks so you can imagine the stiffness of their valve springs. As always, watch
your gauges and listen to what the engine tells you and likely you'll be
fine. FWIW- J Deryke
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