Is it a bad idea to put aluminum roller rockers in a street engine that will be my daily driver? I've heard they could get brittle. Also, what kind of roller rockers will work with centerbolt valve covers and pushrod guideplates?

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91 Z28
Come see The Vicious...

 

Yes, the aluminums are fine for street use. I have used these many times previously on my daily drivers with no problems (Crane's Vacuum Cast 1.6 ratio full roller rockers). Naturally you want the rocker to have some to quite a bit of brittleness (hardness), otherwise your lift would fluctuate alot with soft aluminum. For center bolt valve covers, the consensus is either Crane Gold series or Comp Magnum series. As for the guideplates compatability, use non-self aligned ones.

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George P. Lara
1984 Z28
2001 SS Coming Soon
SCCA, SCFB, SC3GFB

 

I prefer steel for street use. Aluminum by its nature will not last as long.

For the money, it's hard to beat the Comp steel roller-tip ones. Their steel full rollers are also well-priced. I believe you'll have trouble with almost any full roller rockers and stock valve covers, because the trunnions are so wide that the breather baffles don't fit down between them. But they can usually be modified (smashed) enough to work.

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"So many Mustangs, so little time..."
ICON Motorsports

 

RB83L69, will I have problems with the roller rockers even if they're 1.5 ratio? That's what I plan to use because my cam has plenty of lift. I heard I'd only have problems with the 1.6.

 

Your clearance really has little to do with the ratio. The design of the roller trunion area is the same whether the rockers are 1.52:1 of 1.8:1.

Comp Cams Pro Magnums

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

Since when does brittleness mean hardness?
Oh, and I wouldn't go with aluminum. Comp Cams gets my vote.

 

Forever.

As hardness (and strength) go up, toughness goes down (meaning brittleness goes up). This is assuming you are talking about the same material, that is. A brittle material is more susceptible to breakage due to shock. This is typically a function of heat treatment, and can be modified by alloying to improve overall performance.

However, flex is a function of the modulous of elastisity of the material, not the strength (hardness). That is why aluminum rockers are thick & fat, while steel are thin and skinny.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam and intake, World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

Aluminum doesn't get "brittle". The issue is fatigue. Steel has a property called the "fatigue limit", meaning if you keep the stress below a certain percentage of the strength, the material will not fatigue and break due to cyclic loading. Aluminum, however, does not have this property, so will eventually fatigue regardless of the stress level to which it is exposed (unless the stress is zero, of course). The higher the stress of the cyclic loading, the quicker it will happen, but you can't design an aluminum component to last forever. Again, alloying helps improve properties, including fatigue.

 

The aluminum (as with most metals) gets harder as it is repeatedly flexed (work hardening) therefore its limit of elesticity is reduced.

Like bending a paperclip back and forth. The clip will break because you made the steel harder and therefore less malleable (unable to be bent as much the next time)

 

That is only true if you take it beyond its yield point. Typical design practice is to keep the stress below yield (i.e., within the elastic region). One exception is torque-to-yield head bolts, but that's a "static" application, and they are single-use. Does not apply to rocker arms.