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2016 Heron White MT TS stage 2 cam full AR exhaust Katech throttle body OTR CAL Custom Value cover
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Discussion Starter · #1 ·
I was going to have my 2016 tuned today, but the tuner noticed a mis-fire we checked the codes, the misfire codes were turned off by previous owner, showed a misfire cylinder 5 pulled the valve cover has a broken rocker. They look to be Yella Terra 1.7 rockers. Does anyone know if I can get just one cylinder or do I have to buy the whole set?
 

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To be fair, it's not new to see aluminum rockers fail on ls motors in street applications, regardless of Rev limit setting. Yella terras had a documented failure history on ls1tech. I had yella terras on a 383 and preemptively replaced them when I learned of the issue. If you don't want to deal with this, the oem rocker is a surprisingly durable substitute with a trunnion upgrade.
 

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To be fair, it's not new to see aluminum rockers fail on ls motors in street applications, regardless of Rev limit setting. Yella terras had a documented failure history on ls1tech. I had yella terras on a 383 and preemptively replaced them when I learned of the issue. If you don't want to deal with this, the oem rocker is a surprisingly durable substitute with a trunnion upgrade.
Aluminum does not have anywhere near the fatigue life of alloy steel. Cumulative load cycles is the limiting parameter, whether idling at a light, driving on the highway, or at red line on the track. Where the lower mass of aluminum is a benefit in race engine applications, the rockers need to be replaced every year or two. I notice that in drag racing that is personally funded, such as NMRA and NMCA, there is a trend back to steel rockers even for very high-lift, solid lifter applications. With finite element analysis design tools in wide use, a steel rocker can be designed to have adequate strength with surprisingly little weight penalty compared to aluminum.
 

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That's why I went with Comp Ultra Pro Magnums. Chrome moly steel, and since adding the billet rocker stands they feel bullet proof all the way up to limiter. I thought about raising the limit, just not prudent for my daily driver. Over 50K on them and have passed two inspections, survived one lifter failure. My motorsport shop recommended pulling valve covers every 15K once we increased the rocker ratio. He also suggested replacing the springs every 30K, at $400 I may get them tested to see if their needed. That's due in about 4K miles now.

Aluminum does not have anywhere near the fatigue life of alloy steel. Cumulative load cycles is the limiting parameter, whether idling at a light, driving on the highway, or at red line on the track. Where the lower mass of aluminum is a benefit in race engine applications, the rockers need to be replaced every year or two. I notice that in drag racing that is personally funded, such as NMRA and NMCA, there is a trend back to steel rockers even for very high-lift, solid lifter applications. With finite element analysis design tools in wide use, a steel rocker can be designed to have adequate strength with surprisingly little weight penalty compared to aluminum.
 

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2016 Heron White MT TS stage 2 cam full AR exhaust Katech throttle body OTR CAL Custom Value cover
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Discussion Starter · #8 ·
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Here is the damage, I am working with someone from Yella Terra to try to get a replacement.
 

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IMO you should replace all of the rocker arms. This is the first failure, but the rest have the same number of stress cycles.
Yup...
They're all the same age, same load and in the same environment, why wouldn't the others fail?
 
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