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Talked to an old Cummins guy in Lubbock about engine braking yesterday
He said letting the Jake brake rattle at low RPM is how you crack a rocker housing, so now I'm second guessing every downhill I've taken in the last 5 years, anyone else hear that before?
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viola_ward1mo ago
...and the other thing nobody talks about is how much the engine temperature plays into it. I've seen more rocker housing cracks come from cold hammering than from low RPM alone. If you're running a Jake brake with the oil still thick and the block not up to operating temp, that's where the real damage adds up. You get that thermal shock mixed with the mechanical shock and the cast iron just doesn't have any give left. Your mileage may vary obviously, but I always let mine warm up good before I even think about flipping that switch, especially in the winter months.
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the_hayden9d agoMost Upvoted
You know, I always figured the low RPM thing was the main culprit, but you and Viola make a strong case about the cold weather factor. I used to flip the Jake brake on as soon as I left the yard, but I've been taking it easier after reading this thread, letting the temp gauge climb first.
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robertb471mo ago
Yeah that's legit... low RPM Jake braking lets the valves float and slam around, the rocker arms take the beating instead of the cam. I always tell guys to keep it above 1500 RPM before you flip that switch, especially on a long downhill grade where the engine's lugging. Also check your oil level religiously if you run a Jake brake, low oil will starve the actuator and that's a quick way to crack a housing too.
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