Exhaust brake

[Chamberpains]

Dropping a valve only happens in extreme cases. There has to be something seriously wrong with the engine. Like weak worn out valve springs, the engine mechanical timing is wrong, worn out valve seats, faulty valve (usually manufacturers flaw) or maybe if you would happen to run the jakes on full blast with the rpm's screaming up above its rated rpm range but even then I have my doubts that in limited uses up there it would actually drop a valve. These engines are that well designed.

You have an incredibly designed engine from Cummins that was hand built by the best team in the country to build one using only the best parts available. You can have faith that if you keep good clean oil in it and operate it within the ranges rawze describes then you will be able to do very little to that engine to hurt it. That is what the programming geniuses from Cummins have done. They spent millions of $$ on R&D to find the safe limitations of things and put those limits in the ECM. If it's demandated and you completely trust the person that did it then you will also know they haven't severely altered anything as to allow the engine to operate outside those safe ranges.

I drove my demandated cm870 exactly how rawze describes and how I described for 300,000 miles till my stupid neglect of not changing main bearings at a million miles allowed the engine to lose #5 piston wrist pin at 1.1 million miles. I replaced the engine and continued to drive the new reman for 250,000 more miles in the exact same manner. It still fires up today and runs just as good. I never once dropped a valve or had any ill effects running my jakes in the manner I described. Even in my whoopsy doo moments of grabbing a gear too early the rpm's screamed up to 2100-2200 for a second and still no ill effect. And that was in an engine with over 1 million miles.

These are incredibly built engines. The jakes on your engine will easily handle the ranges I described. It absolutely will save you a pile of money on brake replacement. Let them do what they are designed to do. And if all you're seeing out if your cm870 is low 20's or below psi when your on a hard downgrade fully loaded with the rpms up in the 1600-1850 range and down a gear or 2 off the top gear (top gear would operate at 25-28 max) then you're not getting full jake out of that engine. Hard high jaking will easily produce 28 psi if not slide up in to the 30-32 psi range (when in really extreme hard jaking) don't be afraid to allow it to go there.