the unnecessary usage of j-brakes, why????

While I have not read all 53 pages of comments, I seem to have missed anyone actually talking about what happens to the engine when the Jake does damage to it. What actually happens is just like any other engine if you over rev it, but with your jakes on, the exhaust valves have the potential to "float" at lower RPM's which means if the exhaust valve is open when the piston comes up and smashes your exhaust valve, it will bend and then when it retracts, it will straighten. A valve won't do that very many times before it breaks off and then look out. That piece floating around in the cylinder can do a whole lot of damage in a hurry, not to mention having to replace the valves that have broken off.
If you drive right and don't over rev your engine, you should be fine. Check with your engine manufacurer to see what their max is with the Jake activated. I have been told that with my 8v92 Detroit I should not rev over 2100 rpms or risk problems. Watch your RPM's and downshift.

 

I believe you've lost sight of the point. Supply and demand. America would not stop if cashiers walked off the job, we'd just go back to the way it was done, supplies were ordered by the shop owner and he sold the goods. A majority of truckers know or should learn how to work on their trucks, etc, etc, etc.......

The point is simple, you have 3 days of food on the shelf at the local market. The food, shelf, flooring, windows, roof, electrical wiring, doors, etc that make up that local market were all delivered at one time or another by a truck. As I said, supply and demand will dictate whether a store is open or closed, not a cashier. We had one of those, "We have to pay $10 per month for out medical insurance and they are trying to raise it to $12 per month" grocery union strikes about 5-6 years ago. All the cashiers walked off the job, with the meat department guys, deli, baggers, even the fruit and veggie employees, store stayed open and the trucks kept delivering, well the Non-teamster trucks, guess teamsters don't cross picket lines. Hey maybe you're right, if all truck drivers were teamsters, a cashier strike would shut us down. Hmmm. Food for thought. Nah, I like being my own rep.

Point is, your comparing apples and oranges.

 

At wal mart you don't even need a cashier, self checkout. At the gas station you don't even need to go inside, just swipe your card. But how do the goods get to wal mart, how does the fuel get to the gas station? And honestly Having never done it I'm sure I can swipe goods across a bar code scanner, anyone can. Not exactly a skills job. Can any schmuck who never drove a truck hop in and haul a load? I doubt they could even figure out how to make it move, or even start it.

BTW amazing revival of a necro thread.

 

In normal operation of a "Jake" the exhaust valve opens when the piston comes up. That's what it is supposed to do.

 

The key to your phrase is "normal operation" If you over rev the engine the "you will float the valves and they CAN come into contact with the piston" causing significant damage. No two things can occupy the same space at the same time. The normal timing of the operation of the valve and the piston is critically timed, when that timing is off due to the valve floating and being somewhere it isn't supposed to be at the time, it gets hit. Pretty simple. I don't care if you believe it or not, just trying to add some fact to all the other hypothesis. Check with a mechanic!

 

This wasn't meant to be taken as being opposed to abnormal operation, it was meant as this is what it is supposed to do.

Actually this or similar "facts" (such as sucking the valves through the head) have come up before, so I have in the past consulted with others both mechanics and shop managers who said it isn't likely to be true and they have never seen it happen.

I also checked this out some time ago with Jacobs Vehicle systems. It was their position that valves on vehicles with mechanical tappets would not float, only those with hydraulic lifters could which is why JVS does not make engine compression brakes for them.

This is not to say that if you overrun your engine going down a steep hill that you cannot suffer any consequences, because you can. But this can be true whether you have a compression brake or not. If what you are saying is true then the floating valve(s) striking a piston(s) would occur whether you had an engine brake or not. Since we do not usually have hydraulic lifters it's a problem not worth considering.

 

one was bobtail approaching a stoplight with them on for a long time

long enough for me to see why somebody would have jakes on for a level road

 

That would be because you didn't take the time to read all 53 pages and actually attempt to learn something. I'll save you the effort. Jake's do not damage engines.

A valve will not bend and re-straighten. That is absurd. You could bend a valve with a weak spring or by over-revving, or in the case of most automotive engines, a slipped timing belt - but it will not re-straighten.

A Jake Brake releases the compression when the piston is traveling upwards on the compression stroke. When the piston starts traveling downward after no compression/power is achieved, the valves open and close rapidly from the suction generated, creating the noise you hear and the retarding power. There is very little danger of piston to valve contact.

 

Who knows sometimes you simply forget you've got them on although the way around that is to switch them off once you've used them if i do forget though and they go off i just switch them off as fast as possible but boy don't they pull you up quick if your bob tail and going below 20mph. The other thought would be some blokes and gals just get a cheap thrill out of using them it seems to give them a high look at me my shiny noisy truck.

 

#### could be using it because theirs an emegacy this is me I don't care what any body says I love my Jake brake