| Author | Message | ||
| Beefmalone (Beefmalone) (67.33.232.121)
Rating: N/A |
This is just something I've always wondered. Don't these work by closing a valve in the exhaust and forcing the engine to slow down by restricting airflow? Wouldn't this be hell on the seals, valves, & especially the piston rings? | ||
| TomNPat (68.128.42.117)
Rating: N/A |
Probably not any more hell than each explosion caused by fuel burning in the same place. TomNPat | ||
| Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A |
Actually, just the opposite. The valves are closed when the piston is coming up on the compression stroke. After the air is compressed (and the work is done) no fuel is injected into the cylinder and the valve is opened. The work of compressing the air is now just blown out the exhaust as hot air. Richard | ||
| Scott Whitney (66.82.9.32) Rating: N/A |
I swiped this answer from howstuffworks.com . . . *** Many large diesel trucks (and even some larger RVs) are equipped with "Jake Brakes," also known as compression release engine braking systems. They are called Jake Brakes because Jacobs Vehicle Systems is the original maker of this sort of braking system. The basic idea behind a Jake Brake is to use the engine to provide braking power. If you own a stick shift car and have ever downshifted to provide braking, you understand part of the idea. When you brake a car by downshifting, you are using engine vacuum to slow the car down. A Jake Brake goes a step further, and actually turns the engine into an air compressor to provide a great deal more braking power. If you have read How Car Engines Work, then you know that the engine goes through a compression stroke. Compressing the air in the cylinder takes power. If the engine's drive shaft is turning the engine to brake the truck, the power used to compress the air is braking power. However, that power is stored in the cylinder, so if you let it, the compressed air simply pushes the piston back down. Therefore, you don't really get any braking at all from the compression stroke on an unmodified engine. A Jake Brake modifies the timing on the exhaust valves so that, when braking is desired, the exhaust valves open right as the piston reaches the top of the compression stroke. The energy gathered in the compressed air is released, so the compression stroke actually provides braking power. The main advantage of a Jake Brake is that it saves wear on the normal brakes. This is especially important on long downhill stretches. *** Scott | ||
| Geoff (64.1.4.63)
Rating: N/A |
Jakes are not really BAD for your engine, but they shouldn't be used all the time. What you are doing is curtailing the combustion process so the lubricating oil that naturally travels up the clyinder is not burned off or pushed back down by combustion, this leads to oil in the exhaust and build of carbon. Also, while the jakes are working there is still some (despite what some people claim) fuel being injected which adds to the mess. Jakes are great for slowing you down, but use them prudently. | ||
| Tom Hamrick (Tomhamrick) (167.83.101.23)
Rating: N/A |
Sometime back I found a web site that had exhaust brakes to fit the two cycle Detroits. They was even a picture of an MCI conversion as an example. I can't find it anymore. Anybody know where this is? Will exhaust brakes work on our engines and are they harmful? Tom Hamrick Eagle 10S | ||
| Geoff (64.1.0.39)
Rating: N/A |
You can't put exhaust brakes on a 2 cycle engine, and I don't think I would want one in a 4-cycle either! How about transmission retarders? | ||
| Tom Hamrick (Tomhamrick) (167.83.101.23)
Rating: N/A |
Thanks. Guess I'll just plan on the Jake Brake someday. Tom Hamrick | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Every coach should have a Jake. It is kinda like an unlimited supply of cold beer in the summer and numerous young warm bodies in the winter. Broom, broommmm, brrooommmmm!!! If the thing is installed and adjusted correctly, the fuel should be in the "off" position when the Jake is working. Well, welcome to an inperfect world. And..ideally, the timing should be that the cracked open exhaust valve does not hit the decending piston as the valve opens to dump all that compressed hot air. The neat thing about a Jake is that it is kinda like a two-for-one. One is that using the Jake during a long steep decent helps keep the mill warm... By letting the engine cooling system absorb most all that energy of turning the mill into a huge compressor in the first place. How much?....The factory engineers say about 30% of the energy goes out the exhaust pipe as heat and a full 70% of the waste heat/energy is absorded by the radiator/cooling system. The other one is that by using the Jake, you keep your foot off the service brakes and let them remain cool, saving them for when you really need them. And.....the ongoing problem with a transmission retarder is that all that tremedous heat must be handled by the transmission cooler alone, which sometimes (mostly?) is undersized for the task. Transmission retarders work fine in some applications requiring intermediant retarding ability. But for my two cents worth, for heavy duty contineous duty rated braking, a Jake is the only way to go. For more general info on the Jake Brake, try www.jakebrake.com and cruise their site. Very cool indeed. These guys deserve a medal. Thanks. | ||
| Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A |
Hey, Henry, you left out the most important part: Broom, broommmm, brrooommmmm!!! LOL Richard | ||
| Buswarrior (Buswarrior) (64.229.212.43)
Rating: N/A |
This thread is going to end up like the one on wire...... Geoff is wrong. You can put Jakes on two strokes. Henry is wrong. The Jake does diddle to keep the engine warm. Ask yourself: Which makes more heat, 1) compressing air or 2) compressing air, injecting fuel into it and igniting? Have you ever driven a jake equipped vehicle in freezing temps? The engine goes cold and if the hill is long enough, the heater starts blowing cold air. (If you are driving a newer coach, the auxiliary heater (Webasto or Espar) kicks in to keep you warm as the engine temp goes down.) Your "factory engineers" may be quite right at the 30/70 split, but how much "heat" are we talking about? Engineering and Theory are very important, but aren't worth anything if they aren't matched with Reality and Relevance. Sorry, but you shouldn't be misleading the new folks like this. happy coaching! buswarrior | ||
| Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A |
Hey Buswarrior, re-read Geoffs post. He did not say you could not put Jakes on a two stroke. He said you could not put EXHAUST brakes on a two stroke. Two different animals, I believe. Richard | ||
| Jim Ashworth (Jimnh) (172.175.243.92)
Rating: N/A |
Buswarrier- On my 475hp 8V92, without my jakes on, the exhaust temp goes below the 300 degree minimum on my pyrometers. With the jake on a decent hill, the exhaust temp will run about 500 degrees. Driving on the flat exhaust temps are 700 or so. There is a lot of heat being generated by compressing air with the jakes. No theory, just reality. Jim | ||
| Tom Caffrey (Pvcces) (64.114.233.138)
Rating: N/A |
Hey, guys. It's true that there is a lot of heat generated in the engine when using the Jake. But that heat is blown out the exhaust valves, which is why it doesn't heat the engine. That's exactly why Jakes are such a good deal for long downgrades with heavy equipment; the heat that has to be generated from the stored energy of the high elevation rig being lowered to a lower elevation does not plague you in any way. The same thing happens with an exhaust brake except that you have high temperatures from inside the cylinder to the brake valve. The exhaust carries away the generated heat. However, there is a difference in the noise. A muffled Jake is not half bad. I get the impression that exhaust brakes are considerably noisier. Have you fellows noticed that the signs in towns about engine brakes take a lot of different forms? Sometimes compression brakes, exhaust brakes or engine brakes, sometimes unmuffled compression or exhaust brakes are banned. Sometimes, there is only a posted request to avoid using some of the above. For us, the Jake on the two stroke works out well. We get enough supplemental braking, yet the heat and noise are not very troublesome. The hole in the tailgate has been as much trouble as anything. We've never had anyone complain about the Jake noise, and I hope that we don't hear any complaints in the future, either. Tom Caffrey PD4106-2576 | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
I've got an exhaust brake (Not Jake) on my Cummins 220, and it works very well. Definitely not as strong as a Jake by a longshot, but it keeps me from having to use brakes at all coming down 6%'ers at good speed. My point though... it's quiet as can be. In fact so quiet that the only way I can really tell it's working (besides not having to step on the brakes) is to watch the exhaust pressure gauge go up to 20 psi. Other than that, ya can't hear it at all and I have GOOD hearing... Cheers gary | ||
| Phil (204.89.170.126) Rating: N/A |
I run an exhaust brake on a cummins 260. The only way I can tell from noise that it is activated is the PSSSSST from the air cylinder that moves the valve and a very slight change in the type of sound from the exhaust. I can only hear that if I have the drivers window open. While I only have run the hills on the east coast I find the effectiveness to be great. For those of you who have run Monunt Eagle Mountain on route 65 in Tennessee, I have come down both sides without using the brakes (26000 pound total weight). | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Years ago coming down the Grape Vine grade everyday loaded with school kids, the Jake would hold the Crown at 40 mph in 4th gear and I never had to touch the brakes With about the same load, she would climb the same 6% grade at around 20 to 22 mph. The point is that the Jake actually absorbed more power.... Then the 220 Cummins put out. And...yes, absorbing all that power did relate in the water temp never getting below 170 degrees. The energy is converted into heat which was absorbed by the engines cooling system. Jakes Forever!!! | ||
| Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A |
Henry, my experience with my 8V92 is that coming down the grapevine with the Jakes on, I can not hold engine temperature. Usually drops to the 150/140 range. I think most of the heat goes out the exhaust as hot air. Richard | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
One can imagine how much heat has to be absorbed by the service brakes coming down a long steep grade. The brakes are designed to do this. Same thing with the Jake. The unit absorbes the energy holding vehicle speed on a grade and converts it into heat energy... Which is absorbed by the engine's cooling system thru the radiator. Maybe the Cummins being a four stroke design makes a difference in how the cooling system reacts... In comparision to a Detroit two stroke. Also maybe where the thermostats(s) are physically located makes a difference also as to how the particular engine responds. And....finally, maybe the cooling system itself makes a difference. The Crown 220 743 Cummins had 102 quarts of water and 44 quarts of oil---a whole lot for the size engine. JAKES FOREVER!!! | ||
| Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A |
I suspect that the heat generated by the service brakes or the Jake brakes is significantly less than the heat generated by the engine climbing the same grade. This is, in my opinion, due to the gross inefficiency (40%?) of the engine converting fuel to rotating energy. I further suspect that the majority of the heat generated by the Jakes is simply passed out the exhaust as hot air just as the heat generated by the service brakes is dissipated by the brake shoes and drums. As soon as I top a major grade and start down the other side using the Jakes, my engine temperature immediately and quickly drops to the thermostat setting or below. If the Jakes were contributing a significant amount of heat into the cooling system, then it would seem that the engine temperature would not drop so rapidly. Am I missing something? Richard | ||
| Tom Caffrey (Pvcces) (64.114.233.131)
Rating: N/A |
No, I think that you've got it right, Richard. Tom Caffrey PD4106-2576 Suncatcher | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Well there is the time to simply give up and let you guys simply talk to the Jake Brake Engineers. Try www.jakebrake.com and E-mail the factory and ask them like I did. They will probably tell you The same thing they told me---that about 30% of the heat energy goes out the exhaust pipe and 70% Goes thru the coooling/radiator system of the engine. There, quess I told you---now--lets all Go out and Jake our Brakes!!! He he he!!! Broom, brrooommmm, bbbrrrrooooommmmmm!! | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
'course Henry... (heh heh) maybe that Jake engineer ya talked to had his head up the very same portal that the one from PacBrake had his in when he told me emphatically (now remember, this is the MANUFACTURER talking!!) that exhaust brakes would NOT work on non- turbo diesel engines, period. I took it as gospel. Imagine my surprise when I opened the cowl of a Crown in the junkyard to see an engine just like mine with an exhaust brake on it (which is the very unit that's now on MY engine, working very well, thank you PacBrake...jerks...) Just playing Devil's avocado here...  Gary | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Gary; It is almost embarrassing to admit that despite my firm believership in the Jake, I DO NOT currently have one!!! Oh no!! Do have the Williams type EXHAUST BRAKE right now on my 250 hp non turboed big cam Cummins pancake motor on my Crown. While it works kinda OK and is very quiet, it is not a JAKE and I am seriously considering setting aside the money for the REQUIRED conversion. Still have all the positive memories of the Jake working soosssss well on the old Crown school bus I drove 30 years ago. Thank you all. Henry | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
Well Henry, I have to admit that the exhaust brake is "gentle" as compared to the stopping power of a Jake, HOWEVER so far in about 7000 miles of trips now, with at least 4 times over the grapevine and as many up and down the I-15 Riverside/Barstow grade out of LA, I havn't had to use my service brakes once except to avoid nailing a few jerk motorists that cut me off as they always will. I go up the grades (6 to 6-1/2%) at 35-40 mph and come down usually about 60-65. The exhaust brake is perfect. If I wasnt so ballsy and came down in one gear lower, I'd have to use the accelerator to keep speed up. That said, your coach is a bit heavier and with your proposed "I can't believe he's actually gonna do that" battery bank, the power of the Williams might not be enough. I know a place that will sell ya a complete set of Jakes for the 743 for $450... not bad... Cheers Gary |