I'm putting together the last details on our Jake Brake install for this winter/early spring. Right now I'm working through the wiring plan. I've found the wiring diagram in the GM book for the optional Jake Brakes. It indicates the addition of a circuit breaker to an unused spot. Problem is, it doesn't indicate what size breaker.
Running a 24v system. Anyone know what size breaker is needed to run the Jakes on an 8V71?
MCI's have a 6 amp auto-reset breaker for the jake brakes.
I use a 5 amp fuse not a breaker,are going to waste wire and wire your Jakes for a 2 stage ? with a manual transmission a clutch switch will make like easier for you shifting
Quote from: luvrbus on October 27, 2018, 10:09:35 AM
I use a 5 amp fuse not a breaker,are going to waste wire and wire your Jakes for a 2 stage ? with a manual transmission a clutch switch will make like easier for you shifting
Going with single stage - all or nothing. Didn't seem like the two stage made any sense on the 2-stroke engine.
Clutch switch is in the plan.
Quote from: richard5933 on October 27, 2018, 11:08:48 AM
Going with single stage - all or nothing. Didn't seem like the two stage made any sense on the 2-stroke engine.
Clutch switch is in the plan.
That will work the clutch switch is a good idea when hunting for gears some people can master it without one but most have a tough time
There it is again, that "2 strokes need a single stage Jake" myth. Mine is two stage and I use it on first stage more than on second stage. Must be the placebo affect.
Quote from: Lin on October 27, 2018, 12:38:30 PM
There it is again, that "2 strokes need a single stage Jake" myth. Mine is two stage and I use it on first stage more than on second stage. Must be the placebo affect.
Maybe you can explain. You sound like you're advocating adding the extra wiring to have two-stage Jakes, but the more popular opinion is that the first stage doesn't do enough to make it worth the effort. Aside from your personal experience, why is this a 'myth'?
We had single stage on our 4106 with an Allison V730. They certainly were helpful when driving, but I never considered them too strong or wished we could cut the stopping in half.
now we're installing Jakes on a 4108 with a 4-speed manual. At times the Jakes provide too much help, I figure that the engine/tranny will do the job just fine and the Jakes can be turned off.
Quote from: Lin on October 27, 2018, 12:38:30 PM
There it is again, that "2 strokes need a single stage Jake" myth. Mine is two stage and I use it on first stage more than on second stage. Must be the placebo affect.
Standard transmission ?
If you are in the mountains or steep grades the 2 stage are not much good,Lin has spent a fortune adding valves to make his transmission lock up to use the Jakes so he has to be in 1st or 2nd gear using his Jakes.The 2 stage Jakes on the Detroit will not hold you back on the descend from Flagstaff to Phoenix unless you are in 1st or 2nd gear at 15mph with people fliping you off .4 strokes have real Jake brakes 2 strokes make noise
I'll bet they work fine in an MC-6 with a 12V-71.
Quote from: chessie4905 on October 27, 2018, 05:57:51 PM
I'll bet they work fine in an MC-6 with a 12V-71.
could be the trucks worked ok with the manual transmission but Greyhound never used Jakes brakes on their older buses,Jakes are a personal preference on a 2 stroke to me anyways it just makes the oil consumption increase on those old engine also
At least by 1975 the Jakes were an option from GMC. There are wiring diagrams showing the install for all the various configurations (auto, 4-speed, with/without other options). The only thing not there was the size of the circuit breaker.
When I talked to Luke about this bus before we bought it, he mentioned that Jakes were rare to find on east coast buses, but that they were more common on the west coast.
Quote from: richard5933 on October 27, 2018, 07:57:01 PM
At least by 1975 the Jakes were an option from GMC. There are wiring diagrams showing the install for all the various configurations (auto, 4-speed, with/without other options). The only thing not there was the size of the circuit breaker.
When I talked to Luke about this bus before we bought it, he mentioned that Jakes were rare to find on east coast buses, but that they were more common on the west coast.
I never saw Jakes on the old dogs here in the West,the GM transit buses I see those were factory
I always thought Jakes on a two stroke
and prayer were for when there was no option left.
Not a first line of defense.
Quote from: luvrbus on October 27, 2018, 08:07:25 PM
I never saw Jakes on the old dogs here in the West,the GM transit buses I see those were factory
If my understanding is correct, by the time GM was offering Jakes as a factory option, Greyhound was getting all their buses from MCI. Only charter companies or maybe Trailways would have ordered the optional Jakes. From what I've seen online, Greyhound bought their last GM coach in the late 60s, before the Jakes were available from the factory.
Quote from: eagle19952 on October 27, 2018, 08:41:38 PM
I always thought Jakes on a two stroke
and prayer were for when there was no option left.
Not a first line of defense.
First line of defense or last hope, I still think it's better to have the option to flip the switch and have whatever help Jakes provide rather than just having the prayer option.
If you have a manual transmission, you are supposed to have a Jake disconnect switch on the clutch pedal. Second, it is no problem running a three wire loom to the front of the bus for two stage brakes. I got the wire from Home Depot. Third, the reason Jake's are weak (on Detroit 2-strokes) is because the recommended clearance is too loose. Set the clearaces at .035-.040 and you will have strong Jakes and 1st and 2nd stage will make sense.
I had the 2 stage jakes on the 6v92ta and used both stages at different times .
on the cat they work so good sometimes I never need to use the brakes
dave
Quote from: Geoff on October 28, 2018, 06:05:52 AM
If you have a manual transmission, you are supposed to have a Jake disconnect switch on the clutch pedal. Second, it is no problem running a three wire loom to the front of the bus for two stage brakes. I got the wire from Home Depot. Third, the reason Jake's are weak (on Detroit 2-strokes) is because the recommended clearance is too loose. Set the clearaces at .035-.040 and you will have strong Jakes and 1st and 2nd stage will make sense.
Three conductor? High/low and ground? Can it be done with two conductor and chassis ground? We ran a two-conductor cable front to back when we had things opened up for some other work. Would be difficult to run more cable right now.
With two stage jakes you provide power to the buffer switch from the rear electrical panel, run that switched power (though a clutch switch if you need one) to the front dash panel jake switch with two ON positions (one side and both sides) and run two wires back to the Jakes heads, one for each side. With single stage jakes, you provide power to the dash switch from the front panel bus bar, and run one wire back to the Jake buffer switch, and from there to the Jakes heads on both sides. with single stage switch you can run power to the clutch switch either before or after the jake on/off switch. So need either three wires front to back, or one wire. The only ground connection in both scenarios is via the Jake heads on the cylinder heads, so no, you cannot use chassis ground as a live feed control wire.
Study your wiring diagrams. There are spare wires going from drivers elect. panel to the one in engine compartment. No need to run new wire. Some wiring info is in the service manual under the relay, circuit breaker and electrical posts. Get a cable tracker from HF to verify. I have one and it works great. Cliff probably thinks they are junk.lol
Never saw Jakes on Trailways either,when Trailways went to Eagle in the 60's there was never enough clearance on the passengers side for Jakes remained like that till in the late 80's .Greyhound never had Jakes on the MCI even the MCI 9's
A bus with low gearing like in the 4.25 + Jakes do work better, hiway gearing like 3.36:1 they are not much except in 1st or 2nd gear.
Sotra works like on the series 60 and Allison B500 with the hi gearing with my jakes the transmission automatically drops to 4th gear before the Jake's will engage,Richard with your gearing and a manual transmission I wouldn't waste the wire doing a 2 stage Jake on a 8v71. lol I had a guy that insisted on a 4 stage Jake on a 8v92 I told he was wasting wire so he ran the wire and I hooked those up for him in a week he told me yea it was a waste but I have a 4 stage brake and it makes for good conversation though
First line of defense or last hope, I still think it's better to have the option to flip the switch and have whatever help Jakes provide rather than just having the prayer option.
I think it's better to not get yourself into a situation where you'd have to rely on them.
If they don't do what you wished, (and they won't as often as they do in a 2 stroke) all that's left is prayer...
Used two stage Jake on the 4108/8V71. Example is east bound on I24. Approached the Monteagle down grade in 3rd gear, Spicer 4 speed. Reduced to one bank on the Jake. Speed held at 45-48 down the steeper parts.
Two stokes by design work great with a Jake Brake. Every up stroke yields a slow down. Try the Gaspe Peninsula without a Jake and tell me that they aren't worth the price.
Or north on the Alaska Highway with the 4108, big Safari motorhome was behind me all day. He'd catch me on the uphill but wouldn't pass. Stopped in the same place that night, Toad River. Driver commented that we had brake light problem. Really said I with surprise. He replied that usually I had no brake lights on the downhills when he was on the brakes. I had to explain Jake Brakes to him. I did add a wire from the Jake s on the first bank for the brake lights.
Bill
Quote from: Bill B /bus on October 28, 2018, 02:11:32 PM
Spicer 4 speed.
Bill
Makes a huge difference.
Many are hoping for the same result with an Allison.
The design of the 2 stroke with no intake valve makes it bad candidate for Jakes IMO ,Jakes and Detroit were around for years before Detroit ever used a Jake on that engine,I remember in the mid 60's when they first tried it was a big big problem on the 8v71 with the 4 valve head.Jakes on a 2 stroke are over rated compared to a 4 stroke engine.You want good oil pressure on a 2 stroke are they are worthless.You guys keep up the good work promoting Jakes I installed 6 sets so far this year with your help 8)
I have a Suburban GMC RTS with highway gearing that ran commuters from Santa Rosa, CA to San Francisco. They had the Allison V730's set up so they would not upshift when placed in any forward gear. This was done because of the steep San Francisco hills, normally the Allison's would upshift at 2300 rpm's. Great with Jakes.
Quote from: luvrbus on October 28, 2018, 04:13:44 PM
The design of the 2 stroke with no intake valve makes it bad candidate for Jakes IMO ,Jakes and Detroit were around for years before Detroit ever used a Jake on that engine,I remember in the mid 60's when they first tried it was a big big problem on the 8v71 with the 4 valve head.Jakes on a 2 stroke are over rated compared to a 4 stroke engine.You want good oil pressure on a 2 stroke are they are worthless.You guys keep up the good work promoting Jakes I installed 6 sets so far this year with your help 8)
It all in the Jake valve clearances. Adjust them at .035 to .040 and they kick @$# downhill with no problem.
LOL go for it but I am not going to try that adjustment,? what is highway gearing on a RTS 4.10 or something like that
Highway gearing on the V-drive RTS is 4:56 and 4:10, with the slight overdrive of .875 in third gear giving you a highway speed of 70 or 80 mph at 2300 rpm's, respectively.
Quote from: Geoff on October 28, 2018, 04:28:04 PM
It all in the Jake valve clearances. Adjust them at .035 to .040 and they kick @$# downhill with no problem.
Have you ever set a DDEC engine that tight? I would like better Jaking, but not at the risk of catastrophic damage (or worse).
John
Quote from: Bill B /bus on October 28, 2018, 02:11:32 PM
Used two stage Jake on the 4108/8V71. ...
Bill
Did you make use of the first stage only enough to make it worth installing these as two stage Jakes? Our plan was to go with single stage Jakes - all or nothing - until this thread turned to a conversation about two-stage Jakes.
We've got good oil pressure - our engine still has under 50,000 original miles. That won't be a problem. Not too late to go with two-stage install if it's worth the effort.
Here's a copy of the wiring diagram in the GM book for the 4108. Couple of interesting things I notice:
1) The system is installed single stage.
2) GM is really fond of using relays for everything. Not sure why the relay is being used here instead of just the switch. According to this diagram, the engine brake relay is to be installed in the driver's electrical panel about 6" from the switch in the side switch panel.
Seems like they could have just run the hot from the #27 circuit breaker > clutch switch > engine brake switch > panel terminal #77 > engine bay electrical panel.
Only thing I can think of is that the clutch switch isn't rated to carry the full current to the Jakes. Or possibly just in case I've got an extra relay, so I suppose I'll do it like they say.
Would be great if someone could help me understand purpose of this relay.
3) There is a wire running from the engine brake solenoid power feed to the stop light relay. Guess they thought along the same lines as Bill and didn't want that Safari driver to be confused any more.
Quote from: richard5933 on October 28, 2018, 05:54:19 PM
We've got good oil pressure - our engine still has under 50,000 original miles.
Good pressure at throttle.
Detroit's have lower oil pressure off throttle.
Often to low to open a Jake.
Relays used for circuit endurance?
Only signal amperage thru all the switches?
In the hands of a careless paid driver who can't set a speed, who leaves the switch on, every throttle lift makes contact...
That's hundreds in a single day...
Happy coaching!
Buswarrior
Quote from: buswarrior on October 28, 2018, 07:53:43 PM
Relays used for circuit endurance?
Only signal amperage thru all the switches?
In the hands of a careless paid driver who can't set a speed, who leaves the switch on, every throttle lift makes contact...
That's hundreds in a single day...
Happy coaching!
Buswarrior
Even with the relay, wouldn't current flow through the entire system at all times if it was turned on? With or without the relay, current is also flowing through the buffer switch which will open close with throttle action?
Seems like the only thing the relay does is change what the clutch switch is controlling - instead of the clutch switch opening/closing the circuit to the buffer switch, it is opening/closing the circuit to the relay.
Didn't seem like the Jake circuit had that high a current draw to matter, but perhaps it does. I'll install the relay since I've got one.
The relay is there to isolate the control switches - dash switch and clutch switch - from the inductive load of the Jake solenoids to reduce arcing and prolong the life of the switches. The buffer switch has a diode to do the same thing. In terms of current, a 24 volt solenoid draws roughly half an amp, there are four of them, so 2 amps. That is a very small current load. In the GM world many/most buses were 12 volt, so around 4 amps, so they probably felt it was worthwhile adding the relay. Where is the relay located - if it's at the rear of the bus it's also to reduce voltage drop in the 12V application, and they probably just kept the design for the 24V bus. Current will flow through the front half of the circuit - dash switch, clutch switch - all the time the dash switch is on and the clutch is up. That turns the relay on and provides power to the Jake buffer switch. Current will then flow in the back half of the circuit only when the buffer switch is activated when the governor goes to "no-fuel".
More specifically, the signal current vs the load current.
Lots of little DC arcing...
Too many bus conversions out there running load current thru their switches, when a relay would be a better choice.
Happy coaching!
Buswarrior
Richard in 1975 all they had were the 71 Jake heads they took a along time to engage and used lots of power they made upgrades for those then changed to the 71/92 heads.They used capacitors on the master for awhile to help with the engaging on the 71 heads that were not upgraded.Use a relay the later buses still use a relay on Jakes every set I install is on a relay it's one of things what ever flips your switch.FWIW I checked a old Jake manual your wiring diagram is from Jake
I've looked this over again, and am somewhat confused about how they've got the line connected to activate the brake lights when the Jakes engage.
Wouldn't the brake light circuit activate the Jakes every time the service brakes are applied and the brakes lights come on? I don't see anything in the circuit to prevent back feeding. Only thing I can figure is that the stop light relay in the diagram is an added one, so that the line coming from the Jakes doesn't feed the brake lights directly, but rather actuates a relay which in turn lights up the brake lights.
There is a one way diode in the system to prevent that,some folks hook the Jake to the brake light to activate the Jakes and you need to remove the diode
Leave yourself facility to NOT show the brake lights under Jake use.
Few vehicles show the brake lights under Jakes. Some transit/coach properties spec to show an amber light on retarder/jake activation, but not everyone.
Here's the problem: long downgrade, you're dragging the Jakes for some length of time, and have some need to apply the brakes heavily. There will be no change to the lighting displayed on the back, you've conditioned 'em to the brighter lights, yet you are now decelerating hard...
Also, it is no fun following a vehicle with steady burning brake lights. More than sufficient reason for some crazed trucker to drag your driver's side mirror off as he passes, with that trailer he is pulling, that is not his...
Four way flashers on an up or downhill suggest a slower moving vehicle, brake lights are meant to attract immediate reaction. Jakes, when deployed properly, just let you maintain a steady speed, no warning required?
Ok, there's the top off the anthill...
Happy coaching!
Buswarrior
Oh - the choices we must make...
I'll ponder a while, but I understand your message. Too bad there is not a standard of brake lights being variable - mash the pedal hard or suddenly and they go on full bright. Hold the pedal down for a while and they start to fad to half bright.
I'll leave this one sit for a while and ponder...
I plan to install an LED brake light independent of the brake lights on the sides. This would only work off the Jake active hot lead and would be centered at the top rear of the bus. No confusion with this setup.
You don't need any red light on your back for engine brake. The Jakes just hold you back. They don't slow you down so much that you have to warn traffic behind you. Save the brake lights for when you use the service brakes and really slow down.
JC
Apparently some Class 8 trucks and motorhomes already have "auxiliary brakes" activating the brake lights. But you can defeat this feature by reprograming the ECU.
Apparently some Class 8 trucks and motorhomes already have "auxiliary brakes" activating the brake lights. But you can defeat this feature by reprograming the ECU.
I think I got as much done on this project this season as I wanted before the weather turns. As soon as the weather breaks at the end of winter I'll take the bus to the shop where they are going to do the install on the Jakes themselves.
1) I've got the switch installed on the dash.
2) Installed the new circuit breaker on the driver's panel. Went with 8-amp 24v breaker. Advice here was 6 amp, only other reference I saw was for a 10-amp on a 12v system. The 8-amp was the closest that Luke had that would fit into the breaker panel.
3) Wired in a NOS relay to control the Jakes.
4) Installed the bump on the engine bay door.
5) Cleaned and painted the new tall valve covers to match the engine.
I'm not going to bother with the brake lights for now. I can always add them later. Also decided to have these installed as a single stage system. Again, that could be changed if necessary later on, but from everything I've read here and elsewhere the single stage seemed to be the way to go. Especially since all the variations in the GM manual for wiring indicated a single stage system.
Shop is going to rebuild all the Jakes before installing to make sure they are work as well as possible. They've already inventoried and inspected all the parts to be sure I've got what I need to do this. Seems like I do, including a NOS buffer switch with fast idle option. My goal was to get as much prepped as I could - no need to pay them to do what I'm able. I may not know how to install Jakes, but I can run wire and install switches and such.
Unless anyone can point out something I missed in prepping for this, I'm going to call this a successful prep for my first big project next year.
I agree with BK about the lights, I think it's safer without brake lights connected. I rarely use my first stage, it's nice to have when I do but like you said I would wait to see after you use them a while. If you do decide you want 2 stage later it is possible to do it with only 2 wires with some added relays. As far as the debate about jakes on a 2 stroke, I guarantee you will love them, The only time I ever use my brakes on any hill is when that jerk cuts in front of me
After installation, you can see what a two stage would be like by disconnecting one cylinder head temporarily.
Btw, if your engine doesnt have the individual spring loaded rack fingers, now would be a good time to switch over, since things are going to be apart.
My biggest gripe about Jakes on a 2 stroke is they add to the oil consumption to a engine that is high to begin with,then the air drains drip more,plus people won''t spend the dollars to change to the o-ring fuel lines
Cherry on top...
Today I identified an unused spare wire going from the front panel to the rear. Would you believe it was right there at terminal #77, just like the book said it would be.
Now if I could just figure out an easy way to get the cover on the rear panel in the engine bay. I'm a small guy, but even I have to be a contortionist to get near enough to close it up.
If you pull the engine, it is real easy to access....
ya pull the engine it is easy to get at all kinds of stuff
dave
Yeah, that cover is just a little too high, a little too far back. Have mine off right now while checking some wiring and installing some brighter engine compartment lights.
I suppose pulling the engine would make it easier...
The problem I have is that the screws are captive in the panel cover. Since there is no flex in the cover, it's difficult to get one screw started without the others getting in the way. Then there's the issue of the speed nuts flying all over the place. The position to reach the thing is just too awkward for me to stay in long enough to get the cover on.
I've ordered some 1/4-20 extruded nuts to replace the speed nuts. They are similar except that they have actual threads on them and generally work more smoothly. I'm also replacing the captive screws with removable 1/4-20 thumb screws. Hopefully this will make it somewhat easier, that is if I don't lose the thumb screws since they will no longer be captive. (Yes - I ordered extra).
Maybe it's just because I've not been sleeping. Maybe it's just the long list of little things I was racing to get done before the weather turns to total crap. Maybe it's just being bummed about parking the bus for a few months. Whatever it is, I'm glad I'm at the end of the list because I need a break from projects for a short time.
I must apologize for commenting about single verses two stage Jakes and not checking back to see if a followup was warranted. This debate has appeared several times before though not quite as much as the oil debate. I do not have the mechanical expertise to say why or why not a two stage system would work on a 2-stroke. I only know what I have and can evaluate it. First, my situation is different since we installed the Jakes when the engine was out while we were changing to an Allison 647. I don't remember exactly how we wired it, but we did use two relays-- one for the first stage and one for the second that have separate dash switches. The second stage switch is energized by the first switch, so stage two will only engage when stage one is on.
My first stage works great on moderate grades. I can just leave it on and coast down the hill without braking. Don Fairchild installed the Jakes, and there are others on this board that have said he adjusted them so they work better. I would guess that it is something like Geoff is suggesting. The extra wire is not an issue; that's really talking about pennies. Besides, I think we used a three wire heavy duty extension cord, so there are three wires anyway.
Clifford is right that I installed a valve to be able to lockup the 647 in 1st and 2nd. 1st is not much of any issue but second is since that covers a critical speed range on a serious grade with sharp turns. The 740 transmission locks up in 2nd, but for some reason the 640 series is designed not to. Actually, I think it would be better if it did not lock up in 1st. Considering the cost of having a bus, I wouldn't say that I spent big dollars for the alteration. I was surprised though that the valve we needed to do it was 3 or 4 hundred dollars. The braided high pressure hoses were also an expense, so it did cost somewhere between $500 and $600 total. As mentioned, if you had a 740 transmission, you'd be set.
I have never driven a manual transmission with Jakes, so I do not know how different the experience is. Possibly, with the added gear control the 1st stage is less beneficial. If you are using existing wiring, I can see going with whatever that wiring would allow. If you are running the wire, you might as well run several more blanks for the Jake or just for future use. I have always found that extra wires get called into service eventually.
Lin--
Thank you for your time and effort in wtiting a detailed response!
--Geoff
Quote from: Lin on November 02, 2018, 04:43:02 PM
I must apologize for commenting about single verses two stage Jakes and not checking back to see if a followup was warranted. This debate has appeared several times before though not quite as much as the oil debate. I do not have the mechanical expertise to say why or why not a two stage system would work on a 2-stroke. I only know what I have and can evaluate it. First, my situation is different since we installed the Jakes when the engine was out while we were changing to an Allison 647. I don't remember exactly how we wired it, but we did use two relays-- one for the first stage and one for the second that have separate dash switches. The second stage switch is energized by the first switch, so stage two will only engage when stage one is on.
My first stage works great on moderate grades. I can just leave it on and coast down the hill without braking. Don Fairchild installed the Jakes, and there are others on this board that have said he adjusted them so they work better. I would guess that it is something like Geoff is suggesting. The extra wire is not an issue; that's really talking about pennies. Besides, I think we used a three wire heavy duty extension cord, so there are three wires anyway.
Clifford is right that I installed a valve to be able to lockup the 647 in 1st and 2nd. 1st is not much of any issue but second is since that covers a critical speed range on a serious grade with sharp turns. The 740 transmission locks up in 2nd, but for some reason the 640 series is designed not to. Actually, I think it would be better if it did not lock up in 1st. Considering the cost of having a bus, I wouldn't say that I spent big dollars for the alteration. I was surprised though that the valve we needed to do it was 3 or 4 hundred dollars. The braided high pressure hoses were also an expense, so it did cost somewhere between $500 and $600 total. As mentioned, if you had a 740 transmission, you'd be set.
I have never driven a manual transmission with Jakes, so I do not know how different the experience is. Possibly, with the added gear control the 1st stage is less beneficial. If you are using existing wiring, I can see going with whatever that wiring would allow. If you are running the wire, you might as well run several more blanks for the Jake or just for future use. I have always found that extra wires get called into service eventually.
Don is a good friend of mine and we communicate on a regular basis he set Lin's and TomC's Jakes on 0.55 instead of 0.59 like I use.Me i figure Jake and Detroit knew what the were doing so I stick with the 0.59 for 71/92 heads and the 0.65 for the 71 heads we each do things different.
I cannot tell the difference with different setting on a Jake I have tried different setting before and knowing the operation of how they work I need someone to school me on the advantage of a closer setting
Lots of people know this well, but I just spent a few minutes reading the manual so it's new to me. I probably knew it just fine 6 years ago when I set up Jakes on my engine, but I can't reliably remember what I had for breakfast...
Jake brake works by trapping high pressure oil between an activation master piston and a slave piston. The master piston is activated by the injector push-rod, so when the injector is fired (although in no-fuel, the cam still activates the injector) the Jake brake is also activated. It activates by the master piston compressing trapped high pressure oil and causing the slave piston to press down and open the exhaust valve at a specific time - that time being when the injector is being fired. The duration of the exhaust valve opening is somewhat fixed by the timing and profile of the injector lobe on the cam. When the cam causes the Jake master piston to operate, the first thing that happens is the master piston starts to close and the trapped oil is pressurized. The next thing that happens is the pressurized oil overcomes the return spring pressure in the slave piston. Next, the slave piston opens a measured amount, and stays open as long as the cam is operating against the master piston. Finally the cam event passes, the injector pushrod backs down, the master piston releases it's pressure, and the slave piston retracts to it's normal open position. Adjusting the gap between the slave piston and the exhaust valve bridge to a smaller dimension will cause the valves to open fractionally sooner, open fractionally farther, and stay open fractionally longer, all contributing to a greater release of compression energy into the exhaust port. Since the Jake is timed by the injector cam lobe, that event is quite short, so the theory would be that maximizing the release of compression is worthwhile, and that some compression doesn't get out in the short time interval allowed by the injector cam event. The risk is that the injection event happens on the compression stroke, before TDC, the piston is rushing up the bore, and you are dropping the exhaust valves down the bore to meet the piston - almost! Dropping them farther and holding them open longer would increase the risk of a piston hitting a valve.
So, therefore, listening to Cliff, Jacobs, and Detroit, is safer than trying to squeeze out a little more braking power. :)
You could put the piston on tdc and manually depress each valve in that cylinder to see how far down they will go till they contact piston. Then you"d get an idea how much margin you have after subtracting minimum allowable piston to valve clearance. Same thing is done when building race engines, albeit in a slightly different way with spring removed and after final cam timing is set.
You could do that, the info I found is that the injection event starts a 19.5 degrees BTDC and ends 5 degrees BTDC. That is variable based on what the profile of the cam lobe is and what injector height you set your injectors to - 1.460 is more advanced than 1.484. Jake timing isn't dependent on injector heights, of course, just on the cam lobe timing. Advanced timing on the cam would advance the Jake brake event, probably reducing it's effectiveness just slightly.
Quote from: bevans6 on November 03, 2018, 08:53:27 AM
You could do that, the info I found is that the injection event starts a 19.5 degrees BTDC and ends 5 degrees BTDC. That is variable based on what the profile of the cam lobe is and what injector height you set your injectors to - 1.460 is more advanced than 1.484. Jake timing isn't dependent on injector heights, of course, just on the cam lobe timing. Advanced timing on the cam would advance the Jake brake event, probably reducing it's effectiveness just slightly.
If you reduce the Jake clearances the 2 exhaust valves they control would open sooner and be held open longer. Personal experience is they work better as an engine brake with tighter clearances. Having worked for Detroit Diesel in the heyday of the 71-92 series, I worked on many trucks and a lot of them had the Jake clearaces tight. If I worked on one with the Jakes tight, you could really tell the difference on how they shuddered the engine down to an idle. I would just leave the Jake adjustment like it was to keep the driver happy.
I never saw an engine failure from tight Jakes. I have mine set at .035 and they work great. .040 might be "safer", but I don't know from what. The piston isn't going to hit the valves from my experience. But don't blame me if you are DIY and make a mistake. I have certificates from DD to work on the old 2-strokes, before DDEC and smogged engines.
Geoff
This thread is getting mighty technical. Lots of good information, for sure, but I'm am glad that I've got a tech with 40+ years experience working on DD 2-strokes set to do the work. Since things inside the engine are not my strength, I'm going to let him do what needs to be done.
I'm just glad that i was able to get the prep work done and save at least a few hours shop time.
Let us know what your guy sets the Jakes on Richard,I have seen the valves hit the pistons,depending on the cams and pistons clearance will change,you change the valves springs and seals on a 2 stroke by just rolling the piston up to TDC so they are close on clearance .Geoff built his engine and knows what cams and pistons he has,the average person has no idea what he or she has inside the engine
Quote from: luvrbus on November 04, 2018, 05:34:38 AM
Let us know what your guy sets the Jakes on Richard,I have seen the valves hit the pistons,depending on the cams and pistons clearance will change,you change the valves springs and seals on a 2 stroke by just rolling the piston up to TDC so they are close on clearance .Geoff built his engine and knows what cams and pistons he has,the average person has no idea what he or she has inside the engine
Since my engine has less than 50,000 miles, I'm going to assume that the valves are original and still have the factory settings. I'll talk to the guy before he does the work to see what he says.
Is there a way for him to verify current setup and proper settings from inside he valve covers?
I doubt your guy is going to want to go to that much trouble,he is going to be a little on the cranky side anyways installing the Jakes on the upper head >:( the old 71's didn't have all the options the 92 series did
The mechanic installing the Jakes can check the settings and they are right he doesn't have to change them, saving time.
I have a 6V92 I'm going to be working on that will give me time to check the piston to valve clearances and Jake brake clearances.
Quote from: Geoff on November 04, 2018, 07:23:17 AM
The mechanic installing the Jakes can check the settings and they are right he doesn't have to change them, saving time.
I have a 6V92 I'm going to be working on that will give me time to check the piston to valve clearances and Jake brake clearances.
I have a head sitting on two pistons I am going to check the clearance at TDC just for my own piece of mind.I am going to measure it with 17:1 and 19:1 pistons I know there is 0.40 difference in the dome on a N/A piston vs a turbo piston. I did check a DDEC cam and it has a higher lift than a US cam from a 8v92,now i need to dig around and find me a CA cam and measure the lift on it
:) thanks guys!