Rack and Jake adjustment

[windtrader]

I need to get the rack and Jake adjustment done and not confident I can do this 100% right, so want to verify the shop is competent, both in the actual work and time to complete standard job. AI offered this up, so doing sanity check with real busnuts. 



Full rack + Jake adjustment — steps & time1️⃣ Prep & baseline checksTime: 10–15 min

   
• Verify injector model and specs
• Verify Jake model and lash spec
• Inspect throttle/Jake linkage for slop or binding
• Bring engine to correct temp (or confirm cold if cold-lash spec)

2️⃣ Valve lash adjustmentTime: 30–45 min

   
• Set valve lash per Detroit spec
• Required before injector height
• Covers off, engine barred over

Skipping or rushing this guarantees a re-do later.

3️⃣ Injector height & rack synchronization (engine OFF)Time: 45–60 min

   
• Set injector height on all cylinders
• Synchronize all injector racks:
  
        
  • Full fuel together
  • Full shutoff together
• Governor disconnected or neutral so it doesn't influence rack

This is the core "rack" work.

4️⃣ Governor linkage, buffer, idle & max RPM (engine RUNNING)Time: 30–45 min

   
• Set governor-to-rack linkage length
• Adjust buffer screw for:
  
        
  • Stable idle
  • Clean off-idle response
• Set idle speed
• Verify no-load max RPM

At this point the engine should:

   
• Idle clean
• Pick up throttle without stumble
• Not surge

5️⃣ Jake brake mechanical adjustment (lash)Time: 10–20 min

   
• Set Jake slave piston lash to spec
• Verify full release when Jakes are off
• Covers already off → fast step

Too tight here = exactly the stalling symptom you described.

6️⃣ Jake cutout / throttle switch adjustmentTime: 5–10 min
Critical sequencing:

   
• Jake disengages
• Rack moves off idle
• Fuel increases

This prevents stall when transitioning from Jake → throttle.

7️⃣ Final checks & road testTime: 10–15 min

   
• Verify:
  
        
  • Jake ON, zero throttle = normal braking
  • Jake ON + light throttle = smooth recovery (no stall)
• Minor buffer or switch tweak if needed

Total realistic time

Technician experience	Total time
Detroit specialist	2.5 – 3.5 hrs
Good diesel tech (not Detroit-centric)	3.5 – 5 hrs
First-timer / learning	6 – 10 hrs

Jake adjustment adds only ~20–45 minutes when done during a full rack.

[luvrbus]

You left out yellow or white metal mark a lots to mark the one you adjusted not to lose track of the ones that you adjusted,you will need some tools,If you were close to me I could walk you through it and check behind you.Those can be done with only revolution of the engine, I get a little annoyed at people baring the engine over a dozen times to make the adjustments     

[freds]

You also need to ensure access to the valve covers on the engine. On most buses you need remove a floor panel under the bed in the rear bed room. Make sure you can do that first or the payment clock will be running while that is figured out.

[luvrbus]

You also need to ensure access to the valve covers on the engine. On most buses you need remove a floor panel under the bed in the rear bed room. Make sure you can do that first or the payment clock will be running while that is figured out.

Plenty of room in MCI 8 to run the rack through the side and rear doors

[windtrader]

Clifford,


I am driving by your place in a couple weeks, maybe you can oversee the tuneup?  I am surely not confident enough to do this myself then drive to Mexico. lol


I made the post so I can get an idea if these steps are correct and shop time an experienced 2 stroke mechanic should take. I'm calling around this week to get some estimates.

[luvrbus]

How do you know you need a adjustment there is no time frame on a adjustment or tune up of 2 stroke,If I am home I will help you,I will PM my number, it's not hard to do. If your engine rpm goes up and come down the same rate I would leave it alone. I like your chart only thing I don't like is disconnecting the governor from the fuel control DD changed that follow the adjustment in a 92 series manual makes it easier, I showed Yvan the technique using it you won't get rack off unless you try     

[Coach_and_Crown_Guy]

Clifford,


I am driving by your place in a couple weeks, maybe you can oversee the tuneup?  I am surely not confident enough to do this myself then drive to Mexico. lol


I made the post so I can get an idea if these steps are correct and shop time an experienced 2 stroke mechanic should take. I'm calling around this week to get some estimates.

If you can manage to swing by Riverside CA on your way out you should definitely make contact with and plan on having J&R do the job. They are about the only 2-stroke experts left in this neck of the woods. They do this stuff every day and I'm sure many here will testify on how good a job they do. Get in touch with Dusty at 951-453-2667 and make an appointment. You won't regret it.

[windtrader]

Clifford,


Remember, a while back I posted about the problems I was having with the Jakes causing the engine stalling. Whenever I had jakes on and lifted the pedal, it would stall when giving it fuel. whenever I kept the jakes off, this would not happen. The bus also started not shutting down when flipping the switch off. I had to go to the back and use that valve to shut it down. There was also much more oil use and smoke coming out then normal. All these things started around the sane time.


Also, I did not see in the service logs where the rack was run after a complete rebuild in 2008. I got the bus with 4,500 miles and the snap test showed 8% opacity. the engine has 18,000 miles since rebuild and I've never done anything with engine timing, valves, fuel, idle, etc.


With the issues I'm getting now, it seems like a good idea to ensure the fuel deliver and values and governor are 100%.


I'l give the Riverside shop a call as it is on the route if I head over the grapevine and along the 210. If it is something else, they can sort it out.


thanks for the input.

[luvrbus]

Let him check but you have electrical problem on the shut down probably a ground at the skinner valve, you have a jake problem 1 master is stuck open they probably will need to be rebuilt when the control valves in Jakes sticks open or 1 breaks a spring they will suck oil from the engine. I am not a big fan of Jakes on the 2 cycle DD the more you use Jakes the oil consumption increases   

[windtrader]

Rusty was helpful in suggesting a couple things but can't get in for 4 months


He said to check the switch/valve on the governor and something about tubes on the oil box underneath the mufflers to make sure they are clear.


Going to check with DZ services Don Zimmerman today, maybe he can help

[Coach_and_Crown_Guy]

Rusty was helpful in suggesting a couple things but can't get in for 4 months


He said to check the switch/valve on the governor and something about tubes on the oil box underneath the mufflers to make sure they are clear.


Going to check with DZ services Don Zimmerman today, maybe he can help

After reading your post I also thought it may be that microswitch mounted on the governor housing. It touches internally the governor components to sense when it's at zero fuel and then activates the Jake units themselves. The governor is a very, very delicate bunch of spinning weights and balance springs that have to be in perfect adjustment and operating properly. That microswitch is indeed a light touch on the internal system but I've never really trusted it. I've experienced plenty of cases where it wasn't working correctly across a wide range of vehicles and inputting unintended forces into the delicate governor system, sometimes letting them come on with still some partial fuel, and other times not activating at all. I usually resorted to simply using the toggle to turn them on or off as needed. Too flaky otherwise, and actually potentially dangerous to the engine and vehicle safety and operation. If it was bad and flaky enough I simply ignored the Jakes completely and drove accordingly with them turned off.

Early on when Jakes were first introduced to DD Crowns in the '70's I noticed that Embree used a microswitch with a long arm attached to it that sat under the floor, and drivers feet, and contacted the actual mechanical throttle linkage used by Crown at the time. It would only activate the Jakes when the physical throttle pedal was fully up and not asking for any fuel from the governor. I like this a lot and never really experienced any issues with this kind of Zero Fuel sensing. The advantage to this is it does NOT try to read the internal governor fuel rack position which adds outside forces to the delicate balances in play there. It merely guarantees that the driver has lifted his foot completely off the pedal. Easy Peasy.

When you think about it, it's exactly like if you only used the on-off toggle switch to turn on the Jakes, which is really what you do anyway with the toggle on, then the governor microswitch, or alternately throttle linkage microswitch needs to be "on" as well. There's an electronic digital logic name for this kind of behavior, it's called a logical "AND" Gate. Both have to be "on" for the function to happen. You might try looking to see if you can create a substitute for the governor mounted microswitch by simply finding a spot in your throttle linkage that you can mount, really, any kind of sturdy on-off switch to pick off the movement of the throttle when it is resting at no fuel demanded by the drivers pedal. That's all you're looking for.

By the way those governor microswitch assemblies as parts are becoming outrageously expensive and becoming pure unobtanium. It's probably time to come up with a better more available/reliable method that, as an added bonus, doesn't screw up the governor settings. I intend to do exactly that when the time comes to add Jakes to mine.

P.S. His name really is Dusty, with a D. And he is the 2-stroke guru. He keeps busy since he's like the only one left who knows how to work on the DD's, and do them the right way.

[luvrbus]

There a lot of ways to control Jakes,you see switches mounted on the clutch pedals of manual transmissions and mounted on the Allisions controlled by oil pressure.Prevost used the throttle linkage switch for years to save the fast idle,I still mount some on the linkage to save the fast idle.A buffer switch doesn't affect the governor working you set the idle and screw the switch in to you achieve 25 more RPM and your done .You have a fast idle you are replacing that doesn't affect the operation of the governor. I warn people about the adjustment of buffer switch it doesn't take very little of a turn to put a engine into orbit with a buffer switch adjustment. The combo fast idle and buffer switch are very expensive around a 1000 bucks the electronic buffer switches without the  fast idle are $175.00.You can control a Jake hooked to the brake pedal and  brake lights some like Jakes without buffer control using a off and on foot or dash switch it's not big deal Jakes disengage if the oil pressure drops below !5 psi at idle anyways, the engine will stubble when people forget to turn it off on take off with higher oil pressure,I think Don has a master staying on and engaging 2 cylinders, he makes no mention if he  has a single stage or 2 stage Jake brakes       

[windtrader]

I fired it up yesterday and it was behaving properly; I think we are on focusing in that the likely problem is the switch. Being intermittent seems like a flaky switch to me. One note is when the Jake was fully engaged there was a bit of blue smoke, I don't recollect if small amounts is ok or if that indicates another problem like Clifford is suggesting that Jake valve on a cylinder is stuck.


My hunch to not DIY this solo is correct as it seems one can really screw the engine if not properly setting the rack, jakes, and governor. thanks for the help!


The Jake is two settings.


here is the oil sample I had taken at around 1000 miles after oil change and the problems started. there are elevated levels that concerned me. I changed oil again and sent in oil at around 1000 to see if things changed.


The oil test indicates excessive fuel which supports the problem is related to sticking Jake. 

[luvrbus]

Those Jake switches have a 1 way diode that goes bad also,what switch do have ?,they blow blue smoke with the Jakes activated I never saw one yet that didn't, depending on where the exhaust pipe exit  most of the time you will see more oil spots on the rear and the tow vehicle   

[azdieselman]

The fuel in the oil is concerning. I would carefully check the jumper tubes for leaks. You may have to add some fluorescent dye at the fuel filter and use a black light.