Avoiding Cummins Engine Repairs With Regular Tune-ups.

We recently had a Cummins Diesel Engine with a power complaint. One adjustment that gets overlooked is valve adjustment. This particular engine gained substantial power after adjusting the valves which required an average of 1/4 of a turn to meet specs. So this simple tune-up procedure should never be overlooked and must be carried out on regular basis.

The following is a valve adjustment on a Cummins ISB Diesel Engine: Valve adjustment on a Cummins Engine Repair is the final step. Engine position is very important because the intake and exhaust valves must be in the closed position.

Rotate the engine clockwise [looking from the front] until #6 cylinder rocker arms are both rocking. When you're on the correct stroke the exhaust valve will be moving into the closed position, then once it closes keep rotating the engine until the intake valve JUST starts to open. You are now on #1 Compression Stroke & ready to adjust 1/2 of the engine valves.

Note: The crossheads pictured here on top of the valve stems [#5 & #6 Cyl] are located with the elongated contact surface towards the exhaust manifold. The Rocker arms are held down on aluminum cradles with one retaining bolt and torqued to 27 ft. lbs.

Cummins 24 Valve Turbo Diesel Valve Adjustment Specs.

With the Engine on #1 Compression Stroke.

*Adjust #1 #2 #4 Intake Valves to .010 inch.

*Adjust #1 #3 #5 Exhaust Valves to .020 inch.

*Rotate Engine One Full Turn. #1 Cylinder Valves will rock like #6 did previously positioning the engine on #6 Compression Stroke.

*Adjust #3 #5 #6 Intake Valves.

*Adjust #2 #4 #6 Exhaust Valves.

I hope this mechanic information has helped you: It's not hard to adjust valves on a Cummins 24 Valve Turbo Diesel once you get the hang of it. All you have to know is how to position the engine correctly, the valve settings and some basic tools. That's it for now on Cummins Engine Repair.




Recommended: Diesel Engine Repair Manuals

Thomas Buses - Air Throttle Repair

During most of the 1990's before the electronic age the engine throttle was air controlled on Thomas Bus Saf-t-liner models. The high idle was a welcome addition since it was operated with the flick of a switch on the dash.
In the photo the air line can be loosened while the engine is running where there should be no air with the high idle switch turned on. The throttle linkage is moved into high idle with spring pressure[no air]. The regular foot throttle air line is attached to the underside of the cylinder. {Click Photos To Enlarge}

The air is controlled with an electrically actuated air valve that is normally open with full air pressure and no power from the switch. The air pressure moves the internal piston to the idle position compressing the internal springs. When the high idle switch is turned on, battery power closes the switch and blocks air pressure to the air throttle allowing spring pressure to kick the throttle linkage up to high idle[around 1000 rpms].



The disassembled air throttle consists of springs pistons and seals and is easily serviced. The one thing that does fail is the 1/4 inch adjustment bolt on the end cap wearing through the washer that seats on the internal spring. Thomas buses have changed since this decade and are electronically controlled with an onboard computer but if you still own a saf-t-liner pusher these systems are reliable and easy to maintain.

Diesel Engine Oil - Switching to CJ-4 For 2007

To meet 2007 EPA standards low emission engines must use CJ-4 engine oil formulated especially for diesel engines using exhaust aftertreatment systems. New EPA standards are a 50% reduction in oxides of Nitrogen and 90% reduction in particulate matter. CJ-4 is a low ash diesel engine oil that can be used in older engines but comes at a higher price. The warranty becomes invalid if regular CL-4 oil is used in '07 diesel engines but the 10 to 30% increase in price is significant when it comes to a fleet operation.

You could stock both oils but there is a risk of operators who normally add oil to there assigned unit could inadvertently grab the wrong oil and mix the two. Mind you one litre of the wrong oil would not be detrimental to the life of the 2007 diesel engines but over time it would make a difference. The possibility of an engine oil test after a failure could happen.


Our fleet operation only stocks the CJ-4 so there is no confusion and zero risk to jeopardizing the integrity of the DPF [Diesel Particulate Filter]. The DPF has a regenerating cycle when a difference in input and output exhaust gases in the DPF [muffler] are picked up by the engine ECM [electronic control module]. The DPF literally cooks out the carbon build up and it gets kicked out the exhaust pipe which creates extremely high temperatures.


EPA standards are here to stay, with vehicle emission standards being on top of the heap when it comes to environmental concerns. Our School Bus Fleet will be receiving a Hybrid International School Bus next September. This will be an interesting technology to experience and another brand new learning curve to grasp.

Basic Electricity How It Works

Basic Electricity applies to any type of machinery running on a 12 Volt Direct Current system. Once you see how it works it's much easier to understand, instead of making it complicated I will explain the basics in layman's terms. This is the chasis electrical panel on a 1995 Thomas Saf-T-Liner[pusher]. note: Click on the Photos to Enlarge
It looks a lot more complicated than it really is. Any 12 Volt electrical system has a source of power from the batteries, in this case we run on 3 top post 900 CCA [cold cranking amp rated] batteries.

That's a lot of juice available to supply voltage to the body and chasis circuits, but there are environmental and mechanical factors that will cause a severe voltage drop if not detected.

Voltage is like a river, the heavier the flow the stronger the current. If there's a dam down river this will cause resistance and restrict the flow. If the source [the river] is cut off so is the flow.

Any resistance between the battery and the load will cause a voltage drop, this can be caused by a short circuit, open circuit or just plain resistance from corrosion. A good rule of thumb when troubleshooting a 12 volt circuit is to:

Step 1...Check the battery -Sufficient Voltage?
Step 2...Check the load i.e. A Light or Relay, is it working?
Step 3...Check the connections
Step 4...Check the wiring

Very basic steps but most electrical problems are found using these steps, check the simple things first.

Say for instance you have 13.5 volts at the battery and 0.0 volts at the load. This means you have an obvious Open Circuit problem [a rubbed through wire possibly]

Using a digital ohmmeter you can ground one end of the circuit and using the two ohmmeter leads at the other end connect one lead to the faulty wire and the other end to ground. What you're doing here is checking for Continuity [the ohmmeter has it's own battery voltage which runs through the faulty wire].

By the way, the multi-meter you use for newer equipment must be Digital to safeguard the electronic systems that are much more common in new trucks and buses. If the circuit breaker is popping on and off then there is obviously a Short Circuit which can be hunted down using a Short Finder [a very slick tool to have which saves a lot of time and grief]

You hook up the auto-reset breaker then slide the meter along the wiring until it finds the exact spot where the short is [the indicator needle stops moving] along the frame or body.
Clean the connections and check the load i.e. marker light or tail light for poor grounds & connections.
That's a Quick Overview on Troubleshooting a Basic 12 Volt Electrical Circuit.

Bus & Truck Air Brakes System-Bendix AD-9 Air Dryer

The Bendix AD-9 air dryer is easily serviced by disassembling it from the frame and removing the bottom cover bolts. The unloader located on the bottom housing can be removed and a kit installed. The kit comes with new o-rings, spring, valve and seat. The main filter which is filled with dessicant absorbs the oil and moisture that accumulates in the air brake system.
Since the air compressor creates heat this causes moisture to build up, so this is why air brake systems have an air governor that unloads the compressor at 120 p.s.i. and signals the dryer to dump the build-up of water & oil in the bottom housing to atmosphere. That's the quick air release you hear when building up the air system, the air guage should be reading a minimum of 120 p.s.i.
The dessicant filter has a threaded stud attached so it can be easily removed during a service. The Bendix AD-9 is a very reliable component and is usually trouble free but if you notice a lot of oil coming from the bottom housing exhaust port then that's telling you the compressor is pumping out more oil than it should. Bendix has a splash card that you hold under the exhaust port, that gives an indication of how bad the oil loss from the compressor really is. The next step is to replace the compressor and of course, service the air dryer. Under normal conditions the air dryer can be serviced every 1-2 years depending on the condition of the air compressor and highway miles or hours of operation.

The Bendix Air Dryer also have a built-in heater wired up to sense cold weather and keep the unloader valve from freezing up. Every Truck & Bus air system has an air dryer installed from the factory, it's the most important preventive maintenance item and should not be neglected.