Valve lash adjustment

brewster16

brewster16

Well-Known Member
Aug 9, 2009
1,452
Long Beach Island, N.J.
Boat Info
'07 44 Sundancer
Engines
Twin Cummins QSC 8.3
Could someone provide some knowledge about what it is, when it's done, how much it should cost and what symptoms the boat displays when it's an issue? My Cummins QSC's are at 390 hours and I'm just interested in learning about this subject. Thanks.
 
I can't answer all your questions, but I just had mine done on my Cat 3116 engines and it took the guy 5 or 6 hours to do both. With this service he also had to adjust timing on the fuel injection system. On the Cats its the first 250hrs then every 1000 after that. I'm told they will run a little smoother after the service is done but I haven't been to my boat since to tell you if that is true or not. I went past the 250hr mark substantially because of where the boat was and not finding a mechanic I could trust to not actually make it worse so if your past a little I wouldn't worry to much, unless of course they are still under warranty.
 
The valve lash sets how far the valves open and to some degree, when they open. Diesels typically don't require resetting the valves very often, so you should follow the Cummins recommendation on the initial adjustment and the interval between future adjustments.

Ari's answer was relative to Caterpillar engines which have a mechanically driven injection system. His injector timing and opening is set at the same time the valves are adjusted. Cummins QSC uses a common rail electronic system to control injection timing and amount, and that system is not mechanically adjustible so you don't need to worry about injector timing.
 
QSC require valve lash at 600 hrs. Takes about 4 hours and should cost around $500 for both motors. No parts needed all labor to remove the valve cover and access the flywheel to spin the crank.
 
Any body do the QSM11's at 600 hrs? Cost? How important is it to do ?

Thanks,
WarrenG
 
I'm having mine done this winter along with aftercooler service. I'm at 700 hrs, the valve adjustment quote is $440.


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Had mine done when I bought the boat at 1000 hrs. Cummins 6cta. Charged me an hour labor per side (took a lot less time than that). He took off the valve cover. Had some tool to measure something on each cylinder. Turned a screw or something to adjust, then on to the next cylinder. Spent about two minutes time at each cylinder.
 
fwebster said:
The valve lash sets how far the valves open and to some degree, when they open. Diesels typically don't require resetting the valves very often, so you should follow the Cummins recommendation on the initial adjustment and the interval between future adjustments.

Ari's answer was relative to Caterpillar engines which have a mechanically driven injection system. His injector timing and opening is set at the same time the valves are adjusted. Cummins QSC uses a common rail electronic system to control injection timing and amount, and that system is not mechanically adjustible so you don't need to worry about injector timing.
Click to expand...

I want to expand on the injection system used today as a matter of warning. The system we used in OldSkool days had injection PSI around 2,600 PSI. Though this is high, the potential for injury was low. With the new engines injection PSI runs between 25,000-38,000. This type of pressure can be lethal if it comes in contact with the body parts. This potential is increased in common rail where the PSI is built up in the common tube outside the engine between the pumps and the head.

The common rail system builds injection PSI in the injection common tube. It's PSI can be as high as 35-37,000 PSI. Any time the piping is disrupted or loosened they need to be replaced. Leakage from the injection tubing can cause great injury or death. 35,000 psi will pierce bone and remove fingers. Bosch injectors are commonly used in the system.

The injector is regulated by the ECM. When, how much and how long the injector injects is set by the ECM software. There is only one positive and one negative wire to operate them as they are mainly on or off but again regulated but the ECM. No lash adjustment is needed as there is no rocker arm to operate them.
Only certified technicians should work on this system as the potential for injury is real.

Non-common rail engines use the cam and rocker so they do need adjusted. These engine use the rocker and cam to increase pressure in the injector. Delphi injectors have 4 wires, 2 positives and 2 negatives. The first set on +- close the passage way so fuel cannot exit the injector and pressure is increased inside the injector via the rocker pressing down on the injector plunger. The second set of wires allows the injector to fire. These injectors, like the common rail are completely controlled by the ECM. How much, how long, and when, are ECM software controlled.



There are many variation to these 2 type systems. All, other than common rail, have rockers and can be adjusted.

All that being said, setting the lash is pretty straight forward. Either using a feeler gauge or degree wheel and a little time and the lash can be set with either type injection.
 
A local mechanic with 20 years Cummins experience is doing them for around $3000. I hear it's about double that going through Cummins.


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quality time said:
A local mechanic with 20 years Cummins experience is doing them for around $3000. I hear it's about double that going through Cummins.


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Click to expand...
I see such a range of costs for after after cooler cleaning on here. I had a mechanic remove and clean mine, paint them, completely replace one that was toast ($1700 right there), run Barnacle Buster through the rest of the cooling system, replace the coolant and coolant filters, and then put everything back together. All for just under $3000, including the new after cooler and coolant. I have since removed the hard to access port cooler myself to get access to replacing the water pump. It turned out to be quite easier than I feared to remove and re-attach it. In the future I will remove the coolers and take them to a shop to have them cleaned for a few hundred dollars. Since I am in salt and should do this every 2 years, this is about the only way I could really afford this.
 
Oh I know, I made sure this mechanic had lots of QSM experience. We're hoping for a clean/rebuild but won't know until he opens them up. Especially since they're $6,500 each to replace.


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