Wednesday, April 20, 2016

Valve lash adjustment, a diesel engine tune up

We have a big honking Detroit Diesel Series 60 engine in our motorhome, 858 cu. in., 515 HP, with 1650 ft/lbs of torque.  It is pretty bullet proof other than keeping the oil and filters changed, and changing the fuel filters regularly to keep it drinking nice clean fuel. But like any engine it requires a tune up of sorts, the manufacturer says to have the valve lash checked at 60,000 miles initially.  We contacted the dealer at 60,000 miles and were told to wait awhile, get it to at least 80,000-90,000 miles and call back, so when we reached that mileage he said he'd still wait a little longer.  In his experience he had never had one that needed any adjustment at that low a mileage and I would be wasting my money, and it's not cheap to do.  So when we reached 109,000 miles and told him we were planning on a circumference of the US with another 8-10,000 miles this year, he said it's time.

Now what is valve lash?  Remember there is no ignition on a diesel engine, and it runs on high compression, the valves, intake and exhaust open and close by the turning of the camshaft.  The lobe of the cam pushes up on the rocker arm that pushes down on the valve tappet causing the valve to open.  The lash is the carefully measured space between the rocker arm and the valve tappet.  Too little space and the valve will not completely close and too much causes noise and excess load on the valves and valve train components.  It causes the valve to slam open and close instead of riding the cam lobe smoothly.  You can read more about it here if you'd like.

So we set up our appointment with the caveat that the total cost of the job would be determined by how tough it was to access the engine and work on it, a lot more challenging in a motorhome than a truck!  And most of the service places really don't like working on coaches:)  We were quoted between $550- $900 for the job.  We were confident ours would be quite accessible as our manufacturer did a relatively good job of providing real access to the the engine.  

We arrived at the Detroit Diesel service center Sunday afternoon and backed up to our assigned bay door.

Camp Detroit Diesel!
We actually lucked out in that the service manager, Steve, happened to be there when we pulled in, so he confirmed the bay and the job, so we were ready for them at 7:30am in the morning.  Jan and I removed all our stuff from our rear closet, that's where the access is, and we pulled off the access panels and overall made sure we provided as much room  as possible.

Right at 7:30, we met our tech, Steve also, and he remarked that it looked like it would be easier than he anticipated, good news.  

All ready for Steve
He jumped right in and got the valve cover off, he had to remove the air cleaner first to provide room to the engine from the outside as well.
The valve cover

Valve cover popped off

The top of the valves and the two Jake brakes
Now the next question is what is a Jake Brake?  On a diesel engine you don't have any restriction on the air coming into the engine as you do on a gas engine.  On a gas engine you stop the air flow into the engine when you come off the gas providing compression braking. On a diesel the same amount of air enters the engine whether the throttle is open or closed, you just add fuel with the throttle.  With a Jake brake or compression release brake, a device holds open the exhaust valves to release compression from getting to the crankshaft.  This happens when you have the switch in the on position and come completely off the gas pedal, it provides a lot of slowing power.  Anyway the assemblies you see on top of the valves are the Jake brakes and they have to come off to get to the valves.
One of the Jake brakes lying on the floor

Now you can see the rocker arms in the middle and the top of the valves
along the right side.  The camshaft runs along the left side.
So once Steve got to this point he was then able to turn the engine manually and adjust the lash for each valve in sequence, then after the valves were all adjusted he reinstalled the Jake Brakes and then adjusted each one of them.  Finally he buttoned the whole thing up after ensuring each bolt was torqued to the proper value.
Steve has reattached one Jake Brake so far and is
torquing the bolts
After reinstalling the air cleaner and making sure everything was done, we fired it up, ran it at high idle for a bit, making sure there were no leaks.  All done!!  And the verdict, because of our good access and Jan and I making sure everything was completely out of the way, the final bill was $538!  Awesome.  So now that we are all "tuned up", we should get another couple miles per gallon, HA, wishful thinking, but maybe a 1/2 mpg:)  They said we should be good for another 100-150,000 miles.

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