[DK on the road]

 Can you hear loose valve lash in a diesel like you can in a gas engine?

Typically, valve lash is not loose, but too tight. 

As the valve is closed by spring pressure, with 500 down to 200 lbs of progressive spring pressure at 750 (1,500 rpm) times per minute and 1,200 deg temp of exhaust temperature, the valve head gets mushroomed out and the valve stem gets stretched by .002-.004 or more after 2,000 hrs or 80K miles. 

Once the valve is stretched too far, multiple bad things can follow. one example...

The valve can be held open as it rides on the small side of the cam. Also, as its getting close to no lash, the valve and valve seat begin to burn get hotter and weakened further. Depending on the particular motor, the valve touches the piston, and the valve breaks off, and pulverizes the piston and puts a hole in it and/or grabs the sleeve. At times, I've had the piston get wedged, breaking the connecting rod at the wrist pin and spinning the loose balance of a connecting rod around the crankcase for 2-3K times, cutting the cam and block in 1/2.   OHHH the pain, disappointment and expense.

I could go on from all motors I've blown up racing.

IMHO, A maintenance routine is way cheaper than the alternative.

[Little]

That right there is the best explanation of valve lash. Valves get tighter with time, till bad stuff happens. Possible valve head separation. The old NTC Cummins were famous for tightening and causing camshaft issues. In the '70's,80's and 90's we adjusted cummins valves and jakes every 75k miles.

[Richard]

It’s buried in an ancient thread, but several of us who adjusted the valves, injectors, and jakes on S60 engines picked up 0.5 to 1.0 mpg in fuel efficiency. Steve Bare posted some cliff notes on how to get the bathroom floor out to remove the valve cover.

[Tim wade]

Yeah, taking that floor out in the bathroom was fun Richard! I think it was designed to withstand a category 5 hurricane. If anyone needs help. I could probably make a video on how it comes out next week. As I still have to silicon the mirrors back into place. I highly recommend having a multi tool to cut the board next to the vanity drawers. (If you have this configuration) If you do not cut it. I think you would need to take out the vanity.

I was getting almost 8 mpg with the original engine. Now I’m only getting 6.5 mpg. I’m hoping it just needs some time to break itself in. Time will tell.

[Jack Houpe]

Well I got a closet back there might not be so bad, I watched Jeff's video and it looks pretty straight forward. I guess the hardest part is taking out the floor.

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Yes, the customers I have done this for have all said they were seeing better fuel economy numbers. It all depends on how far out the valves were, and if they had been done before. It’s not a bad job, access is key to making things easier. The one I did was under a bed and that was a bit of a pain because I could not sit up under the bed, I was crouched over the engine the whole time.