I adjusted the valve lash for the first time at 100,000 miles this weekend. Each one was off (loose) by .002-.003 except for #6 exhaust which was still in spec. With everything adjusted the engine is much quieter and I feel like there is better throttle response at the low end...although I admit it is possible that I am looking for stuff here. Will I see improved mileage because it had been dropping (16mpg instead of 18mpg as of a few years ago)? Either way...it was a simple job, although I bashed my knuckles a bit, and the tech stuff here was essential to get it done.

Should I do it every 50,000 or is 100,000 enough? It didn't seem like things were that off except for the fact that now it is so much quieter I wonder if I should make sure the tolerances stay tighter.

 

yes it can make diferance on the engines performance. where i work we adjusted the valve lash every 100000 miles on our older big cam cummins and on the n-14. mostly the older engines seem to have more effect on power to my recolection. but when i bought my 98 24-v new i asked cummins and they said to adjust them every 100000 miles that would be enough.

 

forgot to mention that the drivers that checked their fuel milages did state they did notice an increase in fuel milage.

 

I noticed a very slight bump in mileage. Maybe .5. I definately noticed a vastly improved bottom end and a much smoother, quieter engine. The truck was also a let peppier. Mine had ~120k very rough and abused miles on it when I did it.

 

Thanks guys...I thought maybe I was looking for stuff that wasn't there, but I am glad to hear that there are some improvements. It definitely has more pep in the low end and is more fun to drive. Fuel economy won't increase if I keep driving it like I do though .

Take care

 

I did my 99 right after I bought it with right at 99,000 miles. I didn't know the previous history, so I wanted to base line it. It was well within specification with very minor adjustments. Mileage has always been good at 18-19 on this truck (Hand caculated). One of the best things I did was have the PCM programed for the larger tire size.

Steve

 

i just adjusted mine makes a major difference in the responce

 

This sounds like something I may need to do. Can anyone give instructions on how to do this. Or, a link where this is discussed step by step. Thanks.

 

If you go to the "tech facts" link at the top of the page you can look in the 24valve engine section and you will find the instructions for how to do it. I followed them exclusively. Someone put in a lot of work to post pictures, and great instructions and it was very helpful. Was not difficult, but took some time to get the clearances correct. Patience is the key with this one. Also I'm thinking that the barring tool would have been easier to use to turn the engine over. I don't know where to get one, so I used the 7/8ths bolt on the alternator pulley. It worked, but was labor intensive. I also had a buddy come over so I could bounce ideas off of him and make sure I didn't do anything stupid.

Good luck!

 

I did mine at 45K and it made a big diff then. I will do them again (145K) when I get back.

 

Not trying to be argumentative but...two things to consider.
-Most 01's & 02's I have seen tested have been hardly out much! When you say off .002-.003 are you refering to DTR suggested lash of .010 and .020? If so...you were still well within Cummins specs, which is what most members find.
Cummins specs....
Intake - .006 to .015
Exhaust - .015 to .030
-I noticed no response difference when I adjusted mine and they were all off more than .002 from the .010 & .020.... but I have no idea what the factory settings usually are?

I could see quieter...but more pep???? JMO

RJ

 

All mine were within spec, but althroughout the range.
It probably didn't make it peppier, but it sure seemed like it! In fact, even when I wash my truck, it feels like it has more pep. Lol

 

Good question...I should have been more clear. I stopped measuring past .013 or .015 (or .022 for the exhaust). I brought them all back to .010 and .020. So they could have been off more. I didn't intend to mislead...I had everything disassembled and figured I would put it back to spec. It is much quieter. I do feel there is more pep though...not much just right off idle it picks up better and seems to hold on hills much better too. I wouldn't say I picked up any power, it just has a tighter feel to it.

A reasonable question though. Thanks.