royta

It's been quite some time since I last adjusted my valves. So, I took care of them on Tuesday, and I expected them to very loose. They were tight! I would have figured they would have loosened over time. Maybe the last time I did them, the engine was too hot and they felt tight because the engine was cool when I did them on Tuesday. I got home from a 700 mile drive at 4:00A, and did the valves in the late morning, early afternoon. So, the engine certainly had time to cool off. I didn't measure the exact lash, but I couldn't get a .020 under the exhaust or a .010 under the intake.

So, what are the effects of overly tight or loose valve lash?

HaulinBut

Not an expert on Cummins specifically, but I build alot of race engines, so here are some random thoughts:
Tight Valves: More likely to burn as it reduces the time the valve has to transfer heat to the seat/head, more duration, higher lift, tendancyto move the power band down lower in the revs,
Loose valves: Noisier, can be harsher on components, largely depending on camshaft design and how much "valvelash take-up ramp" they build into the design. Might be weaker pulling away, especially under heavy load.

royta

Sounds like I'd be highly unlikely to notice any differences in fuel economy or power when the valves were a few thousanths too tight.

dieselpwrRam

I had my valves adjusted last around 60,000 miles. I last checked them around 130,000 and they were still fine. I did have to replace the valve cover gaskets due to oil leakage and rubber being cracked. Other than that I was a little surprised.

95 ram with 135,000 no mods ,still running strong.

psj12

If the valve lash is decreasing it means the valve seats and/or the valves are wearing allowing them to rise to reduce the gap. This is common. It is why you occasionally reset them.

HaulinBut

Nawh.....a few thou won't make any noticeable difference there. I just did mine at 69K, finding all loose with some being as much as .008 looser. All I notice at this point is a bit less racket.
I can understand them tightening alot sooner than becoming looser. In addition to what the member posted, the valve can also stretch (much more likely in an engine that sees 13,000 rpm, not likely with these grunts), and compression of the head gasket, possibly after someone re-torqued his head.

redramnc

These motors do not notice a few thousandths variance in the lash. Some of the higher power ones running around go to .008/.018 due to the rpms they see but stock or mildly modified can be run many miles between setting them. I went from 125K to 225K miles without touching mine and then I was only loose maybe .0015 on the worst one and 3 of the 12 I didn't have to adjust. Only change I can tell is a little less (not noticable to anybody but me) valvetrain noise at idle. Can't compare idle quality because I kinda changed a few things at the same time. But idle ususally smoothes out a little after running the top end.