Mornin, DTR...
I'm gonna a do a head stud re-torque this weekend, along with that comes resetting the valve lash. I know what the spec is on the lash, however, is it better to set either the intake or exhaust to one end of the spec or another?

I could have sworn I have seen someone post about going closer to on end on one of them... I just can't remember.


Thanks!

mad

 

I think I read on Cummins' page somewhere that if they are anywhere within the published range, there is no need to change them, as it would make no difference in noise or performance.

 

I have always adjusted them to the specs. Engine cold. (INT: .010"/ EXH:0.20") Changing the adjustment changes the timing & duration slightly, & the engineers designed them to be most efficient where they set them in the lab, by the book.
I think Cummins gave the "disclaimer" about them not needing adjustment for emissions, not performance.
$,02 from 25 yr Cummins tech.

 

There was a thread on CompD, where some of the pullers were setting their lash at .008 intake / exhaust .016. They were getting quicker spool up... I was almost convinced to set my exhaust to .016, until it was pointed out to me, that the pullers are most likely checking and adjusting after every run....

I decided to leave them at .010/.020

 

Hmm... I may try it...

 

The most important thing is to be in spec. The cam has geometry to take up the lifer slack and is expecting the bump from the lifter within a certain range.

Other than that if the lash is set tight then there will be a tendency, though probably very slight, to increase the lift, the air flow and the duration, and, theoretically, rasie the point in rpm for performance. The effect of a few thousands is probably not noticable or able to test. However, it is the way to go all other things being equal and as long as a mechanic can set it and measure it and the owner wants to check it more frequently, as lash may either tighten or loosten over time, and being too tight will burn a valve, too loose, noisy and if very loose at high rpm, well, let's not go there!

 

So.... in measurements, what are you saying?

 

When I install studs and heavier springs, I will try .016 on the exhaust, I will not fudge .010 on intake. Egt's may be higher, earlier, cylinder temps should be lower, but less time on the seat for the valve could be a problem.

I am not running high rpm, and my manifold pressure seldom reaches 60lbs. Let us know what you think, if you change to a tighter lash.....

 

i have a few friends that have set theirs to .008 / .016 and have no problems at all.(one of them is running is the 650HP range and drags races)

The two times i have set mine has been to factory specs. I really dont think it matters with the exception of rocker noise. Even if there was dyno referance between the two, i wouldnt image there being more then a few horses/ft-lbs. IMO its best to play it safe and stick with factory specs.

 

Thanks for the input, fellas.

 

what are the hours or milage requirment for valve adjustment

 

I think that it was 100k, but I'd have to look...

 

135,000 according to the 04 dealer manual.

 

I think my book said first one at 100k and every 150k after that. Cummins I think just says every 150k.

 

Valve lash on Diesel engines tend to close up over time, I would lean towards the larger lash. Too close a lash can fry the valves, cause hard starting, and may even "tap" the top of the piston if you float the valves! A little too much lash is just a tad noisy.