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Discussion Starter #1
I just did attempt number two for setting the valve lash. And with the first attempt going poorly I wanted to share some thoughts I gathered which may help others.

The biggest issue I have with Cummins instructions is it says to keep tightening the screw until "some resistance is felt". Me being an engineer which is a blessing and curse, that really chapped my ass. It's a subjective statement and honestly I feel like you could leave that part out and probably get better results the first go around.

Anyways, my attempt I set the valve lash until "some resistance" was felt. Well that gave me a valve train that sounded like a damn rattle trap.

Did some reading during the day and found a few helpful tips to really get a good sense of what the proper drag from a feeler gauge should feel like.

1st example: take 2 glossy magazines and sheet of paper, but the paper between the two and just hold the top magazine in place such that it doesn't get pulled off with the sheet of paper.

2nd example: take a small magnet like one at the auto parts counter that extends out drag the feeler across it.

The 3rd example is the best and sure shot way of making sure you are dead on and it's brutally simple and quite honestly pissed I didn't connect the dots

3rd example: get the proper feeler gauge, let's use the intake for example, .01, throw it under the rocker arm and tighten the screw until you can't pull it out, then just back off just a tinyyyy amount. Leave the feeler gauge under the rocker, torque the nut and see if you still got the same amount of lash. You will have to fiddle here, you may end up not being able to pull the feeler out so you have to keep repeating this until you get it just right. After you think you got the right amount, take a .011 feeler and try and slip it under the rocker. Don't use excessive force. If it's too lose the .011 will slip in. If the .011doesnt slide in, Go back with .01 and then you will have the perfect reference for getting the right drag.

The right drag on the correct sized feeler will be enough such that the larger feeler won't fit.


This may be common knowledge to alot of folks. But those with your head in the sand like me, this put my right on the money.

And it will always be better to be on the tighter side of the specs. Just by a smalllll amount.

Using the 3rd example for the method of setting the lash will give you solid results.

Side note: my Cummins is very happy now.

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"Some resistance" is not a Cummins-specific spec. "Slight drag" or some other synonymous term has been the SOP for feeler gauges since the beginning of time. It is highly subjective. There are many aspects of turning wrenches that are. That's why we have the phrase "skilled mechanic" to differentiate between people who can and can't feel thier way through or around problems.

I've deliberately ran my valve lash as tight as .005"/.010" and as loose as .015"/.030". Aside from the audible clatter, which can be annoying on the loose side, it's not as critical an adjustment as most assume.

My advice, as a former professional OTR and yellow iron mechanic, and current engineer working exclusively on B-series performance parts, if you're going to overthink valve lash to the level of "10 goes in but 11 doesn't," you'll be time ahead to forget the feeler gauges entirely and set lash with a dial indicator.
 

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Discussion Starter #3
Well.... that is your opinion....If I followed your advice about not trying to find a simple method for getting a reference to the drag or deliberately running them on the looserr side of nominal I'd have a poor performing modded 12 valve which is exactly what I had on the first round.

You go tell the gasser push rod guys that valve lash isn't critical and let me know how it goes. Hell it's free power and less noise if you are on the tighter side.

Yeah it may not be the end of the world if it's not 100% all the way through but at least they can check if they are actually set such that they are either AT or BELOW nominal lash.

Skilled mechanics are far and few between. I have never had any luck with finding someone who I can depend on to do the job right for everything I own. I have pissed more money than I care to mention on a mechanics opinion. I know there are some brilliant ones out there but I just haven't met any other than the personal friends I have who are full time mechanics

For my vehicles the only person I trust is me, because I can pick up a book, read, or surf the web, go outside, wrenchy wrenchy, slap it back together and call it good.

And if I got something wrong well I can do it again and get better at it, and also learn how to pay attention the first time around and get it right the first time!

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Thanks for putting the time in to figure this method out. Dial indicator sounds great too.

how did you know you had to get in there and adjust them? What led you there or symptoms did you notice?

New to turning wrenches here and want to learn, thanks
 

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Loosen the lash until there is no drag or friction, whatever. Now, ever so slowly start to tighten it while slightly moving the feeler gauge. You will feel a point where the gauge doesn't slide as easily; that's the point where you want to stop. That's it, easy peasy. Don't over think it.

dauntless89 wasn't saying to use a dial indicator, he was saying that if you feel a need to be that precise, use a dial indicator. I would imagine that nobody short of a F1 race car engineer uses a dial indicator to set valve lash.
 

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Discussion Starter #6
how did you know you had to get in there and adjust them? What led you there or symptoms did you notice?
I bought this truck used, had a little ticky ticky going on that wasnt there a few thousand miles ago. Also learned that the truck has upgraded valve springs when opening them up which the PO did not mention.

Loosen the lash until there is no drag or friction, whatever. Now, ever so slowly start to tighten it while slightly moving the feeler gauge. You will feel a point where the gauge doesn't slide as easily; that's the point where you want to stop. That's it, easy peasy. Don't over think it.

dauntless89 wasn't saying to use a dial indicator, he was saying that if you feel a need to be that precise, use a dial indicator. I would imagine that nobody short of a F1 race car engineer uses a dial indicator to set valve lash.
Agreed. Leave the dial indicator out. But I think my overall point is being missed. If you are really just kind of wondering how much drag you want to feel under the rocker trying to slide a larger feeler in will give you that reference you need for drag on the size you want the lash to be set to (or close to). That takes all but a few seconds to put the nominal gauge down, pick up a larger gauge to see how it fits. It's just a reference!

For example if you want to use .015" on the intake to compare to .01" , great! I am simply just giving the idea to others that have not used feelers before that using another feeler gauge can be used to help establish that drag!

It honestly couldn't get any simpler than that. But just like saying what is the best oil to use, its all opinion! I wouldnt go about setting valve lash without checking how a larger gauge feels. But that is just me!
 

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Well.... that is your opinion....If I followed your advice about not trying to find a simple method for getting a reference to the drag or deliberately running them on the looserr side of nominal I'd have a poor performing modded 12 valve which is exactly what I had on the first round.
No, you'd have an error of a few thousandths and as I mentioned, I've performed controlled testing from half-spec to 1.5-spec lash and there were no changes in power that could be repeatably measured on a dyno. This was on a ~500hp truck with a stock valvetrain other than 60lb springs on intake and exhaust. Every single pull was within the normal margin of error of the dyno and environmental factors outside our control. There were also no repeatable changes in boost or EGTs.

Straying that far from spec may have long-term reliability implications, but that's the risk you take deviating from factory specs. All I can provide there is that I personally ran my lash at .007"/.015" and there was no abnormal valvetrain wear when that engine came apart after about 20k of that.

You go tell the gasser push rod guys that valve lash isn't critical and let me know how it goes. Hell it's free power and less noise if you are on the tighter side.
We're not talking about gassers. We're talking about diesels, specifically old school mechanically-injected diesels, and valve lash being perfect isn't critical on a 6BT.

The notion that you pick up power on one of these engines running "half-lash" as they call it on the forums is an internet myth, nothing more. That's because forced induction (especially at the PRs we see) drastically reduces how important the cam profile of the engine is. Then, considering how minute the changes in duration are running .005"/.010" instead of .010"/.020", it's basically as close to the definition of "F-all on a big ship" as one can get. Sure, you might measurably pick up some power on a NA motor, but again, this is outside the scope of discussion.

Nobody is born knowing what "slight drag" is and everyone has to figure it out at one point or another. "Slight drag" to me is when you can push the gauge through the gap without deflecting, and then to ensure it isn't too loose, when I let go of the gauge and try to move the rocker arm, the gauge doesn't move vertically as a result of the arm moving. Differences in kinesthetic feel within those bounds are often unreliable. As the valve stem and rocker button wear, the surface conditions (and CoF) change. I have one rocker on my engine that grabs the gauge way harder than the rest. It doesn't look "off" or "different" under inspection, and when checked against an indicator, the feeler gauge drag on that valve is way higher than the rest. I don't have an explanation and I don't particularly care to synthesize one. There's also the part where the surface finish of the feeler gauge itself changes over time and extended use (I have .018" and .030" gauges in my set that are noticeably worn from overheads on ISL-G's) so you have to keep that in mind too.

You're talking to someone who's done many hundreds of overhead adjustments on Cummins, Cat, Detroit, Deutz, Isuzu, I-H, Perkins, Ford-Lehman, etc without even getting into the various automotive, powersport, and small engines I've ended up working on over the years. So many they all blur together. I can set the lash on my engine in about 20 minutes. During break-in on my 6.7, when I knew I would be retorqing my head studs (and resetting lash) 3 or 5 times in as many days, I literally set lash by eye. You'd be surprised how close you can get with an experienced "eyecrometer."
 

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Discussion Starter #9
Now see that right there is awesome knowledge. But some of the points you bring up relate to some of the things I noticed when some the valves were being temperamental. But I just kept going because it was close enough.

I do not doubt the experience you have, quite honestly I am actually trying to go backwards and work for a shop. But I have to take a huge pay cut when I leave my engineering job which I am trying to figure out how to handle that.

I am observant and analytical by nature and I will question everything to help myself get a better understanding of what exactly is going on, that's what I am paid to do. But I will always favor first hand experience over theory because at the end of the day it makes my life easier if its coming from a trusted source. But everything on the internet I take with a grain of salt because if it its not right, that person aint going to fix my truck lol

Point is, whenever I am on my own in my own garage and trying to do something that I haven't really done before, I have to read everything I can online, figure out what is BS and what is not. And ultimately try and get a idea of what to expect before I go in. And almost always when i come out the other end, I will learn that what I read was either BS or helpful. lol
 

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You gained 2.5 MPG?!?!?!? Wow. I’m not saying you’re lying, but if that were the case, then I certainly would have seen at least that on my very first valve lash when I bought this truck. I didn’t by the way. Maybe .5 that I forced myself to imagine because the truck ran tighter.


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Discussion Starter #14
You sure it shouldn't be taken with a feeler gauge? I got a better reference for that....
 

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There are engines that went 100,000s of miles with no lash adjustment. They may be rattly but they never blew up. The valve train moves so slowly in these engines they usually don't fail.

I'm not even sure tight or loose of . 010/.020 spec really affects "spool" as some say.. at least not on a stock valve train. My butt-o-meter can't tell anyway... Maybe I should get it calibrated.



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Believe what you want as for my increase in fuel mileage
Its not a matter of belief, it is simply impossible to gain 2.5 mpg (about 15% gain) from only a valve lash adjustment (each cylinder only contributes about 17% to the total work done by the engine).

Something else had to change at the same time for you to see that kind of mileage improvement. Perhaps you inadvertently fixed a boost leak you didn't even know about while you had stuff apart, or you had some old bad fuel before and refilled with some better fuel....... something else HAD to change in conjunction with your valve lash adjustment.

Did you do anything else or have anything else apart during that time frame?
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Me being an engineer which is a blessing and curse, that really chapped my ass. It's a subjective statement and honestly I feel like you could leave that part out and probably get better results the first go around.
I'm also an engineer, and I can work a feeler gauge with no problem. In this case the problem is you overthinking it. When reading any technical publication, you always have to keep in mind who the author is/ was and who is the intended audience. If the spec was that critical, it would have a measurement range like bearing clearances ( 0.0025 to.0.0028 for example), valve lash doesn't, its just 0.010 for the intake and 0.020 for the exhaust. It would be amazingly difficult to set anything to an exact measurement with no range (so 0.010 is ok, but 0.010000001 is not?) . Quite overthinking it and just set the dang lash. Attempt to keep your standard deviation as low as possible if it'll make your feel better
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Discussion Starter #19 (Edited)
I like how it's considered overthinking by wanting to see if a larger feeler will slip under. That's comical.

ITS A FREAKING REFERENCE. Am I trying to make sure it's dead on NO. I am trying to gauge how close I am to where I WANT TO BE OR WHERE ITS TELLING ME TO SET IT.

If I didn't care about where it was I wouldn't have pulled the valve covers off to check it!

You bone heads are right it's not critical or end of the world. But if the book tells me to set it at certain value, I'm gonna make sure I'm there! THATS IT!

ITS A GAUGE!

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