The following is not meant to create an argument just to simply explain my personal results and what I honk is right when doing a valve lash job on my truck. 

So everyone here has told me and untold amounts of other members here to do valves on a cold engine. Wrong. Valve lash must be done on a warm engine to get good results. The reason behind this is simple. When the tappets get hot they expand and when they get cold they contract. So if you adjust your valves while cold when you operate your truck the valves are going to expand and not allow proper intake and exhaust valve operation. I personally tried to complete an adjustment 2 times on a cold engine and both times my truck didn’t seem to sound right. Something seemed wrong so after removing the valve cover and checking the lash I found that the valves were to tight! I reset them and still things weren’t right. I asked a friend who owns an 02 900 hp 24 valve what was up and he asked whether I did them hot or cold. I told him cold and he said ahh there’s your problem and proceeded to explain the expand And contract theory and said go home right now and do it right away. I did as he said and today rechecked the lash at approx 2k miles later and the lash is exactly where it needs to be and the truck is running amazing! This is my personal experience and I’m not saying I’m right and your wrong but I know that my truck now runs very well and I’m happy. 

The typical daily driver can be done cold. Normally they don't expand too much. When you talking 900 HP and track stars well there is going to be a lot of heat and expansion on the valves and such. Like I'll admit I tried going back to my old 0.008 and 0.018 and now that summer heat is here the idle is a bit lopey again. This just proves what your saying has some truth. I'm going to reverse and go 0.012 and 0.022 on this next time. I could today but time is running out. I'll do it most likely on my next weekend. 

Years ago I remember that there was a hot and cold lash on engines . Mostly industrial engines that ran nonstop so they never cooled down and for mechanics that couldn't wait for a cold engine.

Did your friend tell what gaps to set on a warm engine? Just curious. The last time I set mine was on a cold engine at .008 and .0016. I never noticed much difference in how mine ran. Not picking right or wrong, just my experience.

1 hour ago, dripley said:

Did your friend tell what gaps to set on a warm engine? Just curious. The last time I set mine was on a cold engine at .008 and .0016. I never noticed much difference in how mine ran. Not picking right or wrong, just my experience.

Same as a cold engine.  0.010 and 0.020

IDK about setting the overhead on a hot engine. All the engine manufacturers state to set valve lash on engines when engine temperature does not exceed 140*F due to metal expansion. Too much clearance causes premature wear on valve train like rockers, valve bridges, tappets, and push tubes/rods. Too little clearance causes valves to not completely close, white smoke and hazing is indicative of valve clearances being too tight. 

 

I've done thousands of overhead sets over the years on all types of engines. I will only follow manufacturers specs. For a CM550 VP44 ISB engine is .010 intake and .020 exhaust on a cold engine meaning 140*F or less. On a CM849/850 CR ISB 5.9 the manufacturer specs are .010 intake and .026 exhaust on a cold engine.

 

I figure the engineers that came up with these specs are likely a whole lot smarter than me so why would I experiment to try and maybe prove them wrong.

I'm doing my slight changes to see if there is gains or losses above or below spec. Visibly there is loses with slightly tight valves that I now can see with being 2 thousandths tight than normal on hot days. I'm going to back down to 2 thousandths wide.

 

Even though Cummins states a wide range of operational lash

 

0.006 to 0.015 intake (Stated 0.010)

0.015 to 0.030 exhaust (Stated 0.020)

 

These are considered OK ranges according to Cummins specs.

 

 

18 minutes ago, Mopar1973Man said:

I'm doing my slight changes to see if there is gains or losses above or below spec. Visibly there is loses with slightly tight valves that I now can see with being 2 thousandths tight than normal on hot days. I'm going to back down to 2 thousandths wide.

 

Even though Cummins states a wide range of operational lash

 

0.006 to 0.015 intake (Stated 0.010)

0.015 to 0.030 exhaust (Stated 0.020)

 

These are considered OK ranges according to Cummins specs.

 

 

I stand corrected... I always use nominal lash settings as stated by engine manufacturers. The majority of the engines I work on are all over North America so nominal lash is probably best for me to use. As the valve beats itself into the head and the valve stem stretches which is normal wear will cause loss of clearance which is why I like to use nominal lash.  I suppose tighter tolerances  for cold climates and looser tolerances for hotter climates would make sense. 

 

 

Just for the sake of the topic. I found the specs in the FSM.

 

I see what each on of you guys are saying. All I know is my truck ran better and stayed right on 0.010 and 0.020 when I did it hot. 

6 minutes ago, Marcus2000monster said:

I see what each on of you guys are saying. All I know is my truck ran better and stayed right on 0.010 and 0.020 when I did it hot. 

How hot was your engine when set the gaps? Just curious is all. If setting them on your engine hot worked, go for it.

1 minute ago, dripley said:

How hot was your engine when set the gaps? Just curious is all. If setting them on your engine hot worked, go for it.

At least 150 to 170 degrees. I drove home from talking to my friend and let it cool for maybe 15 minutes or less before I tore into it. The valvetrain was still hot enough to almost burn me. 

Ask @hex0rz about the injector change I did on his truck. He ran the 5 hours from Sandpoint, ID show up here at 7pm and I change all 6 injectors in about 1 hour hot. Don't suggest it...

20 minutes ago, Mopar1973Man said:

Ask @hex0rz about the injector change I did on his truck. He ran the 5 hours from Sandpoint, ID show up here at 7pm and I change all 6 injectors in about 1 hour hot. Don't suggest it...

I did that as well, drove an hour home from school on Valentine's day and as soon as I got home I popped my hood, took the valve cover off, threw a fan on it and went to town while it was still hot. Needless to say I won't do that again, and definitely won't do anymore truck work on Valentine's day cause the girlfriend didn't like that, although she was at a softball game