Engine/Transmission (1994 - 1998) Valve lash tolerances?

[JGheen]

I just checked/adjusted my valve lash last weekend and was wondering what the tolerance limits are? I know the lash is . 010" on the intake and . 020" on the exhaust, but how tight or loose can the tolerate? +/- . 002-5"?? Is that too much? When I adjusted them they were all about . 002-3 under what the spec is.



Joe

 

[Hammer]

. 010 intake/. 020 exhaust are the proper tolerances. There are some guys who run at . 008 intake/. 018 exhaust and are safe. When you find them over what factory tolerances are that when you notice more noise out of the valve train and poor performance... ... ... ... ... . Andy



BTW...

You can find all the specs you need on Dave Fritzs website... www.dodgeram.org

 

[SRadke]

FWIW as the valve seats wear the lash will get tighter, as the cam lifters, and rockers wear it get's looser.



-Scott

 

[JGheen]

FWIW as the valve seats wear the lash will get tighter, as the cam lifters, and rockers wear it get's looser.



-Scott

All were pretty tight, around . 007-. 008" so I guess I am getting typical wear out of the seats. I loosened them up to the proper specs and felt just a little bit of resistance with the feeler gauge when I tightened them down.



The main reason for the check/adjustment was due to some poor fuel mileage recently on a 250 mile round trip. I have had this issue before and lash adjustment fixes it pretty good. Mileage seems to be better now, but won't know until I hit another long distance trip. Is poor fuel mileage something you guys typically see when lash is out of spec?



Joe

 

[CEdwards]

When I adjusted the ones on my automatic all the exhaust valves were too tight and the intakes too loose. Last week I adjusted my 5 speed and the exhaust valves were all . 002 too loose so I just left them alone. I have a hard time getting that accurate anyway. It's hard to lock the jam nut down without it accidentally tightening the bolt up just a hare. I hope this is accurate enough. How precise does it need to be? By the way it gets pretty good mileage like that, around 21 on interstate and 14 the other day towing 18000 lbs. It also helped my mileage on the automatic when I loosened the exhaust valves up.

 

[JGheen]

How precise does it need to be?.

That is basically the question I have. How close to . 010" and . 020" do I have to be? Obviously the closer the better, but I guess it all depends on one's "feel" of the feeler gauge.



Joe

 

[RBrunson]

Joe, I know that you are asking about the 12 valve engine, but I would think that the 24 valve lash should be the same. They are both 10 and 20 thou. adjustments. The book on the 24 valve says that the min. clearance for the intake is, 0. 006" and the max. 0. 015". The exhaust is, min. 0. 015" and max. 0. 030". Hope this gives you some food for thought.

 

[Vaughn MacKenzie]

IMO the Cummins acceptance range is WAY too wide!



There is a difference between what the acceptable range is to have all your valves adjusted to, and how close the intake and exhaust valves are to each other. For instance it might be OK to have all the exhaust valves at . 030" but you don't want one at . 020" the next at . 017" & the third at . 024" and so on.



Vaughn

 

[DWitcher]

Better they were too loose than too tight at an adjustment due to the fact of the metal expanding and tolerances tightening.

 

[JGheen]

Joe, I know that you are asking about the 12 valve engine, but I would think that the 24 valve lash should be the same. They are both 10 and 20 thou. adjustments. The book on the 24 valve says that the min. clearance for the intake is, 0. 006" and the max. 0. 015". The exhaust is, min. 0. 015" and max. 0. 030". Hope this gives you some food for thought.

Thanks Ron, those were some of the numbers I was looking for. Interesting I thought the lash in the 24Vs would be a little different with 2 extra valve per cylinder.



Joe

 

[JGheen]

IMO the Cummins acceptance range is WAY too wide!



There is a difference between what the acceptable range is to have all your valves adjusted to, and how close the intake and exhaust valves are to each other. For instance it might be OK to have all the exhaust valves at . 030" but you don't want one at . 020" the next at . 017" & the third at . 024" and so on.



Vaughn

I agree Vaughn that those tolerance numbers are quite a bit too large of a range, especially with how close the valves run to the pistons. But on your comment about running each exhaust valves at different lashes is kind of easy to do and not even be aware of it. I guess it depends on one's consistent "feel" of the feeler gauge for each measurement but that is what was afraid of during my latest adjustment. Each lash adjustment "felt" like they had the same resistance like int the past but I believe it would be pretty easy to get each, exhaust valve for example, at say . 021", . 019",. 018", . 020" and so on. That's where my questions came up about what is the max tolerance. I guess anywhere from . 001-. 003" is a good max range.



Joe

 

[Joe G.]

I use a dial indicator to get them as close to the specs as possible.

 

[MLee]

If we could find socket head-tappet screws like the 3rd gen engines have, the adjustment would be better you can hold the screw better than with the screw driver. just to much room for error. But have you noticed that when you tighten down the lock nut the adjustment loosens just a tad? That happy-medium is kind of frustrating.

Marv.

 

[Vaughn MacKenzie]

JGheen, it's definitely a bit of an art doing valve lash and getting the right, consistent "feel" between each valve

 

[DieselMinded]

Heres the numbers I have



http://www.dodgedieseldatabase.com/valve_lash_limits.htm



DM

 

[Vaughn MacKenzie]

I adjust mine to . 008" & . 018" and shoot for worst-case +/- . 001" (which is . 002" error). Takes some finessing, especially the ones that tighten lash as you tighten the nut (hate those )



Vaughn

 

[JGheen]

Heres the numbers I have



http://www.dodgedieseldatabase.com/valve_lash_limits.htm



DM

Thanks DM, that is a good reference number chart I was looking for. Oo.



Joe