Broken valves

[MSicotte]

I had and 03 truck come into the shop the other week and after disassembly I found the rough running and noise to be caused by a dropped/ broken exhaust valve (#6 cylinder). I contacted the machine shop we deal with and was informed this apparently is quite common, and he had 10 (!!!) engines currently under repair for the same failure. Some engine were higher kilometers (200k+), and some were being subletted by dealers for repair under warranty. From what I was told, the heat in #6 is much higher due to the exhaust manifold design, and there is also an "unofficial" repair from Dodge; replace the stock manifold with an aftermarket design such as ATS or BD. I like to think I'm pretty up on the Cummins, but I've never heard of this before, and don't recall ever reading about this failure. Am I just out of the loop on this one? Or is this a new concern rearing its ugly head? My big concern is my own truck is just under 180k, and I'm not too keen on a wrecked motor from a dropped valve. Just want to hear from others and then decide if I roll the dice or if I should plan a head removal and valve replacement weekend.

 

[SRadke]

It was not uncommon on 03 models. Always an exhaust seat and usually on #4 or #5. Also seems to show up more on engines that have been modified and were run hot. #6 always seems to run hotter on B series but it's generally attributed to the design of the intake manifold, not the exhaust manifold.

-Scott

 

[SRadke]

Broke valve, beat up piston - NWDiesels.com

 

[HBarlow]

I've always heard that cylinder #6 runs hotter than the others but I believe valve failures in a factory stock engine are rare based on reading posts here in the TDR for many years.

 

[Wingate]

hhmm. . I could see how this could be an issue. I think its pretty common knowledge that #6 cylinder run hotter than the rest of the cooling system on these engines... . Couple that with an apparent excessively restrictive port section of the manifold, sounds like a perfect recipe for some valve/seat failures... I dont think the manifold is really the problem, but I believe its the easiest way to prevent a repeat failure.

If the coolant around #6 cylinder is hotter than the rest of the block, then the coolant in/around the valves of #6 is going to be hotter. The hotter exhaust gas is expanded out more, thus compounding the issue of the restrictive port design...

GM/Isuzu had a similar problem with the L/S exhaust manifold on the LB7 D-maxes. .

I wonder what could be done to get control over the coolant temp around #6 cylinder?? Maybe run some auxillary tubing from the inlet side of the pump to the back of the block and draw/recycle some coolant?. .

FWIW, a friend of mine just rebuilt an 06 model for a customer, it punched out #6 cylinder... . valve... piston, cylinder wall. . etc. . had to sleeve the block.

So, apparently the cylinder temp issue with #6 isn't just on the older trucks.

 

[MSicotte]

That was the result on this one too, valve, piston, sleeve, and questionable on wether the head could be reused. The customer decided to not fix it and sold it the way it was.

 

[Wingate]

Did the valve show any signs of guttering??? IF it shows signs of guttering,then the valve burnt BEFORE it broke... meaning that the broken valve is resultant damage and not the source of the initial failure. Guttering usually indicates improper valve clearances. As you may know, a tight valve does not get the cooling time that a properly adjusted valve does.

 

[MSicotte]

The valve sheared off right at the top of the taper where the stem starts. I found the base of the valve in the turbo, and from what was left of it I didnt see any signs of it being burnt before hand.

 

[MMeier]

Was the valve seat still in place ?

 

[HBarlow]

Is it possible to break the head of a valve off through contact between piston top and valve in the Cummins ISB or will this just bend the valve?

I think it is possible to float the valves and cause piston to valve contact by downshifting a manual transmission and overrevving the engine.

Can any experienced mechanics comment on this?

 

[Wingate]

Yes, an overspeed condition can/will cause contact and valve breakage. And, ususally, thats where the valve will break. Typically, the piston isn't completely flat across the area directly under the valve face, so when there is contact, it simply bends the valve over and breaks it.

Another thing that can cause the same result is a valve stem/guide seizure. These can be tricky to detect though. Many times, the valve stem may only be partially stuck. (Stuck just enough to resist the valve spring trying to close it) When the piston/valve "say hello" to each other, many times, the valve stem will unstick, but not before delivering the death blow to the valve face.

I would want to thoroughly inspect the valve and stem section...

IF you have both sections of the broken valve, use a magnet on the stem, than the face and see if one is "more magnetic" that the other.

The reason I say this is to determine if these valves are two piece valves. If so, you would want to determine if the valve failed at the inertia weld... If Cummins has had an inertia weld issue, this could be bad, depending on how many engines may be affected!

(the two pieces of the valve are made of different materials)

 

[JJPage]

As you may know, a tight valve does not get the cooling time that a properly adjusted valve does.

If the tolerance is tighter, wouldn't the valve open sooner, allowing more open time... . or is this why a tight valve would run hotter, because of a longer exposure time, to passing exhaust gasses?



I understand some sled pullers are adjusting their exhaust valves to . 016 vs . 020, they are claiming quicker spoolup because of the quicker/sooner exhaust release. I would believe a tighter tolerance on the exhaust valves would result in lower cylinder temps, or am I totally off track here?

 

[Prairie Dog]

A tight valve doesn't spend enough time against the seat where it disipates its heat.

 

[Wingate]

A tight valve doesn't spend enough time against the seat where it disipates its heat.

exactly, the valve has no way to shed heat other than when it is sitting on the valve seat. If the valve is adjusted too tight, then it does not get the proper amount of cooling time.

Spending too much time at beyond max safe EGT causes the valves to recess, which will tighten the valve clearances. You can quickly use up several thousandths of clearance in recession. Thats where most valve issues start, the engine ends up running with dimished valve clearances which causes more heat and wear. It either gets found and corrected with a valve clearance check, or ends up running to failure and costing a sack full of $$$$. .

I have considered performing a valve recession check on mine, if it weren't such a P. I. T. A. to get the valve cover off, I probably would have already.

 

[Wingate]

I understand some sled pullers are adjusting their exhaust valves to . 016 vs . 020, they are claiming quicker spoolup because of the quicker/sooner exhaust release. I would believe a tighter tolerance on the exhaust valves would result in lower cylinder temps, or am I totally off track here?

If there is significant performance gain to be had by doing this, i'm sure that will take full advantage of it.

Some things that come to mind though... .

If these are highly modded sled engines, they are probably not factory production line multi-piece valves. I would think that they would be one piece, stainless, "tuliped" backcut, with multiple seat angles.

These guys are probably checking valve recession every race weekend and resetting valve clearances between race rounds.

These engines are probably torn down on a scheduled basis for inspection/repair.

This has been being done with race engines for years (gas, alcohol, diesel. . etc. . ) Basically, if the $$$$ or pride is worth it to you, you can lean on parts harder as long as you keep an eye on how quickly they are wearing. .

 

[JJPage]

A tight valve doesn't spend enough time against the seat where it disipates its heat.

exactly, the valve has no way to shed heat other than when it is sitting on the valve seat. If the valve is adjusted too tight, then it does not get the proper amount of cooling time.

Spending too much time at beyond max safe EGT causes the valves to recess, which will tighten the valve clearances. You can quickly use up several thousandths of clearance in recession. Thats where most valve issues start, the engine ends up running with dimished valve clearances which causes more heat and wear. It either gets found and corrected with a valve clearance check, or ends up running to failure and costing a sack full of $$$$. .

I have considered performing a valve recession check on mine, if it weren't such a P. I. T. A. to get the valve cover off, I probably would have already.

All makes sense, Thanks Guys!



My idea of setting my exhaust valves at . 016 next go around, is not going to happen. You both most likely saved me some grief, especially since 03's are already prone to valve seat issues.

 

[rscurtis]

The valve sheared off right at the top of the taper where the stem starts. I found the base of the valve in the turbo, and from what was left of it I didnt see any signs of it being burnt before hand.

How did the valve head manage to get out of the cylinder? It should be too large to fit through the seat.

 

[Wingate]

How did the valve head manage to get out of the cylinder? It should be too large to fit through the seat.

Nah... not after that piston whips on it for a few minutes...

 

[MSicotte]

The valve head got pounded pretty hard, its was kinda rectangle shaped, partially bent over, and looked like the turbine spun on one edge of it for a while. I dont know how long the truck ran after the valve broke, but I was told by the customer that he did "rev it a little" to try and smooth it out, so... ... ... ... ... ... that being said, you can only imagine the damage to the surface of the cylinder head as well.

 

[MSicotte]

My big concern is my own truck. Its on 04 with 175k kilometers (just over 100k miles). I have had Formula 1 Diesel valve springs for about 80k (when I did the headgasket and studs). Is there anyway to find out if the valves are actually 1 piece or 2 piece? If there is a better quality valve, and I'm faced with the possibility of a catastrophic failure, then I need to plan to replace them now, rather than later.