Ram Cummins inline 6 oil cap oddity

[Hohn]

I don't disagree. Which is why post #5, which echos the consensus on the street because of some silly TSB that blamed 15w-40, doesn't capture the multiple issues going on in the 2019+ valvetrain failures.

We know that contact stresses between a roller lifter and a cam are, all other things equal, higher than those between a flat tappet and a cam. It's as simple as round to round contact vs round to flat, and the changing contact angle as the roller enters/exits a lobe.

Roller followers have line contact on the cam. You have no hydrodynamic wedge between roller and cam because by design the roller and cam have no real oil wedge. The wedge, if it existed, would prevent the roller from actually rolling and you'd have roller skidding. Which leads to rapid component failure. Roller fail for similar reasons as needle bearings-- too much stress concentrated on too little area.

A sliding tappet doesn't really "slide" as many people think of it because the "flat" part isn't flat (it's radiused on a large radius) and it spins across the cam surface, crab walking like you might do with a 55gal drum to get it across your shop floor without having to life it or slide it.

 

[johnmyster]

Roller followers have line contact on the cam. You have no hydrodynamic wedge between roller and cam because by design the roller and cam have no real oil wedge. The wedge, if it existed, would prevent the roller from actually rolling and you'd have roller skidding. Which leads to rapid component failure. Roller fail for similar reasons as needle bearings-- too much stress concentrated on too little area.

A sliding tappet doesn't really "slide" as many people think of it because the "flat" part isn't flat (it's radiused on a large radius) and it spins across the cam surface, crab walking like you might do with a 55gal drum to get it across your shop floor without having to life it or slide it.

Roller followers also get side loaded by the cam lobe, and anytime you need to load at an angle you increase the force necessary normal to the surfaces.

All this just means to me that the system needs to be designed to work as a flat tappet or a roller lifter system and unless there's margin in the material properties you can't make a substitution.

It's alleged that the issues in the 6.7 CGI motors is that the lifters/rollers aren't being held perfectly square to the lobe. Thus, they rock and slide, chewing their way into one another.

 

[OLEJOE]

Roller followers also get side loaded by the cam lobe, and anytime you need to load at an angle you increase the force necessary normal to the surfaces.

All this just means to me that the system needs to be designed to work as a flat tappet or a roller lifter system and unless there's margin in the material properties you can't make a substitution.

It's alleged that the issues in the 6.7 CGI motors is that the lifters/rollers aren't being held perfectly square to the lobe. Thus, they rock and slide, chewing their way into one another.

Stelantis just came out with a TSB for a corrective action.
“If customers come in complaining about ticking noises at idle, then install an oil additive and let idle for 15 minutes to distribute the additive.”

 

[Bighorn2500]

Stelantis just came out with a TSB for a corrective action.
“If customers come in complaining about ticking noises at idle, then install an oil additive and let idle for 15 minutes to distribute the additive.”

View attachment 273650

Is that bandaid allowed ever time someone changes there oil for the life of ownership?

 

[OLEJOE]

Is that bandaid allowed ever time someone changes there oil for the life of ownership?

I’m guessing yes because it says in there to wait if the vehicle is going to be serviced. I thought at first it was a joke but it is on NHTSA.

 

[Jetronic]

Boron nitride additive. Isn't that what LM ceratec is?

 

[Hohn]

I've yet to find anyone in my professional acquaintance who knows anything about this stuff. Then again, the Chrysler work is sort of quarantined from the rest of the company.

 

[fantastic]

Right, but why not a

Winter: 5w-30
Summer: 10w-30

recommendation? Why the switch to a 40 in the winter?

There are not very many commonly available 5w-30 CK-4 style oils on the market so that would be a tough recommendation.

Let me guess, you aren't familiar with CK-4 grades commonly available in the US market?

The sun and the snowflake also don't mean summer and winter. If you open the manual there's a temperature threshold. Lots of southern states qualify for sun oil grade in the winter, even if there's snow on the ground.

The most sense wouldn't be that southern states get warmer weather, so therefore they spec a 40 grade in the winter. I'd be more inclined to say fuel dilution would be the main reason to spec a 40 grade in winter over a 30. The 5w-40 is best of both worlds in the winter. Although, I'd just run a 5w-40 all year long. Southern folks can just use the recommended 10w-30 if they wanted to as well.

 

[OLEJOE]

There are not very many commonly available 5w-30 CK-4 style oils on the market so that would be a tough recommendation.

The most sense wouldn't be that southern states get warmer weather, so therefore they spec a 40 grade in the winter. I'd be more inclined to say fuel dilution would be the main reason to spec a 40 grade in winter over a 30. The 5w-40 is best of both worlds in the winter. Although, I'd just run a 5w-40 all year long. Southern folks can just use the recommended 10w-30 if they wanted to as well.

I think the 5-40 is the best of both worlds, north, south, hot or cold. Wish I could run 15-40 even if it had to be synthetic. Truck does more hard work and towing during the summer months in areas where it’s 100+ degrees on a regular basis. Still, it’s doing good on the 5-40 and maybe that helps with the dry starts from sitting and not being used as much in the winter months. I would really like to know if the “Secret Sauce” raises the viscosity of the oil.