Broken Pushrod... Now a big repair

Grumpy Bear · February 17, 2021

1 hour ago, newdude said:

What sounds like that happened to your engine is the solenoid in the VLOM failed on a cylinder and sent oil to the lifter when it wasn't supposed to. Then the solenoid returned to V8 function wrongly timed, causing the lifter to re-engage at the wrong moment (think compression stroke when the valves are closed), and thus bending the pushrod.

Solenoids operate on a signal from the ECM. This isn't random and the VLOM cannot choose a different time to open and close. What can happen and does it varnish slows the plunger which is NOT mechanically linked to the electromagnet delaying the point of minimum pressure required to move the pins or sludge in the screen limits volume to the same effect . Time is measured by the cam in degrees rotation thus slowing the pressure rise moves the place on the ramp the lifter pins move. Milliseconds matter. The solenoid can not choose a different pathway in the VLOM saying think I'll go to cylinder so-and-so instead. The solenoid can not choose a different point of time to accept its signal. They replace a VLOM because there is a screen in each pathway to the solenoid that is not serviceable or the solenoids themselves fail to open period. In which case nothing happens. At least nothing bad. Tosses a code.

DENALIHD66 · February 17, 2021

2 hours ago, newdude said:

VLOM. Valve Lifter Oil Manifold assembly. Its the center valley plate in the engine. The plate consists of oiling passages to 4 solenoids, the oil pressure sensor and filter screen and wiring. ECM controls the VLOM and commands the solenoids to open and close oil flow to cylinders 1, 4, 6 and 7, the AFM cylinders.

When in 4 cylinder mode, oil is supplied by the VLOM solenoids to each of the AFM lifters. The oil pressure applies to the locking pin in the lifter, causing the pin to unlock letting the lifter "collapse" and deactivate the cylinder. When returning to V8 mode, the solenoids close oil pressure to the lifters, allowing the pins to lock back in place and the 4 AFM cylinders to begin functioning normally again.

What sounds like that happened to your engine is the solenoid in the VLOM failed on a cylinder and sent oil to the lifter when it wasn't supposed to. Then the solenoid returned to V8 function wrongly timed, causing the lifter to re-engage at the wrong moment (think compression stroke when the valves are closed), and thus bending the pushrod.

Not the first time I've seen this at work. Seen a couple get lucky with just a new pushrod, others get torn down for AFM lifters, a VLOM and pushrod. Just had a 5.3 two weeks ago in for a miss. Tech found a bent rod on #4.

GM LS Lifter Issue, Melling JB-7011 Tech Tips - YouTube

I guess the part I don't quite understand is that even though I have a tune with AFM disabled, there is still a mechanical piece to the AFM that is still functioning? Because your theory indicates it's when it switched back to V8 mode, but if its always in V8 mode, wouldn't there have been something else going on?

DENALIHD66 · February 17, 2021

Welp... I am having them perform the TSB for the tranny fluid update. The same TSB I took it in under warranty and they "couldn't replicate the issue" and wouldn't do it. So now I'm paying for it. So fed up with how clunky this transmission has been since day 1 I just said the hell with it. If it helps even a little ...

Grumpy Bear · February 17, 2021

1 minute ago, DENALIHD66 said:

I guess the part I don't quite understand is that even though I have a tune with AFM disabled, there is still a mechanical piece to the AFM that is still functioning? Because your theory indicates it's when it switched back to V8 mode, but if its always in V8 mode, wouldn't there have been something else going on?

No, there are other things that can break a pushrod. Like a valve kissing a piston (over rev). A broken valve spring. No mention was made of such.

For it to make noise, which is has for quite some time preceding the 'failure' it was already mechanically compromised. It is excess clearance that makes the noise and/or a lack of oil. It had been loose or dry for some time then one day just finished the job. Hydraulic lifters do have some preload and when it runs out (wear, abuse)...tick tick tick. Eventually BOOM.

The worrisome thing here is the time between the 'noise' the 'disable' and the failure. It was hurt long before the 'straw that broke the camels back". And then there is this...they replace 8 damaged pushrods.

Did the replace the camshaft?

Grumpy Bear · February 17, 2021

4 minutes ago, DENALIHD66 said:

Welp... I am having them perform the TSB for the tranny fluid update. The same TSB I took it in under warranty and they "couldn't replicate the issue" and wouldn't do it. So now I'm paying for it. So fed up with how clunky this transmission has been since day 1 I just said the hell with it. If it helps even a little ...

How many miles are on this truck? Should have asked that to begin with.

DENALIHD66 · February 17, 2021

21 minutes ago, Grumpy Bear said:

No, there are other things that can break a pushrod. Like a valve kissing a piston (over rev). A broken valve spring. No mention was made of such.

For it to make noise, which is has for quite some time preceding the 'failure' it was already mechanically compromised. It is excess clearance that makes the noise and/or a lack of oil. It had been loose or dry for some time then one day just finished the job. Hydraulic lifters do have some preload and when it runs out (wear, abuse)...tick tick tick. Eventually BOOM.

The worrisome thing here is the time between the 'noise' the 'disable' and the failure. It was hurt long before the 'straw that broke the camels back". And then there is this...they replace 8 damaged pushrods.

Did the replace the camshaft?

No. Everything else was fine. 8 rods, manifold, gaskets. I will know Friday when I pick it up if it sounds better

PPK · February 17, 2021

Question Denali HD66 - Is you engine New York sourced or Mexico?

JimCost2014 · February 17, 2021

1 hour ago, DENALIHD66 said:

No. Everything else was fine. 8 rods, manifold, gaskets. I will know Friday when I pick it up if it sounds better

Sounds like you were pretty lucky.

When the pushrod broke on my 16 in cylinder #4, a piece of it made it's way into the block. The cylinder wall was so scored in the two miles I drove home, that they replaced the whole engine.

Edited February 17, 2021 by JimCost2014

DENALIHD66 · February 18, 2021

Truck build says Mexico, however I'm not sure how I check the build location for the engine separately?

I don't know how "lucky" I am since I'm paying for the repairs 7 months post-powertrain warranty. Sounds like you would have at least been covered under warranty for the engine replacement?

Grumpy Bear · February 18, 2021

How many miles do you have on this truck? Curious.

Edited February 18, 2021 by Grumpy Bear

newdude · February 18, 2021

17 hours ago, DENALIHD66 said:

I guess the part I don't quite understand is that even though I have a tune with AFM disabled, there is still a mechanical piece to the AFM that is still functioning? Because your theory indicates it's when it switched back to V8 mode, but if its always in V8 mode, wouldn't there have been something else going on?

16 hours ago, Grumpy Bear said:

No, there are other things that can break a pushrod. Like a valve kissing a piston (over rev). A broken valve spring. No mention was made of such.

For it to make noise, which is has for quite some time preceding the 'failure' it was already mechanically compromised. It is excess clearance that makes the noise and/or a lack of oil. It had been loose or dry for some time then one day just finished the job. Hydraulic lifters do have some preload and when it runs out (wear, abuse)...tick tick tick. Eventually BOOM.

The worrisome thing here is the time between the 'noise' the 'disable' and the failure. It was hurt long before the 'straw that broke the camels back". And then there is this...they replace 8 damaged pushrods.

Did the replace the camshaft?

I'll be honest I didn't even know there was screens in the VLOM besides the one under the pressure sensor. Learn something new every day I guess lol.

Being that's the case, even with AFM turned off, oil still flows through the VLOM and I believe also bleed off from the lifters themselves normally can travel into the VLOM towers in the valley. If a VLOM screen is plugged, it seems possible that any oil in the passages to the lifters, along with the screen restriction, could see an increase in oil pressure to the lock pin and release it. 22psi is the minimum unlock pressure needed for these lifters. Or maybe I'm thinking of this wrong.

In my mind, however, these scenarios seem to fortify that the OEM's drain intervals are...optimistic. And any long drain interval is potentially over time asking for trouble. High quality oils and filters are a must for anything beyond 4000mi it seems.

Edited February 18, 2021 by newdude

Grumpy Bear · February 18, 2021

1 minute ago, newdude said:

I'll be honest I didn't even know there was screens in the VLOM besides the one under the pressure sensor.

High quality oils and filters are a must for anything beyond 4000mi it seems.

I wouldn't have know it either if not for a YouTube video of one being taken apart.

I doubt you're old enough to have worked on a Ford "Y" block. The passage to the rocker gear was a small drilling in the casing. Guys that did not change oil often could have issues with that galley plugging with sludge even if the remainder of the motor was clean enough to eat off of. There was a kit for an external oiler made for this issue and rebuilders today, even with todays oils now internally plumb the rockers to prevent that issue.

Now there were guys, such as my father and a few uncles that changed oil every 1,500-2,000 that never had an issue with this. Used Phillips Trop Artic, a high detergent. (also a no-no) That was about half that the local Ford garage was recommending at the time.

I remember dad shaking his head when garages were telling people they were wasting there money and should go 3,000 miles. Dad's first car was a 29 A. Oil change every weekend. 2K took him forever to get use to. :crackup:

As long as there have been motors people have tired to skimp on the maintenance and it has never worked out well.

DENALIHD66 · February 18, 2021

Picked it up today. Transmission was semi-warmed up and shifted smoothly, no bumping sensation when coming to a stop and no clunky shifts. True test will be the next time I cold start it. No more ticking noise, just that minute ticking coming from the alternator pulley or something. Wasn't cheap but they replaced rods, manifold, and 8 lifters. Fresh oil now of course too. Hoping its a new truck with another 100k left in it.