LM7 Collapsed Lifter or Flat Lobe
Thread Starter
Staging Lane
Joined: Oct 2019
Posts: 57
Likes: 29
LM7 Collapsed Lifter or Flat Lobe Hello All,
I replaced my heads about two months ago because the engine was eating coolant. Turned out the dowel pins had sheared and the passenger side head had walked. Now I have an apparent miss and a persistent lifter tick, the truck sounds great but lacks power, it started as a normal tick and slowly has gotten more persistent and louder. You can hear the miss at 2k, but it isn't audible after that. The truck used to hold 40PSI at hot idle but ever since I did the oil change after the oil pressure sits at 35 and only rises up to 45 at 1500ish RPM this is with half a quart of gear oil, it sat at 30PSI at idle before (Gear oil is better for cams because of zinc, but don't do this if you care about your cats). The lifter tick and decreasing oil pressure makes me think its an oil supply issue but I have no experience with hydraulic lifters.
The truck ended up sitting with the heads off for three days underneath a tree, no rain and the block was in excellent shape for 250k miles. I'm worried that some leaf debris managed to get into the lifter oil feeds, I blew the lifter trays out with air but I never inspected checked them. I read here that blowing air through the push tubes can help with a collapsed lifter and I'm planning on doing so tomorrow but are there any other symptoms of a flat cam lobe compared to a collapsed lifter?
Thanks
I replaced my heads about two months ago because the engine was eating coolant. Turned out the dowel pins had sheared and the passenger side head had walked. Now I have an apparent miss and a persistent lifter tick, the truck sounds great but lacks power, it started as a normal tick and slowly has gotten more persistent and louder. You can hear the miss at 2k, but it isn't audible after that. The truck used to hold 40PSI at hot idle but ever since I did the oil change after the oil pressure sits at 35 and only rises up to 45 at 1500ish RPM this is with half a quart of gear oil, it sat at 30PSI at idle before (Gear oil is better for cams because of zinc, but don't do this if you care about your cats). The lifter tick and decreasing oil pressure makes me think its an oil supply issue but I have no experience with hydraulic lifters.
The truck ended up sitting with the heads off for three days underneath a tree, no rain and the block was in excellent shape for 250k miles. I'm worried that some leaf debris managed to get into the lifter oil feeds, I blew the lifter trays out with air but I never inspected checked them. I read here that blowing air through the push tubes can help with a collapsed lifter and I'm planning on doing so tomorrow but are there any other symptoms of a flat cam lobe compared to a collapsed lifter?
Thanks
Have you pulled the valve cover off to see if there is slop in that rocker?
I would also check to see how much lift that rocker has compared to the others.
I "would" think if the lifter isn't collapsed the rocker arm should have preload on it like the others. If it is collapsed there should be all sorts of slop when you are on the base circle of the cam.
I would also check to see how much lift that rocker has compared to the others.
I "would" think if the lifter isn't collapsed the rocker arm should have preload on it like the others. If it is collapsed there should be all sorts of slop when you are on the base circle of the cam.
Thread Starter
Staging Lane
Joined: Oct 2019
Posts: 57
Likes: 29
Have you pulled the valve cover off to see if there is slop in that rocker?
I would also check to see how much lift that rocker has compared to the others.
I "would" think if the lifter isn't collapsed the rocker arm should have preload on it like the others. If it is collapsed there should be all sorts of slop when you are on the base circle of the cam.
I would also check to see how much lift that rocker has compared to the others.
I "would" think if the lifter isn't collapsed the rocker arm should have preload on it like the others. If it is collapsed there should be all sorts of slop when you are on the base circle of the cam.
Last edited by BoredTruckOwner; Nov 8, 2019 at 08:58 PM.
TECH Resident
Joined: Mar 2012
Posts: 858
Likes: 402
From: Texas
I'm planning on doing that tommorow since I'll be replacing the manifold. That being said I could pull the valley cover since ill be in there anyways to see if I can see anything, going to get a mechanical gauge in there and confirm my oil pressure too. Would I be able to see the cam with a 9mm inspection camera with the valley cover off?
Take the valve covers off first, and follow the instructions that were described.
Thread Starter
Staging Lane
Joined: Oct 2019
Posts: 57
Likes: 29
Will do, ended up not doing it yesterday because my injector harness didn't come in as expected. I did however pull out the stethoscope and it sounds to me like it's one of the exhaust lifters on the drivers side. Weather permitting I'll pull the valve cover and update the thread, just wish I could find my darned IR thermometer.
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Joined: Jun 2016
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From: Central Cal.
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