Cam bearing bore too large
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Teching In
Joined: Apr 2023
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Cam bearing bore too large Hello!
I have a question that I can’t find an answer to. I’ve been searching for a couple of hours without success.
I’m currently installing new cam bearings in my 2005 5.3L iron block. I had a set of EngineTech bearings lying around, so I installed them. However, the oil clearance between the cam and the bearings was much larger than I want — about 0.0075" in bearings 1 and 5.
Because of that, I ordered Dura-Bond CH25 bearings and tried those instead, but I got the exact same result.
I removed bearing #1 and measured the cam bore, and it measures 2.350", while the specification says it should be 2.346–2.348". None of the bearings have spun, so that’s not the issue. I can also clearly see the factory machining marks, so I don’t think anyone has modified the block before.
At this point I’m getting pretty tired of this engine because it has only given me problems. Do any of you have suggestions for what I should do next? I’m almost at the point where I’m considering just buying an aluminum 5.3 block instead.
I know Dura-Bond makes the CH25X3, which is .003" smaller, but even with those I would still end up around .0045" clearance, and I’d really like to be in the .002–.003" range.
Thanks, and have a good day everyone!
I have a question that I can’t find an answer to. I’ve been searching for a couple of hours without success.
I’m currently installing new cam bearings in my 2005 5.3L iron block. I had a set of EngineTech bearings lying around, so I installed them. However, the oil clearance between the cam and the bearings was much larger than I want — about 0.0075" in bearings 1 and 5.
Because of that, I ordered Dura-Bond CH25 bearings and tried those instead, but I got the exact same result.
I removed bearing #1 and measured the cam bore, and it measures 2.350", while the specification says it should be 2.346–2.348". None of the bearings have spun, so that’s not the issue. I can also clearly see the factory machining marks, so I don’t think anyone has modified the block before.
At this point I’m getting pretty tired of this engine because it has only given me problems. Do any of you have suggestions for what I should do next? I’m almost at the point where I’m considering just buying an aluminum 5.3 block instead.
I know Dura-Bond makes the CH25X3, which is .003" smaller, but even with those I would still end up around .0045" clearance, and I’d really like to be in the .002–.003" range.
Thanks, and have a good day everyone!
I would verify the mic is calibrated correctly. Although they usually aren't that far off. The best way to set up a bore gauge is with gauge blocks, which most of us don't have. However, I doubt very seriously your setup is off that much. What is puzzling to me is that you can still see the OEM machining witness marks. Many shops will help out home mechanics. You might want to find a local machine shop, buy a dozen doughnuts, and wander in and ask nicely if they'll set up your bore gauge with gauge blocks. They're dead nuts, and will tell you for sure the measurements are correct. Also, if you're unaware of this, it is best to have as little preload on the gauge as possible, especially on an aluminum block!! Meaning you don't want the gauge needle to rotate 2 times around to reach the desired range. Best of luck.
Thread Starter
Teching In
Joined: Apr 2023
Posts: 33
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I would verify the mic is calibrated correctly. Although they usually aren't that far off. The best way to set up a bore gauge is with gauge blocks, which most of us don't have. However, I doubt very seriously your setup is off that much. What is puzzling to me is that you can still see the OEM machining witness marks. Many shops will help out home mechanics. You might want to find a local machine shop, buy a dozen doughnuts, and wander in and ask nicely if they'll set up your bore gauge with gauge blocks. They're dead nuts, and will tell you for sure the measurements are correct. Also, if you're unaware of this, it is best to have as little preload on the gauge as possible, especially on an aluminum block!! Meaning you don't want the gauge needle to rotate 2 times around to reach the desired range. Best of luck.
but, my mic is infact calibrated, have blocks on my work that is tested and calibrated down to 0.001mm/ 0.00004in and I test my mic with them. The bore in the block is larger than the spec. No way around it. But what can I do?
yes i know it’s weird that I can see the machining marks and still be out of spec, but here you have a photo of it ( hard to get a good photo)
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Teching In
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At this point, though there may be steps you can take to save the block, you have to ask yourself if it's worth it at this point. Maybe there are more blocks like this out there than should be?? Which would explain why cam bearing issues are somewhat common
Last edited by grinder11; Mar 9, 2026 at 10:34 AM.
TECH Fanatic
Joined: Jul 2022
Posts: 1,042
Likes: 392
From: Alaska
Compare Durabond CHP-23 " chill-cast" 2nd design cam bearings vs
CH-23 regular cam bearings for $21 ... What difference ?
or CH-25 as mentioned earlier in thread?
( Hijack thread: I have a couple of LQ4 in tear down, one pushed out and mangled #2 cam bearing, lost most of oil pressure)
CH-23 regular cam bearings for $21 ... What difference ?
or CH-25 as mentioned earlier in thread?
( Hijack thread: I have a couple of LQ4 in tear down, one pushed out and mangled #2 cam bearing, lost most of oil pressure)
TECH Resident
Joined: Mar 2012
Posts: 861
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From: Texas
There was a guy on here about a year ago who had a similar problem. His machine shop said that they'd seen this before, and they sourced some bearings that worked.
Sorry I can't give you any more details than that.
Here's a question for all the smart guys out there: WHY IN THE EVERLOVING **** DID GM USE DIFFERENT SIZES OF CAM BEARINGS FOR THE SAME ENGINES?!
Sorry I can't give you any more details than that.
Here's a question for all the smart guys out there: WHY IN THE EVERLOVING **** DID GM USE DIFFERENT SIZES OF CAM BEARINGS FOR THE SAME ENGINES?!