Cm871 oil pressure issue after cam replacement

[wdm89]

Have a 871 that a cam and roller went bad on #5 hole. Replaced cam, rocker, oil cooler, and put rods and mains in. The rods and mains looked great and they said the cam bearings looked great also. (I didn't physically see those). My problem is when I brought it in the oil pressure was 38 down the road and 20-22 at idle. Now it is 14-18 and 30-35. Do you think I could have an oil pump issue? I was going to check pressure sensor and bypass valve but I don't see them being the reason since I didn't have problems before. Although I've seen weirder things before.

[Bengy88]

Were the bearings in each hole verified to be matching to the new ones? Do you know if the oil pump was shimmed properly? There are a lot of factors that were messed with here. It could be anything from wrong bearings installed to worn cam bearings or even a cracked rocker shaft from not being installed or removed properly.

[wdm89]

(01-17-2026 )Bengy88 Wrote:  Were the bearings in each hole verified to be matching to the new ones? Do you know if the oil pump was shimmed properly? There are a lot of factors that were messed with here. It could be anything from wrong bearings installed to worn cam bearings or even a cracked rocker shaft from not being installed or removed properly.

To my knowledge bearings are the same I did see those. As in oil pump I don't know if they even had it off just pickup tube. I'm starting to wonder if they should have put a new pump on it. This is weird but I did notice if you was pointing downhill the pressure might come up a couple psi at idle then back down. One other thing that was weird is a drove it 150 miles and when I parked it I checked the oil and it was just as clean as new and that has never happened. Maybe the new oil cooler helps that?

[Bengy88]

(01-17-2026 )wdm89 Wrote:  

(01-17-2026 )Bengy88 Wrote:  Were the bearings in each hole verified to be matching to the new ones? Do you know if the oil pump was shimmed properly? There are a lot of factors that were messed with here. It could be anything from wrong bearings installed to worn cam bearings or even a cracked rocker shaft from not being installed or removed properly.

To my knowledge bearings are the same I did see those. As in oil pump I don't know if they even had it off just pickup tube. I'm starting to wonder if they should have put a new pump on it. This is weird but I did notice if you was pointing downhill the pressure might come up a couple psi at idle then back down. One other thing that was weird is a drove it 150 miles and when I parked it I checked the oil and it was just as clean as new and that has never happened. Maybe the new oil cooler helps that?

You have to pull the oil pump to swap the number 1 main bearings, I’m just speculating here but if it’s slightly higher when the truck is down hill the pickup tubes could be sucking air and when you are down hill they are covered with oil. Just a thought and something you could check. These engines are notorious for low oil pressure but I’d be concerned having lower pressure after having the bearings changed

[wdm89]

(01-17-2026 )Bengy88 Wrote:  

(01-17-2026 )wdm89 Wrote:  

(01-17-2026 )Bengy88 Wrote:  Were the bearings in each hole verified to be matching to the new ones? Do you know if the oil pump was shimmed properly? There are a lot of factors that were messed with here. It could be anything from wrong bearings installed to worn cam bearings or even a cracked rocker shaft from not being installed or removed properly.

To my knowledge bearings are the same I did see those. As in oil pump I don't know if they even had it off just pickup tube. I'm starting to wonder if they should have put a new pump on it. This is weird but I did notice if you was pointing downhill the pressure might come up a couple psi at idle then back down. One other thing that was weird is a drove it 150 miles and when I parked it I checked the oil and it was just as clean as new and that has never happened. Maybe the new oil cooler helps that?

You have to pull the oil pump to swap the number 1 main bearings, I’m just speculating here but if it’s slightly higher when the truck is down hill the pickup tubes could be sucking air and when you are down hill they are covered with oil. Just a thought and something you could check. These engines are notorious for low oil pressure but I’d be concerned having lower pressure after having the bearings changed

That's what I'm thinking..they are saying it's within spec which is fine but it was higher before all this work with the bad cam. I'm going to have them put an oil pump on it and hopefully that will seal the pickup tube back up if it is sucking air. Thank you

[Rawze]

(01-17-2026 )wdm89 Wrote:  Have a 871 that a cam and roller went bad on #5 hole. Replaced cam, rocker, oil cooler, and put rods and mains in. The rods and mains looked great and they said the cam bearings looked great also. (I didn't physically see those). My problem is when I brought it in the oil pressure was 38 down the road and 20-22 at idle. Now it is 14-18 and 30-35. Do you think I could have an oil pump issue? I was going to check pressure sensor and bypass valve but I don't see them being the reason since I didn't have problems before. Although I've seen weirder things before.

The oil pressure should be well above 18 psi at idle (typically 24+), and above 34-36~ish+ while going down the road. ... maybe the numbers your saying only when oil gets real hot, above 240+.

- If I had to guess it, it sounds like something is wrong, most likely internally hemorrhaging oil somewhere.

A). Pull the valve cover and crank it up. - See if the overhead rocker shafts are spewing oil somewhere... maybe around a retaining bolt head, etc.

B). Bengy88 was asking you about the rod/main bearings... I don't think you picked up on the gravity of what he was getting at. - read this related article about ISX's in general, as it is VERY IMPORTANT INFO THAT A LOT OF SHOPS HAVE FORGOTTEN ABOUT OR DO NOT KNOW!!! ...
info: https://rawze.com/forums/showthread.php?...5#pid32065

If after-garbage bearings were used... they almost always have issues with clearances.. so plastiguaging EVERY SINGLE ONE is necessary... which is not worth the extra efforts or work vs. oem.. and such, oem replacement bearings should never be used. - OEM OLY BEARINGS!!!.. and VERIFY ALL PART#'s FOR EACH LOBE INDIVIDUALLY AS THE OLD ONES COME OUT ... results in never having an issues with oil pressure losses or wrong clearances after inframe, etc.

In your case, at this point ,... If it is not the top-end hemorrhaging oil due to improper install of the rocker shafts ...

and since it is not likely that anyone bothered to save all the old bearings and labeled then individually... to go back and check them all individually again ...

Someone will most likely have to now go back and pull the bottom end all apart again and plasitguage all the rod/main bearings to ensure one (or more) lobes do not require an alt size.

and btw: changing the number of shimms at the oil pump mounting flange (where it bolts up) does not change the oil pressure. It only serves to set gear train clearances and reduce gear-train whine. - sucking air at the pick-up tube however can cause pressure issues,.. but will also rapidly destroy the engine due to aerated oil... which needs to be taken VERY seriously if that it what is suspect.

(the beer talkin')...
My bets are on a hemorrhaging top-end, near one of the rocker shaft retaining bolts (at cyl 1 or 6) ... or some idiot using a non-oem bearing kit. - Could also be a single crank lobe that requires an alt-size bearing, and that fact was missed.

[wdm89]

(01-18-2026 )Rawze Wrote:  

(01-17-2026 )wdm89 Wrote:  Have a 871 that a cam and roller went bad on #5 hole. Replaced cam, rocker, oil cooler, and put rods and mains in. The rods and mains looked great and they said the cam bearings looked great also. (I didn't physically see those). My problem is when I brought it in the oil pressure was 38 down the road and 20-22 at idle. Now it is 14-18 and 30-35. Do you think I could have an oil pump issue? I was going to check pressure sensor and bypass valve but I don't see them being the reason since I didn't have problems before. Although I've seen weirder things before.

The oil pressure should be well above 18 psi at idle (typically 24+), and above 34-36~ish+ while going down the road. ... maybe the numbers your saying only when oil gets real hot, above 240+.

- If I had to guess it, it sounds like something is wrong, most likely internally hemorrhaging oil somewhere.

A). Pull the valve cover and crank it up. - See if the overhead rocker shafts are spewing oil somewhere... maybe around a retaining bolt head, etc.

B). Bengy88 was asking you about the rod/main bearings... I don't think you picked up on the gravity of what he was getting at. - read this related article about ISX's in general, as it is VERY IMPORTANT INFO THAT A LOT OF SHOPS HAVE FORGOTTEN ABOUT OR DO NOT KNOW!!! ...
info: https://rawze.com/forums/showthread.php?...5#pid32065

If after-garbage bearings were used... they almost always have issues with clearances.. so plastiguaging EVERY SINGLE ONE is necessary... which is not worth the extra efforts or work vs. oem.. and such, oem replacement bearings should never be used. - OEM OLY BEARINGS!!!.. and VERIFY ALL PART#'s FOR EACH LOBE INDIVIDUALLY AS THE OLD ONES COME OUT ... results in never having an issues with oil pressure losses or wrong clearances after inframe, etc.

In your case, at this point ,... If it is not the top-end hemorrhaging oil due to improper install of the rocker shafts ...

and since it is not likely that anyone bothered to save all the old bearings and labeled then individually... to go back and check them all individually again ...

Someone will most likely have to now go back and pull the bottom end all apart again and plasitguage all the rod/main bearings to ensure one (or more) lobes do not require an alt size.

and btw: changing the number of shimms at the oil pump mounting flange (where it bolts up) does not change the oil pressure. It only serves to set gear train clearances and reduce gear-train whine. - sucking air at the pick-up tube however can cause pressure issues,.. but will also rapidly destroy the engine due to aerated oil... which needs to be taken VERY seriously if that it what is suspect.

(the beer talkin')...
My bets are on a hemorrhaging top-end, near one of the rocker shaft retaining bolts (at cyl 1 or 6) ... or some idiot using a non-oem bearing kit. - Could also be a single crank lobe that requires an alt-size bearing, and that fact was missed.

Thank you rawze for chiming in. I was hoping you would. Those numbers was from engine 180 and oil 200-215. Temp outside was 30 degrees not like it was hot out so its to low plus i didnt have problems even before when the cam was bad. I do know they used oem from cummins on everything. But I don't understand the difference between oem replacement and oem oly I guess? They had the bearings at one time but I doubt they do now. I know something is wrong and that's why it's going back Monday to the shop with advice from what you said. I just got the typical stealership reply of well its in spec just watch it