Cm871 oil pressure issue after cam replacement

[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.