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Strange oil pressure after I frame - Nater1977 - 12-13-2024
So I Finished an in frame today 2008 CM871 fired it up and watched oil pressure it was at 60 Psi less Then ten seconds and dropped to 28. I turned it off checked everything over and restart same exact pressure drop in less that ten seconds. Maybe this is ok, but it is weird to me.
Updated the oil bypass and i did add dimes to the oil pump, Not a new pump has shims in it.
Any ideas? Or is this normal. Maybe the pump hitting the high pressure limit and dropping pressure?
RE: Strange oil pressure after I frame - Rawze - 12-14-2024
maybe regulator in pump is sticky?.
also 60 psi is too high. - too many shims in regulator?.
=== maybe put a new pump on it .. not shimmed... and see what the pressures are.
also, is all parts used internally all 100% oem parts?... or anything after-market?.
and ... did someone verify, individually, all clam-shell part#'s and thicknesses on each of the the rods and mains individually, as they came out, to ensure none of them are of alternate size?.
ref...
Rawze Wrote:* When pulling the rod and main bearings --- MEASURE EVERY ONE OF THEM INDIVIDUALLY!!! -- cummins sometimes uses alternate sizes in engines,.. especially the older 870's and 871's... and you can have one size bearings in the first 2 holes, and a totally different size in the next .... IT IS COMPLETELY RANDOM!. The majority of engines have the standard set size bearings,.. but MANY of them do not!. Put the same size back in that came out for each cylinder and block location.
more info: http://rawze.com/forums/showthread.php?tid=3724&pid=32065#pid32065
RE: Strange oil pressure after I frame - Nater1977 - 12-14-2024
Ok I will check and see if the bearings are the same
I did find today my Jake brake won’t hold in the detents going to order some shafts and springs ect. They are not OEM they are Mahle which I have had excellent experience with them in automotive. BUT here we go. It does run at 40 around 1400 and it is like 28 T idle but this is with the dash gauge I really need to use a mechanical gauge.
RE: Strange oil pressure after I frame - tree98 - 12-14-2024
(12-14-2024 )Nater1977 Wrote: Ok I will check and see if the bearings are the same
it's to late now. You have to check each part number as you take them out. Now you will have to plasti-gauge the new ones you put in to see if they are the right size.
If you still have the old ones you could check them to see if you got lucky and all are the same part number. If they aren't, it's time to start plasti-gauging.
RE: Strange oil pressure after I frame - Nater1977 - 12-14-2024
Ya that’s what I figured
RE: Strange oil pressure after I frame - Nater1977 - 12-15-2024
So I got to my shop this morning went through all the bearings thank gosh they’re all standard that rules that issue out.
RE: Strange oil pressure after I frame - Rawze - 12-15-2024
(12-15-2024 )Nater1977 Wrote: So I got to my shop this morning went through all the bearings thank gosh they’re all standard that rules that issue out.
I assume you meant the ones that came out... that's good. Having an alternate bearing in a CM871 is about a 15% chance or so. Less for newer engines. but still not a guarantee.
mahle (germany) overhaul components are fine. Athough personally, I would have measured all of them, each in several places, with dial indicator before putting them in .. Mahle is the supplier for cummins themselves.
BTW: 28 psi is normal pressures at idle ONLY AFTER THE OIL HAS WARMED UP FULLY (215+F), but not so much so while the engine/oil is still at room temp. - What are the pressures with it fully warmed up, oil temp above 218+f?.
Are you sure you don't have a shimm upside down (or swapped from left to right side) between block and pump, at the oil pump?.
Also, 60-psi, I think is the blow-out safety-valve pressure at the top-left side of the oil filter housing. If the pump is making too much pressure due to someone adding shimms to its regulator incorrectly ... or due to a blockage of return oil (from the head, thru and behind the front gear cover), then this valve could be triggering, dropping pressure off after the valve opens, until you shut engine it off again and it resets.
RE: Strange oil pressure after I frame - Nater1977 - 12-16-2024
It sounds like to me the bypass valve is opening up like you’re saying and I did shim the oil pump spring I used 10 dimes, but maybe for some reason that’s why it’s too high. When I installed the pump I cut the one shim like you did, )that is a bad design) and then I put the shims right back in place.(the ones pump to block) Funny thing is yesterday when I was idling it. It was sitting right around 40 psi the whole time. It went up to 60 drop back down and went back up to 40. seems like the valve is bypassing and then closing like you are describing. It is a brand new valve I put in for the update And also, I discovered yesterday I have a seal leak between the motor and the transmission housing. So I’m gonna tackle that job as well this week. This truck is just new to me and I knew I had to do a rebuild when I bought it.
Yes, there is a quite a few little things odds and ends I have to take care of before I start going down a rabbit hole.
RE: Strange oil pressure after I frame - Yauchout - 12-16-2024
(12-16-2024 )Nater1977 Wrote: It sounds like to me the bypass valve is opening up like you’re saying and I did shim the oil pump spring I used 10 dimes, but maybe for some reason that’s why it’s too high. When I installed the pump I cut the one shim like you did, )that is a bad design) and then I put the shims right back in place.(the ones pump to block) Funny thing is yesterday when I was idling it. It was sitting right around 40 psi the whole time. It went up to 60 drop back down and went back up to 40. seems like the valve is bypassing and then closing like you are describing. It is a brand new valve I put in for the update And also, I discovered yesterday I have a seal leak between the motor and the transmission housing. So I’m gonna tackle that job as well this week. This truck is just new to me and I knew I had to do a rebuild when I bought it.
Yes, there is a quite a few little things odds and ends I have to take care of before I start going down a rabbit hole.
Just a thought i could be wrong but you used dimes on a new style pump they may be two small and when they sit in the plunger they could be sideways being higher one one side then thew other on the nub that is in the center causing higher spring pressure most people use 6 pennies on a new style pump although i wouldn't recommend pennies on a new style pump after my experience
https://rawze.com/forums/showthread.php?tid=9601