Oil pressure dropping after rebuild
 

Hey guys, hoping I can get some help here as this is my first engine rebuild and I'm kinda stuck on what to do.
I have a 1971 C-10 that I put a 5.3 LM7 with a turbo in my truck and I recently rebuilt the motor. It has all new bearings, new cam, valve springs, ls9 head gaskets, and rod bolts.
Ive already rebuilt this motor once before and I'm having the same exact issue as I had before so clearly what I'm doing isn't working.
When I first started the motor, I had good oil pressure (not sure what is was exactly because my gauge in the truck just says L to H) but it was most of the way up. But as I let the motor idle and drove it a little bit, oil pressure was steadily dropping at idle as well as at rpm. It has gotten so low now that I can hear the lifters clattering so I know something is definitely wrong and I will be pull the motor to investigate.
What should I be looking for? I am pretty sure I installed the pickup tube correctly but have no idea if the barbell is in the rear of the motor. I never took it out but I have no idea if it's something that could fall out or if it is something that needs to be removed to put the cam bearings in.
Any help would be appreciated because I don't know what to do next since I thought I did everything correctly.

Thanks.

Re: Oil pressure dropping after rebuild
 

Do you have the correct O-ring for the oil pump? There is a blue and a red and it is specific to the pump. Is it the factory oil pan?

Re: Oil pressure dropping after rebuild
 

I have the blue one on it. I resused the one the motor originally came with you

Re: Oil pressure dropping after rebuild
 

I'd start there, put a new one in it. Too many problems from using the wrong one or an old one.

Re: Oil pressure dropping after rebuild
 

The rear galley plug "barbell" is accessible with the rear cover removed. They would have had this cover off during cam bearing replacement. There is no reason to remove the barbell for cam bearing replacement. If you added turbo to this engine, the port for turbo oil, oil filter, and barbell are all in the same area. Errors in this area are usually an "all or none" as far as oil pressure goes. I would guess at oil pump/gasket before anything on the back end (but it is still a guess!).

Re: Oil pressure dropping after rebuild
 

if the barbell is missing, you should have basically 0 oil pressure at startup. It should not take a while for that to become evident

I haven't drained the oil yet but this morning I did check the dipstick and while I had the correct amount of oil there was some metal flakes within the oil. Does this point to damage already being done or is this something I should expect with a new motor? Not sure if that's an obvious question to ask but I'm very new and inexperienced to the engine building process and am trying to decide if pulling the whole motor is the best course of action or if I can get away with replacing the oil pump, pickup, pickup o ring and cam retainer plate without having to pull the whole motor.
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Re: Oil pressure dropping after rebuild
 

This should be obvious, but did you plastigage the rods and mains and make sure you're bearing clearances were correct? (I've screwed this up once - I assembled a motor that I'd had the crank turned undersize without checking the rod and main clearance because the machinist said he'd done it, and it had the wrong bearings - oil pressure at start, but noisy lifters as soon as it warmed up)

Best practice is to have the machine shop measure the installed bearing's diameter with a dial bore and the journal with a micrometer to arrive at a bearing clearance, then double check with plastigage when you assemble. Do you have a build sheet from the machinist?

Did you replace the oil pump, preferably with the higher flow one, during the rebuild? Did you use a new factory o-ring on the pickup? Did you thoroughly clean the screen on the pickup end?

The barbell's purpose is to divert oil through the filter after it leaves the pump so as not to have unfiltered oil going to the bearings and lifters. Leaving it out would let unfiltered oil into the bearings/lifters and cause failure down the road, but I'd think oil pressure would be incrementally higher without it since there's no pressure drop across the filter.

Re: Oil pressure dropping after rebuild
 

If I was sure the bearing clearances were good, (and had a build sheet and I'd plastigaged it to verity) I'd pull the pan and check the o-ring and pickup before I went to the trouble of pulling the engine. I wouldn't replace the pump unless you missed doing that at the rebuild.

I might cut open the oil filter and see how much bearing material is in there too (assuming the barbell wasn't left out and you were bypassing it anyway)

Re: Oil pressure dropping after rebuild
 

Over on LS1tech.com there's a post that says it the barbell is left out that the pump just dumps oil in the pan and you have no oil pressure.

https://ls1tech.com/forums/generatio...hematic-2.html

So like 71CADC10 says, you'd never see any oil pressure if this were the case.

There's also a galley plug under the front cover by the oil pump that has to be there. Did you have the cam bearings replaced? I've heard of cam bearings 'walking' out of the bore and dropping oil pressure but not actually seen one

Re: Oil pressure dropping after rebuild
 

I didn't get a spec sheet from the machine shop but did plastigauge the main and rod bearings and there were all within spec. I'll cut open the filter tonight to see what I find.

When you say that I should check the o-ring, what am I looking for? I think it was installed correctly but then again I'm not sure how to tell if it's in correctly or not.

I reused the oil pump, because I thought that since it worked before the rebuild it would work after, but I ordered a new one today to be safe.

When I install the oil pump, are there any special tricks to making sure it is on correctly, or do you just line it up so it slides on, the bolt it down.

I appreciate you taking the time to help walk me through this.

Re: Oil pressure dropping after rebuild
 

Here's how to install the pump - I've never clearances one like they show - I just put them on and run them

https://www.youtube.com/watch?v=TsC2EtNOOPE

And a bunch of others about installing pumps, o-rings and priming the system

https://www.youtube.com/watch?v=RNiOE4sRALA

https://www.youtube.com/watch?v=539ClWWJMl8

Here's how to take a filter apart. They make a tool to split them, but I usually do it this way

https://www.youtube.com/watch?v=7Lomj36QyZI

Re: Oil pressure dropping after rebuild
 

I usually fit the higher flow GM pump - it is a little cheaper than the Melling.

https://marylandspeed.com/gm-perform...30-p-4796.html

If I had any doubt about what oil pickup tube I had, I'd go to my GM dealer and buy the pickup and o-ring. I think the last time I bought one it was about $30 for the both of them

Re: Oil pressure dropping after rebuild
 

I've never primed one with an external pressure source like they show. I just make sure the gerotors in the pump are wet with oil when I assemble it, then crank the motor with the fuel pump fuse pulled and the plugs out till it makes oil pressure.

Re: Oil pressure dropping after rebuild
 

Thanks for the videos, I went ahead and ordered a new oil pump, pickup, o ring, and cam retainer plate.

I cut open the filter and found a few tiny pieces of metal. Is that something to be concerned about?

Also drained the oil and could not find any metal flakes when I ran my finger through it so maybe I just saw bubbles on the dipstick.

There was however metal on the drain plug

Re: Oil pressure dropping after rebuild
 

Now, I think I have some good news as to what my issue is, but maybe I am just seeing things that aren't actually there.

I tore the front timing cover off and got to the oil pump today. I couldn't look straight at the relief valve but I could get pictures and it looks to me like the valve is open.

Maybe someone who knows exactly what to look for could let me know if I'm right, or break the bad news that the valve is indeed closed.

Thanks

Re: Oil pressure dropping after rebuild
 

whoops here are the photos

Re: Oil pressure dropping after rebuild
 

I'd compare the old pump to the new pump when it arrives. It isn't unheard of to have a relief valve stick, but it isn't very common as far as I know.

It isn't unusual to find some metal swarf on the plug after running when it has been to a machine shop

If you are going to pull the pan for a new pickup tube, I would pull a bearing cap from the rod and main and take a look. Look at an oiling schematic and pick the bearing journal the furthest from the pump.

If the new pump. oring and pickup tube don't cure the problem, and you've verified all the galley plugs are where they are supposed to be , I'd start getting suspicious about cam bearings. Did you mention that the machine shop installed new cam bearings?

Here's an interesting post from LSTech...........look at post 12

https://ls1tech.com/forums/generatio...ure-epic-pursu

Re: Oil pressure dropping after rebuild
 

Thanks for the thread, at this point I am assuming that the cam bearings were installed correctly because of the fact that I had the same symptoms as before with low oil pressure and that was with the stock cam bearings. But who knows, maybe they are in wrong, and if a new pump and pickup doesn't fix it then that's where I will look next.

I am planing on pulling the cam out anyway to check out its condition since all that is left to take out is the rockers anyways.

Glad to here that the metal shavings aren't uncommon, makes me feel a little better about potentially being able to save the motor. Two rebuilds gets expensive and I'm not exactly anxious to do it for a 3rd time.

Re: Oil pressure dropping after rebuild
 

I wouldn't call metal like that 'nothing to worry about'...but it could be depending on where it came from. Is it left over from the last deal, or is it being created new..that's the puzzle.

if it was just debris that didn't get cleaned out - it may be ok... However the hydraulic lifters and that relief valve on the oil pump don't play well with debris like that shown.

I've built roughly 30 LS engines from the base up....and I'm not entirely sure what you have there for a rebuild. couple things that stick out...from the limited picture...block does not look like it was cleaned by a machine shop.

You say it had oil pressure problem before, if that was the case I would want the block thoroughly jet washed at a shop, after the cam bearings are removed...that is best way to get all debris out of the passages. It should be shiny and nice cast aluminum everywhere.
you have to remove the barbell deal and the front cup press in plug, to fully run brushes down that oil galley and get it clean. If that wasn't done a lot of left-over debris could be still on the loose.

orange paint on bolts 'inside' the engine is not great...you'll get flakes of paint loose. Use those painted bolts on the outer cover or the side bolts for the main caps, and use clean unpainted bolts on the oil pump and timing sprocket.

the metal shards like shown I've seen come from multiple ways:
- cam retainer plate...behind the cam. Some of them get a deep groove worn in
- I've had cam bearings walk out after newly installed. The block was a bit over size cam bore...just one hole...cam bearing went in without enough press fit. It walked out within a couple thousand miles...oil pressure dropped as soon as it uncovered the feed hole. It had a half moon shaped cutout in the side of the bearing, where the lifter in front of it was rubbing on it as it slowly walked into the lifter. Put a good bit of metal in the oil LOL. Aluminum expands a good bit more than cast iron...that was a hard lesson learned for me. I measure the 5 bearing bores now and if they are high end of spec, i use the green fluidweld stuff on the bearing when they are put in.
- cams and lifters start wearing you'll see sharp debris like that

Re: Oil pressure dropping after rebuild
 

Well, installed a new oil pump, oil pickup, and cam retainer plate on the motor today and was able to make oil pressure on the stand with just the starter. I wasn't able to make any oil pressure before with the old parts so I'm hoping that my oil pressure issue has been taken care of. Only time will tell

Re: Oil pressure dropping after rebuild
 

Long shot, but I chased an oil pressure problem on a motor this spring for a long time that turned out to be the aftermarket distributor wasn't entirely covering the galley port at the back of the block, so it would bleed pressure off there, but much more so when warm.

I doubt it's related to YOUR issue, just pointing out there are a lot of weird things that can be wrong besides bearing clearances.

Re: Oil pressure dropping after rebuild
 

His engine doesn't have a distributor, so he can cross that one off his list. lol

Re: Oil pressure dropping after rebuild
 

you can check the relief valve in the old pump easy, unscrew that allen plug on the bottom and the spring/valve will fall out. If the bore is scored or trash in there...would explain your issue if it was stuck

Re: Oil pressure dropping after rebuild
 

NEVER re use the pickup tube o-ring. I realized I capitalized never, but it really is that big of a deal. They can look great during the visual inspection, but age and a loss of pliability means it won't seal up correctly upon reinstallation.

For a $1.69 part it can sure cause a lot of frustration.