Hey guys,

I just rebuilt my first engine for my 89 Iroc, and I have a feeling I may have done something wrong. I've been breaking it in, and the oil pressure seems really low. When I first ran it (with a bottle of thick GM EOS in it) the pressure seemed good. When it was cold, up around 50 pounds, and at idle around 30) But I changed the oil, put in 5w30, and drove a while, and when hot, the idle showed right below 15 lbs on the guage. So I thought maybe 5w30 was too thin, and put in 10w30, and a different oil filter. Not really any change. I thought that maybe the sender down by the oil filter was bad, so I changed it, no change. So then I hoped that the factory guage was bad, so I hooked up a kent moore digital pressure tester, and it showed even LOWER pressure at idle when hot. (like 6 lbs!) The engine will hold around 25-30 pounds at 2000 rpms, so I dont think ti can be a galley plug left out. Every time I changed the oil, I didnt spot any metal in it.

I checked all of my clearances when assembling the engine. My mains were between .002 and .003"; within factory specs. The rods were resized with arp bolts and had tighter clearance, around .001". I think that my clearances should be within spec, so I used a regular M55 pump. Standard pressure, Standard volume. I've read on corvette forums that the new M55 pump has been redesigned and is inferior to the old design.

I'm thinking I could try changing my pump with a high volume style. Do you think that could solve my problem, or are there other avenues to travel first?

Thanks for the help!!

 

Noone have any ideas?

 

Your main clearance is high for a brand new engine.

 

Yes, the mains are kind of loose. I rebuilt it, and it was still within specs according to the service manual. Would the fact that its loose warrant the use of a high volume pump? Would that alone explain the low oil pressure? If so, I will try using the higher volume pump.

 

The specs in the service manual are intended to be service limits for acceptable wear after a period of use, they're pretty large for a brand new engine. You could try a higher volume pump, but a better solution would be to use a set of .001 undersize bearings.

 

before you buy a new pump go to GM and get the high pressure relief spring 3848911 . Original for 70 Z-28 LT1 . It will raise your idle/running pressure .

 

No, changing the relief spring won't do a thing to increase idle oil pressure.

 

well, its not a "brand new" engine. I guess my title was misleading. This is actually its second rebuild. The car had a rebuilt engine in it when I bought it, and I ended up rebuilding it because it had poor compression on cylinder 7.

The crank is .010 under. Do they make a .009 undersize bearing?

 

.009 is oversize from .010... you'd want a .011 undersize bearing, and yes they do make them. If the journals have worn that much though, you might want the crank ground anyway.

 

hmm... the engine isnt coming back out of the car unless I have no other recourse. I don't expect it to run forever, just a few years of service would make me happy for my first engine.

I guess my next step if I dont want to take the engine out is to take the pan off, make sure I dont have any metal, and install a higher volume pump?

What kind of clearance should I have shot for instead of reading from the service manual?

 

Those clearances aren't totally awful, the engine will be fine with them for quite a while. A higher volume pump would help the oil pressure a bit, but GM says that 10 PSI per 1000 RPM is more than enough.

 

Thank you, that sounds like good advice.

Hopefully saturday I can swap out the pumps, and re-adjust my valves. The guy who I had do them for me probably did them a little loose, as they are a little noisy.

I will also be nervous until I inspect my pan to make sure I have no metal. As soon as I had low pressure, I thought I wiped a bearing. I have no knocks, however, and the car runs fine.

I read some bad things about the new design melling pumps, and I'm fairly certain thats whats in the engine now. I'll have more peace of mind if its gone.

Thanks again

 

Well, I think I may have another problem, not sure what yet.

I started working on the adjusting the valves after work. I did them while the engine running, and only got the drivers side finished. Adjusting them quieted them down except for cylinder 1's exhaust valve. I tried adjusting it several times, but when I hold a piece of heater hose to my ear, I can pinpoint noice at that rocker. I'm wonder if I have a lifter problem, as I reused my lifters thinking that since they were roller and the engine didnt make noise before the rebuild, that they were fine.

Reading some gm service procedures, one of the things to check for low oil pressure is for a possibly bad lifter. How much can a bad lifter affect oil pressure?

It would be great if I just needed to swap in some new lifters, but it probably wont be that simple.

any thoughts guy?

 

About the only way I could think a lifter would affect oil pressure would be if it was missing entirely.

I looked up the bearing clearances and my memory was off. You should be fine with .002 to .003 for the mains. You're still right around GM's 10 PSI per 1000 RPM though, so while I'd expect your oil pressure to be higher, it's not dangerously low.

 

Yea, I know I'm late but I was going to correct Apeiron on the clearances. I *thought* .0025 is the spec for the mains. I think the front and rear should be a tad wider than the rest IIRC.

.001" on the rods seems REALLY tight to me. I'd be worried about it seizing and spinning once you get the engine warmed up. I'm no pro engine builder, but that's something i'd look into if I were you. Maybe call an engine shop?

A high volume pump (pumping into the same volume of oil galleries) would indeed raise the pressure across the board, until it high the pressure relief spring of course. I used a higher pressure spring with a normal volume pump, just for comparison sake. This means that at higher RPM i'll get more pressure before it bypasses. I've got .0025 on the mains, and about the same on the rods I think (fuzzy memory, and that was with plastigauge anyway...). And with 10W30 dino oil I get 60+ on cold oil, down to 30psi on the nose once warmed up, at a 500-600RPM idle. Then up to 60+ as I bring it up to 2000RPM or so.

Roller lifters are usually fine to reuse. Do the quick easy check - move that rocker to another cylinder. Cylinder 1 exhaust, move it to Cyl 5 intake for example. Relash them both, and see where the sound is. If it's still at #1, then lifter/cam. Lets hope that's not the case

 

Once again, thanks for the advice.

Yes, I agree that the rods were a little tight, and was also afraid of spinning a bearing, but I didn't seem to. Its not knocking, I just have that tap in the valve train, which I've pretty much eliminated on the drivers side from relashing, all except for cylinder one exhaust.

I wonder if the front cam bearing could have a problem, and the sound is traveling up to the front rocker. I guess when I get the other valve cover off ,and I have noise in cylinder 2's intake rocker, that could be an issue.

One other thing I noticed was that when I took the noisey rocker off, where the ball meets it, it looked like it got a little warm. Darkly discolored. I wonder if it was adjusted too tightly, and caused this, or if it was like that before the head went together. It seems to be getting oil there. I guess I could take the pushrod out and blow through it to make sure there is no kind of blockage. I did take that pushrod and rolled it on a table to make sure it was straight. Looked like it to me.

My mains were a little larger. Most were in the mid .002" range, the rear one was slightly over .003" (the service manual says ok to .0035" is ok) and my front was right around .003". So I definitely do have some main clearance. I'm wondering if my problem with oil pressure lies in that rear bearing being clearanced somewhat high. If I can get all of this noise out of it, I'll feel good about the bearings, and maybe just change the pump out to a higher volume unit for some more pressure.

Any more suggestions, or thoughts would be great.

 

You SURE you put all 3 plugs in the front of the motor around the front cam journal? Nothing you said guarantees that you did.

There are about a billion things that can cause valve train noise. A bad rocker ball will certainly do it. If this is a stock rocker, throw it in the trash and jsut get another one; new ball and all. Take that cyl's intake rocker and move it to the exhaust, and put the new one on the intake.

Your clearances sound to me to be on the high side; I prefer to build a NEW motor in the .0015" - .002" kind of range on the mains, and .001" - .0015" on the rods. I also like 0W-20 motor oil... I guess I'm just weird or something. But IMO .001" is not too tight on the rods, if the engine spun freely while building. So if the measurements are accurate - i.e. done with test equipment such as a micrometer on the journals and a bore gauge on the bearings, and NOT Plastigage - then they should still be fine. They won't cause low oil pressure. But if you're giving us Plastigage numbers, they're worthless and cannot be believed. All that stuff is good for, is telling if you have the right bearings (i.e. you don't have .010" undersize bearings for a .020" undersize crank"). It's useless for determining actual bearing clearance within the "acceptable" range.

With the std volume std pressure pump and a new motor, you should see 25-30 psi at hot idle, and 35-40 hot cruising.

IMO you have a problem, and not enough info yet to figure out what it actually is. I don't recommend changing the oil pump, or otherwise indulging in several rounds of "maybe it's this, maybe it's that"; all that's good for is thinning your wallet.

 

I did not install the plugs, they were installed for me by my uncle, who is a machinist. He also checked my clearances for me, and said they were within spec. The numbers I'm giving are plastiguage numbers I took when assembling the engine.

Concerning the plugs, I am pretty certain all three were in it when I was working on the engine, however, I cant say with utter certainty. Mostly like 90 percent sure. He has been doing this for over 30 years, so I have faith in his abilities. However, everyone makes mistakes.

You don't want me to guess at things, but if you were me, what would you do first? I'm trying to avoid guessing, and I'm trying to make choices on very modest experience, thats why I'm looking to you guys.

Thanks

 

I think first thing, would be to check the plugs. I'm not going to accuse anybody of anything; but as you say, anybody can make a mistake, and having myself been guilty more than once of leaving something undone or half-done because the phone rang or something, it's a great place to start.

If they're all there, then the next thing would be to measure the crank journals with a micrometer, and measure the inner dia of the main bearing saddles either with a caliper or a bore gauge.

Since you're using Plastigage, nothing you think you know about your oil clearances can be trusted. If you're going to attempt to build motors, the VERY FIRST THING you need, even more important than a torque wrench (which itself is pretty important!!) is good measuring equipment. Go to Sears or Lowe's or something and check out what they have to offer, or try here or here.

 

I'm pretty certain my main journals should be good. They were measured by two machine shops. My uncles, and the shop that polished and balanced it. My uncle is coming to the garage after I get off work and listening to the valve train noise, I'll ask him about the plugs, and my clearances, although this was long enough ago, I doubt he'll remember.

If its an issue of clearance, I'd rather not take the engine out of the car, and take it all apart. If I could get by for a while, I'd just put in a higher volume pump to bring the pressure up. Do you think this would be acceptable for couple of years at the most? This wasnt an expensive build, and I could just work on another bottom end in the mean time and take my time. I really want to get this car on the road!

 

In the act of replacing the pump, you stand about a 20% chance of actually accomplishing something.

You will be doing approximately 90% of the labor of replacing the crankshaft, the HUGE MAJORITY of the labor being, pulling the motor out of the car and removing the pan.

Where if you replace the crank (or repair it) and the bearings, and maybe put a pump in it at the same time, your odds of fixing the problem approach 100%.

If you think you're going to "save" work by not pulling the motor, then the proportion gets even worse, because what SEEMS LIKE it will save labor, actually makes it MORE work. I'll spend the hour and a half pulling a motor and the 3 hours putting it back in so that I can flip it upside down and work on it in comfort and security ANY DAY before I'll face laying in a puddle of spilled fluids up under a car dripping funk and coolant and oil all over me and reaching all around a bunch of obstructions in every direction, while I'm trying to get the most precise part of a motor rebuild done right and get a pan to re-seal.

You do the math. I know it's not what you wanted to hear; but, not wanting to hear it, won't get your motor to work right. And hearing what you want to hear, won't get it to work right either.

 

Is a main clearance of .002 too tight?