The Stovebolt Site Forums The Shop Area Engine Shop Ruined fresh rebuild-oil pressure issue.

I finished installing the GMC 270 I've spent the last few months rebuilding. This is my first engine rebuild and I did every thing under the close watch of a mechanic friend of mine who has built and raced cars his whole life.

It has new rod and main bearings, rebuilt head, chrome piston rings, and new oil pump. the lower end had been rebuilt at some point and the cam and crank looked like new. In hind site I should have left it alone.

On Monday I primed the oil pump with a half inch drill and the shaft of an old dizzy. My wife was in the truck watching the oil gauge and said every time I ran the drill the pressure went up to 30 psi. My friend said that was good but now I wonder if it should have been closer to 60 psi. I had good oil flow to all the rockers.

Yesterday I checked engine and dizzy timing, valve lash, carb settings, etc. and fired the engine up. It was hard to keep running at first but with a little tweeking of the timing, choke, and idle, she ran and sounded good. I did notice what I thought might be a slight miss as I ran around the truck to get in and back out of the shop. I wanted it outside because the exhaust was a bit stiff in the small shop due to the chrome piston rings. As I was backing out I could feel that the engine ran kind of rough, like the "miss' was more pronounced. I glanced down at the oil gauge and it read -0-! I killed the engine.

When My friend showed up he accused me of not getting the dizzy seated all the way but after checking, he found it was all the way in. We intalled an aftermarket oil gauge and he had me fire the truck back up. It runs great but has a low end knock and oil pressure was maybe 10 to 12 psi. After he left I pulled the dizzy and used the drill to turn the pump and found that the rear main seal is leaking bad, but it didn't lose a drop when the engine was running.

All the external oil lines are rerun using the original fittings and new lines the same diameter as the old lines.

(1) I need to know what the heck just happened. It took me months to build this because I was meticulous. Everything was to specs, and my friend double checked every thing I did.

(2) I also just needed to vent. This is my daily driver and now I'm walking. Rebuiling is out of the question because the costruction outfit I was working for didn't survive the winter, so funds are tight to non existant.

I pulled the oil filter and it's clean and I drained the $75.00 worth of high zinc oil and found no metal shavings but it had a slight metallic sheen. Felt smooth, no grit.

So, what happened? What did I do wrong?

I'm afraid you'll have to pull the oil pan to see what happened.

Maybe something left in the pan got sucked up against the oil pump screen. Maybe the pickup tube wasn't placed just right and wound up sucking some air. Just wild out in right field guesses on my part.

The only way to find out is to pull the pan and look at the pump assembly, the screen, and also the bearings.

What is your line-routing to/from the oil filter - what lines go where?

Are all those lines/fittings clear/flowing?

Is oil reaching the rocker arms?

Relief valve stuck open?

Improper clearance from pump gear to cover?

I don't know if this could be the cause, but in the front of the engine is a 3 way fitting. One of the lines goes to the head and there is a restricted fitting with a very small hole in it. This fitting reduces how much oil will be pumped up to the rocker arms. I have read several times, that the oil pump is powerful enough to pull all the oil from the pan and dump it in the top end.

I replaced my original restricted fitting with a new fitting, filled it with solder and redrilled a hole to the correct size. I do not know if this would leave the bottom end dry enough to cause an issue, but it may be worth looking into.

Someone with more GMC engine experience should be able to confirm or deny this.

Sorry for your loss.

Jeff

Did you check the clearance for the rod and main bearings? I've seen standard size bearings installed on a journal that was. 010 under.

Tclederman, the last 11 photos in my photobucket link show my line routing. All lines are new and match the old lines in diameter and routing. I cleaned and reused all the old fittings when I could and anything replaced matched the old stuff in orifice size. When I pre-oiled I had oil to the rockers and oil filter and the oil gauge read 30 psi.

Pfarber, I have not pulled the pan yet so I don't know about the relief valve, and I'm not sure I understand "Improper clearance from pump gear to cover". This is a brand new pump. Looked just like the old pump.

Rustednuts, When I pre-oiled I had 30 psi but just a trickle at the rockers so I don't believe the three way is at fault. "Sorry for your loss" Thanks man.

Don stocker, all the bearings I pulled out looked great(should have left them alone) All the old main bearings were standard and were replaced with standard. I don't recall what the rod bearings were but we replaced them with the same that came out. My friend was very carefull to check and double check every thing. And of course every time one item was installed or snugged or torqued we rotated the engine once to make sure it felt right.

I know I'm going to learn the most when I pull the pan and tear back into it, but this was my first rebuild and to be honest I'm not going to have the experience to know what I'm looking at and what the root cause of the problem was. My truck is sitting at my friends shop half an hour from here and I've got to borrow a car to get there, so if I can arm myself with knowledge gathered from a few hundred stovebolters, I might be able to find that root cause and prevent a recurrence.

my guess would be the oil pump or the bearings. Probably won't know for sure till you pull the bearing caps. Sure hope you have minimal damage.

I think you might have a bearing failure. Rod inserts can shift when the rod is pushed down onto the crank. If it is done up while shifted, the tangs will cause it to bind and twist. After the pan is off, try moving each rod from side to side. That might tell you something.

Real sorry to hear of that problem. I have to agree with truckernix...from what you've said it sounds like a bearing problem to me, also. Good luck with it.
Jon

Thanks guys Would a bearing broblem cause very low oil pressure?

In worst case scenario I expect it could. I'll admit I'm sort of conflicted here. If you rotated the crank every time you torqued a rod and/or main cap and nothing felt funny, then I wouldn't expect the worst case scenario to have happened. I have not had a GMC 6 apart in a long time...probably somebody who has more current knowledge should answer. Did you replace the plugs in the block...particularly the oil galley plug?
Jon

I've read that low/no oil pressere can be caused by failing to replace the oil galley plug. In this case, no plugs were removed.

Well it is kind of a long stretch on my part, amigo. I was only thinking if your bell housing covered the rear oil galley plug (like the 235 does) and if the bell housing covered it, then it could have taken a while to show up as a problem...your comment about having a large rear main leak and not having one while it was first started made me wonder if a missing plug took a while to introduce itself to you. As I said far-reaching thinking here.
Jon

I appreciate even the most far reaching thinking, Jon. These are all things I'm going to have to look at when I work up the courage to start the autopsy.

I have been running semis for 50 years, building engines and other stuff for longer than that. And sometimes something goes wrong. The quicker you drop the pan and find out what went wrong, the quicker you will stop worrying and start heading in the direction of getting it fixed. It could be just something silly or it could be not good. But the quicker you know what you have, the quicker you will have a game plan to go on.

I agree. I just need to know what to look for when I do drop the pan, which won't be for a day or two. You might drop the pan and see right away what I won't see when it's pointed out to me.

I will update with whatever I find.

To me ,it sounds like you caught the problem in time. you probably "spun" a bearing. This would cause low/no oil pressure,and a rod-knock. Did you "'plasti-gage" the bearings,before the final torque? We installed a Buick Diesel,in a Toronado,that SUPPOSEDLY had 30,000 miles. Since we needed the pan re-welded,(guy drove the car 30 miles with 3 rods sticking out in various places-mostly the pan)! We double checked the bearings..Three or four were out beyond.006! One was .008!! We had the crank ground,and new bearings installed. Hang tight! Don't give up... Spring's around the corner and construction will pick-up. You may be able to do this repair in-frame. There should be play in all of the rods,except for the one,(hopefully not more),that's stuck. Hopefully,bearing brass scored before gouging into the crank. No shavings is a GOOD sign.The sheen in the oil is from the cap(s).it peels like gold foil,then gets diffused through the oil screen. GOOD LUCK!!

You've got my hopes up Willy. In fact after re-reading everyones posts, I've gone from feeling beat to feeling determined. Nothin' to it but to do it regardless of what the damage may be.

Twotone. I feel for you. As a kid dating my first wife my future father in law incouraged me to rebuild a 283 to put in my first truck, 57 Chevy. He left me towards the end to go on a trip and being the wild hare that I was I was determine to get it running before he got home. Well I put the distributor in 180 degrees out of time, No oil to the bearings, roasted them. Of course lesson learned and have never done two things ever again.
1 never put dist in 180 out

2 never not listen to the old man

He's long gone now and I still miss him.

So cheer up and don't let a little set back bother you.

Plus, the old man told me "If you don't try it and f__k it up you'll never learn anything".Larry

Well are you sure that you had enough oil in the engine. I think it takes around 8 qt. to fill that pan. also make sure the oiler for the cam gear is still in. I see it in one of your pictures but it looks strange, they are usually just a crimped piece of tubing with a small hole on one side. last I would not trust that dash gauge get a good gauge and screw it into the block

My 1955 270 took about 12 quarts of oil. Fill it to the mark on the dipstick. Recheck after running, if you used a new oil filter.

yep your probably right, I just fill mine until it hits the full mark.
Jay D.

I believe there are three different oil pans for these 270s, it takes ten and a half quarts to fill mine with the bypass filter.

I used the dash gauge and then rechecked with a new aftermarket oil gauge. They both read the same; 10 psi give or take.

I talked to a guy yesterday who used to build and race 270s. He told me my oil pressure was good and that I don't want more than 20 psi or I'll blow it past the seals(rear main etc.). He basicly told me I'm an idiot for running a 3500 rpm drill to pre-oil. The guy seemed vary knowledgable, but in this case I think he's wrong. My truck came with a 60 psi gauge for a reason.

Question- What should my oil pressure be at idle and, say, 1000-1200 rpm on a rebuilt '59 270? I'm running 10w30 high zinc oil..

My GMC 6 was a 228. It was very well used, but when first started at idle it was in the range of 20 and at 30 or 40 miles per hour it would stay close to 30 or so (by the dash gauge) in cold or hot weather. In the summer at a red light the pressure would drop down significantly at idle. Enough of a drop to make you nervous if you worried about things like that. I think I just ran 30 weight oil in it. Wasn't a bad engine at all, but it didn't have the pep the 235 had. I had to replace a head gasket and while the head was off I had the guides knurled and I lapped the valves. It ran much smoother after that.
Jon

Oil Pressure...... true or not an old timer once told me, at least for an old chevy engine, that if you could get 10 lb pressure per 1000 rpm the engine would be fine. It gave me comfort many times in some of the old jalopies I drove back then!

My '55 270 runs @ 50lbs at around 40 mph, at 60 it's up to 55 lbs. Idling when warm is around 15 lbs. It holds 9 1/2 qts with the oil filter. I'm using Castrol 10/30 high mileage oil.

My fresh rebuilt 270 pegs 60 psi at fast idle cold and once warmed up it stays at 20 psi hot idle.

This is my second rebuilt 270 and my other was the same with oil pressure. My rebuilt 228 also had the same oil pressures. My 302 is at 50 psi cold fast idle and 15 hot slow idle.

That old timer you mentioned might know engines but I'm not so sure he knows these great old gmc engines.

AS I mentioned earlier, I would recommend you drop the pan and look around because you will worry until you find the trouble. The only thing that concerns me is the knock. When I first start a fresh GMC, I don't even look at the gauge. I leave the valve cover off and if the rocker overflow is flowing, I figure the rest of the engine has oil. I'm one of the old geezers that adjust the valves with the motor running when it is hot. Even new oil pressure gauges give false readings. Our Cummins engines are programmed to show a stop engine light for a few seconds and then kill the engine. I keep pressure sending switches on hand because they fail quite often. I also keep two master gauges to check oil pressure. Your original gauge probably wasn't very good and the after market one may well come from China.
You say the rear main leaked. Did you use a rope seal or did you use a National type seal. I use the old rope seals. I kind of pack the ends with a drift punch and then trim the ends. If you leave loose threads, it will get between the cap and the block and you will have too much bearing clearance. But I wouldn't worry that you spun the rear main. It takes a lot of clearance for it to spin. If you do need to replace the rope, Lisle makes a gadget called Sneaky Pete. They are less than $10 and they work. Starving for oil usually shows up on the number one rod bearing because it is the last one to get oil.
Is the machinist you used familiar with valve guide to valve clearance? These old machines require a lot more clearance than newer engines. Too tight can cause valves to hang open which causes a miss and a knock. Did you bore the block. Unless you bored the block to oversize, I wouldn't recommend chrome rings. They just won't seat with just a hone job. Unless you bored it, I would use cast iron rings.

I'm kind of the opinion that people worry too much about oil pressure. It's not the pressure that lubricates, its merely having oil between two objects that rub together. Until the mid 70's, Cummins engines ran between 50 and 60 lbs under load. I think it was in 1976 they went to a 30 lb relief valve. It took some getting used to, but now it is just a way of life looking at 25 to 30 psi on the oil gauge. It takes a couple of extra hp to go from 30 to 60 psi. And HP uses fuel. I built my first GMC engine and drove a 1950 GMC to school in 1957. I finally got a drivers license in 1959. I've been tinkering with GMC ever since. I have over a dozen pre 1959. They don't have much oil pressure at an idle. In fact too much oil pressure alarms me more. It is a good sign of coolant in the oil.

In the mid '60s, Pontiac's low oil pressure lights were set to come on below 3 or 4 psi, anything above that was good to go. Oil pressure does equal hp, I seen a distributor drive sheered off in a motor running 20w50 race oil.

Get that pan off before you worry your self sick, everybody has a engine go down every now and then so it's not the end of the world. I had one spin a bearing trying to get up on a trailer !

Joe

I appreciate everyones input. I've gone from worrying to accepting that I have to diagnose and fix.

I will only have a couple hours Monday in which to push the truck into my friends shop, drop the pan, and learn what can be learned. Everything I do from then on is going to have to be done around his work schedule, and to be honest, I would like to exclude his involvement as much as possible.

I know that I need to check the pan for metal shavings/grit etc. but being rather inexperienced, it would help if I had a 'step by step' of what to check, how to check it, and what to expect so that I don't spend that two hours scratching my head.

crenwelge, my rear main seal is a rope seal from Best Gaskets. I was happy with my installation of the gasket, but after a little research I kind of wish I could do it again. Maybe I'll get my chance

I wouldn't expect metal shavings. We are talking about a motor, not a transmission or rear end. If there were any metal, it would probably be in the filter between the pleats anyway. In fact it probably wouldn't hurt to cut the filter cartridge open and take a look. Dropping the pan on a GMC is a relative simple matter. Check the gasket on the rear main to make sure it didn't slip. It could be the that is all that is wrong. Make sure the float is still on the oil pump and see that the set screw is holding the pump whee it belongs. I would remove all of the spark plugs so you have no compression and let someone turn the engine over while you are under it and look and listen for something out of the ordinary.
If the rear main was was indeed leaking, you need to pull the rear main cap to change the seal. The top shell should still be in the block and the bottom shell should still be in the cap. Describe what the bearing looks like. I would also pull the number one rod bearing cap and take a look at it and let us know what it looks like. If nothing looks bad like a spun bearing (you will know it if you see one) I would check bearing clearances with Plastigauge.
http://www.plastigaugeusa.com/how.html


I think most auto parts houses still have it. Read the instructions closely before you ever start.

If the rear main and the number one rod are within tolerance, you might as well Plastigauge all of them. I would recommend one of the Sneaky Petes to install the rear main seal.

http://www.amazon.com/Lisle-27000-Sneaky-Pete-Tool/dp/B0002SRCJW

Do you have a shop manual that shows you how to reinstall the rear main seal? It will clearly explain how to pack the seal and trim the threads.

There really isn't a step by step procedure for trouble shooting what you describe. However, I always look at the simple things first. As an analogy, an acquaintance of mine was recently worrying about having to take chemo because he just knew he had melanomia. Turned out it was merely an ingrown hair.

LOTS of good advice and things to check. I guess it just may be my nature but once I get the pan off of anything it seems the first thing I do is try move the rods side to side....just to see how they "feel". If I run up on one that seems odd its usually the first one I pull. Otherwise, crenwelge is right on.

If you go back with the Best Gasket, do not pack it, follow there instructions very closely. I packed one in just a little, nothing like the older ropes, and after it ran 20 minutes I shut it down for a check over. It would not turn over again till the next day after the crank cooled off. I ended up replacing the seal and following directions a little closes. Another lesson learned !

Joe

Don't be shocked if one rod journal is a different grind than the others. Back in the day many mechanics had a tool that would grind a crankshaft in the field with the crank still in the block. They would polish out the bad journal and install a +10, etc; rod bearing and put the pan back on. My son found his '53 had its 235 done that way sometime in a past life. Knocked when we fired it for the first time. Pulled the pan and wiggled the rod caps until #4 moved too much. Plastigauged it and put in a +10 bearing. It ran for 10+ years before being replaced by a 350.

Low oil pressure after a rebuild?
Perhaps the 2nd and 3rd crank bearing caps were swapped upon reassembly. Those caps have dowels that locate them to the block Is it possible they could have either been swapped or turned 180 degrees? Installing those caps in the wrong order or direction could cause them to seat improperly. That could cause the bearings to spin and oil pressure to drop.

I was SOOOO careful to make sure everything whent right back in the way it came out, but that doesn't rule out that possability. How would I know by looking at them if that's happened?

Generally I number each rod cap, both the rod side and cap side and I also number the mains using number stamps.

I don't think that a main 2nd/3rd bearing swap is an issue. The bearings are stepped (my 270's numbers from the book: nominal bearing ID #2 2.7145 #3 2.7445) and the 3rd bearing is also a thrust bearing. So things will get tight REALLY quick.

I would simply plastigauge all bearings. If you have a bearing knock excessive clearance is the main culprit.. rod or main.

I am not a huge fan or trying to describe pings, slaps, taps or 'sharp' vs 'dull'.