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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Grim 82 on February 14, 2011, 02:00:38 pm
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I'm hoping you guys can offer some input about my oil pressure readings as of late. I was driving the other day and with the engine fully warmed up, in gear, sitting at a red light the gauge flatlined to 0. It read 50-60 psi on cold startup, 30-40 cruising, and about 10 in park. As soon as you put it in gear it goes to 0.
So, I just installed a Sunpro electrical gauge and sending unit. I replaced the stock sender (by the dist.) with the Sunpro one. At all other conditions, it reads the same as the stock gauge did, except when stopped in gear at the red light it reads in the single digits. (see artistic rendering) At this time I also changed the oil, using Havoline 10w30 and a napa gold (Wix) filter.
So after asking around a bit locally I've narrowed it down to 3 possible things
1. It's normal and you worry too much
2. Everything in between
3. Spun a main bearing
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throwing things out here:
pick up screen on the pump may be partially clogged, but, you are getting 50+ at startup.
Do you have the 3 inch extension, near your distributor, that the sender screws onto? Try removing that to see if that is partially clogged?
I'd be tempted to remove the oil pan and put a new heart in it.
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I have the brass angled extension on there. It had some regular pipe fittings on it with the brass angled piece and a pipe nipple snapped off in the hole when I started removing the old sender, so I had to EZ out that piece from the block. Now it's just the new sender going to the brass angle fitting going to the block, and I cleaned that piece and sprayed it out with shop air.
I need to replace the rear main seal anyway and I picked up a one piece pan gasket like I asked you about a while back, so over lunch today I picked up a new pump also since I'll be in there. I hope that takes care of it.
Do you think it's low enough that I shouldn't be driving it? I won't get to work on it til the weekend.
Also, if it was something serious like a spun bearing wouldn't that have more obvious symptoms than just low oil pressure at a stop? That would affect pressure throughout the whole spectrum, wouldn't it? I'm trying really hard to rule out that diagnosis, just for some peace of mind...
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What's the rpm when you put it in gear? Is it just below 15psi at that point like I think I see on your pic? That's not good, but typical for a tired motor. Pickup screen or new oil pump might help a little, but if its a high mile engine I think its the clearances between main bearings and crank that drop the oil pressure the most. I don't think a spun bearing makes sense in this case, but could be wrong.
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Idle is around 800, and in gear under load it drops to about 650-700 rpm. What bothers me is that the motor really only has about 15-20k miles on it since the build. My brother had it built about 12 years ago and it made good power for a couple thousand miles until the rear diff exploded, then he parked it and bought a new truck. So, it sat for 10 years until I bought it from him and got it going 2 years ago.
If the mark between 0 and 25 is 12.5, it looks to me like it fluctuates below that line, somewhere between what would maybe be 6-10, which doesn't seem like a lot. Before this started last week it never went under 15 psi.
While I'm in there replacing the rear main seal and oil pump, is there any way to visually inspect and rule out a spun bearing?
Also, do I need to prime the new pump or just bolt it up and go?
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If it spun a bearing you'd know it!
If you're going to drop the pan pull a few bearing caps and inspect (plastigauge would be ideal) If it looks like .0025-.003" clearance run a high volume oil pump. Make sure you're using a steel sleeve drive shaft and yes you have to prime the pump. At the very least pack it with vaseline and crank the engine with the spark plugs removed and the coil disabled.
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Well since I posted this yesterday the psi at cruising is down to 20-25. I took the truck over to a friend's shop and hooked the big face mechanical gauge up to it and warm at idle (750 rpm) it reads 5 psi, and now it sounds like there are rats running around in the crankcase. He said to push/pull on the balancer and check for travel in the crank. I could move it 1/8" or so...
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Well since I posted this yesterday the psi at cruising is down to 20-25. I took the truck over to a friend's shop and hooked the big face mechanical gauge up to it and warm at idle (750 rpm) it reads 5 psi, and now it sounds like there are rats running around in the crankcase. He said to push/pull on the balancer and check for travel in the crank. I could move it 1/8" or so...
You should probably try to put a mag base indicator on it to be sure, but that sounds way, way beyond shot. You could probably live with .02" or .03". If you want to continue investigating, Vile's advice (of course) is a good next step. If you have anywhere in the neighborhood of 1/8" endplay there is no way that motor was properly rebuilt.
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put a mag base indicator on it
I'm not sure what that is, but I'll do some research on it. It's always been in the back of my mind that this motor couldn't really be dependable after sitting for so long. Not sure if that has anything to do with it or if it just never was right.
If it has lost the resistance that builds the oil pressure, then I don't suppose a new pump would really make any difference? Does it still pay to plastigage it with that much forward/back travel on the crank?
I'm wondering if I should cut my losses and find a new motor. It's not so much a money issue to me right now as much as it is an issue of carpooling with the wife is not very feasable due to work schedules and locations, and we only have the 2 vehicles. I have no desire at this moment to learn engine rebuilding, but I could swap in a long block in a weekend easily.
Where to from here?
Thanks guys
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In an hour you can have the pan down and check some of the bearings and the pump at the same time. I would say do it or just pop it out and start rebuilding.
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pop it out and start rebuilding.
lol, I can throw it in a crate and have it to your shop by the weekend ;D
I'll have my buddy help me check that stuff, but I need a pretty expedient solution to this, especially with the spring flooding they are forecasting for us. I think I'm past the denial and grief stages, and now I'm daydreaming about what kind of motor I could drop in it...
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It's too bad that you can't find a decent running 305 to swap in there for the time being. . . .
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Funny you should say that. I have a 305 with one weak cylinder but otherwise runs decent. If I go through the work of swapping it all I'd rather just do it once with a new motor and be done if you know what I mean. Maybe build the other one for a future project 8)
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pop it out and start rebuilding.
lol, I can throw it in a crate and have it to your shop by the weekend ;D
I'll have my buddy help me check that stuff, but I need a pretty expedient solution to this, especially with the spring flooding they are forecasting for us. I think I'm past the denial and grief stages, and now I'm daydreaming about what kind of motor I could drop in it...
Send case of beer too please ;D
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;D
So many choices.. I have a line on a couple of really good motors. I'm going to start a new thread.
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I'm back on this rainy day project now. I have the motor out and upside down on a stand. I removed all of the caps and as you guys suspected, there is NOT a spun main bearing. However, the main bearings on the cap side are ground down pretty good and brass or copper material is showing through. There is also a little bit of scoring on the crankshaft surfaces. Pulling the caps and visually inspecting is as far as I have gotten. I tried to replicate the front to back travel and was unable to, so it may have been my imagination or I was drinking. From what I can see from the bottom, the cylinders still have a nice crosshatch pattern and smooth spots, and it looks like one cylinder has a sleeve pushed into it. A few of the cam lobes look a little discolored with minor chipping.
What's the next step as far as inpecting and/or replacing parts to get it going again? If I have to get any machine work done it's probably going to be a deal breaker. Thanks
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I'm not sure what your skill level is so don't take offense but you did mark all of the bearing caps right? Make sure you mark the rods too. What's your goal? Sounds like the engine is tired and needs a rebuild. If the crank is scored you will need to have it ground. If there is no major cylinder wear you can hone and re-ring it.
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Maybe get some pricing from the local machine shops and know what the pricing and time frame would be; It may not be as bad as you think. Just ask around first to be sure you are going to the right place if you don't already know.
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No offense taken, this is as far into a sbc as I have been. Everything was stamped from the previous rebuild, but I also used a 3' piece of 1x12 and drilled a bunch of screws into it and then set the caps over the screws to keep them from getting mixed up or turned around. I left the pistons in it and just pushed them to the top. I talked to a machinist and he estimated that I could have the crank ground and get new main and rod bearings for about $200.
I'll be dropping the crankshaft off at the shop later today, but I'm not sure if it can be ground now. The surface for one of the rod bearings looks horrible, like somebody drove the rod bolts into it when they installed the piston or rotated the crank and mashed the threads against it. It's chewed up pretty bad.
The cylinder bores look perfect, and my goal is to get the lower end put back together cheaply and see if that fixes the low oil pressure problem that I had. If everything checks out after that I would like to put a little bit more aggressive cam in it with some vortec heads and put it in a new project, or maybe swap it into my daily driver and use the 400 for something that's more of a toy since that 350 always used to get much better mileage.
Thanks
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This would be a great time to get the block bored if needed and put in some flat top pistons as well if your budget allows. Also check for a ring ridge at the top of the cylinder walls.
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I'll have too look at my machine shop receipt but I think my crank grind was only like 80 or 120. and main bearings were 30.
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I'll have too look at my machine shop receipt but I think my crank grind was only like 80 or 120. and main bearings were 30.
What shop did you use? I may pick up a 5.3 for the 74 after I pay the rent.
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It was B&B (BAKE AND BOIL) in mesa. Its on broadway and extension? I believe. I think on broadway between extension and country club. Vat, crank grind, magna flux, head check, head magnaflux, and hardened valve seats cost me 320.
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I posted this on the wrong subject.
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My crank was toast, but he swapped it out for a good one and just charged me for the grind. Crank, main, rods, and cam bearings and borrowing the cam bearing installer for $170.
I left the pistons in it cause the bores look good with this motor only having 20-30k on it. It has flat top pistons stamped 030 with 4 relief areas.
I went to a builder to pick up a gasket set, double roller timing set, oil pump, cam, and lifters. IIRC my heads are stamped xxxx993? The guy said those are decent enough heads for my purpose and since I had an RV cam in it before my springs and everything should be good to go, and he recommended an Elgin E923p cam. He said it should be comparable to what I had before, which I liked.
http://shop.enginekits.com/osb/itemdetails.cfm?ID=60
He also borrowed me a spring compressor so I can clean the crap out of the heads. Should I plan on putting new seals in it? Any other suggestion on that task or opinions on that cam is welcome. Also, at this point is it a good idea to install a high volume or a high pressure oil pump, or will a stock replacement work? Thanks
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I run a stock replacement pump and have 60+ lbs all the time. If your budget allows maybe upgrade to a 63cc head, maybe the machine shop has some around(maybe some vortechs). This could be worth an easy 20-30 hp, pretty good bang for the buck and maybe see some better mpg as well.
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i agree with running a stock pump this truck of mine is the only motor ive ever ran a hv pump in and the only reason i am is the guy who originaly built the short block was building it for boost and set clerances to run the hv pump. honestly i hate it lol id rather run a standard pump.
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If you have more than .0025" clearance you may want to run a HV pump