Ok, so I decide that I want to take the truck ('54 Chevy) to the drags last hight to get a 'baseline' time on it since I put the v8 in. It's a used shortblock 350. The top end is all new, as is the cam. I have to soft-shoe the truck off the line since the rear suspension is not up to a clutch drop on launch. What ends up happening is tire-spin all the way through first and a shift at 6K to second. Truck isn't running up to potential and on the return road, it dies after idling very low (not normal). I decide that one run is enough and head home. Truck is running rough and doesn't want to idle. On the way home I notice the oil pressure is rather low, like really low. Under a load the pressure drops to nearly zero. When I let up on the gas and coast, the pressure returns to something that resembles normal. After I get home, I check the oil level, it's fine. Truck still runs rough and doesn't want to idle. Strange sounds softly eminate from under the hood, hard to describe. On the drive into work today, the oil pressure is fine until the engine warms up. Then a return of the previous night's symptoms. Nearly no pressure under load and more when not under load. What did I do to it? r
dude, not for nothing, but if the motor is not running right, especially no oil pressure, why you driving it? you could be doing more damage to it. find out the problem, maybe needs a new oil pump., but don't drive it.
I understand, BUT, this is my daily driver and It's raining here, so I couldn't take my roadster... r
SBC should have a minium of 10PSI per 1000 RPM. i know a filter does make some difference in pressure. But you're saying you have some noise and pressure goes down as it warms up so I'm thinking a bearing might have spun
That is what I'm suspecting. I just wanted to check out other possiblilities. But would that cause the pressure to go down only under load and come back up when not under load? r
I believe its due to the wear as you pump more oil there is less pressure as it is flowing out the worn area .Which should be at its greatest under a load . when you let off the load not as much sterss on the worn area so you get some pressure
a bearing would be constant.use another gauge, mechanical, or another electrical sending unit. the bad idle is probably loosening something up in the tank. ck the filter, and regap the plugs.
The guage is mechanical, don't truc those electrical ones myself... What 'tank' are you referring to? It idled fine before this incident... r
It's possible that the oil pump pick up tube is not tight enough in the pump and had fallen against the floor of the oil pan. Can't get enough oil through it at higher rpms...You might have hurt the motor.
Two problems..........the rough running may be from over reving.Could be a bent valve or maybe just the intake gasket or a million other things that make funny soft sounds under the hood The oil pressure is interesting if the gauge is accurate.I heard of a problem like this recently,I believe the pick up tube got loose,like said above.
you say the top end is new , what about the bottom end?, hydraulic lifters?, sounds to me like the oil pump relief spring is failing, is it a stock pump? the noise would more than likely be lifter noise from hydraulic lifters due to the low pressure.
I was gonna tell you not to waste your time changing the oil, cause you wore out the main bearings. Maybe just the last one. And that's a big internal oil leak. But take the filter off and cut it open see what color the metal shavings are.
Ok, I believe that something is amiss on the bottom end. Would that cause the fluctuating oil pressure under load/no load? r
Time for a tear down. That's what shakedown runs are for, to find the hidden flaws. You found it, now tear it down and post some pics for us all to enjoy. You should be able to fix it fast since it's a small block.
Chrome moly pushrods, new Comp Cams lifter (and cam), dual roller timing chain and gears, heavy dual valve springs, big new stainless steel valves. I just didn't do anything to the shortblock (yes, that was dumb, I know). I'd be surprised if it's a bent pushrod, really. It ****s because this is my daily driver. I drove my roadster most of the summer while I was putting the new motor/****** in the truck. I don't think I can resort to the roadster in light of the weather here this time of year... r
As some one said the pick up may have come off the pump. Pull the pan and look. Also pull the Valve covers and look for loose rockers thay may indicate a bent push rod.
Under condition that should push pressure UP, it goes down...and vice versa. I think I am agreeing with the loose pickup tube people...had a friend with a '55 with those symptoms. Pump could lap up enough oil at idle to maintain normalcy, as soon as it got going more oil went upstairs and pressure drooped. As a stupid kamekaze experiment, one that I would try, dump in 2 extra quarts when you head to the store for new oil and a filter. If that does good things, drop that pan and find a less improvised way of hammering the ney tube into the pump! The most bestest is essentially free: A Vizard Chevy book shows how to grind the tip of a piece of water pipe into a perfect driver.
I am with Bruce on the pickup tube. I always tack weld those it place.I had a 61Chevy do the same problems shortly after a rebuild well over 30 years ago ....never took a chance again. I also would replace the Filter with a WIX or AC. I have seen a bunch of Junk Fram filters.
toasted bearings may have smacked a valve when over revved msd soft touch rev limiter dont leave home without one.
Robin....I'd say it's now running rough because there's not enough oil pressure to pump up the hydraulic valve lifters..valves are barely opening. The noises are probably the bled-down lifters clicking because ther's no oil in them, causing HUGE valve lash...may even had a rocker arm come off a valve. I'd suspect a pickup tube came off [or came loose] as well...or the pickup is too close to the bottom of the pan...either way the pan is gonna have to come off..and all bearings checked. Also.........I once made the mistake of using brittle grade 8 bolts to mount my oil pump.......worked great 'til a cold morning when the oil was thick. The mount bolt sheared and the pump dropped down into the bottom of the pan..
Why would you take your daily to the track and crank it to 6 grand in the first place. Sounds like you had a lot of time and money to burn. This one is gona cost you and it was running so well. Hows your base line now. Iceman
It could be a loose pickup tube but, since it happened on the run I'm leaning toward a spun bearing or bearings, especially with noise. As far as low idle and running rough all of a sudden, I'm thinking the distributor may have moved and retarted the ignition timing. Hope this is some of ***istance to you, however, its like diagnosing a car problem over the phone, its not like being there to see it! I would pull the oil pan as soon as possible for inspection
sbc are notorius for low preesure. 5-7 lbs per 1000 is normal. I would 1 check your guage, 2 check for damaged rocker arm, bent pushrod, or pulled rocker stud. 6 grand ain't that much if that's as far as you went. I doubt you spun a bearing, sbc are hard to tear up. Had a crate motor that had the same problem. Turned out to be a carb problem. I have run the PISS out of these motors and never spun a bearing. Look for simple things first. I have tourtured stock motors alot more than that and NEVER had a bearing failure. Pretty tough to grenade one of these motors.....
Pull the distributor and check drive gear for damage. Will cause timing problems and potential oil pressure fluctation. Fast and easy to check and rule it out.
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