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Thread: 350 Oil Pressure Issues

  1. 350 Oil Pressure Issues

    I bought a '48 Chevy pickup with a Buick 350 in it. The number 7 and 8 rod bearings were completely trashed. After debating whether to rebuild the Buick or swap in a Chevy, I decided to go with the non-bellybutton Buick. I had a local respected machine shop do all the machine work, including magnafluxing, which was my education in Buick head cracking. I installed a high volume oil pump and a booster plate from TA. I was disappointed to learn that the oil pressure, while adequate at startup, dropped alarmingly when the engine warmed up. The truck has a Classic Instruments quad gauge that measures pressure from 0 to 100 lbs, and it would barely register at light throttle cruise. I spoke with TA, and they said the high volume pump was a bad idea, and that the timing cover was the probable culprit. I replaced the timing cover with a brand new one, and swapped in a new "stock" oil pump. I also installed a mechanical pressure gauge directly on the block. I primed the new pump and saw a full 60 lbs with the electric drill. But when I drive it, the same problem remains. 50 or so lbs at startup, dropping to 7 -8 at idle, and less than 20 at a few thousand RPM when hot. I knew oiling systems were a problem with Buick engines, but I didn't anticipate this much trouble. Any suggestions?

  2. I would start by checking how much end clearance there is between the oil pump gears and the pump cover. I believe that the minimum is somewhere around .002" and you should be as close to this as you can. You may need a different gasket as every gasket maker seems to have a different thickness when it comes to this gasket. You can use plastigauge to check the clearance if need be. TA also sells a gasket selection for just this purpose. In theory the gears should protrude a very small amount from the housing. This can be checked with a straight edge and some feeler gauges. Measure how much protrusion you have and add .002" or .003" and that is thickness of the gasket you need as measured with a micrometer. If you do not have any protrusion you are going to have a tough time getting the tight clearance that you need. You may have to take some metal off of the housing. This can be done with a flat file but takes a skilled hand to do it properly. The two other areas that will create the problem you describe are crankshaft bearing clearances that are too loose and a front cam bearing that is tore up or too loose. The main reason that you are advised to not use the high volume kit on a new engine is that it loads the hell out of the front cam bearing and will tear it up in short order because the gear on the cam is what drives the oil pump. Also, you are sure you used a gasket between the oil pickup tube and the block. I think you will find the problem in one of these areas. Good luck.

  3. the SBB shares many overall design principles ( not dimensions ) with the BBB.

    try the FAQ page for BBB oil mods:

    and pay special attention to the page on checking oil pump clearances:

    timing cover wear is probably what took out the main bearings originally but you need to check with your mechanic on what clearances he put on the bearings. .002" is the MOST clearance that you should have on your main and rod bearings for a Buick. Chevy guys aren't used to building our engines.

    if you want more oil pressure simply shim the bypass valve spring with washers. you can put enough pressure on the stock pump to blow an oil filter can apart.

    AM&P has a page specifically for building a 350 here:

    any good Buick turbo v6 builder or Land Rover mechanic would be a good choice to work on your engine. the Buick v6 is a short deck version of the 350 with two less cylinders and the Land Rover v8 from 1965 up through 2004 is a metric version of the original SBB, the 215ci aluminum v8 from 1961-63.

    i believe you can source neoprene front and rear main seals for your engine by using parts for the Buick 231. you can also swap timing covers with the v6.
    Last edited by bob k. mando; 11-17-2010 at 04:27 PM.
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

  4. Thanks for the input. I'm thinking there must be some problem with the bearing clearances or the block itself, since everything with the pump and timing cover has been checked and double-checked. I guess the motor is coming back out. Shoulda went with the Chevy! No offense guys, I'm an old Buick man myself...drove a '54 Skylark all through college, had a beautiful '66 Skylark GS, but those nailheads never gave me the headaches this 350 does.

  5. Really, one bad experience and your ready to throw in the towel and condemn a whole division of GM? Come on. I've worked in the machine shop business for 22+ years and have seen people drag in all sorts of mucked up Chevy jobs over the years. "Just do a quick valve job and bore the block and we'll do the rest". Yea right, the car comes in on a hook a week later. " Won't start, what the hell did you cheating, lying bastards do?" " Whadda you mean you have to keep the rod and main caps in order", "I never heard of that." What the hell is plastigauge?" "Bullshit that old pump was workin' fine on the old motor!" Yadda Yadda Yadda. I'm not saying your that guy but I've heard the same thing about other engines and things like Quadrajet carburetors for years. "They just ain't no **** good!" Bull! The 350 Buick was in production for 12 years and they built tons of them. And its little brother the 3.8 V6 was in production for over 30 years and is considered one of the top engines of all time. They might not be as dirt simple as a Chevy, but they weren't built for dirt simple people. Again, I'm not saying your that guy. But if ya sling mud about Buick on a Buick website ya might get a little tossed back at ya. I hope you find the problem and it turns out to be cheap and easy and you get years of happy motoring from your Buick. Good luck. And "No Offense".

  6. I admire your passion, BigRivy. My Dad used to drive a '71 boattail, by the way. Guess you missed the part where I said I'm a big Buick fan, I restored and drove a '54 Skylark for a dozen years. Had a killer '66 Gran Sport. I wish I had both of those cars still, and many other Buicks I've wanted. The fact this Chevy truck had a Buick motor in it was a big part of why I bought it. BUT...I'm sure you can understand my frustration. The number 7 and 8 rod bearings were dust when I got it and tore it down. I tried to follow all accepted practices for improving oil flow when I had it rebuilt. In doing research I found out that this engine didn't have the best reputation for having great oiling to begin with. All bearing clearances were checked. The original timing cover was not scored so I re-used it, but installed a high volume pump and a TA booster plate. Unrelated, but had to locate and go through three sets of heads before finding two that weren't cracked; another little feature of this engine that I found out the hard way. Put it all back together only to find oil pressure at startup that goes away as the engine warms. Replaced the timing cover anyway, and threw in a stock oil pump while I was at it. Same problem. I love me some Buicks, but I gotta say I could have built a Chevy engine for a lot less money that would not have either the cracked head or the oil pressure problems. Fact. I don't mind taking the shots, but I would rather have the answer. I want this thing to work. Really. But taking the engine out again and tearing it apart without any idea of what exactly I'm fixing is not a terrific option.

  7. DO check the oil pickup tube. if it is not "suction tight" warm oil wont
    get picked up.

    have you checked the oil pressure right at the block. there might be air in the oil lines on the guage.

    just a couple things I would check

  8. Thanks, Kitty. Big Rivy also mentioned the absence of a gasket on the pickup tube as being a possible problem. That makes sense, and to tell the truth I don't remember if a gasket got installed there on assembly. I do know the bearing clearances were checked. That is also something I can check without pulling the engine again, which is a huge plus. Oil pressure is better since putting the new timing cover on; 80 lbs on startup vs 50 lbs before. Still goes south when engine hits 165 -180 degrees, though.

  9. Low 48, thanks for having a sense of humor. There is no way you are going to know what it is until you find it. All we can do is offer ideas as to what it might be. Every so often you get one that doesn't work out like ya want. That's life. Like I said previously, you won't know what it is until you tear into it and look until you find something. The things that can cause low pressure at operating temp are the same for just about every engine. We listed the most common ones first. There are other things that it could be, such as a cracked main web that an oil passage goes through or the lifter diameter being too small, or the oil pressure relief valve not working or improperly installed, or front oil gallery plugs leaking like a sieve. Obviously you look for what changes when the engine warms up. The operating clearances change and the oil gets thinner. Most often the problem is crank bearing clearances or the end clearance on the oil pump gears on a Buick that has the problems you describe. You have stated that these have been checked and double checked, so what are they? How much measured end clearance do you have on the pump and what are your bearing clearances? The importance of these two items cannot be understated. Now that I have said that, Murphy's law will make it be the craziest oddball thing you can think of that is causing the problem. I am a little surprised at the luck you had finding good 350 heads. To be honest, I have never seen a cracked one in all my years at the machine shop, and have only seen one cracked 455 head. And that was a car that came in on the hook and was SEVERELY overheated. I could have filled a train car or two with all the cracked Chevy heads and blocks I've scrapped over the years, especially the later light weight ones. Don't get too discouraged. This ain't rocket science or black magic, and you are certainly not the only one who has ever had these kinds of problems. Fate just decided that it's your turn. The type of engine you decided to build has nothing to do with it. Just ask the guy I know who, several years ago, had 3 Chrysler Hemi crate motors fail on him in a row within minutes of start up. Strangely enough he is still a hard core Mopar nut. I think he bleeds Hemi orange. Keep at it you'll figure it out. If I lived near ya I'd be happy to come over and help. Good luck.

  10. I just re read your earlier post where you stated that you " followed all the accepted practices for improving oil flow". If I may ask, what modifications did you make? Some of these things are for race only engines. I personally have built several Buick engines and for a street engine, even a modestly warmed up one, I don't usually change or modify the oiling system. I grew up driving boat tails myself, over the years I've had 5 of 'em, and I beat everyone of them like they owed me money and I never blew one up. They'd get loose over the years and start loosing oil pressure at idle and I'd go in and tighten up the bottom end or, if the car was shot too, I'd look for a new one. Yea the oil pump design leaves a lot to be desired, but Cadillac used it too and so did Ford when they ripped off the Buick V-6 to make there own. It has the same shitty aluminum housing with steel gears that any sane man knows can't work. But if you learn the tricks to making it work you can live with it and get a pretty darn good service life out of it. Do you remember in the '70's when Chevy was having their huge problem with camshafts going flat? I guess nobody's perfect. Building cars for the masses is tougher than one might think. Sorry I got so long winded, I just wanted to ask about the oiling mods you might have done.

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