labrat Posted July 8, 2004 Share Posted July 8, 2004 Okay guys, help me tackle this one. Conversion complete, I have about 200 miles or so on the newly rebuilt 4 bolt main 350. When idling cold, I have good oil pressure, around 20-25 psi. When hot, however (180*), my oil pressure drops to almost nothing and the engine even knocks occasionally. What did I do wrong? If I rev it to even 1000 rpm, it shoots back up quickly to around 15-20, but at 600 rpm idle I'm lucky to get 5psi. I'm sure my lower bearing clearances were good, they were all plasti-guaged before install. Is the oil pump bad? Did the bearings wear excessively on the initial startup? I primed the oil pump with a drill before the intial start. The one thing that has bothered me about this motor is the fact that I overheated it on it first good drive, during the break-in period. I have replaced the heads and entire top end since then, but the shortblock is the same. Could this have caused the low oil pressure I'm getting? More importantly, do you think I could fix it with a high volume oil pump, or do you think more serious problems are afoot. Damn, I just got this thing running, now I have to pull the motor again. I'm thinking about just buying a shortblock from an engine shop. I'm tired of dealing with this... Bill Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted July 8, 2004 Share Posted July 8, 2004 labrat , I wish you were MUCH closer, Id just say pull it in and well have a look at that engine! IF your sure its not the gauge, and thats the correct oil pressure readings,the SMART move would be to pull the engine and check ALL the bearings and clearances,yeah a high volume oil pump will tend to boost the pressure reading on the gauge at idle but it WON,T fix your problem, YOU need to find out WHATS causeing the low pressure readings, PRESURE is the result of the volume the oil pump flows and the BEARING CLEARANCES resistance to that flow, if your clearances alow little resistance SOMETHINGS WRONG and needs to be fixed BEFORE major parts failure occures! and with that oil pressure its SURE to happen soon if you don,t fix the problem! HERES some posts that might help (yes you need to look at the sub links too!) http://kustomauto.2.forumer.com/index.php?showtopic=276 http://kustomauto.2.forumer.com/index.php?showtopic=423 http://kustomauto.2.forumer.com/index.php?showtopic=417 http://kustomauto.2.forumer.com/index.php?showtopic=403 http://kustomauto.2.forumer.com/index.php?showtopic=312 Quote Link to comment Share on other sites More sharing options...
labrat Posted July 9, 2004 Author Share Posted July 9, 2004 Thanks grumpy, you confirmed my worst fears. This is my first engine rebuild, and after this, probably my last. I'll leave it to a competent machine shop to take care of it from now on. I can get a stock shortblock minus cam and timing set for about $350.00, so I'll probably go that route. I'm not sure aobut this motor anyway, as I didnt' do a complete rebuild on it, just freshened it up a little. When I bought it, it had been rebuilt, just had some broken rings and blown headgasket. (comnpression was WAY down on 3 cyls.) but everything else looked good, so I just threw new bearings and rings in it and reassembled it. If I'm going to all the trouble of pulling the motor out YET AGAIN, I'm putting in something I know will work perfectly. Bill Quote Link to comment Share on other sites More sharing options...
Tim240z Posted July 9, 2004 Share Posted July 9, 2004 Awwww Bill, don't give up. Just take the bearing caps off (mains and big ends) and plastigauge them to check the clearances. It may be as easy as just getting another set of bearings. Or at most, just pull the crank, have reground to new oversize bearings, recheck clearances and put back together..... Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted July 9, 2004 Share Posted July 9, 2004 LIKE Tim240z said it COULD be something minor! its best to take the time and find out.......look at this as a learning experiance besides youll probably get out cheaper fixing the problem than starting over with a new short block Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted July 9, 2004 Share Posted July 9, 2004 I agree about not giving up on the engine. At least try to find the problem prior to buying another engine. Since you dont know the true history of this engine I would suggest looking at the "Oil Galley Plugs" in the front of the block surrounding the Cam opening.., and the "LITTLE KNOWN" oil galley plug just under the rear main cap inside one of the two larger holes: specifically the larger hole on the oil filter housing side of the block. Remove the oil pump and rear main cap to gain access to the two larger holes under the rear main cap. Yet if the rear galley plug in the rear main oil filter supply line was replaced in the past ... AND DRIVEN IN TO DEEP..., then oil flow from the filter will be restricted. If this plug remains removed your oil will bypass oil filter. This rear plug doesnt have to be removed in order for a machine shop to prep the block, however, if your engine was rebuilt by a methodical machine shop the plug could have been removed and replaced. It is supose to be dropped down about an inch freely where the passage gets smaller...from here it is suppose to be tapped down 3/8 of an inch. If someone before you has driven this plug down say an 1/2 inch, then your oil supply will be restricted. You will have a better understanding of what I am talking about if you go to the lower left of page 38 and upper right of page 107 in the book: "How To Build The Small Block Chevrolet" by Larry Atherton & Larry Schreib Publisher: SA Design Copyright: 1993 It is a light sky blue book with chromed out SBC engine on an engine stand painted racing red: you'll see a snap-on tool chest behind the engine. This is a very good book as it proclaims to be a "Step by Step" book on how to build the SBC and is chock full of pictures. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
tjcannon Posted August 2, 2004 Share Posted August 2, 2004 Problem solved. I'm a good friend of "the dj," and I've been working on this car since he went back up to Austin for work/school and left the car at his house down here. The stumbling issue was fixed by putting a gasket under the distributor (looks like someone forgot ), as it was rotating freely even with the hold-down tightened. It runs VERY consistently now. However, this thread is about oil pressure... I went to the local 24-hour Autozone last night and picked up a stock '81 Datsun Oil Pressure Switch. Upon examining the fitting currently in the block, and the one on the stock Datsun sender, I discovered that the two were EXACTLY the same thread. And given the length of pipe before the sender flared out to 2 inches, I slapped some teflon tape on 'er and screwed it in. THANK YOU LABRAT FOR NOT CUTTING THE ORIGINAL OIL PRESSURE LINE!!!!!! This made my work IMMENSELY easier. I simply plugged in the line to the Datsun sender, and presto changeo! Oil pressure! I believe the problem you were having was related to the air in the line between the block and the aftermarket gauge. I REALLY like the look of the factory gauge, so this worked out pretty nicely. I'm getting pretty much constant 45psi at idle all the way down to 800rpm. Past that, it drops off. I'm not sure if that oil pump is made to operate at such a low RPM, but it works great at 800RPM idle now. PS.. thank you for a relatively clean install. It is making things a lot easier in getting this car up to the shape it deserves to be in. EDIT: I'm talking about the same car this thread was made about. The problem has been resolved. Quote Link to comment Share on other sites More sharing options...
Guest butlersZ Posted August 3, 2004 Share Posted August 3, 2004 I would check the clearences on the mains and such but also the check the oil pump. I've heard that for each thousandths clearence between the teeth inside the pump will lower the oil pressure 10psi. Quote Link to comment Share on other sites More sharing options...
Guest 305240 Posted August 3, 2004 Share Posted August 3, 2004 I've seen dozens of home shop refreshed engines. Almost all of them ran low oil pressure after doing so. Common denominator was none of them changed cam bearings! This you want to have done by a comp machine shop. They need the cam also when they install them. Just my opinion, even if it's an old one. Quote Link to comment Share on other sites More sharing options...
Guest butlersZ Posted August 3, 2004 Share Posted August 3, 2004 I can't see why a machine shop would build or refresh an engine without installing new cam bearings. Do the cam bearings have that much of an effect on oil pressure? Quote Link to comment Share on other sites More sharing options...
Guest butlersZ Posted August 3, 2004 Share Posted August 3, 2004 Anyone ever tried running the high volume oil pump with the low pressure spring? In a engine I recently built I smoothed out some of the oil passages and ran the high volume pump with the low pressure spring installed. The results are 27-30 psi at idle(800rpm) and a full 55-60 psi above 1500 rpm's. No problems so far. Quote Link to comment Share on other sites More sharing options...
labrat Posted August 4, 2004 Author Share Posted August 4, 2004 I'm glad you were able to get it straightened out, it's been bothering me for weeks. The gasket under the dizzy i knew about (i've had that thing on and off 17 times in the past 6 weeks), but I didn't know it was affecting the timing like that. Nice job on the oil pressure thing, i was certain that there was some crucial point that was increasing clearance (like a rod bearing) when it got hot. I'm glad you were able to find the correct wire for the fuel pressure guage. I tried to keep as much wiring as possible intact and labeled, although the labels didn't fare too good after 3 years and 3 coats of different color paint. The guages I had installed were strictly temporary to monitor the engine while I got the stock guages working. If you get the tach working, then I will be impressed Anyway, you two take good care of the car, and call me if you have any questions about how anything was done. I will help you out any way I can. Sorry the wiring is in such a mess, but I had a couple of issues and had to tear into my harnesses. Anyway, enjoy... Bill Quote Link to comment Share on other sites More sharing options...
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