worn bearing cause low oil pressure?
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From: hls on 7 Jun 2010 11:35 "Don Stauffer" <stauffer(a)usfamily.net> wrote in message news:4c0cf11c$0$87071$815e3792(a)news.qwest.net... > Yes, a modern engine does use a closed loop oil system. If it didn't you > would have to replace lots of oil every time you drove the car. > > The oil pump pushes against resistance. If the resistance to flow is > substantially lowered, the pressure in the system will drop. The bearing > clearances definitely affect the flow and hence the pressure. The concern > is that the flow may then end up short circuiting, and not getting into > some passages, taking the road of least resistance through the main and > rod bearings. Lots of flow for them, but not enough for other important > places. Pressure is little more than a parameter of oil flow in traditional sleeve or insert bearing engines as far as lubrication goes. If you have a roller or needle bearing engine, as Porsche had some 60 years ago, the pressure may not mean very much as long as the oil flow through the bearings is adequate. (Those cars, IIRC, didnt mess around with hydraulic valve lifters either.) Here is an interesting link showing what Timken did with an engine converted to roller bearings: http://engineeringtv.com/video/Rollerized-Engines
From: Jason James on 7 Jun 2010 17:45 "Nomen Nescio" <nobody(a)dizum.com> wrote in message news:489d17b28a1eac6bb4836a6d940d2e19(a)dizum.com... >I noticed low oil pressure when the revs are down. > So I get out the workshop manual, and it lists among the > possible causes "worn bearings". How is it so? > I can't see that oil is pumped through the bearings in > a closed fashion, such that worn bearing would reduce > the back pressure. If you find the engine has noisy bearings when you stab the throttle and release quickly (engine temp must be normal, as otherwise the bearing running clearances will be deceptively small), and you decide to pull it down, dont be fooled by the "maximum bearing wear clearance" Many manuals say up to 4 thou of an inch or 0.1 mm. This is way too wide, and many a backyarder has put an engine back together thinking things are dandy, only to find the low OP and general noise is still there. Some use Plastigauge which is a soft strip of plastic which is left in the journal-bearing space. Once the bearing caps are torqued up, you reverse the procedure an examine the P-gauge for how much its been flatterned. There is a scale on the PG to assist. I haven't found PG to be much good to accurately give a clearance indication. Personally, I go by either readings taken by a micrometer on the crank-journals (these may be worn oval and you need to take 3 readings around the journal), and a micrometer measurement taken inside the conrod bigend with bearing fitted,..or use a technique recommended by VW for backyarders>> Fit a new *oiled* bearing, install the conrod on the crank, move the conrod to straight up (12 oclock),..then tip it gentley so it starts to fall around the crank journal. It should take about 6 seconds to fall completely over. Sounds a bit hit and miss? Maybe,..but when you do the same test on a worn engine,..the conrod falls over in about a second :-) Jason
From: Noddy on 7 Jun 2010 18:23 "Don Stauffer" <stauffer(a)usfamily.net> wrote in message news:4c0cf11c$0$87071$815e3792(a)news.qwest.net... > Yes, a modern engine does use a closed loop oil system. If it didn't you > would have to replace lots of oil every time you drove the car. There's nothing "modern" about such a system. They've been in place for over 100 years. -- Regards, Noddy.
From: Don Stauffer on 8 Jun 2010 09:51 On 6/7/2010 5:23 PM, Noddy wrote: > "Don Stauffer"<stauffer(a)usfamily.net> wrote in message > news:4c0cf11c$0$87071$815e3792(a)news.qwest.net... > >> Yes, a modern engine does use a closed loop oil system. If it didn't you >> would have to replace lots of oil every time you drove the car. > > There's nothing "modern" about such a system. They've been in place for over > 100 years. > > -- > Regards, > Noddy. > > True. But some engines in 1910 may have used older designs. Some had individual oil cups at each bearing surface, and these were open- oil was wasted and not returned with a pump. Some had no pump, merely a reservior high up and gravity feed. No return/re-use of oil- open system. Didn't Chevy go to pressurized rods only around 1940 or so?
From: jim on 8 Jun 2010 11:06
Don Stauffer wrote: > > On 6/7/2010 5:23 PM, Noddy wrote: > > "Don Stauffer"<stauffer(a)usfamily.net> wrote in message > > news:4c0cf11c$0$87071$815e3792(a)news.qwest.net... > > > >> Yes, a modern engine does use a closed loop oil system. If it didn't you > >> would have to replace lots of oil every time you drove the car. > > > > There's nothing "modern" about such a system. They've been in place for over > > 100 years. > > > > -- > > Regards, > > Noddy. > > > > > True. But some engines in 1910 may have used older designs. Some had > individual oil cups at each bearing surface, and these were open- oil > was wasted and not returned with a pump. Some had no pump, merely a > reservior high up and gravity feed. No return/re-use of oil- open system. > > Didn't Chevy go to pressurized rods only around 1940 or so? I believe it was 1953 maybe '52. The 216 six had rods with a cup like thing on the rods that dipped into the oil in the pan and that lubricated the rods, pistons and piston pins. I think it was the mid 30's when they started using an oil pump but the pump only lubricated the valve train and the main bearings. The rest was splash lubrication. -jim |