nosechunks said:
yep, try using thinner oil. more like a 5w-30 or even a 10w-30. that way you actually get some oil flow. bearing like flow, to get flow your gonna need thinner oil.
low rpm knock advice
- Thread starter ATL88Supra
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yep, try using thinner oil. more like a 5w-30 or even a 10w-30. that way you actually get some oil flow. bearing like flow, to get flow your gonna need thinner oil.
its not oil, cause it wont happen when the car is cold if it was a sqwrter that was cloged it would do it even more so when cold. when cold i have 60 pounds psi cold at idle when hot it levels off at just under 40 pounds 39 ? at idle, when driveing it holds at 60 pounds
thats really high pressure to have on a 7m. seriously need to think about thinner oil, pressure doesnt mean protection. those bearing need to have flow.
too high oil pressure can possible scrub the bearings...
the oil is far too thick unless you have an odd build and clearances (like IJ)
try changing to a 5w-30 and see if the problem persists
the oil is far too thick unless you have an odd build and clearances (like IJ)
try changing to a 5w-30 and see if the problem persists
Thinner oil would make it worse.
Im going to go ahead and make an educated guess or hypothasize on the situation.
You have too much oil clearance in the bearings and or gears in the oil pump and or the oil pressure gauge you have is inaccurate. when cold the oil is thicker, making the pressure increase as a result of higher resistance to flow therefore giving the bearings more support from higher pressure. when the engine warms up the oil temperature increases, the oil thins as a result of temperature increase in turn decreasing oil pressure due to less resistance to flow to the point where the support between bearings is insufficient subsequently causing the low rpm, Hot, knock.
it wont do it when cold because the oil is thicker and "filling" the clearance between bearings, and wont do it at above 900rpm because then the oil pump is spinning fast enough to move enough oil to "fill" in the clearance space between the bearings.
the coincidence between cold and low rpm makes me believe its a low oil pressure issue.
This is all assuming there isnt any blocked passages starving bearings of oil flow/pressure.
Im going to go ahead and make an educated guess or hypothasize on the situation.
You have too much oil clearance in the bearings and or gears in the oil pump and or the oil pressure gauge you have is inaccurate. when cold the oil is thicker, making the pressure increase as a result of higher resistance to flow therefore giving the bearings more support from higher pressure. when the engine warms up the oil temperature increases, the oil thins as a result of temperature increase in turn decreasing oil pressure due to less resistance to flow to the point where the support between bearings is insufficient subsequently causing the low rpm, Hot, knock.
it wont do it when cold because the oil is thicker and "filling" the clearance between bearings, and wont do it at above 900rpm because then the oil pump is spinning fast enough to move enough oil to "fill" in the clearance space between the bearings.
the coincidence between cold and low rpm makes me believe its a low oil pressure issue.
This is all assuming there isnt any blocked passages starving bearings of oil flow/pressure.
nosechunks said:
gonna have to disagree, bearings need flow, not pressure. you guys need to understand this. bearings need flow nosechunks your thinking that thicker oil will "coushin" the bearings. thinner oil after 900 rpm will give the bearings the "flow" they need. to "fill" the clearance space between bearings they need "FLOW" more oil flow. how can you think it has low oil pressure issues? he has way way to high of pressure for a 7m.
supramike7m said:
If that pressure reading is accurate.... i look at facts that cant be miscalibrated.
If water is visibly/audibly boiling at sea level but the thermometer in the same water reads 85 degrees Fahrenheit what are the chances of it burning you? obviously since the water IS IN FACT boiling the temperature must be equal to or above 212F (100C) no matter what any thermometer says.
The facts are he has a knock at low rpm when hot, at that time oil pressure (regardless of what it is) is at its lowest. Show me another Fact that coincides with his condition. The only other facts are above 900rpm, when oil pressure is higher then that of 900rpm, the knock is gone and when cold at 900rpm the knock is not herd, also when oil pressure is higher then that of hot idle.
I understand flow of oil is necessary to insure lubrication to all vital parts, but 15-40 isnt so thick as to resist flow enough to create 40psi of hot idle pressure and starve anything from oil flow. When i bought my car it had rod knock, i ran 20-50 in it all summer (70-90 degree weather) and never had any problems, yet did reduce the knock. Having oil moving threw the bearing surfaces doesn't keep them apart, pressurized flow does, its a compromise.
If he really has 40 psi of oil pressure on an accurate gauge, then something is blocking a passage in the block/crank post oil pressure port. Even running on straight 90W Gear oil i doubt would not knock with 40 psi of pressure.
Your correct bearings need flow more then pressure, but how will oil stay in the bearing without being pressured in? 1-2 psi of oil pressure wont keep a 300 horsepower engines parts from contacting each other at high RPM no matter what the flow.
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Positive displacement pump......
If the motor is turning it's flowing Oil, 1 to 1 right up until any of the internal leaks open (ie: Squirters,relief valves and so on).
If anything is open at low rpm it could possibly be bleeding enough pressure at 900 rpm to allow metal to metal contact and noise, soon as rpm increases so does pump flow/volume and you float whatever was making the noise and it stops.
Heavier oil will not displace as easily as light oil so this might be enough to prevent the contact.
Saying "Heavier oil ISN'T flowing and is just making pressure due to resistance" is not quite correct (it's not like it's 90 weight gear oil which flows quite well once it's warmed to operating temps), almost as much as "too high a pressure scrubs bearings" NEVER seen an instance of this ever but it's quite often quoted as fact.
If the motor is turning it's flowing Oil, 1 to 1 right up until any of the internal leaks open (ie: Squirters,relief valves and so on).
If anything is open at low rpm it could possibly be bleeding enough pressure at 900 rpm to allow metal to metal contact and noise, soon as rpm increases so does pump flow/volume and you float whatever was making the noise and it stops.
Heavier oil will not displace as easily as light oil so this might be enough to prevent the contact.
Saying "Heavier oil ISN'T flowing and is just making pressure due to resistance" is not quite correct (it's not like it's 90 weight gear oil which flows quite well once it's warmed to operating temps), almost as much as "too high a pressure scrubs bearings" NEVER seen an instance of this ever but it's quite often quoted as fact.
Whoa Guys 
We don't know what condition the bearings are in and what the clearances are. He's showing 60 psi at idle cold...40 psi hot, even running a 20W-50 wouldn't make it cause a low rpm knocking noise. He's getting plenty of flow...the high pressures he's showing at idle and cruise is the resistance to the 15W-40 going through the bearings. You guys are right though...a 0W 0r 5W-30 will give him better flow and help keep the bearings cooler...it would be better for the motor over the long term, but I don't think the 15W-40 is the cause of this.
And if his clearances were on the wide side, sometimes a thicker oil will buy you some time before full blown rod knock develops...it doesn't exactly "fill the gap" per say, but it does have a thicker film layer and works better under extreme pressure where the oil is squeezed to the point of boundary lubrication. This is exactly what you'd see with bearing gaps opening up and taking the hit from the piston/rod on the power stroke. I don't think this is the case here...his pressures are too good. It is possible an oil squirter is robbing pressure to the bearings like IJ said, but there's other things that can cause a low rpm knocking sound.
This sounds like something in the motor is heating up and "ticking" against something else. He needs to get a stethoscope and narrow the noise down. A couple of things to look at:
- I had a pair of AEM cam gears that was bumping against one of the bolts holding the back plate to the head...I could hear it big time at low rpm, but it went away at 1500 rpm or so. Finally found it and did a bit of a "clearance adjustment" on the gears with a lathe...no more noise.
- The bolts holding the flex plate on at the back of the motor on an auto tranny can loosen up...creates a knocking sound. Seen this one too.
- Might want to check the timing belt idler pulley and make sure it's not wobbling on ya.
- Might want to take a look at the oil pump drive gear...been a couple of them self destructing lately.
Question...did you take ALL the belts off and run it?
We don't know what condition the bearings are in and what the clearances are. He's showing 60 psi at idle cold...40 psi hot, even running a 20W-50 wouldn't make it cause a low rpm knocking noise. He's getting plenty of flow...the high pressures he's showing at idle and cruise is the resistance to the 15W-40 going through the bearings. You guys are right though...a 0W 0r 5W-30 will give him better flow and help keep the bearings cooler...it would be better for the motor over the long term, but I don't think the 15W-40 is the cause of this.
And if his clearances were on the wide side, sometimes a thicker oil will buy you some time before full blown rod knock develops...it doesn't exactly "fill the gap" per say, but it does have a thicker film layer and works better under extreme pressure where the oil is squeezed to the point of boundary lubrication. This is exactly what you'd see with bearing gaps opening up and taking the hit from the piston/rod on the power stroke. I don't think this is the case here...his pressures are too good. It is possible an oil squirter is robbing pressure to the bearings like IJ said, but there's other things that can cause a low rpm knocking sound.
This sounds like something in the motor is heating up and "ticking" against something else. He needs to get a stethoscope and narrow the noise down. A couple of things to look at:
- I had a pair of AEM cam gears that was bumping against one of the bolts holding the back plate to the head...I could hear it big time at low rpm, but it went away at 1500 rpm or so. Finally found it and did a bit of a "clearance adjustment" on the gears with a lathe...no more noise.
- The bolts holding the flex plate on at the back of the motor on an auto tranny can loosen up...creates a knocking sound. Seen this one too.
- Might want to check the timing belt idler pulley and make sure it's not wobbling on ya.
- Might want to take a look at the oil pump drive gear...been a couple of them self destructing lately.
Question...did you take ALL the belts off and run it?
damn good idea. try it and see what happens, its worth a shot.
also i see your what your saying nosechunks. not tryin to say your wrong or that im right. i can see exactly what you mean.
Question...did you take ALL the belts off and run it?[/QUOTE]
also i see your what your saying nosechunks. not tryin to say your wrong or that im right. i can see exactly what you mean.
Question...did you take ALL the belts off and run it?[/QUOTE]
well got my stethascope out and found that it is not comeing fromt he bottom end, it is infact comeing from where the flywheel meets the autotrans
drive plate maybe bust TC ? hmmm i think i will pull the eng this weekend
drive plate maybe bust TC ? hmmm i think i will pull the eng this weekend
Based on what you just said...my money is on the drive plate
Cracked or a bandit bolt...busting a TC is not too common.
Edit: BTW - running a 0W or 5W-30 oil is not going to hurt ya with those pressures...I'm betting your bearing clearances are nice and tight. It will actually help over the long run.
Cracked or a bandit bolt...busting a TC is not too common.
Edit: BTW - running a 0W or 5W-30 oil is not going to hurt ya with those pressures...I'm betting your bearing clearances are nice and tight. It will actually help over the long run.
ATL: It's pretty easy you just discard the back plate that goes between the Crank and the driveplate then get another driveplate cut the ring gear off put it in a lathe to true up and fit it in place of the discarded spacer.
Been doing these since the old Big Block Chev days and even used one to make a flywheel for my Toyota V8 in the Datsun way back by bolting a piece of 1/2" plate steel to a double driveplate.
Been doing these since the old Big Block Chev days and even used one to make a flywheel for my Toyota V8 in the Datsun way back by bolting a piece of 1/2" plate steel to a double driveplate.