I ask this out of curiosity, but if the main & rod bearing clearances are a little looser than what the TSRM calls for, but the oil pump is shimmed, would there still be an increased risk of trouble?
clearance vs. oil pressure......
- Thread starter rakkasan
- Start date
why chance it? you could speculate that the increased oil pressure would keep the loose bearings safe, but then again loose is loose, right?
Mark, the relief will not open until 40 psi in stock configuration.
The main and rod clearances (along with cam bearing and oil drive shaft clearances) determine oil pressure at idle. With the pump shimmed, you can see upwards of 60 psi at higher rpms, but it does nothing to protect you down low.
The main and rod clearances (along with cam bearing and oil drive shaft clearances) determine oil pressure at idle. With the pump shimmed, you can see upwards of 60 psi at higher rpms, but it does nothing to protect you down low.
IHI-RHC7 said:
that makes sense. Switching to a full flow (ie getting rid of the relief valve) would solve that problem, right? Fot the record, I'm looking for some added protection from rod knock.
The problem is that the pump is a positive displacement pump. At idle, it is full flow and it simply doesn't move enough oil to build substantial pressure above 10 psi. The only way to cure this is to tighten all the clearances so the engine "consumes" less oil at any given moment, or increase the displacement of the pump, or overdrive the pump.
The only reasonable thing to do is make sure that the engine is assembled on the tight side of toyota specs. If the clearances are loose, and you are stock grind or 10 over, you can get genuine toyota bearings to bring the clearances into spec...
The only reasonable thing to do is make sure that the engine is assembled on the tight side of toyota specs. If the clearances are loose, and you are stock grind or 10 over, you can get genuine toyota bearings to bring the clearances into spec...
I've got mine shimmed...I used 2 washers and it gives me 10-15 psi at idle and 35-40 psi at 3000 rpm using 0-30W synthetic with the motor at ops temp. I was thinking the same thing as you Mark...seeing 5 psi at idle makes me nervous.
But the most important thing for the rod bearings is:
But the most important thing for the rod bearings is:
:biglaugh:IHI-RHC7 said:
IHI-RHC7 said:
Here's a little problem. I'm not exactly sure what the clearances are, although the motor is assembled & waiting to be picked up. My machinist died a few hours after assembling my motor, so there's no way of telling what the exact clearances are. While I'm 99% positive that he has the clearance correct, the other 1% of doubt will bang in my head like a drum until I either blow the motor or I sell it.
I just asked his dad to tear it down & go through the motor. He said that he has no problems what so ever doing it, as he wants it done right too. He even said that he would do it over the weekend.
The thing we forget is that the 7m has 7 main, 6 rod, 2 aux, 14 cam, and 2 turbo bearings to oil plus 6 piston oil squirters that aren't supposed to open until pressure gets above 20 psi.
That's 31 bearings in all.
The turbo right off the bat sucks down 15-20% of the oil flow from the pump.
So you're left with 85% of the oil pumps capacity to oil 29 bearings.
The bearings consume oil based on two main variables, surface area and oil clearance.
So the mains have the largest surface area, so consume the largest volume of oil per bearing at any given time.
Next in size are the rod bearings.
Then the two aux shaft bearings.
Finally the 14 cam bearings.
So, if the mains are set loose, the seven largest bearings begin to require much more oil to float the crank.
If the rods are set loose, six if the second largest bearings begin to require more oil.
Same with the aux shaft and especially with 14 cam bearings.
Now the head is fed oil through a 3/16" or so port in the block. When the cam bearings are loose, the pressure in the head decreases and this hole becomes a sort of internal oil leak. Does it drop the pressure in the block? not if the pump is deliviering enough volume to keep pressure up. Does this happen at idle? No. The pump delivers a hearty amount of oil, but loose bearings outflow the pump very quickly. Sure, once the revs are up, the pressure perks up. Because the bearings need a flow rate of oil in volume per time, not volume per rev.
When the pump spins faster, the ratio of volume per time over volume per rev increases proportionally, thus the oil flow outflows the bearing consumption and the pressure rises.
In fact, the pressure rises until something gives. That's why we have a relief valve, to regulate maximum oil pressure. I'm sorry, but at idle, the relief valve cannot help you unless the pump were moving enough volume of oil to overwhelm the bearings ability to drain back. If this were the case, we would all have 40 psi at idle and our pumps would explode once the revs got over 3000 rpm... [/rant]
Have him check them. Rods and mains should be no looser that 0.0015"
That's 31 bearings in all.
The turbo right off the bat sucks down 15-20% of the oil flow from the pump.
So you're left with 85% of the oil pumps capacity to oil 29 bearings.
The bearings consume oil based on two main variables, surface area and oil clearance.
So the mains have the largest surface area, so consume the largest volume of oil per bearing at any given time.
Next in size are the rod bearings.
Then the two aux shaft bearings.
Finally the 14 cam bearings.
So, if the mains are set loose, the seven largest bearings begin to require much more oil to float the crank.
If the rods are set loose, six if the second largest bearings begin to require more oil.
Same with the aux shaft and especially with 14 cam bearings.
Now the head is fed oil through a 3/16" or so port in the block. When the cam bearings are loose, the pressure in the head decreases and this hole becomes a sort of internal oil leak. Does it drop the pressure in the block? not if the pump is deliviering enough volume to keep pressure up. Does this happen at idle? No. The pump delivers a hearty amount of oil, but loose bearings outflow the pump very quickly. Sure, once the revs are up, the pressure perks up. Because the bearings need a flow rate of oil in volume per time, not volume per rev.
When the pump spins faster, the ratio of volume per time over volume per rev increases proportionally, thus the oil flow outflows the bearing consumption and the pressure rises.
In fact, the pressure rises until something gives. That's why we have a relief valve, to regulate maximum oil pressure. I'm sorry, but at idle, the relief valve cannot help you unless the pump were moving enough volume of oil to overwhelm the bearings ability to drain back. If this were the case, we would all have 40 psi at idle and our pumps would explode once the revs got over 3000 rpm... [/rant]
Have him check them. Rods and mains should be no looser that 0.0015"
Pulling the oil pan and checking the clearances with a flexi guage should be no problem...easy with the motor out of the car.
keep in mind that as with the turbo
pressure is RESISTNACE to flow (Bernoullis principle at work). Or in scientific terms
as Pressure increases VOLUME MUST DECREASE!! See all electric fuel pumps for proof. You can PLUG all the oil holes and see 100+ psi but you are flowing NOTHING
pressure is RESISTNACE to flow (Bernoullis principle at work). Or in scientific terms
as Pressure increases VOLUME MUST DECREASE!! See all electric fuel pumps for proof. You can PLUG all the oil holes and see 100+ psi but you are flowing NOTHING
figgie said:keep in mind that as with the turbo
pressure is RESISTNACE to flow (Bernoullis principle at work). Or in scientific terms
as Pressure increases VOLUME MUST DECREASE!! See all electric fuel pumps for proof. You can PLUG all the oil holes and see 100+ psi but you are flowing NOTHING
That's true, but in order to increase pressure in a 7M (or any motor), volume must increase because the oil passages don't decrease in diameter....
Ok...here's how I see it. Pressure is rate, diameter of the pipe (oil channel or bearing clearance) is volume. Since we can't change the volume, we have to change the rate. That will work only to a certain point...the cross section of the channel will only support so much flow; as the pressure increases past that the resistance to flow makes it a moot point (this is where figgie is correct). In fact past that point pressure will increase dramatically and start exceeding design limitations. However, below that point, you can get better flow with increased psi.
That's why I only shimmed the pump with 2 washers...I wanted higher pressure at idle more than higher pressure at high RPM. That's with the rest of the system stock...so far, it's worked beautifully. I've read where using 5-8 washers was advocated..IMO that's nuts...stuff is going to start blowing apart from the pressure.
That's why I only shimmed the pump with 2 washers...I wanted higher pressure at idle more than higher pressure at high RPM. That's with the rest of the system stock...so far, it's worked beautifully. I've read where using 5-8 washers was advocated..IMO that's nuts...stuff is going to start blowing apart from the pressure.
Jake: You forgot the 6 squirter holes in the beam of the rods....
Our motors are a huge controlled leak.
Our motors are a huge controlled leak.
I thought about putting them in there, but I thought it'd be too cluttered!
Figgie:
If the oil were not allowed to leave the bearing surfaces, you would have mondo pressure with no flow and aside from lack of cylinderwall lube, this would be ideal.
Pressure is a restriction to flow. In a turbo, it is also the byproduct of adiabatic compression, which is NOT a restriction to flow.
By shimming the oil pump, you are NOT restricting the flow to the motor.
The idea to increase the pressure in our motors is to restrict the flow of oil away from mating surfaces. That is, tighten tolerances. The pump is posative displacement, so when the shaft turns, oil moves. The pressure of the system is completely independant of the flow rate due to this fact.
By your logic, you are suggesting that when one shims the oil pump relief, or increases the pressure by means of tighter clearances, the pump of the shaft spins slower. Well, last time I checked, it was connected to the crank by a timing belt.
Figgie:
If the oil were not allowed to leave the bearing surfaces, you would have mondo pressure with no flow and aside from lack of cylinderwall lube, this would be ideal.
Pressure is a restriction to flow. In a turbo, it is also the byproduct of adiabatic compression, which is NOT a restriction to flow.
By shimming the oil pump, you are NOT restricting the flow to the motor.
The idea to increase the pressure in our motors is to restrict the flow of oil away from mating surfaces. That is, tighten tolerances. The pump is posative displacement, so when the shaft turns, oil moves. The pressure of the system is completely independant of the flow rate due to this fact.
Electric fuel pumps are not PD pumps, they are vane pumps which opperate at a constant speed and flow a rate that is inverseley proportional to pressure. Our oil pumps DO NOT behave in this fashion.figgie said:
By your logic, you are suggesting that when one shims the oil pump relief, or increases the pressure by means of tighter clearances, the pump of the shaft spins slower. Well, last time I checked, it was connected to the crank by a timing belt.
LOL but they're one of the worst leaks we have!
Looser tolerances will mean more space for the Oil Wedge to be displaced increasing the chance of Metal to Metal contact between the bearing and the crank surface.
While modern bearings are robust even the best of them will only do this a limited number of times before you start getting pickup on the crank surface which in turn increases bearing wear with RodKnock only being a short time away.
Looser tolerances will mean more space for the Oil Wedge to be displaced increasing the chance of Metal to Metal contact between the bearing and the crank surface.
While modern bearings are robust even the best of them will only do this a limited number of times before you start getting pickup on the crank surface which in turn increases bearing wear with RodKnock only being a short time away.
Ditto my Pauters don't have the extra holes
I figure the piston coatings save it at idle and the squirters do their thing at about 1500 rpm.
I figure the piston coatings save it at idle and the squirters do their thing at about 1500 rpm.