My ls2 motor (turbocharged) has a main bearing clearance of 2.2 thousnaths I have been running castrol gtx synthetic 5w40 a recent teardown inspection at 8000 miles showed either heat or scuffing on the bearings. I want to go thinner but worry about oil film crush. what to do?
oil weight with 2.2 thousanths bearing clearance
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MolaKule
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Was it run-in gently or aggressively new?
What are the bearing loadings from the bolts?
What about oil flow?
You need an oil pump to circulate enough oil for cooling.
I.E., there are many variables that can cause bearing wipe and overheating.
What are the bearing loadings from the bolts?
What about oil flow?
You need an oil pump to circulate enough oil for cooling.
I.E., there are many variables that can cause bearing wipe and overheating.
Do you mean .00022?
Twenty two ten thousandths or .0022 twenty two thousandths.
No help from me, just like math- that's all.
Twenty two ten thousandths or .0022 twenty two thousandths.
No help from me, just like math- that's all.
And what oil exactly were you using? GTX is not synthetic, Edge is, unless I have missed a re-branding.
You can and should go to a lower number oil. But, your issues are more environmental. You live in a strange world of nitrous and 8,000 mile inspection teardowns.
You can and should go to a lower number oil. But, your issues are more environmental. You live in a strange world of nitrous and 8,000 mile inspection teardowns.
typical factory (stock) design, main bearings clearances run between 0.8 thou to 1.5 thou, seldom seen factory spec running beyond 1.6 thou.
2.2 thou IMO is excessive.
Q.
2.2 thou IMO is excessive.
Q.
Originally Posted By: nitrouspaul
My ls2 motor (turbocharged) has a main bearing clearance of 2.2 thousnaths I have been running castrol gtx synthetic 5w40 a recent teardown inspection at 8000 miles showed either heat or scuffing on the bearings. I want to go thinner but worry about oil film crush. what to do?
If your bearings are showing contact with the crank at 8000 miles, I definitely wouldn't be going thinner. Why was the engine torn down? Due to a failure?
My ls2 motor (turbocharged) has a main bearing clearance of 2.2 thousnaths I have been running castrol gtx synthetic 5w40 a recent teardown inspection at 8000 miles showed either heat or scuffing on the bearings. I want to go thinner but worry about oil film crush. what to do?
If your bearings are showing contact with the crank at 8000 miles, I definitely wouldn't be going thinner. Why was the engine torn down? Due to a failure?
Originally Posted By: Quest
typical factory (stock) design, main bearings clearances run between 0.8 thou to 1.5 thou, seldom seen factory spec running beyond 1.6 thou.
2.2 thou IMO is excessive.
Q.
I agree, .0022" is on the loose side of the range for an LS.
That would push the oil viscosity requirement to a thicker grade to maintain film thickness.
typical factory (stock) design, main bearings clearances run between 0.8 thou to 1.5 thou, seldom seen factory spec running beyond 1.6 thou.
2.2 thou IMO is excessive.
Q.
I agree, .0022" is on the loose side of the range for an LS.
That would push the oil viscosity requirement to a thicker grade to maintain film thickness.
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Originally Posted By: A_Harman
Originally Posted By: nitrouspaul
My ls2 motor (turbocharged) has a main bearing clearance of 2.2 thousnaths I have been running castrol gtx synthetic 5w40 a recent teardown inspection at 8000 miles showed either heat or scuffing on the bearings. I want to go thinner but worry about oil film crush. what to do?
If your bearings are showing contact with the crank at 8000 miles, I definitely wouldn't be going thinner. Why was the engine torn down? Due to a failure?
Don't forget that for any given contact surface area RE: main bearings, the load exerted on them (and still able to suspend the rubbing surface via hydrowedge means), you need good, consistent performing oil pump and very low leaks (throughout all oil pressured moving parts, such as Hydraulic valve adjusters, cam and crank bearings, etc.), and also being able to maintain that hydrowedge film during high speed, high load, and most important of all, oil temp.
higher oil temp means oil "thins" out more; higher main/rod bearing clearances means high rate of oil pressure leaks through excessive clearances. Lastly: if the engine (assuming modified from stock) stock spec. doesn't have enough headroom for performance upgrades besides structural rigidity for rotating components, etc.), crazy boosting power output w/o due consideration in investigating the stock main bearing and con rod bearing areas, will definitely lead to disaster.
Too many a time I've seen shops who do the aftermarket boost using off the shelf parts (chips, manifolds, add-on turbos, etc.) will lead to bearing wiping or even engine block bottom end exploding or rod breakage due to no consideration how well the stock bottom end can handle the boost.
2.2 thou is excessive IMO, and I'm sticking to it regardless of oil viscosity you or your shop has told you to use.
Q.
Originally Posted By: nitrouspaul
My ls2 motor (turbocharged) has a main bearing clearance of 2.2 thousnaths I have been running castrol gtx synthetic 5w40 a recent teardown inspection at 8000 miles showed either heat or scuffing on the bearings. I want to go thinner but worry about oil film crush. what to do?
If your bearings are showing contact with the crank at 8000 miles, I definitely wouldn't be going thinner. Why was the engine torn down? Due to a failure?
Don't forget that for any given contact surface area RE: main bearings, the load exerted on them (and still able to suspend the rubbing surface via hydrowedge means), you need good, consistent performing oil pump and very low leaks (throughout all oil pressured moving parts, such as Hydraulic valve adjusters, cam and crank bearings, etc.), and also being able to maintain that hydrowedge film during high speed, high load, and most important of all, oil temp.
higher oil temp means oil "thins" out more; higher main/rod bearing clearances means high rate of oil pressure leaks through excessive clearances. Lastly: if the engine (assuming modified from stock) stock spec. doesn't have enough headroom for performance upgrades besides structural rigidity for rotating components, etc.), crazy boosting power output w/o due consideration in investigating the stock main bearing and con rod bearing areas, will definitely lead to disaster.
Too many a time I've seen shops who do the aftermarket boost using off the shelf parts (chips, manifolds, add-on turbos, etc.) will lead to bearing wiping or even engine block bottom end exploding or rod breakage due to no consideration how well the stock bottom end can handle the boost.
2.2 thou is excessive IMO, and I'm sticking to it regardless of oil viscosity you or your shop has told you to use.
Q.
Originally Posted By: A_Harman
Originally Posted By: Quest
typical factory (stock) design, main bearings clearances run between 0.8 thou to 1.5 thou, seldom seen factory spec running beyond 1.6 thou.
2.2 thou IMO is excessive.
Q.
I agree, .0022" is on the loose side of the range for an LS.
That would push the oil viscosity requirement to a thicker grade to maintain film thickness.
That is a prime candidate for Mobil 1, 15W-50 AND properly managed oil temperatures. I've used that oil with stunning success in my turbocharged engines. I'm not sure of your specific output, but I typically run 200HP per liter on that oil with just slightly lower clearances. (about 0.0020 inches)
If I run into temperature problems during the South Florida summers, I step up to M1, 20W-50 motorcycle oil. It's slightly more viscous at extreme temperatures, without being too viscous at startup. Keeps the oil pressure exactly right.
I am very careful to warm up my engines carefully. I don't blast, full throttle on a stone cold engine, like some drag racers do.
Originally Posted By: Quest
typical factory (stock) design, main bearings clearances run between 0.8 thou to 1.5 thou, seldom seen factory spec running beyond 1.6 thou.
2.2 thou IMO is excessive.
Q.
I agree, .0022" is on the loose side of the range for an LS.
That would push the oil viscosity requirement to a thicker grade to maintain film thickness.
That is a prime candidate for Mobil 1, 15W-50 AND properly managed oil temperatures. I've used that oil with stunning success in my turbocharged engines. I'm not sure of your specific output, but I typically run 200HP per liter on that oil with just slightly lower clearances. (about 0.0020 inches)
If I run into temperature problems during the South Florida summers, I step up to M1, 20W-50 motorcycle oil. It's slightly more viscous at extreme temperatures, without being too viscous at startup. Keeps the oil pressure exactly right.
I am very careful to warm up my engines carefully. I don't blast, full throttle on a stone cold engine, like some drag racers do.
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Originally Posted By: Quest
2.2 thou is excessive IMO, and I'm sticking to it regardless of oil viscosity you or your shop has told you to use.Q.
I called my BIL, a third gen machinist. he said that is too much clearance, clarence. period.
If you need the name of the best machine shop in the SE US just PM me...
2.2 thou is excessive IMO, and I'm sticking to it regardless of oil viscosity you or your shop has told you to use.Q.
I called my BIL, a third gen machinist. he said that is too much clearance, clarence. period.
If you need the name of the best machine shop in the SE US just PM me...
Its not excessive really, I run my honda engines (real tight clearances from factory) at .002-.0025 all day when making over 100hp per liter and spinning 9000+ rpm you had better have some clearance! Use a good oil pump and don't use todays "water" they call oil!
2.2 thousanths? clearance link
If the difference in the journal size and ID of the bearing is .0022", then the clearance between the bearing and journal is .0011".
I've seen people start their engines and rev them to the moon before the oil pressure is on the gauge.
I've seen people start their engines and rev them to the moon before the oil pressure is on the gauge.
Neither oil pressure nor flow provide hydrodynamic oil films, it's the difference in surface speeds and the geometry, viscosity and applied loads.
The hydrodynamic wedge is formed by the closing gap that drags the oil into the clearance between the rotating shaft and the stationary bearing.
If the bearing is too loose, the shaft load is spread along a narrower line of pressure axially along the bearings, versus a tighter clearance having a wider support (think stilletos versus loafers).
The ultimate load carrying capacity will be lower for any given viscosity within the bearing.
But the wider clearances will allow a cooler running bearing, due to more side leakage, provided the oil pump can keep up.
Looks like the stilletto has won in your case, and I agree that the clearances are excessive...
The hydrodynamic wedge is formed by the closing gap that drags the oil into the clearance between the rotating shaft and the stationary bearing.
If the bearing is too loose, the shaft load is spread along a narrower line of pressure axially along the bearings, versus a tighter clearance having a wider support (think stilletos versus loafers).
The ultimate load carrying capacity will be lower for any given viscosity within the bearing.
But the wider clearances will allow a cooler running bearing, due to more side leakage, provided the oil pump can keep up.
Looks like the stilletto has won in your case, and I agree that the clearances are excessive...
Originally Posted By: Shannow
and I agree that the clearances are excessive...
Those clearances are within or very close to the limits for new engines. Con rods are allowed 0.0025 (new) and 0.003 (service limit)
Main bearings are allowed 0.0021 (new) and 0.0025 (service limit)
And, those clearances are well within limits for highly loaded racing engines. Which remain about 0.001 inches per inch of bearing diameter. Because when power adders such as nitrous oxide, turbocharging or supercharging are used, or the engine’s power output gets to 500 plus horsepower range, looser bearing clearances are safer to accommodate crankshaft flexing, main bore and rod bore distortion.
Again, use a more viscous oil and manage temperatures properly. It will solve your problem.
and I agree that the clearances are excessive...
Those clearances are within or very close to the limits for new engines. Con rods are allowed 0.0025 (new) and 0.003 (service limit)
Main bearings are allowed 0.0021 (new) and 0.0025 (service limit)
And, those clearances are well within limits for highly loaded racing engines. Which remain about 0.001 inches per inch of bearing diameter. Because when power adders such as nitrous oxide, turbocharging or supercharging are used, or the engine’s power output gets to 500 plus horsepower range, looser bearing clearances are safer to accommodate crankshaft flexing, main bore and rod bore distortion.
Again, use a more viscous oil and manage temperatures properly. It will solve your problem.
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TomYoung: And what oil exactly were you using? GTX is not synthetic, Edge is, unless I have missed a re-branding.
Cujet: That is a prime candidate for Mobil 1, 15W-50 AND properly managed oil temperatures.
SR5: What those two say, makes sense to me.
Castrol GTX is a mineral oil (or Semisyn. at best), use a full synthetic like Castrol Edge. I would use the Edge 10W60 myself, or at least the 0W40 if you want to go thinner. The LS2 engine is very popular over here.
Cujet: That is a prime candidate for Mobil 1, 15W-50 AND properly managed oil temperatures.
SR5: What those two say, makes sense to me.
Castrol GTX is a mineral oil (or Semisyn. at best), use a full synthetic like Castrol Edge. I would use the Edge 10W60 myself, or at least the 0W40 if you want to go thinner. The LS2 engine is very popular over here.
Cujet: Which remain about 0.001 inches per inch of bearing diameter
SR5: Glad to hear that is still valid, it's what I learnt when I was machining, but that was awhile ago. A Thou per Inch, easy to remember, even for somebody raised on metric.
SR5: Glad to hear that is still valid, it's what I learnt when I was machining, but that was awhile ago. A Thou per Inch, easy to remember, even for somebody raised on metric.
Originally Posted By: SR5
Cujet: Which remain about 0.001 inches per inch of bearing diameter
SR5: Glad to hear that is still valid, it's what I learnt when I was machining, but that was awhile ago. A Thou per Inch, easy to remember, even for somebody raised on metric.
It is still valid in many situations. The exception would be purpose built racing engines with specifically designed, robust components. This does not include highly modified street car engines.
If we purpose build an engine for very high specific output, we take steps to minimize distortion in all critical areas. This results in robust components with well understood dimensional changes under load. Crankshafts, blocks, bearing supports and so on are extremely robust. This allows us to reduce clearances, use thinner oils and reduce friction. Expect costs to start at a low of about $30K for a purpose built Nascar type engine and go up to well North of $100K for other racing engines. Again, these engines are designed for a purpose. Automotive engines are, in general terms, not the same.
Consider my car, a Honda S2000. It's 2.2L engine is designed for 238HP, and it falls short of that in real world tests. However, with my turbo setup, it produces 407 RWHP, or about 440 at the crank.
More importantly, the torque produced goes from 118 foot pounds to 280 foot pounds! (at boost onset, then drops) The crankshaft distortion caused by this torque is enough to create havoc in that engine. The result is to be expected, short life under heavy loads.
Cujet: Which remain about 0.001 inches per inch of bearing diameter
SR5: Glad to hear that is still valid, it's what I learnt when I was machining, but that was awhile ago. A Thou per Inch, easy to remember, even for somebody raised on metric.
It is still valid in many situations. The exception would be purpose built racing engines with specifically designed, robust components. This does not include highly modified street car engines.
If we purpose build an engine for very high specific output, we take steps to minimize distortion in all critical areas. This results in robust components with well understood dimensional changes under load. Crankshafts, blocks, bearing supports and so on are extremely robust. This allows us to reduce clearances, use thinner oils and reduce friction. Expect costs to start at a low of about $30K for a purpose built Nascar type engine and go up to well North of $100K for other racing engines. Again, these engines are designed for a purpose. Automotive engines are, in general terms, not the same.
Consider my car, a Honda S2000. It's 2.2L engine is designed for 238HP, and it falls short of that in real world tests. However, with my turbo setup, it produces 407 RWHP, or about 440 at the crank.
More importantly, the torque produced goes from 118 foot pounds to 280 foot pounds! (at boost onset, then drops) The crankshaft distortion caused by this torque is enough to create havoc in that engine. The result is to be expected, short life under heavy loads.
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That's diametral clearance, right? The clearance you would see using Plastigauge. Seems too much to be radial clearance.
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