Too much bearing clearance?
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Joined: Nov 2003
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From: St. Louis, MO
Too much bearing clearance? I got my block assembled by the machine shop and they put my rods at .002 and my mains at .0025 clearance. This is a forged 347 setup (except crank) and I told them it will also be sprayed. Is that too much clearance and will I have any problems? Also what weight oil is recommended?
thats what my LS2 418 is clearanced at and runs fine and the oil pressure is at 45psi at idle and 65psi at cruse 55mph. That with a LS6 ported and shimed spring & double o-ringed, oil pump.
Rods are ok. Mains are a little loose. When the oil is hot your idle pressure may be a little low. Machine shops seem to forget aluminum blocks expand more than steel so they should keep the mains at .002 maximum cause when they are at operating temp they are probably at .003. If your oil pressure is ok at higher rpms you will be fine or you could go with a higher volume pump. I would try it the way it is if it was me. Chuck
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From: San Diego
Originally Posted by shortdog
I got my block assembled by the machine shop and they put my rods at .002 and my mains at .0025 clearance. This is a forged 347 setup (except crank) and I told them it will also be sprayed. Is that too much clearance and will I have any problems? Also what weight oil is recommended?
Thread Starter
Joined: Nov 2003
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From: St. Louis, MO
IF I have low oil pressure, a heavier (40w-50w) weight should cure the problem? Is there anything else I should be concerned with? I used federal mogul main/rod race bearings if that make any difference. Thanks for the help.
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From: San Diego
Originally Posted by shortdog
IF I have low oil pressure, a heavier (40w-50w) weight should cure the problem? Is there anything else I should be concerned with? I used federal mogul main/rod race bearings if that make any difference. Thanks for the help.
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FormerVendor
Joined: Nov 2001
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From: Houston, Tx.
Originally Posted by GOaT Cheese
Oil pressure is largely decided by the rod side clearance, and not so much the bearing clearance. Heavier oil viscosity, will raise pressure a bit, but it is sort of false security because it only masks a larger problem.
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From: San Diego
Originally Posted by racer7088
Bearing clearance and eccentricity determine oil flow as these are much tighter clearances than the rod side clearance. I run rods with as much as .030 side clearance and I can have positively high oil pressure and I also have stock stuff at .012 side clearance that has really low oil pressure because of loose bearing clearances.
FormerVendor
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From: Houston, Tx.
Almost every engine with aftermarket rods on LS1tech already has .020-.025 on the rods and they have great oil pressure.
I've built hundreds.
Now you put the rod bearings and main bearings in at like .0030-.0040 clearance and you will see much lower oil pressure especially at idle no matter whether rod side clearance you are running is,even still .010 like it is on some stock LS1s.
Remember as well that the rod journals are not always completely surrounded by metal anyway so anotherwords the oil could leak out much easier than you think at the sides reguardless of side clearance anyway.
Some OEM rods even have "cutouts" in the side clearance area to direct oil spray on the bottom of the piston or the cam as well with no problems maintaining oil pressure either like the new Hemis.
Finally you probably don't know but some Nextel Cup NASCAR engines run over .100 side clearance and they do not have any oil pressure problems whatsoever. They do still run the rod clearances at about .0020-.0025 though.
I've built hundreds.
Now you put the rod bearings and main bearings in at like .0030-.0040 clearance and you will see much lower oil pressure especially at idle no matter whether rod side clearance you are running is,even still .010 like it is on some stock LS1s.
Remember as well that the rod journals are not always completely surrounded by metal anyway so anotherwords the oil could leak out much easier than you think at the sides reguardless of side clearance anyway.
Some OEM rods even have "cutouts" in the side clearance area to direct oil spray on the bottom of the piston or the cam as well with no problems maintaining oil pressure either like the new Hemis.
Finally you probably don't know but some Nextel Cup NASCAR engines run over .100 side clearance and they do not have any oil pressure problems whatsoever. They do still run the rod clearances at about .0020-.0025 though.
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From: San Diego
Originally Posted by racer7088
Finally you probably don't know but some Nextel Cup NASCAR engines run over .100 side clearance and they do not have any oil pressure problems whatsoever. They do still run the rod clearances at about .0020-.0025 though.
FormerVendor
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From: Houston, Tx.
These NASCAR engines do not have any excess oil usage with the huge side clearance again though as they DO NOT WANT tons of oil and windage in those engines. They do it to get rid of weight but with the new now rules hardly anyone does it anymore.
The same engines with normal rods and side clearance don't have a different oiling systemn and you don't need a dry sump to run pin guided rods or have normal oil flow and pressure with the huge side clearance setups. The bearing clearance is the restriction in the oil flow like I said.
The oil pressure won't be determined by side clearance unless you had absolutely tiny side clearance and the rods are 100 per cent sealed around the whole journal which they often are not since they have other leak paths as well.
The same engines with normal rods and side clearance don't have a different oiling systemn and you don't need a dry sump to run pin guided rods or have normal oil flow and pressure with the huge side clearance setups. The bearing clearance is the restriction in the oil flow like I said.
The oil pressure won't be determined by side clearance unless you had absolutely tiny side clearance and the rods are 100 per cent sealed around the whole journal which they often are not since they have other leak paths as well.
Here is an engine build sheet for an iron block 415 CID stroker that Lingenfelter Performance Engineering auctioned on eBay a while back. Notice that all of the rod and main clearances are set to a target of about 25 ten thousandths.
Steve
Steve
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From: San Diego
Originally Posted by racer7088
These NASCAR engines do not have any excess oil usage with the huge side clearance again though as they DO NOT WANT tons of oil and windage in those engines. They do it to get rid of weight but with the new now rules hardly anyone does it anymore.
The same engines with normal rods and side clearance don't have a different oiling systemn and you don't need a dry sump to run pin guided rods or have normal oil flow and pressure with the huge side clearance setups. The bearing clearance is the restriction in the oil flow like I said.
The oil pressure won't be determined by side clearance unless you had absolutely tiny side clearance and the rods are 100 per cent sealed around the whole journal which they often are not since they have other leak paths as well.
The same engines with normal rods and side clearance don't have a different oiling systemn and you don't need a dry sump to run pin guided rods or have normal oil flow and pressure with the huge side clearance setups. The bearing clearance is the restriction in the oil flow like I said.
The oil pressure won't be determined by side clearance unless you had absolutely tiny side clearance and the rods are 100 per cent sealed around the whole journal which they often are not since they have other leak paths as well.
First of all, it's important to affirm that the oil clearance dimensions that shortdog stated should be fine and give him good oil pressure assuming that other things are within reason (cam bearing oil clearance, oil pressure regulator setting and pump volume at the normal operating RPM's, etc.).
GOaT Cheese - I don't think that you are properly understanding the point that Erik is trying to make. As the oil flows into and out of the crankshaft journals (first to the mains then to the rods) the first (and truly primary) restriction to flow is the cylindrical gap between the bearing and the journal called the oil clearance. Once the oil flows past this "oil clearance", the side clearance has virtually no influence on oil pressure assuming that the side clearance is sufficiently wide for normal operation. I just looked in my GM factory manual and the rod side clearance range is from .0043" to .020". By the time the oil migrates out to the fore and aft ends of the journal bearings and is ready to turn the corner to get slung out, the oil pressure is down to about zero even with an engine oil pressure of 70 PSI or more. If the side clearance is the pressure determining restriction to oil flow, there is insufficient clearance to be operating the engine.
Steve
GOaT Cheese - I don't think that you are properly understanding the point that Erik is trying to make. As the oil flows into and out of the crankshaft journals (first to the mains then to the rods) the first (and truly primary) restriction to flow is the cylindrical gap between the bearing and the journal called the oil clearance. Once the oil flows past this "oil clearance", the side clearance has virtually no influence on oil pressure assuming that the side clearance is sufficiently wide for normal operation. I just looked in my GM factory manual and the rod side clearance range is from .0043" to .020". By the time the oil migrates out to the fore and aft ends of the journal bearings and is ready to turn the corner to get slung out, the oil pressure is down to about zero even with an engine oil pressure of 70 PSI or more. If the side clearance is the pressure determining restriction to oil flow, there is insufficient clearance to be operating the engine.
Steve
Last edited by Steve Bryant; Nov 22, 2006 at 10:16 PM.
Originally Posted by shortdog
I got my block assembled by the machine shop and they put my rods at .002 and my mains at .0025 clearance. This is a forged 347 setup (except crank) and I told them it will also be sprayed. Is that too much clearance and will I have any problems? Also what weight oil is recommended?
FormerVendor
Joined: Nov 2001
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From: Houston, Tx.
Originally Posted by GOaT Cheese
I think you are misinterpreting what I am saying. Let's exclude exotic race applications. The hydrodynamic wedge that "floats" the crank begins to degrade at anything beyond .004 oil film clearance. 99% of all street/strip engines have less than that amount of bearing clearance. Given that restriction, the rod side clearance will have the most effect on low speed oil pressure. The absolute maximum factory limit on all LSX engines, including the LS7, is .020 rod side clearance. If the side clearance comes in more than .020, the engine is not allowed in service. The factory prefered rod side clearance for ALL LSX engines including the dry sump LS7 is .012". I don't know how else to put it.
I am not one of them since I have run aluminum rods at .012 and had no problems and at .030 and had no problems either. It matters whether the rod is crank or pin guided as one of the two has to have more side clearance in case the thrust bearing fails so you don't **** all the pistons sideways and blow up the engine when the crank moves forward.
FormerVendor
Joined: Nov 2001
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From: Houston, Tx.
Originally Posted by shortdog
I got my block assembled by the machine shop and they put my rods at .002 and my mains at .0025 clearance. This is a forged 347 setup (except crank) and I told them it will also be sprayed. Is that too much clearance and will I have any problems? Also what weight oil is recommended?