Engine Building Services at DBTuned.
08-13-2010, 11:14 AM
#22
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Why would you use any other spec?
But, it depends on the application, on what the customer wants, etc.
Regardless, we do not use weaker, ground crankshafts; either its qualified STD or a new crankshaft.
Same goes for the rods; no reman'ed con rods.
08-13-2010, 01:00 PM
#23
Completely agreed on the new cranks. With how cheap they are brand new, there's really no point in regrinding them.
We spec our bearing clearances based on the application. A looser clearance allows you to run a heavier weight oil while still maintaining good flow past the bearing. This allows for additional cooling of the bearing, crank, and rod surfaces under extreme conditions and use.
-- Ed
We spec our bearing clearances based on the application. A looser clearance allows you to run a heavier weight oil while still maintaining good flow past the bearing. This allows for additional cooling of the bearing, crank, and rod surfaces under extreme conditions and use.
-- Ed
08-13-2010, 01:37 PM
#24
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You're not concerned with the associated pressure drop that a larger clearance can bring about?
If you're not grinding the crank journals, how are you achieving the desired clearance(s)?
If you're not grinding the crank journals, how are you achieving the desired clearance(s)?
Last edited by FW Motorsports; 08-13-2010 at 01:39 PM.
08-13-2010, 02:58 PM
#25
There's no pressure drop as long as you run the appropriate weight oil for the clearance spec. You certainly wouldn't want to run a 5w-30 in an engine with looser than factory bearing clearances.
We achieve the desired clearances by using different size bearings. ACL's HX series bearing, for example will give you an extra thousandth of clearance as compared to their H series. Cosworth has various sizes as well. We also do a very light line hone on the main bearing housings to achieve a more consistent clearance across the block.
-- Ed
We achieve the desired clearances by using different size bearings. ACL's HX series bearing, for example will give you an extra thousandth of clearance as compared to their H series. Cosworth has various sizes as well. We also do a very light line hone on the main bearing housings to achieve a more consistent clearance across the block.
-- Ed
08-13-2010, 08:05 PM
#26
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With the extra one thousandths clearance, what weight oil do you require?
What does your spec achieve?
What problem does it rectify?
What does your spec achieve?
What problem does it rectify?
08-14-2010, 12:13 PM
#29
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Some very good information:
CLEARANCES
Proper clearances are another factor that are extremely important bearing longevity and oil pressure. Crankshaft bearings generally need at least a .0001 inch thick oil film between themselves and their journals to prevent metal-to-metal contact. This requires assembly clearances that are loose enough so oil can flow into the gap between the bearing and journal to form an oil wedge that can support the crankshaft. The clearance must also be sufficient to allow enough oil flow to cool the bearings. But the clearance must not be too great otherwise the oil will escape before it can form a supporting wedge.
Excessive bearing clearances (more than about .001 inch per inch of diameter of the crankshaft journal) can allow a drop in oil pressure that can adversely effect lubrication elsewhere in the engine such as the camshaft and upper valvetrain. Excessive clearances also increase engine noise and pounding, which over time can lead to bearing fatigue and failure. Fatigued bearings will typically be full of microscopic cracks and have flaking material on the surface.
The amount of clearance between the bearings and crank journals will obviously vary depending on the application and the preferences of engine rebuilder. Some want closer tolerances to maximize oil pressure while others want looser tolerances to allow for machining variances and contaminants that often end up in the crankcase.
One large production engine rebuilder says they try to build all their passenger car and light truck engines with about .001 to .002 inch clearance in the main and rod bearings. This compares to as much as .004 inch of clearance that may have been present in the OEM engine. But on some engines, such as the General Motors 173, more than .0015 inch of clearance can result in noise problems.
Proper clearances are another factor that are extremely important bearing longevity and oil pressure. Crankshaft bearings generally need at least a .0001 inch thick oil film between themselves and their journals to prevent metal-to-metal contact. This requires assembly clearances that are loose enough so oil can flow into the gap between the bearing and journal to form an oil wedge that can support the crankshaft. The clearance must also be sufficient to allow enough oil flow to cool the bearings. But the clearance must not be too great otherwise the oil will escape before it can form a supporting wedge.
Excessive bearing clearances (more than about .001 inch per inch of diameter of the crankshaft journal) can allow a drop in oil pressure that can adversely effect lubrication elsewhere in the engine such as the camshaft and upper valvetrain. Excessive clearances also increase engine noise and pounding, which over time can lead to bearing fatigue and failure. Fatigued bearings will typically be full of microscopic cracks and have flaking material on the surface.
The amount of clearance between the bearings and crank journals will obviously vary depending on the application and the preferences of engine rebuilder. Some want closer tolerances to maximize oil pressure while others want looser tolerances to allow for machining variances and contaminants that often end up in the crankcase.
One large production engine rebuilder says they try to build all their passenger car and light truck engines with about .001 to .002 inch clearance in the main and rod bearings. This compares to as much as .004 inch of clearance that may have been present in the OEM engine. But on some engines, such as the General Motors 173, more than .0015 inch of clearance can result in noise problems.
08-14-2010, 12:33 PM
#30
Indirectly by measuring the oil temperatures under extreme conditions.
How have you measured crank/bearing temperatures?
How much power and RPM are the stock specs good for?
How have you determined these ranges?
What oil do you recommend for your built engines and under what conditions?
-- Ed