Obtaining Desired Clearances

Indycars

Indycars

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The range of sizes for the main bearing bores in a SBC Dart SHP block are 2.6405"-2.6415". Is there a direct relationship between the bore size and main bearing oil clearances. For example if the main bearing bore is 2.6405" and the clearance is .0015", then I increase the main bore by .001" to 2.6415". Will the clearance increase to .0025" or something less???
 
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theres no DIRECT constant , predictable & reliable relationship,between the two,because bearings themselves will vary in thickness and rigidity, between manufacturers or even different sets and styles of bearings,and even though your bearing CRUSH will obviously be a bit tighter with the smaller main bearing bore diam. , and that tends to reduce the bearing clearance, between the bearing surface and crank journal, but that has no absolute direct repeatable and predictable mechanical reference to the bearing bore size, in that clearance relationship, so it needs to be checked and confirmed with some plasi-gauge.
obviously researching the application and having accurate tools to measure all clearances with is a basic point youll want to start at, so you can at least have a good idea what your trying to accomplish and know if your close.

I generally use CLEVITE (H) style bearings as they have a bit extra clearance bevel on the edge for the crank radias

calipersaa.jpg

torqueplt1.jpg

plastigauge3.jpg


read thru these links

viewtopic.php?f=59&t=1026&p=4327&hilit=plasti+gauge#p4327

viewtopic.php?f=53&t=2726

viewtopic.php?f=53&t=3449

viewtopic.php?f=53&t=852

viewtopic.php?f=50&t=1222&p=4721&hilit=+assembly+lube#p4721
 
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If you don't really have control over the main bearing oil clearance with the size of the main bearing bore, then what is the preferred size of the main bearing bore???

Should I have the DART SHP block line honed to obtain the preferred size or just measure to confirm the size is within manufacture's tolerances???

The Scat crank is Nitride hardened, so I'm reluctant to polish the crankshaft to gain any clearance. I can juggle my Std bearings to adjust for a few tenths, but if I need to gain additional .001", my only option for adjusting clearances is by using the bearing with additional .001" clearance.

Below is a quote from Dart about the size of main bearing bore when shipped.

"Main journals are finish line honed to the low to middle of the specification.
They should be measured for your preference. If you have need for a different
diameter you must realign hone this yourself."
 
Indycars said:
If you don't really have control over the main bearing oil clearance with the size of the main bearing bore, then what is the preferred size of the main bearing bore???

Should I have the DART SHP block line honed to obtain the preferred size or just measure to confirm the size is within manufacture's tolerances???

The Scat crank is Nitride hardened, so I'm reluctant to polish the crankshaft to gain any clearance. I can juggle my Std bearings to adjust for a few tenths, but if I need to gain additional .001", my only option for adjusting clearances is by using the bearing with additional .001" clearance.

Below is a quote from Dart about the size of main bearing bore when shipped.

"Main journals are finish line honed to the low to middle of the specification.
They should be measured for your preference. If you have need for a different
diameter you must realign hone this yourself."
Click to expand...


ITs crazy to get worried about something your probably not going to have to deal with,the stock clevite or king main bearing set, main bearings in that block with that crank will more than likely give you acceptable clearances, just take the time to verify in case you've got a rare case of them being to tight or loose.
your very unlikely to need to have the block line honed.
Id just select bearings that gave you clearances on the median to loose end of the clearances the manufacturer suggests ,in most cases the components manufactured to be used as stock parts are stock dimension components ,with clearances that will fall in that range for the engine. after doing a bit of research , like checking the shop manual and checking with DART and the bearing manufacturer, (clevite,KING,etc.), thats generally in the .0023-.003 clearance range for main bearings (depends on engine family) with anything in the .0025-.0027 range being acceptable, on most sbc engines., If you need that additional .001 than you should just bite the bullet and buy the .001 oversize clearance bearings.
don,t go nuts chasing a .0002 change, a slightly thicker or thinner viscosity oil can do a good deal to change flow rates and oil pressure when your dealing with minor clearance issues.

this thread, and ITS SUB LINKS has got clearances and torque specs
viewtopic.php?f=50&t=1222
 
grumpyvette said:
ITs crazy to get worried about something your probably not going to have to deal with,the stock clevite or king main bearing set, main bearings in that block with that crank will more than likely give you acceptable clearances, just take the time to verify in case you've got a rare case of them being to tight or loose.
your very unlikely to need to have the block line honed.
Click to expand...
Ok, it's looks like I should be good to go if clearances fall in the typical range. I purchased Clevite MS-909H and CB-663HN when I got the block and rotating assembly.

To verify clearances can I use snap gauge on the bearings or are they too soft for that???

I have a 0-1" ball mike that would measure the bearing thickness, so I could also measure the bore size, bearing thickness and journal size to come up with the oil clearances.
 
a snap gauge will work but your getting far to involved here, just assemble and use plasti-gauge to verify the bearing oil clearance, the crank sitting in the assembly lube coated bearings with the main caps torqued to spec should rotate with under 10 lbs of torque applied, once each of the rods and pistons, with correctly gaped rings are added there will be an increase in resistance to rotation but it should peak with all 8 cylinders rods installed at under 40 ft lbs and 20-25 ft lbs is about ideal

bearingchart.jpg

http://catalog.mahleclevite.com/lv/search.php

http://www.jegs.com/v/Clevite/695

http://catalog.mahleclevite.com/bearing/

http://www.summitracing.com/search/Bran ... -Bearings/

http://stealth316.com/misc/clevite-77-r ... arings.pdf

http://www.kingbearings.com/
http://www.king-bearings.com/cat/

viewtopic.php?f=53&t=247

http://www.stockcarracing.com/techartic ... ewall.html

viewtopic.php?f=53&t=509

viewtopic.php?f=53&t=2726

viewtopic.php?f=53&t=3449

viewtopic.php?f=53&t=852
 
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