Dumb bearing question
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,164
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From: Beringen
Dumb bearing question
I took the bearings out of my original block. Some are indicated .0006 and some .0012. No plus or minus.
I haven't measured them torqued down, but does the absence of the + or - mean they are oversize ?
BTW these are original GM's apparently
I haven't measured them torqued down, but does the absence of the + or - mean they are oversize ?
BTW these are original GM's apparently
Drifting
Joined: Jun 2010
Posts: 1,781
Likes: 15
From: Oxford Ohio
Which bearings, are those figures what you have measured or stamped with that number? That first number is 6 / 10,000s not much oversize. The second is 15 / 10,000s or 1.5 1,000s. It looks like the + or - numbers to me.
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Mixing bearing sizes is a common way even today to get a specific bearing clearance. It's not shoddy workmanship - simply a tool to get the clearance wanted. I'd expect on the production line there were just more options 
Interesting article on this if you've never done it...
http://www.carcraft.com/techarticles...e/viewall.html
Interesting article on this if you've never done it...
http://www.carcraft.com/techarticles...e/viewall.html
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Mixing bearing sizes is a common way even today to get a specific bearing clearance. It's not shoddy workmanship - simply a tool to get the clearance wanted. I'd expect on the production line there were just more options
Interesting article on this if you've never done it...
http://www.carcraft.com/techarticles...e/viewall.html
Interesting article on this if you've never done it...
http://www.carcraft.com/techarticles...e/viewall.html
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
Mixing bearing sizes is a common way even today to get a specific bearing clearance. It's not shoddy workmanship - simply a tool to get the clearance wanted. I'd expect on the production line there were just more options
Interesting article on this if you've never done it...
http://www.carcraft.com/techarticles...e/viewall.html
Interesting article on this if you've never done it...
http://www.carcraft.com/techarticles...e/viewall.html
The bearings are dated 1981, so this was only 2 years after the car was built. History on the car is unknown, so i do not know who did it.
Anyway, there are domed TRW pistons in there, i suspect them being parts from an earlier high CR engine. Among other things it had an M22. I doubt this was a bubba deal. Car was original Belgian import. I don't think a Belgian Bubba would have parts like that lying on a shelf to perform this type of operation when the car was only 2 years old, but i guess you never know.
So, the get back to the issue : is this an oversize or undersize bearing or is there really need to measure, to be sure.
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Race Director
Joined: May 2006
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From: Dayton, Ohio
A crank journal that is machined under STD takes a thicker bearing to make clearance correct-GM refers to this bearing as undersized,when actually the bearing itself is oversized.
It's all math,use your micrometer,basic clearance is .001
For instance ,not actual:
If the crank is 2.450, you would use a STD bearing
If the crank is 2.449, you would use a .001 undersize
If the crank is 2.448,you would use a .002 undersize
edit-( the GM manual says the max diameter on #1 is 2.4493 so that would take the STD bearing )
Last edited by ...Roger...; Sep 25, 2011 at 09:31 AM.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Without a +/- stamped on the bearing, the only thing for certain is that the bearings are non-standard. Measuring the bores is the one means I can think of to determine what they are.
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
The oversize and undersize is most likely where the misunderstandings come in.
A crank journal that is machined under STD takes a thicker bearing to make clearance correct-GM refers to this bearing as undersized,when actually the bearing itself is oversized.
It's all math,use your micrometer,basic clearance is .001
For instance ,not actual:
If the crank is 2.450, you would use a STD bearing
If the crank is 2.449, you would use a .001 undersize
If the crank is 2.448,you would use a .002 undersize
edit-( the GM manual says the max diameter on #1 is 2.4493 so that would take the STD bearing )
A crank journal that is machined under STD takes a thicker bearing to make clearance correct-GM refers to this bearing as undersized,when actually the bearing itself is oversized.
It's all math,use your micrometer,basic clearance is .001
For instance ,not actual:
If the crank is 2.450, you would use a STD bearing
If the crank is 2.449, you would use a .001 undersize
If the crank is 2.448,you would use a .002 undersize
edit-( the GM manual says the max diameter on #1 is 2.4493 so that would take the STD bearing )
On main bearings we have bore gauged quite a few of them over the years and if you calculate out the clearance you would be really close from what we have seen.
For instance housing bore is 2.6406 minus shaft size 2.4490 equals .1916 now add shell thicknes of both bearing shells of a standard bearing is .0955 times 2 is .1910 and minus .1916 from .1910 is .1916 is .0006 clearance which is way to tight in my book.
On rods they have to be bore gauged or at least checked with plastigauge, Calculating out rod bearing clearance will not work as when a bearing is crushed in a rod it will distort the rod. Depending on how good the rods are bearing clearance will very.
Thats why rod bearing have a lot of bearing eccentricty in them as when they are torqued they seem to get tighter at the parting line and bigger on your verticle clearance.
On a main bearing you won't see this beacuse your not going to distort a housing because of the mass around the bearings.
GM does selective fit there bearings to get an exact bearing clearance and some times you will see all different size bearings because of housing bore sizes and jounal sizes.
Race Director
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From: Dayton, Ohio
Blockman,I was hoping you would show up in this thread. My statements are more general.
My understanding is bearings go down from STD,in general if the standard crank is 2.450,did GM make a bearing for a crank journal of 2.451 ? I think the answer is NO.
The OP was asking about the numbers on his bearings. My thoughts are those numbers can only mean his bearings go on a journal that is slightly smaller than STD. Is this correct ?
My understanding is bearings go down from STD,in general if the standard crank is 2.450,did GM make a bearing for a crank journal of 2.451 ? I think the answer is NO.
The OP was asking about the numbers on his bearings. My thoughts are those numbers can only mean his bearings go on a journal that is slightly smaller than STD. Is this correct ?
Race Director
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From: Dayton, Ohio
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Main bearing housing sizes are very important as that is the first measurement you should take, not doing so starts to stack tolerances. Many name brand high quality cranks are not straight, you start to get straight crankshafts in the $800-1000 range.
Federal Mogul doesn't even give you 1 thou to play with for a STD small block 400 ci chevy housing they give 9/10,000", 2.8406" to 2.8415"
Federal Mogul doesn't even give you 1 thou to play with for a STD small block 400 ci chevy housing they give 9/10,000", 2.8406" to 2.8415"
Drifting
Joined: Dec 2005
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From: NORTHEAST
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
You have to remember not knowing what the housing bore is it you could get into some trouble with your assumption here.
On main bearings we have bore gauged quite a few of them over the years and if you calculate out the clearance you would be really close from what we have seen.
For instance housing bore is 2.6406 minus shaft size 2.4490 equals .1916 now add shell thicknes of both bearing shells of a standard bearing is .0955 times 2 is .1910 and minus .1916 from .1910 is .1916 is .0006 clearance which is way to tight in my book.
On rods they have to be bore gauged or at least checked with plastigauge, Calculating out rod bearing clearance will not work as when a bearing is crushed in a rod it will distort the rod. Depending on how good the rods are bearing clearance will very.
Thats why rod bearing have a lot of bearing eccentricty in them as when they are torqued they seem to get tighter at the parting line and bigger on your verticle clearance.
On a main bearing you won't see this beacuse your not going to distort a housing because of the mass around the bearings.
GM does selective fit there bearings to get an exact bearing clearance and some times you will see all different size bearings because of housing bore sizes and jounal sizes.
On main bearings we have bore gauged quite a few of them over the years and if you calculate out the clearance you would be really close from what we have seen.
For instance housing bore is 2.6406 minus shaft size 2.4490 equals .1916 now add shell thicknes of both bearing shells of a standard bearing is .0955 times 2 is .1910 and minus .1916 from .1910 is .1916 is .0006 clearance which is way to tight in my book.
On rods they have to be bore gauged or at least checked with plastigauge, Calculating out rod bearing clearance will not work as when a bearing is crushed in a rod it will distort the rod. Depending on how good the rods are bearing clearance will very.
Thats why rod bearing have a lot of bearing eccentricty in them as when they are torqued they seem to get tighter at the parting line and bigger on your verticle clearance.
On a main bearing you won't see this beacuse your not going to distort a housing because of the mass around the bearings.
GM does selective fit there bearings to get an exact bearing clearance and some times you will see all different size bearings because of housing bore sizes and jounal sizes.
Mains are 2.641, and all equal. Crank is 2.448 almost perfect on all mains.
If i use a standard bearing and use the .0955 shell thickness, i end up with an clearance of .002. I have a set of standard bearings and will check them. However i think clearance would be better around .024-027.
What do you guys think ?
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
Ok, i measured the naked bores (without the bearing shells) and the crank.
Mains are 2.641, and all equal. Crank is 2.448 almost perfect on all mains.
If i use a standard bearing and use the .0955 shell thickness, i end up with an clearance of .002. I have a set of standard bearings and will check them. However i think clearance would be better around .024-027.
What do you guys think ?
Mains are 2.641, and all equal. Crank is 2.448 almost perfect on all mains.
If i use a standard bearing and use the .0955 shell thickness, i end up with an clearance of .002. I have a set of standard bearings and will check them. However i think clearance would be better around .024-027.
What do you guys think ?
However i think clearance would be better around .024-027
If your looking for .0024 to .0027 you can either split a set of bearings or get a set of coated X bearings or get the block aligned honed to 2.6415
We just mocked up a crank that was 2.448 and the main line was 2.6415 and we came out with .0025 to .0026 on the money using a bore gauge.
.002 on the mains for a street build is fine!!!