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Old 10-10-2010, 04:43 AM
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What rod bearings do i have GM SBC 350

My rod bearings are stateing
GM A-100 8 87.

What seize do I have and what would be the aftermarket replacement no.

What bearings do you recomend?

see picture.

BR Bob
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Old 10-10-2010, 04:55 AM
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GM A-100 is an OEM standard size bearing. manufactured 8/87.

The crank size/condition will determine the correct replacement bearing size.
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Old 10-10-2010, 07:27 AM
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Ditto

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Originally Posted by BOBCRMAN@aol.com
GM A-100 is an OEM standard size bearing. manufactured 8/87.

The crank size/condition will determine the correct replacement bearing size.
Ditto on Bob's post.
You should mic your crank to determine whether it needs to be turned.
Factory installed bearings almost certainly.

However if you're doing an old fashioned low tech overhaul and you feel that the journals are smooth enough to go back STD, you might polish up with some crank polishing tape. I think our old crank polishing belts are about 320 grit. And once polished the mic almost always reads safe to go with a .001" oversize bearing.
As for brand, I'm kind of on the "King Bearing" bandwagon lately. But for a daily driver, pick up or something, I think a good fit and clean installation is more critical than the brand/type bearing you buy..

Note: if using the low tech overhaul approach <no micrometer< feel for any big changes in resistance when hand turning the crank as you install the pistons..I still use a torque wrench to turn on install, so I'll notice how much each piston assembly is adding..
And we should go easy for the first few hundred miles.. Good luck..
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Old 10-10-2010, 08:00 AM
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what bearing to use?

Duntov
never though about using a torch wrench to turn the crank as installing each pistons. Sounds good, but what should your first reading be on the first piston and how much should it rise as the other pistons are installed? what if you bore the cyl. would it change and how much? what about different rings (cast iron or chrome-moly)?
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Old 10-10-2010, 08:21 AM
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Torque readings would change. Cylinder finish, ring material/tension, clearance. All determine crank torque.
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Old 10-10-2010, 08:37 AM
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It's really by feel though

Quote:
Originally Posted by lanier ledford
Duntov
never though about using a torque wrench to turn the crank as installing each pistons. Sounds good, but what should your first reading be on the first piston and how much should it rise as the other pistons are installed? what if you bore the cyl. would it change and how much? what about different rings (cast iron or chrome-moly)?
Yeah, all those things cause variations; high tension rings more than other factors.
I've had them start off at 5#s or more and add 5#s or more per cyl with high tension rings and a rough hone from the old days. But they are never very consistent, <maybe because of natural geometry.
I just watch for one to add twice or more than what has been the average.
Of course it is all by feel really, because it has to do with the speed you turn the torque wrench.

I've been wanting to use a smaller DC motor on my turning stand with an ammeter to more accurately register the energy it's taking. A fine honed cylinder and low tension molys with perfect fit bearings takes very little, sometimes 3#s or even less per, enough to go to the inch pound wrench probably, but the only time I've used the inch pound wrench is on the main bearing installation. I still like to spin a bare crank by hand with all the mains installed and see it coast more than one revolution.. gives me a good feel the main alignment.
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Old 10-10-2010, 10:08 AM
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"""However if you're doing an old fashioned low tech overhaul and you feel that the journals are smooth enough to go back STD, you might polish up with some crank polishing tape. I think our old crank polishing belts are about 320 grit. And once polished the mic almost always reads safe to go with a .001" oversize bearing."""

That should be .001 UNDERSIZE.

I've been using a lot of King bearings lately. For years I avoided them because back in the eighties they had a bad reputation for de-lamination problem under high load conditions. One of those things that bug me.. Never lost a motor from use of their bearings. But when you see the bearing material flaking from the backing. Makes you cautious..

Now I have been running into QC problems with Clevite's and prices are going out of sight.. Back to good ole ACL's and Kings..
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Old 10-10-2010, 01:00 PM
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too many exceptions to that rule!

I've put that backwards for as long as I can remember... because the journal in actually undersize.... and of course the bearing itself is actually larger than std...
But I know they are listed 90% of they time as undersize.. I also have a few words that I have never been able to spell. The worst one is "thier" <<their... I guess it was the "I before E, except after C" rule that handicapped me back in '57.

too many exceptions to that rule!

Ps.. It's hard enough to find one's in stock anymore; I doubt he'd accidentally get the opposite. I don't imagine they are on any shelf in the world. maybe custom for some plated app?

Anyway "their"<< while it's fresh on my mind... still looks funny though

Last edited by Amigo406; 10-10-2010 at 01:06 PM.
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Old 10-16-2010, 02:12 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com
"""However if you're doing an old fashioned low tech overhaul and you feel that the journals are smooth enough to go back STD, you might polish up with some crank polishing tape. I think our old crank polishing belts are about 320 grit. And once polished the mic almost always reads safe to go with a .001" oversize bearing."""

That should be .001 UNDERSIZE.

I've been using a lot of King bearings lately. For years I avoided them because back in the eighties they had a bad reputation for de-lamination problem under high load conditions. One of those things that bug me.. Never lost a motor from use of their bearings. But when you see the bearing material flaking from the backing. Makes you cautious..

Now I have been running into QC problems with Clevite's and prices are going out of sight.. Back to good ole ACL's and Kings..

I am using Dana plasticgauge to check the clearance. I trust that method more than a micrometer. I can measure the play in an installed combination.

What is a good clearance to archieve for rods.? .0006? to 0012?

BR bob
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