Main bearing clearance specs - Team Camaro Tech
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post #1 of 4 (permalink) Old Mar 11th, 01, 06:27 AM Thread Starter
Join Date: Oct 2000
Location: North Richland Hills, Texas
Posts: 19

I've done a search and can't seem to find any postings regarding this. Checking the main clearances w/ Plastigage on a sb355. Approx. .002 on 1 thru 4, but the rear comes in at .006, and I think this might be excessive. I know that I should have a rebuild manual handy, but that is not the case, and the machine shop is not open today. Your thoughts and comments are most appreciated. Thanks in advance.


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post #2 of 4 (permalink) Old Mar 11th, 01, 06:52 AM
Senior Tech
Join Date: Nov 1999
Location: West Richland, Wa. USA
Posts: 175

.002 to .003 I believe. .006 is too much. Plastic gage is not the best (works when you have nothing else), can you mic the crank and bearing (inside mic are harder to find).
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post #3 of 4 (permalink) Old Mar 11th, 01, 08:46 AM
Join Date: Aug 1998
Location: Waldorf Md. USA
Posts: 3,291

The factory specs are about (depends on what book you read) .001-.003 on the first 4 and .0025-.0035 on the rear main. .006 is definitely too much. Take a very fine file and make sure that there are no burrs that might be keeping the rear main cap from seating all the way. Just go over it lightly, or put a piece of 200 grit sand paper down an a flat piece of glass and run the cap over it lightly. If all this checks out ok, you could have a defective bearing (rare) or the block needs to be align honed. Also, if the crank was not reground, it could be the problem. I guess it could also be if it was ground and not done properly. The rear main is supposed to be a bit smaller than the rest, but only about 1/2 thousanth. More than likely it is the block. If you are not sure, take the crank and bearings out, install the main caps and torque them in place. Then take the block to your machine shop and pay them a few bucks to check the block with a bore gauge. This is the only way you can really do it correctly. Inside mikes just are not accurate enough for this job. Have them check the crank also. This is one part of engine building where you do not want to cut corners.
Hope this helps,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md
1971 Chevelle "Heavy Chevy" original owner
1973 Z-28 family car...Brother bought it new in 73

[This message has been edited by BillK (edited 03-11-2001).]
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post #4 of 4 (permalink) Old Mar 11th, 01, 02:47 PM Thread Starter
Join Date: Oct 2000
Location: North Richland Hills, Texas
Posts: 19

Thanks for the replies guys. Looks like the front 4 bearings are fine. Bill, I'll double check for burrs, etc., on either the cap or the block, and remedy as req'd. I thought I had been extremely clean upon mockup, but I could have missed something. I hope that is indeed the case. The crank was supplied by the machine shop (.010) to fit a block that a friend gave me.

One other question: the bearings halves for 3 & 4 are not flush when inserted into the saddles, but rather stick up a couple of thousanths. The halves in the caps are flush. When torqued down to check the clearance (using the plastigage)the clearnce seems to be ok, as indicated earlier. How can this be?! Is it possible that the bearing half does not seat all the way into the saddle until the cap is installed and torqued down? I can't discern any gap between the saddle and outer part of the bearing. And when the cap is torqued down, the cap seems to be seated properly. It's a mystery to me.

I haven't build an engine for close to 25 years now, and some of it is kind of fuzzy. But boy, I'm I having a great time getting back into the car thing! When I get this finished (as if that could ever happen!) this is what I'll have:

'69 Camaro coupe
355 4-bolt, 9.5:1, Sportsman II heads, XE274, Performer RPM intake, Holley 750 vac., headers, TH350 w/ 2500 stall, 3.73 posi. Should be fun!

Thanks again for replies,

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