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Discussion Starter · #1 ·
i have a 350 sbc and im in the process of rebuilding. i got the motor without knowing anything about it.when i got down to the bearings, the rods are .0005 and the mains are all diffrent, the first has a "0",the second has a".0006"as well as the third, and the fourth has a ".0012", finally the last one is".001".what the heck????????can anyone shed some light on my stress!!!thank you. :confused:
 

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I put up the tools against$300
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is that on the crank or the bearings? If its on the crank it may be how much was removed if it was ever polished. If it's on the bearings, someone else will have to answer that one for ya
 

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ASE Certified Master Machinist
1967 Chevrolet Biscayne 10-71 blown 433 Big Block Chevy, T400 & 12 bolt 3.73 rearend
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If the engine hasn't been disassembled before and the crank is standard, it is more than likely the bearing under size or over size to get the desired clearance on the assembly line. This is if the numbers you are referring to are on the backing of the bearing.

Barry
 

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Discussion Starter · #4 ·
bearings problem

my main question is what type of bearings can i replace them with.as far as i know the motor is a virgin.it has a standard bore and all the bearings have gm stamped on them.also the main bearings hav "gmm 400" stamped on them.all the bearings i can find are"std",".001",".002",".010",".020",etc.how can i find the ".0005"and the ".012",etc.any ideas are greatly appriciated. :D
 

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... & Insanity Ensues .....
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could "GMM" mean General Motors Mexico?

just throwin that out there ... could be wrong...
 

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aka Duke of URL
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ajh86 said:
my main question is what type of bearings can i replace them with.as far as i know the motor is a virgin.it has a standard bore and all the bearings have gm stamped on them.also the main bearings hav "gmm 400" stamped on them.all the bearings i can find are"std",".001",".002",".010",".020",etc.how can i find the ".0005"and the ".012",etc.any ideas are greatly appriciated.
topfuel said:
If the engine hasn't been disassembled before and the crank is standard, it is more than likely the bearing under size or over size to get the desired clearance on the assembly line. This is if the numbers you are referring to are on the backing of the bearing.
Correct, what you are seeing is factory assembly selective fit. It is their method of allowing for varying machining tolerances (being dead on is expensive).

FORD (and I am sure the rest are similiar) has parts known as RED or BLUE and have the tiniest bit of different fitment measurements.

For replacement, you buy regular replacement bearings (rings-pistons) and install. You can mix and match different sizes to get that near perfect fit. Just depends how far you want to get into it.
 

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Discussion Starter · #7 · (Edited)
wierd bearings

so can i just use "std" bearings?i sure do thank you :) also i am building the 350 mild or more less stock.i am curious as to wether or not to use moly rings vs. cast. i can get them for about $10 more than cast, is it worth doing?the motor is 350 cid with port matched stock "624" gm heads,full roller rockers,a dual plne alum. intake, not sure on cam yet[any sug.]itll be in a camaro with a manual and a moser 9" with a spool and 4.56s.any quick tips,or ideas are awesome in every way!!! thanks a whole big ol' bunch :thumbup:also what the h*ck are the gm "x" rods.good-bad,yey-ney,it all helps
 

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aka Duke of URL
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Do you have a machinist yet? He would most likely be your best source of info (your being a newbie) and can supply quality parts at a reasonable price.

For the cam, call COMP CAM TECH and they will recommend a suitable grind for your application.
 

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Discussion Starter · #9 ·
bearings and whatnot

i dont have a machinist yet,persay, ok so i just dont have one :( i am what i would like to call a "budget builder".i have a engine repair degree through tenn. tech, but i could have fooled myself. :embarrass i have never seen the bearings in offset sizes such as these.i realize it would be best to have a machinist but i really cant afford it right now.tuff times you know!!?? :mad:i had a motor in it that an "ase" guy built and it flew to pieces,[the cam broke in 7 pieces and twisted two rods and broke the cylinder walls on no.1 and no.3], so i figure what the he!! ill give it a go.the main bearings and rod brgs had some minor wear so i figure its apart, ill invest a little insurance.the block is immaculate and the motor was a freebie. i sure am glad to be able to ask yall about these problems of mine.thanks alot :thumbup:
 

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aka Duke of URL
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You can also buy a crank kit where the crank has been turned and has the matching bearings (PlastiGuage at assembly).

GOOGLE the term BLUEPRINTING AN ENGINE and it should give you a lot of information regarding assembling an engine.

It will give you an introduction into SELECTIVE FIT and SAME COMPONENT WEIGHT (mix and match) so you can assemble one on the cheap.
 

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GMM is probably GM Morraine

The Morraine is one of the bearing names mentioned in the small-block books. If the bearing numbers are all over the map, I'd be tempted to try and by the same bearing numbers from GM if possible -it could be that it's not the crank that is out of spec, but the block bearing bores. GM doesn't seem to make reliably sized bearing bores (obviously others will write that they have never found one out od spec here). Other than that and some mixing / matching, grinding the crank AND line-HONING the block would fix it. I have just run into a simialr problm -the 350 I am rebuilding had a rough crank, so with a regrind by a reputable machine shop I ended up with variable clearances all about 0.001" over max. Irritating problem.. so far I am considering checking a Target Master crank with 0.001" under bearings to see if this lands in an acceptable range. I don't even want to think of balance at this point...

'Reminds me of the saying 'Measure twice, cut once"...
 

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1967 Chevrolet Biscayne 10-71 blown 433 Big Block Chevy, T400 & 12 bolt 3.73 rearend
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Since the numbers you gave in the first post had 2 bearings .001 or over, I'd take the advice KULTZULZ gave and consider purchasing a crank kit if the funds are available. You will be far better off in the long run. If you put std. size bearings on crank journals that are .001 us, you will have oil pressure that is lower than you'd like. It is also possible to have a shop grind the mains only if the rods journals check ok for size, roundness and taper.

Barry
 

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Discussion Starter · #14 ·
bearings

i am going to a machine shop to get it checked soon. what are the average costs of turning the crank vs. buying new.my main thing is funds are low but i dont want to sacrifice my reliability.also does anyone know any info on the gm "x" rods???much thanks :thumbup:
 

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Check Federal Moguls on line catalog,they have main & rod bearings available in different sizes,.009 .010 .011 etc. This might help you,but these are the competition series and are a little more expensive than standard ones.
 

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What you have found is not out of the ordinary at all. It is an example of the f actory selectively-fitting bearings to get a specific clearance. Have an experienced automotive machinist mic the crank and tell you what it needs. As was said, a .010"-.010" grind should clean it (as long as the thrust is ok) up and remove any doubts from your mind.

tom
 

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Discussion Starter · #18 ·
bearings

thanks alot guys.i have tried to get the same size bearings and have come up on no luck.i got an estimate to turn the crank and it was $100. when i can get a new gm crank fro $150 i dont want to turn the old.thanks alot though. :thumbup:
 

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X and O rods are the heaviest SBC rods. The old "Pink" rods were made from these cores.

As you have seen, for many years, GM has used under and oversizes in building an engine. Most are not available to the public. Std. .001 over and .001 .002 under are the available sizes. To get correct clearances you use whatever combo is available. Thicker bearing in the top. Or regrind to next undersize.
 

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Discussion Starter · #20 ·
bearings

great news!!!!!! i got a new crank and bearings for $83.i couldnt say no.i figure that was the cheapest way to solve my problem.but also, are the "x" rods any good??? :drool:
 
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