Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks



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#97464 03/15/07 01:02 PM
Joined: Dec 2001
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Hi group,
I have a rather odd question that hopefully someone can answer. The front main bearing is supposed to be 1 3/8", center 1 11/16, and rear 1 3/4". What are the diameter sizes of the front, center, and rear bearing holes in the block with the main bearing shells removed?

Thanks much,
Ron

Last edited by RustyFender; 03/15/07 01:03 PM.
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Hi Rusty
Just measured some shells that I had, and they are--
Front- 1.625" diameter
Middle and rear- 2.000" diameter
I'm not sure whether the block/cap was bored with shims between or not- if you are thinking of modern inserts this will make a big difference, as you don't want shims with inserts, and if they were in the gap when the boring was done, the hole won't be round when they are removed. Why do you ask?
Herb


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I have built engines, both 4 & 6 by removing the shells and poring directly into the block. Holes must be drilled into the block to stabilize the pore, and then oil access holes must be provided, and finally oil groves in the final pore.

Ten years on a 4 cylinder and about the same on one of the 6 cylinders without problems.

Agrin devil


RAY


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1925 Superior K Roadster
1928 Convertible, Sport, Cabriolet
1933 Eagle, Coupe
1941 Master Deluxe 5-Passenger Coupe
1950 Styleline Deluxe 4-Door Sedan
1950 Styleline Deluxe Convertible
2002 Pontiac, Montana, Passenger Van
2014 Impala, 4-Door Sedan, White Diamond, LTZ
2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ

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Thanks for the replies and measurements. I have a 28 engine with inserts and custom crank with enlarged journals. An unexplained minor vibration and visible wobble developed in the flywheel where none existed before. This prompted me to pull it apart. The crank looked ok but had some unusual wear on the front and rear mains that was consistent with a bent crank. I had it magnafluxed and it turned out to be cracked. I am considering going back to babbitt and original crank vs junking the motor and starting over. I was wondering if the block had been enlarged to support the insert bearings. If not, maybe I can find some original bearing shells and go from there. I'll take some measurements this weekend. Otherwise, it's good to know the babbitt may be poured directly onto the block. How does one fashion the center main thrust surface if the babbitt is poured onto the block?

Also, can someone tell me how to search back prior to one year ago on this forum? There's a lot of useful info from several years back and I can't seem to get to it. :( Also, I have to wait several minutes between searches. mad

Ron

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Go down to Tech Talk, scroll to the bottom and select "show all dates' from the pull down menu.

If you are looking for the "School is in Session", it is still there in three sections. Some of the pictures are missing because a Webmaster deleted without checking. Sorry!

If you use re-babbited shells or pore in the block it will be mandatory to line bore before laying the crank.

Forgot to mention for better accuracy the distance from the center of the crank to the center of the cam should be measured before disassembly. This measurement is necessary to aline the boring bar.

Agrin devil

Last edited by AntiqueMechanic; 03/15/07 06:27 PM.

RAY


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http://www.vccacolumbiariverregion.org/



1925 Superior K Roadster
1928 Convertible, Sport, Cabriolet
1933 Eagle, Coupe
1941 Master Deluxe 5-Passenger Coupe
1950 Styleline Deluxe 4-Door Sedan
1950 Styleline Deluxe Convertible
2002 Pontiac, Montana, Passenger Van
2014 Impala, 4-Door Sedan, White Diamond, LTZ
2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ

If you need a shoulder to cry on, pull off to the side of the road.
Death is the number 1 killer in the world.


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Yes, the babbit can be poured directly into the block, and will work, but it is MUCH easier to pour the shells, plus if the shells are "tinned" first (difficult with the cast iron block) the babbit will adhere much better. Also important is the fact that since babbit is relatively soft, a thin layer is better than a thick one- look at a moderen insert- the babbit layer is only a couple thousanths thick. Either way, you have to line bore.

Herb


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HerbK #97512 03/15/07 11:17 PM
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I pretty much figured any course of action would require an align bore. Now that I'm home for the evening, I took some quick measurements with my dial caliper. Looks like center and rear are pretty darn close to 2.000". I think I'm in trouble on the front however. I get approx 1.765" (what is that, 49/64"?) which is well beyond the 1.625" specified above. One of the front main inserts is a Clevite CB-727P with journal on the cracked crank measuring 1.625". This one may be a candidate for a poured bearing. I'll dig into it a little further this weekend.

Ron

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I took some more measurements and called up a couple of babbitt guys and they basically refused to do the direct pour on the front main bearing quoting issues with tinning the cast iron, thickness of the babbitt and transfer of heat, problems align boring, impracticality of machining new shells due to cost of materials (copper) and labor involved. Looks like this engine has just become a parts donor. Unfortunate but time to move on.

Regards,
Ron

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Ron,
I could suppy you with used 1928 main bearing shells.
E-mail me bwbugay@aol.com


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