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Old 05-08-2021, 09:45 PM
Rar_421 Rar_421 is offline
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Default 400 crankshaft

Checking around with local machine shops about having a 400 crank ground one reputable shop emailed back and said they had 1 in stock,300.00 with bearings,last crank I had reground in 09' cost 135.00,plus bearings,so 300 seems like a good deal but I'm kinda wondering if the bearing clearance's are going to be hit& miss in my block&con rods which will be clipped and honed to factory specs,anyone have any experience buying a reground crank?

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Old 05-08-2021, 10:10 PM
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I’am confused here I guess because in the beginning of your paragraph you say one shop is reputable, and at the end of that sentence you are questioning them!

If your putting a motor together you should have the needed tools to Check any shops work where it relates to Bearings, and don’t buy anything that can not be returned if it does not check out right during a Mock assembly,

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Old 05-08-2021, 10:45 PM
Rar_421 Rar_421 is offline
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The last motor I had rebuilt in 09 was a 67 Buick gs 400,45k miles on it so we ordered .010 under rods & mains,he clipped the caps and rods and honed to factory specs,Then installed the bearings,measured each rod and main called me up and asked what clearance's I wanted to run and ground it to those specs, I guess what I'm asking is wise to buy a crankshaft just ground to a generic undersize with out having rods&mains measured for the block it will be used in?

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Old 05-08-2021, 11:11 PM
Schurkey Schurkey is offline
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Is the block going to be at the high side, or the low side of "factory spec"?

A pre-ground crank will probably be near the small side of the tolerance. Given a choice, I'd want the crank ground to best suit the block, and the block cut to give optimum bearing crush.

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Old 05-08-2021, 11:27 PM
Rar_421 Rar_421 is offline
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Quote:
Originally Posted by Schurkey View Post
Is the block going to be at the high side, or the low side of "factory spec"?

A pre-ground crank will probably be near the small side of the tolerance. Given a choice, I'd want the crank ground to best suit the block, and the block cut to give optimum bearing crush.
Just a daily driver,so hoping to get as close to factory clearance as possible,I wanted to bring the block there and have them clip and hone the rods& mains ,bore it .030 and install cam bearings etc and then see what type of clearance's the crank would be at in my block but they are so busy with dirt track motors I'd have to wait until the end of July so it's probably better to bring my parts to another shop that's closer to me rather than 2hrs away

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Old 05-09-2021, 06:29 AM
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Well first off it sounds like you don’t even know if the rod big ends are out of round and need to be honed, or if the main bores are off and if the line bore needs to get worked on, is this the case?

You do not want the block line bored if it’s only just a hair out of spec, you want a shop that can line hone the mains!

You can tell a lot about the crush fit of any bore that has been run by looking at the impression left by the numbers and letters on the back of the Bearings in the bore itself !

If these impressions are clear and not smeared then the Bearing in question was gripped by its bore just fine and then it’s just a matter of for example the line bore falling within spec and the crank being cut to what should be the low side of the clearance spec.

Unless there was a mistake done or the crank was specifically cut for added race clearance, all shops that have the expensive equipment needed to cut a crank will cut to the low side of the tolerance.

This is especially true with cast cranks where you can’t just weld them back up to start over!

To me the Bearing clearances for the rods and mains on a pure street motor making less then 500 hp and expected to be able to rev to 5500 to 5800 is .002”

To tell you the truth, with the low price these days for new much better then cast Rods I don’t know why one would even pay to get all the rods resized , as if you do so you should change out the Rod bolts and all of this work and parts cost brings you very close to a new set of street worthy Rods!


Last edited by steve25; 05-09-2021 at 06:37 AM.
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Old 05-09-2021, 11:16 AM
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What year 400?

400 cranks were also made in both thin and thick counterweights varieties, plus several different materials, nodular iron, PMI, Arma-Steel, etc.

There are quite a few different 400 crankshafts out there, so at a minimum you want to make sure it is a correct replacement for your engine......

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Old 05-09-2021, 12:33 PM
Rar_421 Rar_421 is offline
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They did ask what yr my engine is(74) when I inquired and said they had one,I'll contact them and get the casting number to be sure.thanks

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Old 05-10-2021, 08:04 AM
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Most early cranks were "heavyweight" and had a big N cast right on them.

In the early to mid-1970's they started lightening them up and changing the "recipe" using "softer" materials. Can't remember exactly when the lighter/weaker cranks started showing up. I used to know all that stuff but lots of cases of CRS these days and even worse cases of DGS!......Cliff

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Old 05-10-2021, 09:08 AM
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In 1976 they did the rear crank flywheel hub a different size. (but not all)
Seems 1975 could have some different cranks, but definitely 1976 on.
Then the earlier years like 67 and earlier were different somehow.


I think there is a lot of the DGS (DGaS?) now.



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Old 05-10-2021, 09:50 AM
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Thankfully the last of the 455 cranks in 76 where never scrwed with in terms of weight.

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Old 05-10-2021, 10:02 AM
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Quote:
Originally Posted by Rar_421 View Post
Quote:
Originally Posted by Schurkey View Post
Is the block going to be at the high side, or the low side of "factory spec"?
Just a daily driver,so hoping to get as close to factory clearance as possible...
What was being hinted at is that there are different versions of "factory spec".

Quote:
Originally Posted by Cliff R View Post
Most early cranks were "heavyweight" and had a big N cast right on them.

In the early to mid-1970's they started lightening them up and changing the "recipe" using "softer" materials. Can't remember exactly when the lighter/weaker cranks started showing up. I used to know all that stuff but lots of cases of CRS these days and even worse cases of DGS!......Cliff
the lightweight stuff was phased in during the 1975 model year;
this was when the 557 blocks started showing up after the 350/400's went on a weight savings program.

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Old 05-14-2021, 10:14 AM
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Most reputable crank grinders are going to "shoot" for the middle of the spec. If memory serves me, the spec for the mains on a Pontiac 400 crank is 2.9990-3.000 standard, so the spec for a .010 should be 2.9890-2.990. I'd like to see a journal 2.9895-2.9897. The rod spec is 2.2487-2.2497. The .010 standard should be 2.2387-2.2397. One question: what are your rod bores and main saddle specs? These affect bearing oil clearance as well as journal size. How about your bearing thickness?

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Old 05-14-2021, 01:49 PM
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This may help some:

http://www.pontiacpower.org/PontiacCranks.htm

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