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  #1  
Old Apr 27th, 09, 04:07 PM
mark191 mark191 is offline
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Default 3914638 is it a 307?

Hi guys this is my first post on this site and I have to say that the info here has been very helpful! The problem I am having is the confusion over the casting number 3914638.The guy I bought it from swore it was a 68 327 truck motor but after tearing it down I found forged domes in it with the stamp std on the top which indicates standard bore.Well with the cylinders being in good shape i gave it a good honing job and got a set of 327 standard 4.00 pistons and they do not fit.Was wondering if anyone had this problem and if so what did you do.Thanks
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  #2  
Old Apr 27th, 09, 04:28 PM
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Default Re: 3914638 is it a 307?

thats a 307 cu inch motor
but you can bore to fit I assume
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Old Apr 27th, 09, 05:13 PM
mark191 mark191 is offline
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Default Re: 3914638 is it a 307?

I dont understand how half the sites list it as a 327 and the others list it as a 307.
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Old Apr 27th, 09, 05:58 PM
BillK BillK is offline
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Default Re: 3914638 is it a 307?

Mark,

My engine builders software and Mortec both show it as a 307. Which "site" says it is otherwise ??

Got to ask .... why would you buy a set of pistons without measuring the bore first ?
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Old Apr 27th, 09, 06:14 PM
mark191 mark191 is offline
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Default Re: 3914638 is it a 307?

chevrolet car club is one site that lists it as a 327 2 bolt truck.And as for measuring the bore it was stupidity.But pretty sure i can just bore to size because the stroke is the same for 307 or 327
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Old Apr 27th, 09, 06:39 PM
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Default Re: 3914638 is it a 307?

I'm sure a machinist should be saying this but I wouldn't try to bore that block .125.
307 is 3.875 bore and 327 is 4.000
Jeff
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Old Apr 28th, 09, 05:40 AM
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Default Re: 3914638 is it a 307?

look for a suffix code on the block to find out if in fact its a 307 or 327 but you already tried a 4" piston and it didnt fit so you have a 307
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Old Apr 28th, 09, 04:39 PM
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Default Re: 3914638 is it a 307?

I'd sonic check it and bore away if it's OK..

pdq67
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Old Apr 28th, 09, 06:24 PM
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Default Re: 3914638 is it a 307?

Quote:
Originally Posted by yellow69RS View Post
I'm sure a machinist should be saying this but I wouldn't try to bore that block .125.
307 is 3.875 bore and 327 is 4.000
Jeff
This is true! You must get new pistons.
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  #10  
Old Apr 28th, 09, 06:37 PM
GOSFAST GOSFAST is offline
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Default Re: 3914638 is it a 307?

Had a unit in here some time ago for a build, block #3914638. Most definitely a "stock" 327" (4.000" bore) core!

I do show a casting #3914636 as a 307"?

Thanks, Gary in N.Y.

P.S. Make certain the posted numbers are correct, some of these early casting's are difficult to read, especially while they're still somewhat dirty.
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Old Apr 29th, 09, 03:53 PM
mark191 mark191 is offline
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Default Re: 3914638 is it a 307?

Quote:
Originally Posted by pdq67 View Post
I'd sonic check it and bore away if it's OK..

pdq67
what is sonic checking? thanks
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  #12  
Old Apr 29th, 09, 04:49 PM
pdq67 pdq67 is offline
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Smile Re: 3914638 is it a 307?

A sonic checking device is like a sonar gun that can measure part thicknesses once it's calibrated in.

You hold it's transducer, (i.e., sending head), tight against the part, (cylinder wall in this case ), a sonic wave goes out, returns and then it is converted electronically into thousandth's of inches or whatever...

A good Machine Shop should have one, imho.. It can tell you if the cylinders are thick enough before boring to bore an 1/8" over. As well as check for thinner rust spots and even sand cast pinholes and such.

The one I've seen is like the size of an old hand-held transistor radio w/ a transducer and cord on it. Nor much bigger than a dwell meter as I recall??

And if it won't bore an 1/8" over, heck, bore her a 1/16" over and turn her into a highly HOPPED UP 292 and go big engine hunting!!

pdq67
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Old Apr 29th, 09, 05:11 PM
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Wink Re: 3914638 is it a 307?

Quote:
Originally Posted by GOSFAST View Post
Had a unit in here some time ago for a build, block #3914638. Most definitely a "stock" 327" (4.000" bore) core!

I do show a casting #3914636 as a 307"?
...

The confusion comes from the fact that GM used the 3914638 casting for some 307's - just underbored* it to 3.90"...
I've tore apart a 'DF' coded 307 a couple years back with a 638 block.
It is more common to find 307's using the 3914635 or 636 blocks though

As stated, bore it to fit your pistons you ordered and be done with it.
It will take a 4.0" bore, I've never run into a problem boring one to standard oversizes yet.



* = vs. a 4.0" bore for a 327 or 350 - don't start hate mail...
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  #14  
Old Apr 29th, 09, 05:52 PM
pdq67 pdq67 is offline
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Default Re: 3914638 is it a 307?

And I'm figuring most "round bottom" 283's will bore to .155" over just like a .030" 302" engine block!

BUT I would sonic check 1st!!

pdq67
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