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Discussion Starter #1 (Edited)
o.k. so here's where i show just how young i am at building a motor. i bought a block that i was told was bored 45 over. in my experience, i've only seen the usual 30, 40, 60 etc. the pistons that are in the block say .040. it's the rings that make up the difference right? i don't see pistons advertised anywhere at ".045" over so i'm scratching my head a little here. sorry this is such a dumb question, but i just want to make sure.

p.s. stop laughing, i admit i ain't the brightest bulb in the bunch.
 

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well if the pistons are .040 oversize then hopefully the block was also only bored .040 oversize...cause if they did the block .045 and then installed .040 pistons in it you will have WAY too much skirt skirt clearance...the piston will likely rock more than it should due to the excessive clearance and I would bet both blowby and oil consumption would be increased too....is this the same motor where they used 350 pistons/rods along with a 400 crank to get a 383 and now the pistons stick out of the block?
 

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Discussion Starter #3
yup. that be the one. maybe i'm looking at the piston #'s wrong but it seams to me that they say .040 i have one of the pistons/ rods out of the block and looked up the numbers and thats what it seams to read. maybe i shouldn't have bought it. for the money, it seamed like a good idea at the time. i'm gonna go double check the numbers. i really don't think he would be that incredibly dumb, but again, he did think he could use those rods. supposedly he had already bought the rebuild kit for the 350 and then decided to try the stroker crank. he said he was going to use open chamber heads so he didn't change out the pistons because they were "only" 80 thousandths out of the block. uggg.
 

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To check the piston to wall clearance you need to measure the piston skirt then the bore and see what the difference is. You are correct the standard oversizes are 10, 20, 30 and always even numbers. The motor may have been bored properly, used, then freshened up a couple times so the honing of the cylinder walls could make it a 045 overbore now. As previously stated not the best condition for a street engine. Just check or have someone check you PTW cleanance then you'll know what you have. Cast pistons run tighter than forged. Type and make pistons influence what those numbers should be. Hope that helps. JMHO
 

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IMO you need to fully dissassemble inspect and measure that motor...the person that "tried" to build it had a few gaps in his know how and that is why the pistons are "only" .080 out of the hole....BTW I would be surprised if the heads could be installed and bolted down with the pistons like that...the quench area of the head would very likely be hitting the pistons already...
 

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Discussion Starter #6
ok. so i guess i'm gonna have to try to figure out the bore vs. piston size. any tips on doing this? if it is at 45, am i gonna have to get it re-bored?
 

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well If you dont have the tools, or dont know someone with them, you could take it to a good machine shop to have the block checked...:)
 

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Discussion Starter #8
o.k. so i'll figure out a way to get the bore size checked. but now i'm wondering if it'll be worth it. they don't make 383 pistons in a .045 over bore do they? i can't find them listed. should i just say heck with it and have them bore it over to .060 so i can get propper pistons? and be done with it?
 

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[QUOTE='74hatchback]o.k. so i'll figure out a way to get the bore size checked. but now i'm wondering if it'll be worth it. they don't make 383 pistons in a .045 over bore do they? i can't find them listed. should i just say heck with it and have them bore it over to .060 so i can get propper pistons? and be done with it?[/QUOTE]

you would have to go .050 or more likely .060 over size...BUT that is only IF the bore is not useable as is:)
 

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Discussion Starter #10 (Edited)
o.k so after thinking about it, this motor is really only to get me through the summer anyway. i plan on building another one next winter with a fresh block, and the best of the best parts to build a high horsepower tank of a motor. unfortunately, if i start purchasing all those parts now, i won't have a complete motor to use in the car for the summer. thats why i originally bought this cheapo short block, so i would have something i could throw in the car. my question, just how bad will the blowby be, and how and how will this affect the performance of a motor that is gonna get ripped out after the summer anyways? i know the right thing to do is to get it bored, put all the best parts in now etc. but i just can't bare to let the car sit in the driveway for another summer. i hate to spend money on a re-bore for a cheapo beater motor that could go towards the one i want to build next year. the weather is finally getting nice enough here in cleveland to bring the car out and i can't bare to let it sit in the driveway. (i know, i have no patience) so honestly, could i get away with the .45 overbore for the time being? or is it just not going to work? what would be the worst that could happen? every dollar i don't have to spend on this, means another dollar i can apply towards the beast i want to build in the future.
 

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Discussion Starter #12
on the top of the pistons:

345NP .040
067-02+04-c

also, each piston has a number(1 through 8) stamped on the top from the place that put them on the rods

on the sides

345NP
645p

and a 3 on one side and a F on the other
 

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If the pistons are coming out of the block by more than about.005 you better get someone to look at this thing and figure out what you actually have going on. That little overbore is nothing compared to the pistons out of the block. Get some help before you waste any time or money on this thing. JMHO, RM
 

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Someone check my math...

Stock deck height is something around 9.025", total 'on paper' of stroke + rod + compression height should be around 9.000"

400 crank stroke total = 3.750"
400 rod length = 5.565"
350 rod lenght = 5.700"
345NP piston compression height = 1.560"
3.750/2= 1.875" crank stroke height

1) 1.875" stroke + 1.560" compression height + 5.565" rod = 9.000"

2) 1.875" stroke + 1.425" compression height + 5.700" rod = 9.000"

So...you have two choices:

1) change to 5.565" rods and use the existing pistons
2) change to pistons with 1.425" compression height and use the 5.7" rods
 

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Discussion Starter #15 (Edited)
patman, wow! thanks a million!!! i never was to good with numbers. it's replys like that, that make this forum a truly great place! that helps out a lot. so i guess since this is a temporary budget build, i'm just going to go ahead and try the 5.565 rods. i only need it to get me through the summer and $50 bucks for rods beats $300 for pistons. i hate spending good money on a temporary motor.
so any thoughts on what might happen if i keep the .045 bore? what would the affects be? i don't really know exactly what increased blowby it would do? would compression be different? how would performance be affected? while this is motor is only gonna be used for the summer, i don't want to take it out and have it die on the first day.

thanks again for everybody's input.
 

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well, i would gauge the cylinders and check the bore...if it is 45 over, then i would have it bored 60 over buy some cheapo pistons (sometimes machine shops will even trade you for your 40 over pistons or give you money toward other pistons, thats what they did for me)...that way you could have a motor running for it, start collecting parts for your other motor, and then when you have it, you could sale the 350 short block...it would be worth more then with it all cleaned up. at least you could get something back out of it...put a thumpy cam in it, and drive it for a while, others notice and want the motor (ive been offered several times to buy my motor...) so...thats what i would do. get it going....
 

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Discussion Starter #17
o.k. so i called around earlier, and most place want to charge a couple bucks(like $20) to check the bore but i guess i'm gonna eat the 20 and have it checked tomorrow. i found a place that would bore and hone for $120. cheapest i've found so far but i only called a few places. i'm gonna wate on buying the 5.565 rods until i find out if i absolutely need it bored. if i do, then i might as well keep my 5.7 rods and just get correct stroker pistons. somehow, i just know this "cheapo" summer shortblock is gonna get real expensive real quick.
 

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Nobody answered what is going to happen if 40 over pistons are ran in a 45 over bore. IMO it is going to run like a worn out engine. It won't run as good as a new, fresh engine should. There is also a possibility that it will have some piston slap, so it'll make a little knocking noise on startup. Blow-by will reduce your cylinder pressure, and contaminate your engine oil faster, and it may also cause it to use a bit more oil than it should. Nothing horrible is going to happen, it just won't run like a fresh engine should.

Randy (It'll run like my Nova!):eek: :rolleyes:
 

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I don't think you have a .045 over bore.
That would be a special bore for a special set-up and most reputable machine shops I know would not do something like this (normally).
Someone could have gotten carried away with the honning.

FWIW
Don
 

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69NovaSS in POST # 2 said:
well if the pistons are .040 oversize then hopefully the block was also only bored .040 oversize...cause if they did the block .045 and then installed .040 pistons in it you will have WAY too much skirt skirt clearance...the piston will likely rock more than it should due to the excessive clearance and I would bet both blowby and oil consumption would be increased too....is this the same motor where they used 350 pistons/rods along with a 400 crank to get a 383 and now the pistons stick out of the block?

72GreenRally said:
Nobody answered what is going to happen if 40 over pistons are ran in a 45 over bore. IMO it is going to run like a worn out engine. It won't run as good as a new, fresh engine should. There is also a possibility that it will have some piston slap, so it'll make a little knocking noise on startup. Blow-by will reduce your cylinder pressure, and contaminate your engine oil faster, and it may also cause it to use a bit more oil than it should. Nothing horrible is going to happen, it just won't run like a fresh engine should.

Randy (It'll run like my Nova!):eek: :rolleyes:
Just call me NoooooBoooddddddy...lol:)
 
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