Do I need to bore over 30 to put in pistons? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Blue71LWB · 04-26-2007, 03:32 PM

I'm thinking of putting in some flat top pistons in my inline 250.

I feel the engine is fine , but I was told I would need to have it bored if I was going to go with new pistons.

I really don't want to bore the block.

So will it be OK , to put in new ones without boring ?

Zac

grayw0lf · 04-26-2007, 03:34 PM

If you want oversize pistons, you must have it bored.

Depending on how much of a ridge you have at the top of your cylinders, you may get by with just a hone & new rings on your existing pistons.

You are best off going to the machine shop.

nvrforgotten52 · 04-26-2007, 03:35 PM

it would be best to bore it. chances are you have cylinder ware.. but you could get away with it if you use the same bore pison thats in there now.

**truckdude239** · 04-26-2007, 03:35 PM

pull it apart and take it to a machine shop they will tell you if you need to bored it or not but if the motor is old you will probley need to bore it i am building a 305 that i had bored 30 over it doesn't hurt the motor any it helps with performance

glock35ipsc · 04-26-2007, 03:36 PM

It all depends on the amount of cylinder wear. Is there a lip at the top of the cylinder? You should have the bore checked by a machine shop, they will be able to tell you in minutes whether or not you can replace with standard size pistons or if it will need bored. Why the change to flattops? Are the ones in there now dished?

glock35ipsc · 04-26-2007, 03:37 PM

Wow, 4 like answers inside of 2 minutes! Guess that should confirm the answer to his question!

Blue71LWB · 04-26-2007, 05:30 PM

Quote:

Originally Posted by glock35ipsc

Are the ones in there now dished?

I was told they were dished (1970 -250). I don't know though.

I'm planning on pulling it and painting / headers/ 4bbl intake.

So I thought I might dig a little deeper while I had it out,

hootlube · 04-26-2007, 05:48 PM

I say, if you're gonna have it out and torn down and you're replacing the pistons anyway, have it bored .030 over. I bet those pistons would be easier to find than stock...

JAKES 68GMC · 04-26-2007, 06:24 PM

Might as well throw a higher-lift cam in there while you're at it.

cdowns · 04-26-2007, 06:31 PM

anytime i have a block bored i go for the max// cost the same 30 or 60 pistons cost the same rings cost the same ITS FREE CUBIC INCHES

Down south truckin · 04-26-2007, 07:05 PM

you can use new pistons in the standard bore but you'll need to have someone measure your cylinders to see how much it's worn if it's excessive you'll need to bore it. me personally i don't like to bore the block more than it needs because if you have problems later you may need to bore it again

RACINJASON22 · 04-26-2007, 07:27 PM

Quote:

Originally Posted by cdowns

anytime i have a block bored i go for the max// cost the same 30 or 60 pistons cost the same rings cost the same ITS FREE CUBIC INCHES

I usually agree with cdowns on most replies but, not this one.

The main reason for an over bore is to provide a new and proper cylinder bore. Not to add HP by adding cubic inces.

The in crease in HP out put by boreing in very very minamal on the cubic in" matter. The real gain is from attaining a new and proper piston to cylinder enviorment thus increasing HP output.BETTER PISTON AND RING SEAL

IMO every thing that was stated about having the machine shop check the block out is right on the money and if the block does need bored go with the minimum over bore allowed to take out any imperfections and out of roundness.

Since this is on a 250 there is probably not as many options out there as say a 350 sbc but its worth checking into IMO.

Sammy · 04-26-2007, 07:46 PM

Speaking about boring engines. Sm block 350's for example. Some folks are going 60 over. Doesn't that cut pretty close to water jackets? Until recently I had never heard of going 60 over. Now several shops do a 60 over bore. Old school was always stop at 30 over( 283/327's).

glock35ipsc · 04-26-2007, 08:09 PM

Quote:

Originally Posted by Sammy

Speaking about boring engines. Sm block 350's for example. Some folks are going 60 over. Doesn't that cut pretty close to water jackets? Until recently I had never heard of going 60 over. Now several shops do a 60 over bore. Old school was always stop at 30 over( 283/327's).

In general, going .060 over will decrease the cylinder thickness and could possibly increase water temps, but usually not noticable in most small blocks. However, 400's are more prone to that problem when going over .030.

RACINJASON22 · 04-26-2007, 08:19 PM

Core shift comes into play on some blocks and I always recommend that a sonic test be done when boring upto and including .060 over.

I agree with what glock35ipsc said on the matter.

jkeady · 04-26-2007, 08:21 PM

I think if there is any significant amount of mileage on that block (50k+) then you're looking at machine work. And why not? Why would you want to tear down the motor and up the compression, only to risk having it smoke like a tire fire when the rings don't seat correctly?

Another thing to think about is future work. If you go .060 over now, you're buying another block if something happens to a cylinder wall.

bean · 04-26-2007, 08:36 PM

Take it to the machine shop. I bored my 250 .040 and have been extremely pleased with the results. IMO, the 250's are work horses that were normally worked really hard. If you're going to take the time to rebuild it do it once and do it right.

nvrforgotten52 · 04-27-2007, 01:00 AM

Quote:

Might as well throw a higher-lift cam in there while you're at it.

GREASEMONKEY72 · 04-27-2007, 05:08 AM

i agree with whats been said and i also very much agree with NOT going .060 over right now if .020 over will clean it up then do that if it takes .030 then stop there, dont bore out anymore than you need to clean it up, if you want more power out of it rebuild the head with valves and springs and add a cam and stroke the block a bit and theres your HP

**'68OrangeSunshine** · 04-27-2007, 06:09 AM

A 250 L6 @ stock stroke bored .030 over has 254 cubic inches.

**truckdude239** · 04-27-2007, 06:28 AM

the only reason i bored my 305 30 over is because in case it ever gave up the ghost i will be able to bore again

GREASEMONKEY72 · 04-27-2007, 06:44 AM

Quote:

Originally Posted by truckdude239

the only reason i bored my 305 30 over is because in case it ever gave up the ghost i will be able to bore again

thats the exact reason why you shouldnt go the max on the first time out, never know if youll have to bore it again

RustyParts · 04-27-2007, 09:03 AM

Have 'em throw on the torque plates while your at it, makes for nice straight cylinders.

EAST SIDE LOW LIFE · 04-27-2007, 02:39 PM

Quote:

Originally Posted by Sammy

Speaking about boring engines. Sm block 350's for example. Some folks are going 60 over. Doesn't that cut pretty close to water jackets? Until recently I had never heard of going 60 over. Now several shops do a 60 over bore. Old school was always stop at 30 over( 283/327's).

**********************************************************

I agree with Sammy!!! I would think more then 40 over on a 350 is the begining of leaving the comfort zone. Some old 283s were bored as much as 80 over but I would not go more then 60 over if it were mine. 327 same thing 60 over is fine but a 350 40 over max.

Where is longhorn Man when you need him.

esll.

LMN8UR · 04-27-2007, 03:47 PM

Typically blocks are cheaper than good pistons. So if you bore to the max and something fails, you'll have to replace the block and rebore. If something goes wrong and you damage a piston, you'll probably not have a block either.

There are a lot of theories out there. . Start with the machine shop, decide from their.

04-26-2007, 03:32 PM	#1
Blue71LWB Registered User Join Date: Nov 2006 Location: Alabama Posts: 120	Do I need to bore over 30 to put in pistons? I'm thinking of putting in some flat top pistons in my inline 250. I feel the engine is fine , but I was told I would need to have it bored if I was going to go with new pistons. I really don't want to bore the block. So will it be OK , to put in new ones without boring ? Zac

04-26-2007, 03:34 PM	#2
grayw0lf Registered User Join Date: Apr 2004 Location: Clanton, AL Posts: 1,253	Re: Do I need to bore over 30 to put in pistons? If you want oversize pistons, you must have it bored. Depending on how much of a ridge you have at the top of your cylinders, you may get by with just a hone & new rings on your existing pistons. You are best off going to the machine shop. __________________ 85' CUCV M1009!!! The newest addition! 6.2diesel, Th400, NP208, & only 36k miles! 70' C-10 LWB Fleetside - Looking good these days! 05' Dodge Neon 88' Winner Escape Sport 1750 - 4.3v6 94' Seadoo SP 84' Honda TRX200, bare nekkid. Just a frame & tires. Always looking for another project or any good deal!

04-26-2007, 03:35 PM	#3
nvrforgotten52 Registered User Join Date: Jan 2006 Location: Morro Bay C.A Posts: 179	Re: Do I need to bore over 30 to put in pistons? it would be best to bore it. chances are you have cylinder ware.. but you could get away with it if you use the same bore pison thats in there now. __________________ '69 C10 SWB 350 edelbrock int/carb .420 .442 cam 700r4 70 lwb c10 work truck 250 I6 with two inch lift springs and a two inch bodylift and 33/12.5s

04-26-2007, 03:35 PM	#4
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,233	Re: Do I need to bore over 30 to put in pistons? pull it apart and take it to a machine shop they will tell you if you need to bored it or not but if the motor is old you will probley need to bore it i am building a 305 that i had bored 30 over it doesn't hurt the motor any it helps with performance __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube Last edited by truckdude239; 04-26-2007 at 03:37 PM.

04-26-2007, 03:36 PM	#5
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,685	Re: Do I need to bore over 30 to put in pistons? It all depends on the amount of cylinder wear. Is there a lip at the top of the cylinder? You should have the bore checked by a machine shop, they will be able to tell you in minutes whether or not you can replace with standard size pistons or if it will need bored. Why the change to flattops? Are the ones in there now dished? __________________ *Bob* 1970 Chevy K10 LWB "Goldie" 350/TH350 *next project!!* 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE

04-26-2007, 03:37 PM	#6
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,685	Re: Do I need to bore over 30 to put in pistons? Wow, 4 like answers inside of 2 minutes! Guess that should confirm the answer to his question! __________________ *Bob* 1970 Chevy K10 LWB "Goldie" 350/TH350 *next project!!* 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE

04-26-2007, 05:48 PM	#8
hootlube Registered User Join Date: Apr 2007 Location: muskogee, ok Posts: 32	Re: Do I need to bore over 30 to put in pistons? I say, if you're gonna have it out and torn down and you're replacing the pistons anyway, have it bored .030 over. I bet those pistons would be easier to find than stock...

04-26-2007, 06:24 PM	#9
JAKES 68GMC Aluminum slot wheels rule... Join Date: Jan 2006 Location: Maine Posts: 6,212	Re: Do I need to bore over 30 to put in pistons? Might as well throw a higher-lift cam in there while you're at it.

04-26-2007, 06:31 PM	#10
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Do I need to bore over 30 to put in pistons? anytime i have a block bored i go for the max// cost the same 30 or 60 pistons cost the same rings cost the same ITS FREE CUBIC INCHES __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

04-26-2007, 07:05 PM	#11
Down south truckin Senior Member Join Date: Feb 2006 Location: Lilburn Georgia Posts: 1,240	Re: Do I need to bore over 30 to put in pistons? you can use new pistons in the standard bore but you'll need to have someone measure your cylinders to see how much it's worn if it's excessive you'll need to bore it. me personally i don't like to bore the block more than it needs because if you have problems later you may need to bore it again

04-26-2007, 07:46 PM	#13
Sammy Registered User Join Date: Apr 2000 Location: Bonne Terre, Mo Posts: 3,005	Re: Do I need to bore over 30 to put in pistons? Speaking about boring engines. Sm block 350's for example. Some folks are going 60 over. Doesn't that cut pretty close to water jackets? Until recently I had never heard of going 60 over. Now several shops do a 60 over bore. Old school was always stop at 30 over( 283/327's). __________________ '69 Chevy Long Fleet & '71 GMC Short Step & Project "ODD BALL" "You can wash a pig, soak it in most expensive perfume. In the end it is still just a pig." ODD BALL build thread http://67-72chevytrucks.com/vboard/s...d.php?t=478629"

04-26-2007, 08:19 PM	#15
RACINJASON22 GEARHEAD Join Date: Jan 2007 Location: CENTRAL,PA Posts: 2,284	Re: Do I need to bore over 30 to put in pistons? Core shift comes into play on some blocks and I always recommend that a sonic test be done when boring upto and including .060 over. I agree with what glock35ipsc said on the matter. __________________ 72 SWB 2WD MY PROJECT 72 LWB 4X4 FUTURE PROJECT SUBSCRIBE HEREBOARD VENDORS HERE NORWOOD MEET SURVIVOR!

04-26-2007, 08:21 PM	#16
jkeady Registered User Join Date: Apr 2004 Location: Salem, OR Posts: 127	Re: Do I need to bore over 30 to put in pistons? I think if there is any significant amount of mileage on that block (50k+) then you're looking at machine work. And why not? Why would you want to tear down the motor and up the compression, only to risk having it smoke like a tire fire when the rings don't seat correctly? Another thing to think about is future work. If you go .060 over now, you're buying another block if something happens to a cylinder wall. __________________ Josh '70 Custom Camper / 20 Last edited by jkeady; 04-26-2007 at 08:22 PM.

04-26-2007, 08:36 PM	#17
bean Registered User Join Date: Jun 2002 Location: Fort Worth, TX Posts: 920	Re: Do I need to bore over 30 to put in pistons? Take it to the machine shop. I bored my 250 .040 and have been extremely pleased with the results. IMO, the 250's are work horses that were normally worked really hard. If you're going to take the time to rebuild it do it once and do it right.

04-27-2007, 05:08 AM	#19
GREASEMONKEY72 Registered User Join Date: Aug 2006 Location: Bakersfield,CA Posts: 7,893	Re: Do I need to bore over 30 to put in pistons? i agree with whats been said and i also very much agree with NOT going .060 over right now if .020 over will clean it up then do that if it takes .030 then stop there, dont bore out anymore than you need to clean it up, if you want more power out of it rebuild the head with valves and springs and add a cam and stroke the block a bit and theres your HP __________________ -steven Alte Seele S.S. "Allison" '72 C/10 LWB 350SB/TH350 - DD PITBULL IS NOT A CRIME



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04-27-2007, 06:09 AM	#20
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,205	Re: Do I need to bore over 30 to put in pistons? A 250 L6 @ stock stroke bored .030 over has 254 cubic inches. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not.

04-27-2007, 06:28 AM	#21
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,233	Re: Do I need to bore over 30 to put in pistons? the only reason i bored my 305 30 over is because in case it ever gave up the ghost i will be able to bore again __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

04-27-2007, 09:03 AM	#23
RustyParts Registered User Join Date: May 2006 Location: Wyman, Kentucky Posts: 403	Re: Do I need to bore over 30 to put in pistons? Have 'em throw on the torque plates while your at it, makes for nice straight cylinders. __________________ 1972 GMC Jimmy, 4WD, 454 CI, 350 Turbo, 4" lift, 35" tires The math teacher said my son "Bubba" could be a mathmatical genius. cause he's got 13 fingers! Last edited by RustyParts; 04-27-2007 at 09:03 AM.

04-27-2007, 03:47 PM	#25
LMN8UR Registered User Join Date: Jun 2005 Location: Midlothian, VA Posts: 148	Re: Do I need to bore over 30 to put in pistons? Typically blocks are cheaper than good pistons. So if you bore to the max and something fails, you'll have to replace the block and rebore. If something goes wrong and you damage a piston, you'll probably not have a block either. There are a lot of theories out there. . Start with the machine shop, decide from their. __________________ 72 Chevy C-10 Custom LWB 383 Stroker - Edlebrock Air Gap intake and 670 CFM Holley Street Avenger carb. Hooker Comp Headers w/ X-Pipe and 2.25 duals TKO-500 & 3.08:1 rear I Love HEMI's, they're soft & chewy!

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