400 sbc weighted flywheel?

Bryank · January 15, 2012, 04:46:19 PM

I got a 400 block number 330817. It shows it's a 1972-1980 400 2 bolt. It has the weighted balancer but not the flywheel.... Should i get a balanced flywheel or not? It runs good and don't shake or vibrate and when i called parts stores they sell em with or with out. any help would be appreciated.

RaZiN KaNe · January 15, 2012, 04:50:32 PM

it depends on weather the motor is internally or externally balanced...

tree · January 15, 2012, 07:10:02 PM

i have a 406 sbc and was told by the engine builder that all 400's are externally balanced so I had to get externally balanced flywheel. I got one from summit and it works great, no vibrations at all.

Bryank · January 15, 2012, 07:28:22 PM

well i imagine it won't hurt to just get a weighted flywheel even if it don't need it. there only $25 at oreily's.

Jjay78 · January 16, 2012, 12:28:42 AM

all 400 chevy small blocks were externally ballanced, did you have the weight plate behind the flywheel?

Bryank · January 16, 2012, 12:55:58 AM

no it had just a plain flexplate like a 350 no weights at all

Boggerram87 · January 16, 2012, 06:58:25 AM

Quote from: Jjay78 on January 16, 2012, 12:28:42 AM
all 400 chevy small blocks were externally ballanced, did you have the weight plate behind the flywheel?

That Will Do It

RaZiN KaNe · January 16, 2012, 12:24:19 PM

if it didnt have a weighted flywheel on it i would do some more checkin on it...i run a sbc 400 block and mine is all internally balanced man if u do put a weighted flywheel on a internally balanced motor ur gonna TEAR

UP INSIDE ...

Kyle · January 16, 2012, 06:21:12 PM

400s are weighted externally like evreybody has said. what ive always heard is that when ya build 400s and change internals ya gotta have everything rebalanced, crank, rods, pistons, damper, and flexplate all together. i know i had it all balanced when i built my motor......

Bryank · January 16, 2012, 09:29:26 PM

i don't know what to do! should i tear the oil pan off and look up the crank number? why does it have the 400 balancer on the front? I did notice a pilot bearing in the crank and this motor came out of a truck with a stickshift, thing is was that flywheel weighted? did the previous owner that i got truck from not know to put a weighted one on it? I think they didn't know because when i got the truck they said it was a 350 bored .060 over, after i got it and got it running right i checked the numbers and it is a 400! See they didn't run the truck much and gave up on it so i'm thinking i got it in time to save it. I looked in the cylinders with a bore scope and it is bored 060 over. Luckily i am putting my drivetrain in it and when i took the tranny out i noticed no weight on flywheel or behind it. When i first got the truck and it ran like

it did shake and make noise by the flywheel but when i made it run right and on all cylinders it smoothed right out no shimmies,shakes or noises.

old school truck dude · January 16, 2012, 11:51:40 PM

Let me clear this up for you. If the internals are original and have not been machined, you need a weighted flywheel because thats what goes on a 400. Your motor is not original as you said its 60 over, which means the crank has most likely been ground or replaced. 400s are externally balanced meaning the balancer and the flywheel have weights and machining to balance them. When people rebuild and modify, they often like to have the entire rotating assembly balanced. Its not always totally necesary, but it helps if youre going for high rpm. When they balance the rotating assembly, they usually do it WITHOUT the balancer and flywheel so that the 350 stuff will work which is more common and easier to come by. If you have a 400 balancer on the front, put what is called for going by the balancer on the front - the matching flywheel to that balancer.

A 60 over 400 aint gonna last long, thats too thin on the cylinder walls. You take it easy and it may last, but rawhide it and itll probably blow head gaskets or crack between the cylinders on the deck. Sorry, just the nature of the beast. I learned to stay away from that thing many years ago because they get expensive quick and often.

Bryank · January 17, 2012, 12:03:02 AM

oh great so now your telling me it's junk oh great lol! i don't know i did investigating and some 400's can handle 060 over good if they have been sonic tested and have thick walls. Regardless i'm gonna give it a beating and see what it's got! I did a compression test on it and it's got 150 pounds of compression in every cylinder and 60 plus oil pressure so weel see i guess? unless someone wants to buy it lol

Kyle · January 17, 2012, 01:40:00 AM

id just run it till it blows. its for a mud truck so ya dont have to worry bout reliabilty to get ya back and forth to work and everything seems to check out ok

Bryank · January 17, 2012, 01:44:26 AM

Quote from: Kyle on January 17, 2012, 01:40:00 AM
id just run it till it blows. its for a mud truck so ya dont have to worry bout reliabilty to get ya back and forth to work and everything seems to check out ok

yeah this is the first on i've ever owned! i'm curious to see if it's got any nutz or not

old school truck dude · January 17, 2012, 01:45:35 AM

Quote from: Bryank on January 17, 2012, 12:03:02 AM
oh great so now your telling me it's junk oh great lol! i don't know i did investigating and some 400's can handle 060 over good if they have been sonic tested and have thick walls. Regardless i'm gonna give it a beating and see what it's got! I did a compression test on it and it's got 150 pounds of compression in every cylinder and 60 plus oil pressure so weel see i guess? unless someone wants to buy it lol

Nope, not sayin its junk. Its a 400 60 over. They will fail prematurely at 40 over. Itll be fine for a good while, but it wont last as long as other similar motors such as a 350. Its also not gonna be re-buildable unless its sleeved.

old school truck dude · January 17, 2012, 01:47:01 AM

Quote from: Bryank on January 17, 2012, 01:44:26 AM
Quote from: Kyle on January 17, 2012, 01:40:00 AM
id just run it till it blows. its for a mud truck so ya dont have to worry bout reliabilty to get ya back and forth to work and everything seems to check out ok
yeah this is the first on i've ever owned! i'm curious to see if it's got any nutz or not

Of course it does, its a 400 and theyre lots of fun - give it hell!

Kyle · January 17, 2012, 01:49:53 AM

Quote from: Bryank on January 17, 2012, 01:44:26 AM
Quote from: Kyle on January 17, 2012, 01:40:00 AM
id just run it till it blows. its for a mud truck so ya dont have to worry bout reliabilty to get ya back and forth to work and everything seems to check out ok
yeah this is the first on i've ever owned! i'm curious to see if it's got any nutz or not

its the biggest factory small block gm made! of course it does! its like a 383 that everybody so loves but bigger bore! i love mine other than the fact i have an incredibly too small carb on it....

Bryank · January 17, 2012, 01:55:02 AM

i put my 750 seed demon carb on mine and it sounds way better than the 600 holley, i just havent got to take it for a spin yet!

Kyle · January 17, 2012, 02:05:38 AM

Quote from: Bryank on January 17, 2012, 01:55:02 AM
i put my 750 seed demon carb on mine and it sounds way better than the 600 holley, i just havent got to take it for a spin yet!

thatll run way better on it. i had to go way up on the jets(basically what a 770cfm runs) on my 670 just to feed mine and im still not done tweakin and tuning it....

Bryank · January 18, 2012, 10:01:48 PM

got weighted flywheel today. guess time will tell whether it helped or not.