Thread: 383 Shaking Like H@[[,3000 To 4000.why!!

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JUST ONE TIME I WOULD LIKE TO COME ON HERE WITHOUT A PROBLEM! HERES WHATS WRONG,IM HOPING SOMEONE CAN HELP.FINISHED BUILDING A 383 STROKER.THERE IS PROBABLY 2 HOURS ON THE ENGINE,GIVE OR TAKE 5 MINUTES EITHER WAY.JUST STARTED TO SHAKE PRETTY VIOLENTLY BETWEEN 3 AND 4 THOUSAND.I DISCONECTED ALL THE BELT DRIVEN PARTS,STEERING PUMP,ALTERNATOR,AND WATER PUMP,TO SEE IF THIS WAS WERE THE PROBLEM WAS.NO. IT DONT MATTER IF ITS IN GEAR OR OUT,NOR DOES IT MATTER IF ITS UNDER HEAVY OR LIGHT THROTTLE. THERE IS NOTHING VISIBLE THAT WOULD LOOK LIKE THE PROBLEM.ALSO,THE ENGINE IS NOT MAKING ANY UNUSUAL SOUNDS OR NOISES. GUYS,IM STUMPED!!! COULD IT BE THE HARMONIC BALANCER,I PUT A NEW ONE ON AT REBUILD,IT IS A STOCK 400 8 INCH REPLACEMENT.I ALSO PUT IN AN SFI RATED FLEXPLATE[FLYWHEEL].???????HELP!!! THANKS IN ADVANCE!!!

did you balance the mass with the fly wheel and your damper do you have the right fly wheel ? my guess you never balance it ?

I Got The Engine Used And Not Running.it Has Scat Rods And Crank.i Put The New Flywheel On Right Out Of The Box.could This Be It? What Remedy Would You Suggest? Thanks!

well what scat crank is it they come both ways so it could take the 400 damper and fly wheel or a 350 damper and fly wheel .it needs to come down and get re balance it or at lest pull the oil pan down and look at the mains for hammer marks if you find the right damper and fly wheel combo

It Came With The 400 Parts,im Guessing They Were Right.well Time To Pull It Out And Take It Back To The Shop...thanks Pat.

well that a bad deal but then you will know it is right. go thru the firing order check 5and7

Originally Posted by SMOKEDOG7142000

JUST ONE TIME I WOULD LIKE TO COME ON HERE WITHOUT A PROBLEM! HERES WHATS WRONG,IM HOPING SOMEONE CAN HELP.FINISHED BUILDING A 383 STROKER.THERE IS PROBABLY 2 HOURS ON THE ENGINE,GIVE OR TAKE 5 MINUTES EITHER WAY.JUST STARTED TO SHAKE PRETTY VIOLENTLY BETWEEN 3 AND 4 THOUSAND.I DISCONECTED ALL THE BELT DRIVEN PARTS,STEERING PUMP,ALTERNATOR,AND WATER PUMP,TO SEE IF THIS WAS WERE THE PROBLEM WAS.NO. IT DONT MATTER IF ITS IN GEAR OR OUT,NOR DOES IT MATTER IF ITS UNDER HEAVY OR LIGHT THROTTLE. THERE IS NOTHING VISIBLE THAT WOULD LOOK LIKE THE PROBLEM.ALSO,THE ENGINE IS NOT MAKING ANY UNUSUAL SOUNDS OR NOISES. GUYS,IM STUMPED!!! COULD IT BE THE HARMONIC BALANCER,I PUT A NEW ONE ON AT REBUILD,IT IS A STOCK 400 8 INCH REPLACEMENT.I ALSO PUT IN AN SFI RATED FLEXPLATE[FLYWHEEL].???????HELP!!! THANKS IN ADVANCE!!!

Is this an int. balance engine or an ext. balance engine?

Originally Posted by erik erikson

Is this an int. balance engine or an ext. balance engine?

that was my point he not sure he did not build it or balance it he has no way of knowing

With what he is experiencing I'd bet it's externally balanced.
When I put a stock 400 in a '62 pickup I first hung a 283 flywheel on the end of it. To say that it shook is an understatement. I only drove it around the block and in that short amount of time it wiped out the rear main seal and I was told that there was a great possibility of breaking the crank. I solved the problem with a 454 flywheel.

Knowing What I Do,and From What Ive Been Told,the Engine Is Externally Balanced.the Guy I Got It From Had It Running Until A Cam Lobe Was Trashed Due To Him Adjusting It Down Too Much.i Had The Block And Crank Cleaned Up And Checked,the Machinist Said Everything Was Good And Within Tolerances.i Put A New Stock Replacement Balancer On Along With A Flexplate For A 400 I Got New At Summit.the Only Other Thing That Seemed Strange When I Was Putting The Bottom End Together Was None Of The Pistons Or Rods Were Marked With A Number.i Thought They Had To Go In In A Certain Hole.the Pistons And Rods Were Cleaned But Not Taken Apart,so I Put Them In The Proper Way But Possibly Not The Way They Were When It Ran.i Know They Went In Different Because As I Was Putting It Together,i Had To Grind The Number 6 Rod Bolt Head Cause It Was Hitting The Cam Lobe.not The Same Lobe That Was Torn Up When I Got It.

Knowing What I Do,and From What Ive Been Told,the Engine Is Externally Balanced.the Guy I Got It From Had It Running Until A Cam Lobe Was Trashed Due To Him Adjusting It Down Too Much.i Had The Block And Crank Cleaned Up And Checked,the Machinist Said Everything Was Good And Within Tolerances.i Put A New Stock Replacement Balancer On Along With A Flexplate For A 400 I Got New At Summit.the Only Other Thing That Seemed Strange When I Was Putting The Bottom End Together Was None Of The Pistons Or Rods Were Marked With A Number.i Thought They Had To Go In In A Certain Hole.the Pistons And Rods Were Cleaned But Not Taken Apart,so I Put Them In The Proper Way But Possibly Not The Way They Were When It Ran.i Know They Went In Different Because As I Was Putting It Together,i Had To Grind The Number 6 Rod Bolt Head Cause It Was Hitting The Cam Lobe.not The Same Lobe That Was Torn Up When I Got It.

hey Smoke, there are alot of things going on here. I think that a 400 sbc is both internally and externally balanced. Your flywheel and dampner both need to be balanced with the rest of the rotating assembly. When you ground off the bolt on the rod you also changed the balance on the assembly. I suffered major engine failure as a result of poor balancing of the assembly. Broken crank, rod, camshaft, oil pump, pickup, oil pan, and block. Stop running this engine until you figure out and correct the problem!!

you would have to grind more then the bolt head to get it to shake like you say sure the cam not hitting the rods ? there was never a internal 400 sbc from gm all external. but the after market crank throws that out the window

Any luck figuring it out?

It shouldn't be a balancing issue if it only started after two hours of running the engine. That would have been noticed before. If it ran well at the beginning and it's vibrating now, then I guess something's loose. If the rods weren't numbered, is it possible you put some of them in ON THE WRONG SIDE OF THE ENGINE? Crank and rod-bearings only match in ONE WAY. Make a mistake here and you're guaranteed to break a bearing on at least two rods. Spun rod-bearings will losen up and shake... Grinding off just one rod bolt makes less of a weight difference than the oil you have on the crank in different places at different positions, that alone won't throw you off balance. But it might cause that bolt to fail. Having a rod only hang on one bolt will certainly shake like hell...
Any news?
Good luck, Max