stout383

I have had a 383 stroker built by an interstate engine mob that has a voilent vibration through the engine at most engine speeds. It is enough to bash the extractors on the chassis rails and create an very unpleasent enviroment in the car. The engine is a 383 stroker, New GM block, world product heads, performer manifold, 750 hp Holley, cam specs i don,t know. This engine was supposed to be a mild, but i am sure it is going to smash itself to bits. It has a harmonic balancer with a big weight inside it and the flex plate has also got somesort of weight welded to it on the engine side.

Can anyone shed any light on this as i don,t know whats going to break first, my old HK ute or the engine i have been supplied.

Thanks in advance
Stout

wabbit

the weights on the flexplate and balancer are for external balancing.

i reckon the balance is the issue.
you should only be able to fit the flexplate in one position, so I'd say it was balanced at a different clock position.

how much of the engine was delivered to you?
were the balancer/flexplate/converter supplied as part of the balanced package?

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PRO-GMH

Sounds like you might have ripped an engine mount or two. By the sounds of it this motor is not even near 'mild' with the parts youve listed lol.

My bet would be engine mounts or possibly even a gearbox mount... but engine mounts are most likely.

allports

Has it vibrated since day 1? Did it come with a flex plate?? Or did You put one on it??? A 383/400 is external balance so if you've put a 350 flex plate on it the balance is way out of whack!

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stout383

Engine was supplied with flex plate which i fitted and i think it had a dowl so could only locate in one spot (could be wrong). The balancer was supplied and fitted by the engine builder. The converter and box (TH350/3200 STALL) was suppiled by the engine builder a month or so later and fitted by me. There is no broken mounts etc as this is a full restoration that has cost big money. I have tried the converter at the 3 different mounting locations just in case there was i drama there. Still the same.

This has been a 3 year build and today i drove it around the block (with straight out 4 into 1,s), hoping the vibration may dissapear. It was worse than it was stationary.

Do you guys think it is posible the engine builder has used and internal balanced crank and then stuck on external balancing via the damper and flexplate?? or do i just resign to the fact i need to rip it out and get someone to balance the complete bottom end which was supposed to be done originally?

gas 84k

Could be an internal balanced crank but the flex plate and balancer should have been balanced with the rest of the rotating assembaly if a engine builder is any good he should be balancing it within a tenth of gram i balance my rods and pistons then give the weights to my machinist.But if i were you i would be tearing it down as it all hasn't been balanced together the weights could be all over the shop.

richo

get another mech to look at it and hear it running kidnap one if you got to. don't drive the thing another meter and only start it to show the problem to another mech. i know what it's like to spend all your time and money on something that don't go properly, my 383 stroker was a nightmare but once it was sorted man i had some fun. you'll prob find that your engine builder doesn't build engines he prob pieces together high performance parts and tells someone else to put it together. hope i' wrong . find some one who knows what their on about to listen to it cause the thing sound like it'll be tough

stout383

After todays events and discussion with the engine builder it looks like Gas84k is right.

Last night i removed the weight from the balancer and refitted it and fired the engine, with an 50-60% improvment in running quality, a lot a vibration gone and the engine revs much quicker and cleaner.

The engine builder rang me today and tracked back thru his records and supplier records and tells me it has an internal balanced crank (9000 series scat) and should,nt of had the weighted flex plate and balancer fitted at his end. GRRRRRRRRR

When i get the chance i am going to knock off the weight on the flexplate which i can sorta get to without dropping the box and (hopefully) all will be good.

I am smiling a bit more now. Thanks for your input to all and i will let you guys know what happens when the other weight is removed.

(SHOULDA BUILT IT MYSELF) (MARINE MECHANIC 18 YEARS)

Jason

gas 84k

Stout it should have a neutral balancer to and ask him to what percentage of a gram he balances to and what were the weights .Whats your combo? as you dont want this thing shaking itself to bits or decreasing engine life.

gas 84k

And like i said if it was balanced properly whoever was balancing it would have picked it up if all components were there.Mate dont let him get away with it if its not done properly it would be a much better option to attend to the problem now give you peice of mind and then you no its right even though its a pain in the ass.

richo

how can it be a 383 if it's internally balanced then, does he have to run with the standard 350sbc balancer,

banaro

Many of the after market 3.75" cranks are made for internal balancing and require a neutral balancer and flex plate. You would normally try and fit a larger diameter aftermarket neutral balancer to cope with the greater harmonics generated by these engines.
Normal GM 400 cranks used in 383 conversions can be internally balanced but it takes a bunch of time and money.
I agree that Stout383 needs to track the truth and get it right to ensure no further damage. Knocking the weight off the flex plate will not ensure the plate is neutral, both the balancer and plate need to be removed and checked individually.

Tip: For those running a 168 tooth external balance flex plate, always have the flex plate balance weight tig welded to the plate, if not already, as they are famous for flying off and smashing bell housings.

stout383

Today i got the time to remove the weight on the flexplate with a bit of ****in around. After this i fired the engine to a sweet sounding and smooth small block chev.

Some expected (cammy) vibration at idle, but clean and crisp from off idle to high revs. This is now a different engine. It staggers me what 600grams (i weighed the components) of counter balance can do to the running quality of this sort of engine.

To the guys that have advised me to pull the engine down and check mains etc, i have explained to the engine builder that once i get this thing on the road i will spin this thing to 7000-7500 rpm and if i have any drama, its all his problem. And They are happy to back (warrant) the engine.

All good so far
Stumpy

Thanks for your input everyone.

greenhj

Get it in writing mate, and well done.

hxchev

good news mate. your ute's gonna make one tuff streeter

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