Internal balanced..what damper do I need

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340Duster247

340Duster247

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So my new 408 has a scat internal rotating Assembly, but I have a nasty shake. I'm still using a stock damper, is this wrong?
No matter what I do I can't find what's causing it. Only at idle, or slowing down while driving(coming to a stop). Motor mounts look good I also have a torque strap. My air fuel ratio is good. New wires new ignition.
 
what tranny? All 360's had weights on their convertors. neutral is neutral, any 273-318 LA or forged 340 balancer will be neutral. When you say it was a SCAT internal rotation assy, do you mean that its made to get balanced without a weighted convertor or was it balanced for the piston.rod combo you bought with it (and it was balanced TO it)? Internal usually means its got the meat on the throws to compensate for the heavier 360 rods you may use, NOT that its balanced already. You can make any crank an internal as long as you can make the reciprocating as light as the throws.
 
The question is what dampner are you using on the engine a internally balanced unit or a externally unit,one is forger crank unit one is a cast crank unit,mrmopartech
Need pictures or numbers from the unit.
Are you using a stock torque,and does it have weights on it? Because if it,s a internally balanced unit,you can not have a weighted torque,and need the 360 flex plate,mrmopartech
 
Whoops I left out some info I forgot to mention the scat kit is internal balanced from them.my torque convertor is a tci super street fighter 142222. I'm using a sfi (forgot the brand name)flex plate for internal balanced. ..well I just messaged a friend who works at my engine builder and he is looking into what damper they used.. To me it looks like a stock damper.
Ive done some research since starting this thread and have found lots of answers I was looking for, hopefully will find the problem soon.
 
My scat 410 stroker is inturnal balanced. Neutral harmonic balancer - neutral flywheel (4 speed car).
I've seen this shake your talking about with bad timing. Was the rotating assembly spin balanced at a machine shop or did you install a balanced assembly your self?
 
Mrmopartech said:
The question is what dampner are you using on the engine a internally balanced unit or a externally unit,one is forger crank unit one is a cast crank unit,mrmopartech
Need pictures or numbers from the unit.
Are you using a stock torque,and does it have weights on it? Because if it,s a internally balanced unit,you can not have a weighted torque,and need the 360 flex plate,mrmopartech
Click to expand...
This info is what you need to find out.

OP, we need to know if you engine was a 360 or 340, and if 340, is it a 68-early 72 or late 72-73? If your balancer is the stock one from a 360 or very late 340, then it is wrong. The same goes for your flex plate and torque converter; neither should be weighted.

Pishta, the SBM SCAT assemblies are all available as internally balanced.
 
340Duster247 said:
No matter what I do I can't find what's causing it. Only at idle, or slowing down while driving(coming to a stop). Motor mounts look good I also have a torque strap. My air fuel ratio is good. New wires new ignition.
Click to expand...

Wouldn't an out-of-balance rotating assembly cause a vibration that gets worse as the RPM's go higher? Does it vibrate in neutral if you slowly rev it up? Sounds more like a timing issue, or maybe you have a loose plug wire or two of them are swapped?

I agree with 66340 though stock damper is pretty weak for a healthy 408.
 
Dampers are designed to damp vibrations at a certain range of RPM's; that range all depends on at what RPM's things like the TC or flywheel/clutch mass wants to set a twisting vibration along the crank in conjunction with the rotating masses inside the engine; that resonance is excited by the engine torque 'pulses'. But having an intentionally imbalanced damper or TC/flex plate on an internally balanced assembly is not about the damper doing its normal job. It's about having an incorrectly weighted/imbalanced rotating 'thing' at one end of the engine or another, without the opposite internal imbalance, and it would be hard to say at what RPM's the vibrations will show up for this unbalanced combination.

And yeah, it surely could be some sort of low RPM misfire or uneveness in combustion, but the OP needs to fix the situation if he has a 360 damper, TC, or flex plate on an internally balanced assembly.
 
The 408 is based off a 360. I have an internally balanced 408, a flex plate for internal balance, a 10" 2800 stall converter in a 200R4 transmission and a Fluidampr balancer. I've been fighting a vibration for years. I've tried driveshaft balance as well. Mine is rhythmic and comes in around 60 and higher. Sometimes it goes away when I let off the gas, sometimes it doesn't. I wish I had an answer for you, brother, but I am subscribed and will be watching to see if you fix the issue. This has been a three year problem for me.
 
340Duster247 said:
Whoops I left out some info I forgot to mention the scat kit is internal balanced from them.my torque convertor is a tci super street fighter 142222. I'm using a sfi (forgot the brand name)flex plate for internal balanced. ..well I just messaged a friend who works at my engine builder and he is looking into what damper they used.. To me it looks like a stock damper.
Ive done some research since starting this thread and have found lots of answers I was looking for, hopefully will find the problem soon.
Click to expand...

Well I ran the part number for that TC, nowhere does it say it has external balance weights. If you look at the front of the damper does the outer hub section have a recessed part that goes roughly half-way around, or is it smooth and the same thickness all the way around?
 
Sorry I've been away for a bit. I've tried everything with the timing and dosent change anything. So right now I'm locked out at 34. Like I said the engine smoothens out about 1300 rpm and is dead still. AFR is 12.5-13 at idle. Entire ignition is new. Starts instantly. No miss when revved. So I'm confident the ignition is good. The flexplate is brand new and is for a internal balanced engine. And the torqe convert or is a tci super street fighter.

This may sound stupid but the shake is at the top if the engine. When I look down at te mounts there's no movement at all.
Another weird thing the shake gets worse the longer I've been driving the car. (Only at idle or slowing Down below 1300 rpm) I can feel it. Is like a chopping.
I hAvent driven the at since I locked the timing out. Before it was 21 initial. 32 total. It's almost like a lean shake issue but my AFR reads around 12.6 when this is happening.
I know I'm rambling and repeating myself but I'm just trying to give as much Info as I can. I've also checked everywhere for vacum leaks.

Even tho I don't think it's gonna fix I'm gonna try new engine mounts. Anyone know of a good brand or where to get good ones.

As far as the damper it is solid on the front smooth. And a groove/knotch I can feel on the backside. All the way around. I can't see any part numbers yet on it.
360 to a 408 scat stroker that's internally balanced from scat. My machine shop did all the work.even assembly.

I'll try and take a video.
 
Mopar to ya said:
The 408 is based off a 360. I have an internally balanced 408, a flex plate for internal balance, a 10" 2800 stall converter in a 200R4 transmission and a Fluidampr balancer. I've been fighting a vibration for years. I've tried driveshaft balance as well. Mine is rhythmic and comes in around 60 and higher. Sometimes it goes away when I let off the gas, sometimes it doesn't. I wish I had an answer for you, brother, but I am subscribed and will be watching to see if you fix the issue. This has been a three year problem for me.
Click to expand...

You have probably checked already. Pinion angles?? Your issue is differnt then mine as mines only at idle or coming down to an idle.
 
I'm interested to see a video please do try to post one up. From what you describe your damper seems to be neutral balanced. Have you double-checked the plug wire routing? I could be wrong but again it sounds a lot like you have a misfire at idle, either a loose or mismatched plug wire i.e. two wires switched by accident. Maybe even something as "dumb" (not you lol) as a loose spark plug. I'm willing to bet it's something simple related to the ignition system even though you said it's good.
 
I do believe the 'BI' at the end of the part number means 'Balanced, Internal'......

So is this the same car with the Mutha Thumpr cam? With a rough cam like that, I would expect the AFR to bounce around, so you will only get a general or average idea of AFR. The mixture can be bouncing around quite a bit from cylinder to cylinder, so I would not take the AFR info as being accurate for all cylinders.

With that cam, it is no surprise to be rough at idle....
 
No different cam lunati 60405. Everyone who is helping, I have two threads now going on the same topic... And don't wannabe that guy, so if you look at thread "engine shakes badly" I've updated on my recent testing and fooling around trying to figure this problem out. It's a thread that started with my old engine ...and now with my new engine.
So I'll be posting all updates and hopefully help from you guys there.

Please read my most recent post there.
 
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