Need help with vibration

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Freezerman

Freezerman

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This is frustrating. Finally got engine running and now it has a vibration. Here is what I have.

1972 Dodge Dart original 318/904. Now has a 1974 motorhome 360 with 40k miles. Bottom end looked great when changed oil pan.
Added comp cam XE268H and a set of x heads.
I put in a B&M balance flex plate and neutral balance torque converter from t-flght Pat.
Used the original harmonic balancer but checked top dead center and matched exact.
Broken in cam well. Seemed smooth under the hood at break-in never sat in car.
Now from in the car has a bad vibe starting at about 1200 rpm and up. Vibration drops off as rpms are falling. Can't find anything rubbing or touching.
Any ideas?
 
Freezerman said:
This is frustrating. Finally got engine running and now it has a vibration. Here is what I have.

1972 Dodge Dart original 318/904. Now has a 1974 motorhome 360 with 40k miles. Bottom end looked great when changed oil pan.
Added comp cam XE268H and a set of x heads.
I put in a B&M balance flex plate and neutral balance torque converter from t-flght Pat.
Used the original harmonic balancer but checked top dead center and matched exact.
Broken in cam well. Seemed smooth under the hood at break-in never sat in car.
Now from in the car has a bad vibe starting at about 1200 rpm and up. Vibration drops off as rpms are falling. Can't find anything rubbing or touching.
Any ideas?
Click to expand...

You have to use the 360 balancer if you mean original being the 318 balancer.
Original 360 balancer would/should be fine.
 
Sorry I wasn't clear. I used the original 360 balancer. Does it sound like out of balance?
 
You have an imbalance in the engine. 360 have a counterweighted harmonic balancer as well as a counterweighted torque converter. The amount of counterweighted torque converter depends upon wether your engine is a Magnum 360 or a Commando 360. the weights are easy to weld on while in the car. There is a diagram of how much and where they go in the MP book.
 
It is an LA360. I'm using the B&M 360 weighted flex plate with a neutral converter and the original 360 balancer. Is it possible for the balancer to be bad even though the timing mark was TDC when I put it together?
 
no. sounds like U are doing everything correct. U can see that the balancer is counterweighted? and there are no weights on the converter? and the b+m flexplate has a big bite out of it? and it vibrates in park?
 
Yes, the balancer has the big off center weight. There are no weights on the convertor and is the flex plate with the bite out of it. It vibrates in neutral and park. Like I said when you left of the gas the vibration goes away almost instantly. It is a steady vibration pretty good above about 1200 rpm.
 
If it was a balance problem it would not go away when you let off the gas, are you sure it isn't a bad misfire or plug wires switched??
 
That's good to know! So when I let off the gas and the vibe stops almost immediately that's not imbalance then? That would be awesome.
I triple checked firing order with wires but that doesn't mean it's not another problem. Just pulled the plugs, they are black as coal soot. Obviously too rich which will be another problem to address. Just trying to eliminate the imbalance possibility now.
 
For what it's worth, after reading all the added information it sure does sound like an engine miss causing it.

If it were my engine I think the very first thing I might do is pop a timing light on all 8 wires and see if it' sees spark on them all.
The possibility of a cracked plug is there also, so even if a spark is going down a wire it doesn't mean it's actually making it across the plug gap.

I have also seen where the problem was actually just the plugs also.
Had an HEI customer that bought a kit and couldn't get his engine to run worth a crap and come to find out it was just the plugs all along.

With a cracked plug it can be really hard to tell which one it is unless you start pulling plug wires while it's running a find the one that makes no or very little difference when disconnected.
Of course you can find the wet plug also, but that requires pulling the plugs all out right after a shutdown.
 
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Thanks for the advice, a miss I can find and fix. Imbalance means yanking the engine. I did try the timing light before i pulled the plugs. All were lighting the gun. But they are sure black so im guessing too rich making the miss.
 
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For your 360 and 904 trans, you should be using the 10239 flexplate. There are multiple B&M flexplate with the bite out of them, some for the 727 and some for the 340 cast crank, so be sure you have the right one.

Since the vibration goes away when you let off the gas, it certainly does sound like a cylinder miss. After you check the park and plugs, then I'd run a compression check to see if any cylinder is way off form the others. If so, then use air in the cylinder with the valves fully closed to see where the air is leaking out.

At some point, if nothing else pops up obvious, then pull the valve covers an carefully check the lift on each and every valve, looking for one that is not lifting fully, to see if a cam lobe is wiped out.

What do you have for a carb? As a first check, look down the carb throat with a mirror while running and see if you have drops of gas dipping or dribbling down the throat.
 
All of the plugs are definitely sooty and it definitely runs rich. I started doing compression check. 1,3,5,7 and 2 averaged 120 to 125. Starter died when trying last 3 cylinders, so have a new one but need to get installed.
It has an Edelbrock 1406 which was running pretty well on the old 318. Will have to check on flooding issue when get the starter in.
 
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