351W engine vibration???

Started by Jbird, September 29, 2009, 12:45:42 PM

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Jbird

September 29, 2009, 12:45:42 PM
We did up a 68 mustang fatsback with a slightly modded 351W engine. The customer supplied the longblock. Now we have a really annoying vibration it starts at about 3K and sort of smooths out at about 5K. We changed balancers (28oz) flexplates (28oz) and even the torque convertor. No help. Has anyone had a similar problem? Hopefully we won't have to pull the engine down and hunt for a drastic imbalance in rods and pistons. Any input is appreciated.   Jay 8)
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tomslik

#1
September 29, 2009, 07:23:08 PM
Quote from: "Jbird"We did up a 68 mustang fatsback with a slightly modded 351W engine. The customer supplied the longblock. Now we have a really annoying vibration it starts at about 3K and sort of smooths out at about 5K. We changed balancers (28oz) flexplates (28oz) and even the torque convertor. No help. Has anyone had a similar problem? Hopefully we won't have to pull the engine down and hunt for a drastic imbalance in rods and pistons. Any input is appreciated.   Jay 8)


doesn't have a 302 camshaft in it. does it?
(firing order is different)
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wayne petty

#2
September 30, 2009, 01:13:17 AM
has anybody ever verified balance with a tire balancer???   clamped the flywheel on and spun it up????

the harmonic damper hole may be too small to spin up on a tire balancer...

this would be to compare a known 28 ounce or 50 ounce unit to a replacement unit..   since you have the offending units off... perhaps you have something else in the shop to compare them to...

i have a vague memory of a flex plate with removable weights to convert it from 28 to 50 ounce inches..

i would imagine  the flywheel could be done on a bubble balancer..
with a few tire weights placed to balance it...  then see if the other matches...

there are just so many things that it could be...

i wonder if you could talk the customer out of where he bought the motor..  along with the receipt..     call them .. see if they know exactly what the motor is...  

how are the 7 and 8 spark plug wires routed...  usually over the left hand valve cover.. i run the wires through the separator.. 7, 5, 6, 8   as the 7 and 8 fire 90 degrees apart...
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