340 vibrates

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dgibby said:
The ignition system and balancer are the only things that were on the old engine that haven't been checked or rebuilt.
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Have the ignition system checked on an oscilloscope. New plugs and wires are not good enough when chasing down the problem you have.
 
forced 340 said:
sounds to me like it is in the trans. possibly a worn converter hub bearing, or a broken converter... could also be the front pump of the trans. good luck!
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I would look here, too
 
Having a hard time with the converter theroy....

first converter was wrong, external balanced, knocked weights off and it got better but still there. New converter made no change, re stalled the new converter and no change. Drove it tonight, not too bad cruising but can feel it. Much worse in park or neutral but either way, cruising or parked the sweet spot seems to be 2500 rpm
 
No noise except things kind of rattle as it comes and goes. Will try the pully test tomorrow.
 
Another vote for momentarily removing the fan belt. Had an alternator that was messed up so bad you could feel a vibration though the entire car.
 
Got side tracked this weekend, going to try to pull the belts tonight and give it a try.
 
Pulled the belts, no change..... back to the drawing board.
 
knocked weights off and it got better but still there.
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OK, you knocked the weights off, is there still little bit of weld material left? Or is this from a different converter? What kind of converter is it?
 
Have not done a cylinder balance test yet.
Not the same converter that I knocked the weights off. FTI is the brand
 
I know it not a 340 but an engine is an engine. My cousin bought a fox-body mustang with a crate 302 for stupid cheap because it had a weird vibration. It was okay at idle but at about 2000RPM it would shake, it shook so bad after a test drive it broke the starter off. We thought it was the harmonic balancer or the flywheel, but that wasn't the problem, we checked everything...and then we pulled the motor. The crank was DONE, two main bearings were scored really badly, the crank is what caused the vibration. It was a shame too because the motor had maybe 1000km on it.
 
I wish I could actually be there to observe the problem...but typically, if you have a vibration like that, it's engine balance or related to the same (like a converter or something.

If you're confident the balance is not a problem, perhaps press on with the cylinder balance test.
 
DartVadar said:
I know it not a 340 but an engine is an engine. My cousin bought a fox-body mustang with a crate 302 for stupid cheap because it had a weird vibration. It was okay at idle but at about 2000RPM it would shake, it shook so bad after a test drive it broke the starter off. We thought it was the harmonic balancer or the flywheel, but that wasn't the problem, we checked everything...and then we pulled the motor. The crank was DONE, two main bearings were scored really badly, the crank is what caused the vibration. It was a shame too because the motor had maybe 1000km on it.
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Ouch...:( 302s are easy to imbalance though in all fairness...depending on the year model, they could be either 28 or 50 oz imbalance.

But, the OP said the shortblock was reassembled by his machinist...might want to call that guy and have him involved.
 
Pretty sure the engine balance is good, well known shop with referral from good friend who's dad started with this guy way back when. Of course anything is possible. Might try to see if I can get it on video, not really a shake the sh#$t out of the car but seems like it shouldn't be there. Did it before any of the rebuilds/upgrades and is pretty much the same after. Would think with all the rebuild/upgrades it would have changed some but no really except for when I knocked the weights off the original converter. Not sure if it even changed then or if the external weighted converter was covering it up.
 
Carter 9636sa (625cfm)

Good idea on the vacuum gauge, haven't done it but will be.
 
dgibby said:
Yeah, complete rebuild, friction, bearing, all bushings and seals, servo, valve body etc. etc. ... Did it myself, checked and rechecked all tolerances.
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I think you missed something.
 
I don't know if you have a 318/340 4 spd flywheel/ bellhousing but if the balance test doesn't show anything I'd pull the trans and bolt up the bell and flywheel then fire it up. That's a lot of work but you're not getting anywhere this way.
 
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