vivivivivibration

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j.d.duggan

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did the break-in on my 340 a couple days ago.things went fairly well.had a couple of friends over to help me out.one started the car and kept it around 2k while I set the timing to 34*.It smoked something terrible out the left bank.don't know if it was oil in the exhaust system, or the rings in number 7 cyl. that I had to wet sand do to some rust from being stored for years.anyway the smoke was so thick you could,nt see the end of my 60' shop.anyway about 14 minetes in it finally cleared up.A friend that was familiar with this car,when it had the old 340 in it,said it always hade a vibration in it.well I still do.I used the same balancer,flywheel,pp,and clutch disc.I need to find what it is.I thought I read something on here about the 340 had a special balancer on it,not the same as a 318 or 360,is this correct? or not?thought I'd barrow a balancer and see if that fixed it ,before buying one.whats your thoughts?:poke:
 
Check the convertor for weights by the drain plug
 
Is there anyway to know if it is a cast or forged crank in an assembled engine?
 
Early 340 are all internally balanced, and used the same damper and flywheel as the 318. The later 340's had external balance weights on the damper and 3 shallow holes on the flywheel to purposely imbalance it for external weighting, to go with the later 340 cast crank. The later 340 external weighting is different than the 360.

So, OP do you mean that the crank that went in was a '71? Or just came from a '71 block? Any crank could have been put later in any block, so you can't go by the block
 
engine in and running,not really sure how to look at crank,I'll ck pics and see if I have any of crank
 
Look at the counter weights on the crankshaft. Steel crankshafts kinda have a rounded counterweight compared to a cast crank
I should have said FULLY assembled engine. i think you would have to pull the oil pan.
 
If it is already in the car & it's an automatic; you could always tack weld two counter weights on either side of your converters drain plug & see if it clears it up. This happened to me on my first 340 build back in the 80s
 
OK, will take a shot at this. nm9stheham is on the right track with diagnosing this. Always fun to figure things out. I call this "Process of Elimination".

OK you state that you have a 1971 340 with a steel crank, that would be internal balanced. 4 speed car so it has a Flywheel and not a torque converter for the automatics so that rules out the torque converter part. That sounds correct so far, the 72 and 73 340 had the external balance cast cranks . . so lets count them out. The internal balance 340 steel crank should have the same front balancer as the early 318s, not needing any special balancing on the balancer because it is an internal balanced crank just like the early 318s. So if your front balancer has any type of lopsided weight on it or a cut out on the back side of it like 160 degrees, then it is the wrong front balancer.

I am going to assume that you have the correct front flat disc style balancer on it. So now next consideration is the Flywheel. Everyone on here knows how 50 year old parts and many different people working on things over 50 years can get things mixed up.

Thinking that you have the wrong later 72/73 340 flywheel on it, 3 shallow holes on the flywheel to purposely imbalance it for external weighting. Need the flywheel without the 3 shallow holes drilled into it for the internal balance crank. Should be able to pull bell housing inspection cover, look up in there while someone rotates the engine over slowly to get a look. Use of some small mirrors and good light will help with the task.

Knowing how things go, could have been an automatic car converted to a 4 speed putting in the wrong flywheel at that time. 3 speed manual to 4 speed manual upgrade with wrong flywheel. You guys get it, things can go wrong. Maybe needed a resurfaced flywheel and had good one around but not knowing it was for an external balance crank and put it together.

Hope this helps . .
 
I agree with George Jet. Another thing.I had vibrations driving not in park. ( Auto trans.) and finally discovered the motor had 4 speed dowel alignment pins on the motor. This drove me crazy for 2 years ! Just something to think about.
 
OK,cars on the lift and I will try to get a look at the flywheel,the balancer has a small drill inset in it,no weights on it,drill inset might be 1/2" drill about 1/4" deep.does that sound like the right balancer?think I have a pic of that.the flywheel cuts are on the engine side?correct?
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George jet has it absolutely correct,I have owned this car for 90 days,what happened to it for the 48 years before I got it is anyone's guess.auto,3 speed,6 cyl.newer parts,older parts,ect.ect.ect.So let's just do a little process of alimentation.THANKS FOR ALL YOUR HELP.
 
Show us a front pix of your damper....that is where the stock later 340 damper is imbalanced. It may look like the right hand one in the 7th pix in this thread:
340 balancer question | Unlawfl's Race & Engine Tech | Moparts Forums

All dampers and flywheels are almost 100% certain to have a few holes in them; these are drilled in balanced dampers and flywheels to balance them. So WHERE on the flywheel the holes are located is the critical part. That is why I linked the diagram; you have to check at a specific angle relative to the crank bolt pattern in the flywheel to see if the hole/holes are in the right area (on the engine side). So you pretty much have to pull the clutch to see the crank bolt pattern to be 100% sure.

If the damper and flywheel are not imbalanced (i.e., for neutral balance crank), then you're going to have to pull the pan to inspect the crank to see if it is forged (early) or late (cast).

OP, what pistons were used in the rebuild? Are they stock or what?
 
BTW, OP, run a compression test on all cylinders. And inspect the motor and trans mounts.
 
under the car this morning and did notice one possible problem ?.Flywheel has one Heli coiled hole for a pp bolt.Just for sake of experimentation I added a 1/4" longer bolt in it to see if that might make up for the lost metal in the flywheel.haven't tried starting it yet,thought I would get your opinions first.there is enough room for 1/2" longer bolt.anyway here are some pics of flywheel and dampener
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.the balancer has two partially drilled holes in it.one on front one on outer side.
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OK this is all really good stuff here. The orange early 318 style front vibration dampener is correct for your 71 340 Steel Crank application. Would not worry about the helicoil in the flywheel as the helicoil pretty much replaces the old thread material.

Let's go on to the Flywheel. Good Pictures, looks like you have the "Single Drilled Hole" 340 external balance cast crank Flywheel in your car now. They Drill the Single Hole to remove weight to work with the later 72/73 340 external balance cast crank applications. See attached picture of the diagram of the 340 external balance cast crank flywheel. Figure 5 - 21, this is the wrong flywheel for you.

A Standard 318 internal balanced steel crank style Flywheel should take care of your vibration issue. Think they call that neutral balance non-drilled flywheel.

Same neutral balance flywheel the steel crank internal balance early 340s will take.
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If you order in a new 318/340 neutral balance flywheel you should be able to see the difference between what you have and the new Neutral Balance one.

On the thought of your long bolt idea in the flywheel. Could try a simple test like this to prove all of this is true.

Take the bolt out of the pressure plate closest to the Large balancing drill hole on the flywheel put in a 1/4 inch longer bolt with 4 flat washers stacked on top of the pressure plate to offset the missing weight in the flywheel and bolt it down tight. Roll it over by hand a couple of revolutions to make sure there is plenty of clearance on everything and will not catch on something.

Then give it a quick start (only as a test, do not drive it down the road like this) and see if your vibration problem starts to go away. If so then you know you need to swap out your flywheel.
 
the bolt hole that has been drilled and Heli coiled is drilled all the way true the flywheel.the heli coil only goes thru about half the thickness of the flywheel,that means that about half the thickness of the flywheel has a oversize hole in it.that far out on the flywheel,a small difference in the hole size might cause a lot of balance difference,IMO.The hole that is drilled in the flywheel goes all the way thru,hard to tell by the pics,but just thought I would let you know that.:thumbsup:
 
So the flywheel in figure 5-21 is the wrong flywheel for my app.?Is the correct flywheel the same with no hole?anyone have a pic. of the correct flywheel?
 
nm9 why the compression test?just for good practice,or what?motor mounts and tranny mount look good.It has a solid motor mount on left side,and rubber on right.motor seems to be sitting a little off level .will address this issue at a later time.I guess I will put some spacers under the mount to level.Is this normal to have to do this?:thankyou:
 
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