I picked up a 68 Dart Convertible for my wife and is a project car. It came with a 73 340 and a 904 trans. Took them both apart and was looking at the converter, knowing a 73 340 is externally balanced I took the transmission off the engine and noticed the converter doesn't have any balancing weights. Looking up the transmission it is a 1968 273 unit so not sure if this thing is going to vibrate when it's back together.anyone here know what converter would be correct for 73 340 904 combo?
Thanks in advance.

You should be able to get a balanced flex plate from B&M that will fix your issue.

I thought only the 727 came behind the 340?

They show 360/904 or 340/727 I don't want to guess

That's one I don't know but I've seen 904s behind externally balanced 904 set ups...all the flex plates only show 360 and 904 , no 340/904...
I may just look for a 727...

B&M 10235 should work with a cast crank 340/904. The multi-bolt pattern on B&M flexplates cover most OEM & aftermarket converters. It's all in the bolt pattern and bolt hole sizes. If the B&M plate is for an external balanced 340, it won't matter if the converter is a 727 or 904 as long as it bolts to the neutral converter..

* When you disassembled the 340/904, was the flexplate neutral?

* Does the 340 have a "FOR 340 CAST CRANK ONLY" balancer on it now?

* Pull pan to confirm if it's a cast or forged crank. (Even though '73 "should' be cast. (Check parting line on crank.)

* Possible but not probable that it's internally balanced.

* Direct Connection use to have a converter balance kit to add weight to converters on engines that were externally balanced. I believe their race manuals had converter location templates and the weight required to do it from scratch.

* Can you ask the previous owner if he had any vibration issues?

I have seen a few converters with the weight on the back side. Did you check there?

Yes, no 340/904. After 50 years, who knows what's inside the motor...could have had a forged crank swapped in.

When I took the engine apart as I was told "It's been Overhauled"... It actually was. New pistons, rod & main bearings. What threw me knowing 73 340 is supposed to have a cast crank, the ballencer looked like steel crank balancer so I pulled it , checked the part number in the G Govei books and the part number came up as 1975 only cast crank 318...the rubber was cracked so I ditched that balancer and bought one that you can add the correct weights for that spacific crank. I did check the crank number and is 73 340 only. No obvious balancing marks on the crank. As I stated I bought it as a project and just trying to make sure I don't end up with vibration. Flex plate is a standard small block flex...I'll try to attach some pictures.

Yes sir, thanks

Balancer

That number sounds very familiar. I think it's a later 318 crank which means "internally balanced".

Any other weights added to the crank counter weights? I'm assuming you looked for those already, but some shops don't put the slug into the edge, some will actually machine into the side, so that might be hard to see and/or notice otherwise.

I ask b/c you could certainly neutrally balance a build in order to avoid having to run the offset stuff. I did that with my previous 360 motor and most recently with the 408 W2 stroker, although that really did require a "ground up" balance job b/c of the stroker.

340 cast crank states for 340 cast crank only right on the balancer. The casting number you show was used both for late 318 and 340.
Doug

Are there any signs of balancing on the crank journals where weight is removed?

It is possible to internally balance a 340 with much lighter rods & pistons than OEM.
Are the rods 340/360 sized or the earlier, less beefy, 273/early 318 rods. Any grinding/polishing?
What brand pistons? Forged? Part #? Weight?
Any machining in the undersides of the pistons?

If you can't come up with examples of significant reciprocating weight reduction over OEM, taking the parts to a machine shop to check the bob weights & overall balance may be the only way to be sure if it's done correctly or if you will have a vibration.
Was the engine run at all or was a fresh rebuild/overhaul?
It's possible that the previous owner had a vibration after the rebuild and sold the engine because of it.

I had a 73 340. used a 904 behind it with b&m 727 flex plate because they quit making the 904 at the time. just had to check near the starter to make sure it didn’t hit, the 727 flex plate was bigger. At least that’s what my memory tells me lol

What rods are in it?

Yes, casting number 3751841 is a 318 crank used from '80-'94 so it's internally balanced in the 318 and should be OK with the lighter '73 340 pistons.

My info states this crank is used in both the late 318 and the 73 340. To my thinking the 340 pistons being a larger bore and using beefier rods is why the 340 application would requires external balance. When its used with the slimmer 318 rods and smaller bore pistons internal balance is possible.
Doug

Did you have it running with that transmission?
As strange as it sounds my 360 had a 904 behind it with no weights on the converter. Don't know if they did something inside the converter or what because it ran fine and came out of a car from a friend's Dad who owned it for years and had that transmission put in it.
The second I put a different transmission behind it you could tell it had issues and I had to get the weight added on to it.