**1973 bastard 340 balance??**

-
Mad Dart

Mad Dart

Nothing to see Here!
Joined
Sep 24, 2008
Messages
8,485
Reaction score
496
Location
Murrieta California
I have done some research and found out that the 340 I have is a 1973. I know that 72-73 had Cast Cranks in the 340's and they were supposed to be externally balanced but different than the 360 is balanced..... So if it is supposed to be externally balanced but balanced different than ALL 360's...... How were they balanced different??

Can someone shed some light on the subject?
 
Today I found that my engine has a Professional Products balancer on it with a weight bolted to to back of it and when dropping the inspection cover at the trans it has a B&M Flex Plate in it with the 1/4 moon cut out. The Converter has no weight on it at all and it looks as if someone knocked the weight off of it. There is evidence of this cause of the partial welds that are still on the face of the converter behind the flex plate.

Houston I think I have a problem but I need someone to verify what it is.

The plate I have looks like the one with the cut out in the picture.

View attachment bmm-10230.jpg
 
There should be some numbers stamped on the flex plate. I have a similar on my 360, but they make them for 340's too. Get the number and see if it is a B&M product and if they list it's use.
 
First off, you need to know if the original cast crank is still in the engine or was it changed to a forged piece at some point.....If it is the original cast crank you should have a damper on the front that says right on it "use for cast crank 340 only" also originally they had a weighted torque converter and a neutral (no weights ) flex plate ....So to use an aftermarket torque converter (with no weights) you need the weighted flex plate ......I have one setting right in front of me and yes it has the half moon cutout like in the bottom picture but the moon cutout doesn't look as big as the one pictured.....it is a little smaller....I have the B&M one setting in front of me now and if you look directly across from the moon cutout it will have the part number....It should be 10235.....here is a link to a new one on summit
http://www.summitracing.com/parts/bmm-10235

The 360's had a different bob weight than the 340's so they are weighted different
hope I answered your question
 
the distance of the moon cutout from where it starts to where it ends is a little over 3-1/2 inches....actually 3-9/16 to be exact
 
bbrroowwnn said:
First off, you need to know if the original cast crank is still in the engine or was it changed to a forged piece at some point.....If it is the original cast crank you should have a damper on the front that says right on it "use for cast crank 340 only" also originally they had a weighted torque converter and a neutral (no weights ) flex plate ....So to use an aftermarket torque converter (with no weights) you need the weighted flex plate ......I have one setting right in front of me and yes it has the half moon cutout like in the bottom picture but the moon cutout doesn't look as big as the one pictured.....it is a little smaller....I have the B&M one setting in front of me now and if you look directly across from the moon cutout it will have the part number....It should be 10235.....here is a link to a new one on summit
http://www.summitracing.com/parts/bmm-10235

The 360's had a different bob weight than the 340's so they are weighted different
hope I answered your question
Click to expand...

First off this is a car that I bought so I have no Idea what the previous owner did. After all the work I have done on this car. I would not doubt that somthing is not right. I have a slight vibration in park or neutral from 1500-3000 RPM. It just feels like it is not balanced correctly. Driving down the road it is harder to feel but still I know something is not right.

Yes it is a B & M #10235 and the cut out is not as big as the picture I posted.

I have not took off the crank pulley as of yet but it does have a Professional Products Balancer on it. I looked up that part and that balancer comes with 3 Different counter weights that can be bolted on. Is the correct one installed on it???? Who know's..... From what I have went through on this car it could be the wrong weight I don't doubt that for a second.

As far as knowing if the engine has been rebuilt with a Forged Crank..... I highly doubt it but again I would not know unless I drop the pan.

Per the research I just did. The weight on the balancer is correct..

http://www.summitracing.com/parts/pfs-91014/applications

View attachment php6zzKqkPM.jpg

View attachment phpTxgrZNPM.jpg
 
1---Just because an engine is externally balanced does not mean that it's the same as a different type engine that's externally balanced, AKA, 360LA and 360 Magnums are both DIFFERENTLY externally balanced just like 340s and 360s are different, etc.

2--This means that unless you can justify the part # on the aftermarket flex, it may not balance the complete setup

3--If the internals of the engine have been changed, IE the balancer, the torque converter, the rods, the pistons, ANY of the rotating mass, then it won't be in overall balance anyhow.

The 70 440 sixpacks are a good example. So far as I know the only thing the factory changed between the 69 neutral 440s and the 70 engines is larger, heavier rods, and presto, "external balance."
 
Robbie2734 said:
There should be some numbers stamped on the flex plate. I have a similar on my 360, but they make them for 340's too. Get the number and see if it is a B&M product and if they list it's use.
Click to expand...

Thanks. Yes I have verified that it is the correct flex plate for and External Balanced Engine.
 
67Dart273 said:
1---Just because an engine is externally balanced does not mean that it's the same as a different type engine that's externally balanced, AKA, 360LA and 360 Magnums are both DIFFERENTLY externally balanced just like 340s and 360s are different, etc.

2--This means that unless you can justify the part # on the aftermarket flex, it may not balance the complete setup

3--If the internals of the engine have been changed, IE the balancer, the torque converter, the rods, the pistons, ANY of the rotating mass, then it won't be in overall balance anyhow.

The 70 440 sixpacks are a good example. So far as I know the only thing the factory changed between the 69 neutral 440s and the 70 engines is larger, heavier rods, and presto, "external balance."
Click to expand...

Yes I understand all of this. However I do not think anything has been done to this engine. I could be wrong but the only way to check is to drop the pan. I will not be doing that because I have a 410 Stroker that is done and going in the car. If the pan gets dropped it will be when it is on an engine stand.
 
It's the offset weight amount in the balancer and flexplate.

360 balance
360castbalance.jpg


340
340Castbalance.jpg


That's the correct flexplate for a ext balance 340
 
One more thing, on my 360 I have Eagle rods and KB pistons. They are much lighter and I had to rebalance the assembly. Maybe they didn't on yours???
 
crackedback said:
It's the offset weight amount in the balancer and flexplate.

360 balance
360castbalance.jpg


340
340Castbalance.jpg


That's the correct flexplate for a ext balance 340
Click to expand...

So if there is excess weight from them busting the balance weight off the converter "welds not ground down" do you think that could possibly be the vibration?

I know I'm pissing in the wind cause I didn't build the engine. Someone could have replaced just 1 piston/ rod during its life and I wouldn't know at this point.
 
louis, if it has thewrong balance that motor will be jumping around,feels like it anyway.it won't be any kind of slight. your prob right to just get it out of there.man hitting that 410 with a 400 shot, it's gonna be a monster!:glasses7:
 
IIRC, there are three different balance weights that come with those balancers.
 
bad440 said:
louis, if it has thewrong balance that motor will be jumping around,feels like it anyway.it won't be any kind of slight. your prob right to just get it out of there.man hitting that 410 with a 400 shot, it's gonna be a monster!:glasses7:
Click to expand...

Yeah now I am really busy working so I don't know how fast I will get out there for the swap...... I need to buy a converter too! I already have a brand new Neutral Balance B&M Flex plate and ARP hardware for it.
 
You must log in or register to reply here.
-

Back
Top