340 SB 727 torque converter and flex plate.

Demon James · Post by **Demon James** » Sat Feb 06, 16 10:08 pm

I'm now going round in circles after researching, reading other posts (Miles for example ) and I've totally confused myself.

I wish to install a higher stall (2400/2700 rpm) torque converter and also a B&M flex plate to my 340 motor and 727 trans.

I've been on so many different web sites now and I'm lost. Internally, externally balanced, balanced converter or not, what goes with what crank, forged or cast

aaaarrrrgggghhhhh

If somebody would be so kind as to give me a face slap to bring me back and guide me in the right direction, I would be very grateful

Pete · Post by **Pete** » Sat Feb 06, 16 11:17 pm

Dave Bishop is the guy to advise you, James.
He certainly have a thing for small blocks.

Blue · Post by **Blue** » Sun Feb 07, 16 8:42 am

first thing is to find out if your engine has a forged or cast crank, that will determine if it's internally or externally balanced. The spec of the cam determines the convertor stall speed, simples!

shovelheadrob · Post by **shovelheadrob** » Sun Feb 07, 16 9:26 am

As you have the motor apart, post up a couple of pics of your crank showing the flash marks (the bit where it looks like a join) if it's a narrow line you have a cast crank, if it's around 1/2" wide you have a forged crank.

Pete · Post by **Pete** » Sun Feb 07, 16 9:49 am

I would say that it was a Cast Crank looking at the Damper, etc...

Demon James · Post by **Demon James** » Sun Feb 07, 16 12:52 pm

Yes Rob, Pete, cast crank

MilesnMiles · Post by **MilesnMiles** » Sun Feb 07, 16 1:33 pm

James, I was doing mine this morning by comicidence. Cast crank is external balance so you need the same flex plate I got from B & M. I have also got a 2,400-2,700 convertor from JW transmissions who have an excellent rep. It has no balancers welded to it and nor did the BM convertor I removed. So copy my approach, I guess.
Do get a good convertor if you have the dollar. If I had more money I would have bought either PTC or DYnamic. Both about $6-700 though.
Mine was $390 from Jegs with $85 for shipping and arrived in 5 days, really good service. It's a step up from the cheaper TCI and BM range and I'm hoping it will provide some real flash when I jump on the throttle.
Have fun taking the flex plate off the crank; as you try to undo the bolts the entire motor turns over!
I scratched my head and then made a wooden wedge to hold the flex plate in place, wedge against the flor and the bolts cracked off.
They wil need loctite and go 55lbs of torque when you do them up.

yabadaba · Post by **yabadaba** » Sun Feb 07, 16 2:11 pm

Hi Miles first,
The 340 crank in your engine is aftermarket cast steel, not a cast Mopar crankshaft, I believe!
You need to speak to Jon Connolly as he has the spec sheet when he bought the kit, in NEW from the USA.
It was a pre-balanced kit and NEUTRAL BALANCE, NO CUT-OUTS on Flexplate!!!
Not to be confused with the 73 Mopar oddball set-up.

Hi James
340 cast crank engines need a special damper and converter, external balance!
A real oddball set up from Mopar as they used the HD 318 crank!!!
Some 72's and all 73 340 engines.

Why not convert to a 340 steel crank whilst the engine is apart.
Cast crank 340's are Ok, but the steel crank will be a big step up, internal balance, SIMPLES!!!
Got one here if you need it.
Yabs

MilesnMiles · Post by **MilesnMiles** » Sun Feb 07, 16 3:33 pm

Yabs if you are correct and I have this crank
http://www.ebay.com/itm/Eagle-103403310 ... 0899725527

Then I have the wrong B and M flexplate as mine is for external balance.

Furthermore, my damper has no weights on it which I believe means it is for internal balance crank.

James, your front damper should be marked 'for external balance only' or words to that effect if it is a external balance 340. It is also,likely to have a counter weight on it somewhere....and you might want my new flexplate for it..

Blue · Post by **Blue** » Sun Feb 07, 16 4:01 pm

Demon James wrote:Yes Rob, Pete, cast crank

Externally balanced then.

Demon James · Post by **Demon James** » Sun Feb 07, 16 5:17 pm

Balancer has "for 340 cast crank only"

I'm keeping the crank as it is, it's just a street/daily car. This is the least of my worries now having just damaged a compression ring on fitting the second from last piston

gutted.

Everything was going so smoothly, no rush so no idea what I did. All the others went in no probs, this is a poo, poo and triple poo set back

Looks like I'll start another thread on that one, or stick it on my engine build one, Ho-hum .........

mad machs · Post by **mad machs** » Sun Feb 07, 16 5:54 pm

MilesnMiles wrote:
Then I have the wrong B and M flexplate as mine is for external balance.

Blimey that was close

MilesnMiles · Post by **MilesnMiles** » Sun Feb 07, 16 6:21 pm

Yes Mike,only reason it's not on the motor is I've run out of loctite today!

yabadaba · Post by **yabadaba** » Sun Feb 07, 16 6:28 pm

Thats it Miles!

NEW Cast STEEL Cranks are INTERNAL Balance!

Original 340 cast cranks are external with a special DAMPER and CONVERTER too.
They are in fact 318 HD cast-cranks that are too light for 340 rods and pistons.
Therefore a special set up was needed, not unlike the 70-71 SP 440 engine.

Clear as MUD

yabs

yabadaba · Post by **yabadaba** » Sun Feb 07, 16 6:34 pm

Hi James,

Busted rings happen to the best of us!
Sometimes you get lucky and there is an extra one in the pack.
Check your old rings and you may get LUCKY?
One of them may still be within tolerance...
Put them square in the bore and feeler gauge the gaps, 16 to 20 thou is fine.
If your running NITROS you can go to 30 thousanths all day long...

It may be your lucky day after all?
Miles has got a 340 EXTERNAL flex-plate he doesn't need now!
B and M 10235 is the cast crank flexplate you need.
Then you can buy a NEUTRAL BALANCE converter!!!

YABS