Flex Plate Help !!

[Pentastar Pete]

1974 Challenger..  I replaced a 360 with a 70 340 enigine. I have a 727 Auto Trans. When we put the enigine in, the top of the trans meets the enigine, the bottom has a 1 inch space between the trans and engine. With that, the tourque converter is so tight, it won't spin. And from what we can see there is about a 2 inch space between the converter and flex plate.  We took the engine out, and matched the converter to the crank. With the flex plate on, the nub from the converter does not fit into the rear of the crank. There is about a 2 inch gap between the flex plate and the converter. 
Is there a different flex plate, or is there a different converter for the 340 and the 360???  We didn't have this problem with the 360....

Thanks

[Moparal]

The converters are different since the 360 is a cast crank and external balance. The 73/74 340 is external balance too, but has it's own weights installed on the converter. Your converter should show 2 wieght tabs next to the drain hole in the front of it. A neutral balance or internal balance forged engine will not have these weights. Plus, it sounds like you may have the flex plate on backwards, or something odd with the converter. Like you didnt set it in all the way into the trans before slipping it up there. The converter should go deep into the trans leaving a space around 3/4 of an inch or so from the ring gear to the outer edge of the trans bell on the bottom.  I would bet it's something simple. But we need to know what 340 you have, what year 360/trans...and if you had weights on the converter or not.

B&M  makes a special flexplate to handle internal to external differences, but you will need to proceed one step at a time and determine just what you have


pic help

[422STROKER]

Sounds like the flexplate is on backwards to me too.  Didn't think that could be done though.

Tom

[Pentastar Pete]

Thanks guy's..   The converter is a stock mopar, I had the weights taken off. The 340 is a 1970 with a steel crank.  The 360 was a 1972 truck motor.  The trans is a 727.
I thought I lost my mind and the flex plate was on bachwards, I did flip it, but then the bolt holes will not line up.. It seems like the nub on the converter is out too far, and it doesn't fit into the crank. I don't have the old motor anymore to look at it.
Is a steel crank bigger at the opening then a cast???
Is there another flex plate or are they all the same???

[422STROKER]

What bolt holes don't line up?  They will only fit a certain way on the tq converter and maybe the engine too.

I usually line the flexplate up on the converter on the floor and shoot a little spray paint on it so in the car it goes easy.

Tom

[71chally416]

Maybe somebody put one of those big roller bearings in there for a 4 speed and you need to remove it.

The convertor hub has to fit in that hole or you're screwed.

[nivvy]

I put my tranny back in recently and you had to mess with it some to get it to seat into the back of the motor wth the right angle.... yes the flexplate only goes on 1 way... the bolt holes are offset ever so slightly... dont tighten them down completely when you spin the crank for alittle bit of play to get all four converter bolts in ...   

also make sure the converter is in the WHOLE way and fits into the slots in the tranny.... 

[71chally416]

also make sure the converter is in the WHOLE way and fits into the slots in the tranny.... 

EXCELLENT POINT! You have to turn it and jiggle it until the convertor slots align and it goes all the way in......

[tactransman]

It sounds like the converter is not in the pump all the way.

http://www.tciauto.com/Products/Instructions/instructions/TorqConvTransInstallInst.pdf

[Pentastar Pete]

Ok, Up-date... Heres one for the books....   1970 340 engine, with steel crank. After walking away from it for a day, I went back. The opening on the 340 crank shaft where the nub for the converter fits into is just over 1/8th smaller then the original crank in the old 360. 
here it is:: the steel crank on the 340 is 1 9/16 I.D.   
The opening on the old crank is 1 13/16 I.D.
The nub on the mopar converters is just under 1 13/16 O.D.

Has anyone run into this before?   

[Supercuda]

The only "small-hub" cranks I've seen for the LA engines were in the 273's. I ran into this centuries ago when I swapped a 273 into the bay that once held a 318. We fought with that thing for at least an hour before we stopped and said, "something must be wrong." After checking everything, I took the convertor out and tried to fit it to the crank- too big! Perhaps the crank in your 340 is from an earlier smallblock. The 273 used forged steel, but with the small index.

[tactransman]

Ok, Up-date... Heres one for the books....   1970 340 engine, with steel crank. After walking away from it for a day, I went back. The opening on the 340 crank shaft where the nub for the converter fits into is just over 1/8th smaller then the original crank in the old 360. 
here it is:: the steel crank on the 340 is 1 9/16 I.D.   
The opening on the old crank is 1 13/16 I.D.
The nub on the mopar converters is just under 1 13/16 O.D.

Has anyone run into this before?   

Yes. Like Supercuda said,it is common on earlier engines.

Example:

   
No Weights (18 Splines Early 1.550" Pilot)
62-67 6 Cyl, V8 (122 Tooth Ring Gear)
Type: Non Lock Up   Hub: Slotted
Diameter: 11"   Input Splines: 18
Bolt Circle: 10"   122 Tooth Ring Gear
Mounting: 4 Pads   Pilot Dia: 1.550"

   
No Weights (Low Stall)
77-Up 225, 318 Low Stall
Type: Non Lock Up   Hub: Slotted
Diameter: 11"   Input Splines: 27
Bolt Circle: 10"   122 Tooth Ring Gear
Mounting: 4 Pads   Pilot Dia: 1.810"

[Pentastar Pete]

Up-date.  This is a 4-speed steel crank. The only way to make this work is to take the crank back out, put it on a lathe and open it up. It should be 1 13/16 opening. Thats the normal pilot opening for a auto 727 trans. The small opening 1 9/16 is the 4-speed crank and the old type 273 crank.
so engine went back to the machine shop....  Still waiting..........

[tactransman]

You should be able to turn down the converter pilot.

[Moparal]

Me being old school, I would have probably just used my die grinder and special tip to radius a new circumfrence. It wouldn't of taken much to make it work