Flexplate not sitting flush against crank flange - is that normal?

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xgregx

Member
Hello all,
I got my 1966 401 Nailhead back together and I'm starting to put the flex plate on. I noticed that it doesn't sit against the crank flange but rather rides on top of register, which I thought was odd. I don't recall what it looked like when I took it a part almost 2 years ago. One would assume the flex plate would want to rest fully on the crank flange and not be floating. The car was not running when I got it, but previously had been used until it sat for many years.
The crankshaft and flex plate are the same that came out of the car, I'm not swapping anything. I don't think the machine shop would have given me a different crank without telling me (or charging me).
As I torque the bolts down it pulls the flex plate in towards crank flange but that seems wrong. I know it's called a flex plate but pulling it in that far doesn't seem right. This is my first time dealing with an automatic/flexplate/torque converter etc so I'm not sure what to expect.
Normally you should be able to 'hang' the flex plate off the crank shaft before bolting it up right?. I can't do that.
Did someone mixup flex plates at somepoint? Please help!
Thank you,
Greg
 
Short answer - NO, that is not normal. Something is really off, and no, it can't "float" and survive, for multiple reasons.

Are you saying that the hole in the middle of your flex plate won't fit over the crank? That sounds like a heck of a mixup.

Per the book, you pull those bolts down to 50-65 ft-pounds. If the flex plate is "floating", guaranteed 50+ ft-lbs is going to do *bad things* if that flex plate won't willingly slide over the crank.

Curious: If you have a caliper - how far off are you? Does everything else line up?

Anyone know if there are different sized flex plate center holes for different sized engines (or cranks), perhaps?
 
Thanks for the fast response ! Yeah I didn't think that was right. I didn't think that was possible. I checked with calipers and the crank register is 2.9" and the flexplate hole is 2.5" - that seems like a mismatch of parts.
I've been doing some reading and it sounds like there are some different versions of flexplates out there between various Nailhead years and Dynaflows vs ST400s. Seems like I might need a different flexplate.
The mystery now is how the hell did this car run before I got it? As far as I know, the engine was never rebuilt and the transmission was original to the car. All the crust and the condition of the trans mount would suggest the same.
I took apart the transmission and it was very clean and had some new looking seals. I wonder if somebody swapped or rebuilt the trans and got a hold of the wrong flex plate.
I'll do some more digging and see if I can figure this out.
 
Definitely a mystery to solve.

I'd think you could take your engine size, your outer measurement on the crank, the model of the transmission you're bolting up...and with that info someone could tell you what flywheel you'd need.

Those Nailheads are externally balanced, too, right? So it has to be the RIGHT flywheel, mounted in the CORRECT orientation...it all has to line up and work.
 
Right - I'm aware of the pilot hole in the bolt pattern. It looks to have the correct style flexplate based on what Centerville auto sells. It looks like this one: used 64 to 66 flexplate | Centerville Auto Rep
I'll have to talk to the machine shop and see if they had to source a new crank for me. That was not in the itemized list, just 'grind crank' and he said the crank was in good shape. I'll double check with him and I'll call Centerville auto and see what they say. They know their Nailhead stuff real well.
Thanks for the help. I'll post back what I find out soon.
Greg
 
Ok - so I dug through my old pictures and found some shots of the back end of the crank when I sent it out to the machine shop and compared the crank I have now in the engine. They are clearly different. The one on the pallet is what I sent out, the clean one with no bolts is the one I got back and used to build the engine. I'll have to talk to my machine shop.
Anybody know the year of crank I got back based on the picture? It has the large register (2.9", flex plate hole is 2.5") and tapered hole. Looks like there are adapters out there. I'd hate to have to tear down my freshly built engine.
Thanks!
Greg
Original_Crank2_zoom.jpgCurrent_Crank.jpg
 
I think that I would be bringing in the pictures and explaining your experience to the machinist right quick. They probably will know exactly what happened... after all, they were there.
 
Dynaflow crank, maybe, from an earlier year? That's really strange.

I see adapter flex plates/bushings for sale, so I suppose it can be done, but that's a heck of a surprise.
 
mgaugustine said:
I think that I would be bringing in the pictures and explaining your experience to the machinist right quick. They probably will know exactly what happened... after all, they were there.
Click to expand...
Of possibilities, someone else has the crank or the original didn't survive the machining. Machine shops if they are disorganized can lose track of parts. If you ever get parts chrome plated, you know to take pictures, so you get your parts back. I wouldn't adapt anything; I'd want my original back.
 
I suppose you only have the casting number of the crankshaft you have now, but post it, along with a picture of the flywheel you have showing the counter weight.
 
Yeah - so the crank got mixed up at the machine shop. I got an earlier Nailhead crank with the larger register. They admitted the mix up and found my crank and are going to make it right. Mystery solved! Thanks for helping me figure this out!
Greg
 
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