Shimming torque converter flexplate mounts.

[janjon]

So, on my small block Chevy / Powerglide FED combination, I just replaced the flexplate. the ring gear teeth had some major damage. Ordered one from Jegs, the previous one was also from Jeg's, apparently identical, to the naked eye. I was able to slide the engine forward on the frame rails enough to swap it without pulling the engine. I noticed that the ring gear teeth were a lot closer to the 1/4" motor plate than they had been on the old flexplate, after installing the flexplate bolts. Having pushed the convertor all the way back into the transmission through this process, when reinstalling the flexplate bolts to the converter mounting pads, I had to pull the convertor about 3/8" forward to install the previous shims of approx. 1/8", and that seemed to be too much to me, possibly losing too much of the engagement of the stator support slots, and the trans pump gear tangs, to drive the trans pump with sufficient engagement.   Any help on how this should be se
t up is greatly appreciated.
Thanks,
John

[bikeguy307]

1/8" to 3/16" is the range, change your shins to get in this range.

[THE FRENCHTOWN FLYER]

I would also install the starter motor with the solenoid cover removed and manually engage the solenoid to make sure the pinion gear on the starter is not going to over-stroke the ring gear and cause a bind against the ring gear.

[msundstrom]

I have found a big difference in flex plates where they stamp the crank flange in both depth and squareness to the ring gear. The cheaper the flex plate the more lax on quality control, it seems to me. I have had good results/consistency from TCI and B&M. You can buy flex plate to crank shims to move the flex plate away from the motor plate and toward the converter. I believe Speedway sells them but I have never used them.

[Roger]

I had the same situation with the current engine and the previous engine. The first engine was a 1 piece rear seal deal and I had to put in a 0.090" shim from Competition Engineering (1 piece seal shims are different from 2 piece shims). Had about 3/4 starter to flywheel tooth engagement at that point and still had too much space. So I took the advise of someone on the board and placed a Grade 8 flat washer between the flywheel and the convertor mount pad. Work perfectly, just be sure all 3 of the washers are exactly the same thickness.

When I installed the newest engine it also required a shim but didn't require any flat washers to get the correct 1/16" to 3/16" spacing. As long as you have at least 3/4 engage of the solenoid gear and the flywheel gear you should be fine.

[THE FRENCHTOWN FLYER]

I would like to make one additional observation about converter shims. I have found that as the shim thickness increases so does the likelihood that you will see fretting of the shims against the flex plate and the converter tab surfaces. So I put three small tack welds on each shim to keep them solidly against the flex plate. I also like to turn a small pilot on each bolt to aid installation. I weigh each bolt on a gram scale after machining.

[BK]

What would be the minimum pilot engagement into the end of the crankshaft?
That's what lines everything up.

[THE FRENCHTOWN FLYER]

I've gotten by with 1/4" of engagement. What you don't want to see is the pilot bottoming out in the crank. That will lead to thrust bearing failures.

[Draw 3D]

Make sure that the flex plate is not installed backwards, it should be marked as to which side goes against the motor.


On my initial build, the converter to flex plate gap was a little over 3/8", took it to Hughes and they built up the converter pad and now fits pretty good. As I replace the flex plate, I sometimes use washers between the pad and flex plate but not more of a combined thickness 1/16, I like to keep around 1/8" gap for the pads. I also use a thin shim between flex plate and motor for motor plate clearance and starter engagement.

[janjon]

Thank you all for your input.
I wound up with shimming to the high side of the recommended range.
As regards Frenchy's caution about fretting, I see I need to regularly make sure the bolts stay tight.
I think the convertor pilot engagement into the crankshaft counterbore is sufficient.
I ran the car last weekend, it seems good and nothing came undone.
I posted some video of my runs in the Front Engine Dragster section, check them out if you like.
Thanks again,
John