schmendog

iTrader: (10)

Ive got a B&M flexplate on, and a TH400 with a FTI converter. The bolt holes are not lining up for the converter to flexplate. Its the correct flexplate for my application, and Im at a loss here. Im reading that drilling out the mounting holes on the flexplate is sometimes required...is that right?

ss performance

iTrader: (17)

How far off are they?

I would check with both manufacturers for the proper spec on the hole spacing.

Drilling out by hand might result in the holes not bring properly aligned resulting in a off center wobble. BAD

schmendog

iTrader: (10)

I haven't measured, because Im trying to avoid pulling everything back off the car if its just something stupid Im overlooking...but its starting too look like that's not the case.

Eyeballing it with everything on the car Id say its off by 1/16-1/8" or so. The flex plate is the LSX plate which should fit my application (iron 5.3 block, TH400, FTI converter specd for my build). Here's a picture of it, Im still trying to figure out which set of holes Im supposed to be using. At this point, the yellow holes are lining up closer, where I can get one in fine, but then the other two are just slightly off. The red holes, with the embossed edges aren't even close.

schmendog

iTrader: (10)

Just went out and double checked, the holes circled in yellow are definitely closer. id say two of them are off by about 1/16" and the third one bolts in just fine.

Circle-D_Brian

The larger pattern on the flexplate is the LS 11.062" bolt circle. The one you have circled in yellow is the LT/th350 10.75" bolt circle. Drilling the bolt holes out slightly larger to fit should not be an issue as there could be a stackup of tolerances with the two aftermarket parts. The converter is centered by the pilot that engages the crankshaft of your motor. The bolts simply secure it to the flexplate. Make sure you use a bolt with a large enough head and proper thread engagement so you don't have issues there.

-Brian

schmendog

iTrader: (10)

Awesome thanks Brian. Odd that I am closer to the yellow holes isn't it? I mean the red holes are nowhere even close to either of the two threaded holes on the converter pad. The converter was built specifically for my application (th400 5.3) I wonder why that is?

mrvedit

Really impressive that CircleD is answering questions and helping out on a Sunday morning! I don't think the OP is even their customer.

schmendog

iTrader: (10)

No Im not, and yes it is!

Circle-D_Brian

That might be a question for FTI. The other thing you should check is pilot length. If this converter was built for standard 350 pattern, it is possible it has the standard shorter GM pilot. If this is the case, you will need a pilot extender to essentially make it LS length. We can quickly determine this if you place a straight edge on the pilot and measure down to the converter pad. Standard gm measurement should be About .250 or 1/4" and if it's LS style, it will be closer to .500 or 1/2".

-Brian

jrpimp00

iTrader: (17)

OP, id take it apart and get the correct flexplate, if you just purchased that one. A good thing to do is lay the flexplate on the ground and put the converter on it to check the alignment before bolting it all up

Launch

I just fitted this B&M flexplate and same deal. Lucky for me my Turbo 400 converter has both small and large bolt patterns, so the yellow holes are lining up perfectly. But im paranoid the T350 holes (yellow) are too close to the edge of the plate where the 6 large holes are, and could cause it to eventually crack through. So when I ramp up the engine HP I will remove the plate again and redrill the large T400 bolt pattern fresh, adjacent to all of the other holes, so the new T400 large pattern holes are not close to any edges of where the plate is open/missing.. if that makes sense!

Why can't a part just fit for once without a drill or grinder.

Circle-D_Brian

The large pattern on your converter is likely 11.5" where as the large pattern on this flex plate is only 11.06" (LS bolt pattern). Not really the flex plate's fault.

-Brian

Launch

Yes I realize that. Though it would be nice if they had drilled the 11.5" turbo pattern on it knowing that many LS swaps run a turbo 400.

For a cheap plate im not complaining.