Why doesn't my flex plate fit?

by Sinister Thu May 10, 2012 1:26 pm

Ok,day was going well,started at 3:00 am,and was installing my 2002 5.7 motor and trans.
I thought I was pretty much done,but no.
The flex plate from the 2002 motor doesn't line up with my earlier turbo 350 torque converter.
I have another available,external balance from a 91 5.7.
When did they change the bolt pattern on the flex plate?
I was under the impression all external balance flex plates had the same bolt pattern.
I've never read or heard of anyone not being able to bolt on their torque converter.
Any help appreciated.
Thanks.

by 1973 454 MONTE Thu May 10, 2012 7:38 pm

i always thought they had 2 different patterns. as if to say the F-P has 6 T-C holes

by bigredlaguna Thu May 10, 2012 8:57 pm

Found this info on a retrofit site.

"Transmission Retrofits

Installing a LS1 engine with another transmission such as a early 200/700R4, THM350/400 will require the installation of flywheel GM part number 12551367.

If using the F-body and C/K trucks with the 300 mm bolt pattern will require the flexplate with PN 12563136.

The 4L80E or 6 lug converters will require PN 12551367. This flexplate is flat and will require the use of a spacer (PN 12563532) and bolts (PN 125635330 which is included with flexplate assembly.

If using a early manual transmission will require, which will use a 11.7" (298mm) clutches:

PN 12562765: 6 speed flywheel assembly
PN 12561680 Early style 4 speed flywheel
The LS1 crankshaft is also shorter relative to the bell housing than the earlier small-blocks. Special pilot bearing PN 12557583 is needed to compensate for this difference."

by bigredlaguna Thu May 10, 2012 9:20 pm

Unless you have the last year of the gen I vortech engine, then my previous post doesn't apply.

My 1992 305 matches with the TH350 torque converter. Just had to use the 1992 starter because of the small diameter of the flexplate.

by 77mali Thu May 10, 2012 9:37 pm

If the motor is an '02, that's an LS style engine, no?

by Sinister Thu May 10, 2012 10:48 pm

Came out of a 2002 Workhorse...L31 motor.
I have another flex plate from a 91 that matches the original turbo 350 torque converter bolt pattern.
I've just never heard of anyone running into this problem.
I thought I read just about everything on engine swaps.
Thanks for the numbers.

by Sinister Fri May 11, 2012 4:59 pm

Usually torque converters have captive nut.
The one I'm working on has very short nuts and bolts.
Besides using thread locker,what are the safest nuts to use.
Thanks.

by jerry46765 Fri May 11, 2012 11:07 pm

77mali wrote:If the motor is an '02, that's an LS style engine, no?

No.

by Biomedtech Sat May 12, 2012 7:07 pm

Odd, I just dropped in a 97 vortec motor and had no issue with the TC bolting to the flexplate. My issue is happening with trying to get the mini starter to line up right! Cant the damn gear to engage.

by Sinister Sat May 12, 2012 9:27 pm

Which transmission are you using?
The flex plate that didn't fit was from a motor home chassis and had a mini starter...with the 4l80E
Might want to try a regular production starter.
I plan on using the original full size starter,although I will be using a remote solenoid.
Try some starter shims.

by Biomedtech Sun May 13, 2012 3:52 pm

Thats the plan. I'm going to put on the Tahoe starter and put a heat shield on it to attempt to prevent heat soak from the hookers.

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