How thick are 350 flywheels?

Discussion in 'The Garage' started by Russell, Mar 8, 2007.

  1. Russell

    Russell LLY Escalade Status Premium Member GMOTM Winner

    Jun 23, 2000
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    Edmonton, Alberta
    Sorry about all the questions -- Just trying to figure out how to bolt a transmission onto an engine that never had a standard behind it stock, lol

    Basically the story is that the 5.3L's crank snout is about .400" recessed as compared to that of a 350's. So, if you take a standard that normally bolts to a 350 (aka, an NV4500) and bolt it to a 5.3L, the input shaft will be about .400" too short to reach the pilot bushing and the clutch will sit about .400" too far forwards on the input shaft, if it engages at all.

    So, my idea is this:

    They make crank spacers to allow a guy to use an earlier 4l60e flexplate that has an LSx crank bolt pattern on it, but shares the same spacing as the old style TH350 / TH400 / 700r4 flexplates. Lots of guys use them to bolt a 700r4 etc onto the back of an LS1 by ovalling the torque converter holes, since the new LSx torque converters have a slightly different bolt pattern. If a guy could use that spacer to bolt a flywheel from another LS1 engine on, and assuming that the ID of the spacer is the same as that of the crank's pilot bushing hole, a guy could make a .400" spacer for the pilot bushing to press in first, then push the actual pilot bushing in afterwards so it would be resting inside of the spacer rather than the crank. That should technically set it up so the input shaft properly engages the pilot bushing using the stock bellhousing.

    Now, I know that the LSx flywheels use the same bolt pattern for the pressure plates as the old 350 flywheels, and use the same size clutch disks. The only things you have to do to bolt an old pressure plate up is to drill the holes out so you can fit the metric bolts through, and remove two dowling pins used to position the pressure plate onto the flywheel in the stock application. So if you were to bolt the stock NV4500 pressure plate on, with a stock NV4500 clutch disk, you should technically be good to go as far as the throwout bearing etc goes.

    Now, the only problem that could still arise is that the flywheel from an LSx engine may be a different thickness, which would place the clutch disk in the wrong place on the input shaft.

    But, if a guy could figure out what the difference is, if there is one, you could custom make a crank spacer that has that size difference accounted for and suddenly you midaswell be bolting that transmission onto the back of a 350! No messing around with funny sized throwout bearings etc :D

    So, out of all my ranting and raving here, how thick is a stock 350 flexplate suppost to be? Once I know that, I can compare it to the thickness of the stock LSx flywheels, and see what happens :D


  2. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Dec 14, 2001
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    Pleasanton, CA.
    I'm pretty sure advance adapters has what you need. Ryan B did a NV4500 behind his LS6
  3. Russell

    Russell LLY Escalade Status Premium Member GMOTM Winner

    Jun 23, 2000
    Likes Received:
    Edmonton, Alberta
    yeah they do, but my pockets don't run $1400 deep for a bellhousing, and some fancy flywheel...
  4. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
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    Roy WA
    Not really helping, but I have a friend that used a transmission from behind an LS motor to a gen1 SBC.

    It was a lot of effort to find/get parts that worked together. :(

    Here are snippets of a few emails he sent me. It seems like it would apply, since the reverse is essentially what you are doing.

    "I bought the McLeod throwout bearing (application was 93-97 T56 with
    clutch) which was too thick front to rear to fit with a "normal" T5
    Everything else about that item was workable. McLeods customers at
    times are
    their R&D dept. though. I just have no reasons to be a fan of the TO
    brg. in
    any application. Granted I've worked on a GMC 1995 diesel 5spd truck
    and the
    stuff works but it doesn't have any inherent advantage, other than
    ease of assembly and it's less able to be "messed with" by the car
    owner /

    "Actually it has. There is one throwout bearing (other than the clipped
    LT1 F-body brg) that fits and would work with a push clutch. But the
    distance between the base of the brg retainer & PP fingers and fork
    geometry and all sucks.

    I have driven my T56 behind Robs 408 (when it was Bills 408) with a 750
    Holley, not sure on the clutch, and a car 12bolt with 3.90s in an 87

    I drove it in my car once around the neighbourhood in Abq.

    But now it'll take 82-83 F-body parts. The Lakewood fork (from you)
    minor grinding in the "u" to clear the bearing sleeve but the OEM(?)
    made of thinner metal also had previously been ground there."

    "Not really. 86 has the rod-end clutch linkage in, the T56 sitting in
    with the "hacked" bellhousing & front case to accomodate mech linkage
    (refined setup) and the Hooker Y-pipe (from the catback) + flowmaster
    mufflers and flowmaster tailpipes needs hung. The Y-pipe isn't quite a
    fit with the other parts."

    LOL, those go back from fairly recent to Apr 2005. :)

    At some point these type of conversions are easier to accomplish if someone (company) has already done the R&D. You can do the stuff yourself, but if what's out there already done, your *time* is what gets pinched. If it's a long term project and in no hurry at all, great. Otherwise, lots of

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