Ring gear to torque converter bolt size advice, please

[bevans6]

I'm back at my MT647 install into my MC-5c, what with sudden warm weather and all.  I'm adapting a Cummins ring gear to the torque converter, since I could not source the special MCI flex-plate/ring gear.  The TC has 3/8" NF thread bolt holes, the flex plate I do have has 3/8" holes, the Cummins ring gear has exactly 7/16" holes (as in .438") so a zero-clearance fit to a 7/16" bolt.  A day's worth of corrosion and the bolts would be frozen in place.  So I wondered if Cummins installs have special shouldered bolts, or if I should just use 3/8" bolts.  The bolts will not be loaded in shear, friction between the parts will take up all of the starting torque load.

Thanks for your thoughts.

Brian

[Iceni John]

Here's some stream-of-lunacy way-out-the-box thinking:

There's 0.0625" difference in diameter between 3/8" and 7/16".   Why not make a spacer tube from 3 wraps of 10-thou stainless shim stock, or slightly less than 3 full turns if it's too tight to get the bolt through it.   I often do this when I'm trying to reduce the gap between bolts and oversize holes  -  I recently did it when I installed my brand-new Webster KB hydraulic pump on the back of the engine, and the 1/2" bolts were much too loose in the pump's holes.   I didn't want any risk of the pump's drive gear and gear coupling being misaligned or off-center, so I used good ol' soda can aluminum that's 5 thou thick and nice and soft to prevent fretting the pump's aluminum ears.   If you make a little tube from several wraps of shim stock and insert it in the hole, it will spring out to its maximum ID, sometimes with a little help from a lubricated tapered drift, then the bolt should cleanly go through it.   If it catches on the end, just relieve the edge of the first turn of thread.

I learnt this trick when working with bicycles that often have lousy tolerances.   I know of several high-dollar bikes with bits of Coca-Cola can between their handlebar and stem  -  one customer got pissy because the red color was slightly showing, so we just reinstalled it the opposite way!

John       

[stevet903]

Hey Brian, check out these ARP flywheel bolts.  They look like they have a larger shoulder and might be close to what you are looking for.
- Steve


http://www.jegs.com/i/ARP/070/206-2802/10002/-1

[Oonrahnjay]

Hey Brian, check out these ARP flywheel bolts.  They look like they have a larger shoulder and might be close to what you are looking for.  - Steve

http://www.jegs.com/i/ARP/070/206-2802/10002/-1 

     It appears that they have a 3/8 x 24 thread, which is standard fine thread (UNF),  that's what he needs but I don't think that the shoulder is long enough or large enough.   Too bad, that looks close.   

[bevans6]

Thanks for the thoughts!  I may use a version of the first idea by buying some 1/32 wall tubing and cutting some sleeves.  Those flywheel bolts brought back memories - I used to to stock those when I was building race engines, they got used in a lot of different flywheel applications.  They are just a quality 3/8" bolt, no shoulder to speak of.  I probably still have some in my bolt bucket...

Brian