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  #1  
Old 04-15-2005, 10:47 PM
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eckertt@epri.co eckertt@epri.co is offline
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Gripe Stripped out flex plate bolt

We have been running the Cuda's 360/904 some and started hearing a funny noise. Crawled underneath and noticed that the 4 flex plate to torque converter bolts were very loose. Tightened them and realized that one was stripped (hole in torque converter is stripped.)

Thread is 7/16-20 UNF. Should I use a helicoil and get back to 7/16 UNF?? or should I drill and tap for 1/2-20 UNF? Does helicoil even make inserts for the UNF? Think I can do this thread repair without pulling the engine/tranny out of the car?

Tim
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Old 04-16-2005, 02:12 PM
John Kunkel John Kunkel is offline
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The threads in the converter drive lug are pretty shallow, a Heli-coil would work if you could manage to drill and tap for it but I kinda doubt if it could be done.

In the future, always use Locktite on the converter bolts, they're notorious for coming loose.
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Old 04-16-2005, 02:28 PM
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never had them come loose, loctite? jeez, is that reccomended? (i asways just clean em real good and put em on dry)
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Old 04-16-2005, 02:51 PM
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Biggrin

Just drill and tapp to the next size up. We've done that to several converters over the years. You'll have to enlarge the flex plate hole too. Easy to fix that way.
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Old 04-16-2005, 04:03 PM
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Using one larger bolt may introduce a balance problem, youll have a heavier bolt whipping around. Might drill the opposite one out too or better yet, get them all to the same size. It would make for an easier phasing of the convertor to the flex plate if one were a different size though!
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Old 04-16-2005, 07:17 PM
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Default Flex plate

Thanks,

I will probably drill and tap to the next size. from 7/16-20 the next size should be 1/2-20

Tim
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  #7  
Old 04-16-2005, 07:42 PM
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Quote:
Originally Posted by John Kunkel
The threads in the converter drive lug are pretty shallow, a Heli-coil would work if you could manage to drill and tap for it but I kinda doubt if it could be done.

In the future, always use Locktite on the converter bolts, they're notorious for coming loose.
I'm with John. I have this sneakin' suspicion that he really knows his stuff here. I also think Locktite is very cheap insurance, regardless of how well you clean the bolts or your past experience. I also think pishta is right on target about a balance problem, particularly if you intend rev it high.

But, it's your car and your call.
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Old 04-16-2005, 07:48 PM
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Biggrin

It won't take much drilling. The tap drill for a 1/2-20 (75% thread) is 29/64 (.453) If the hole is stripped out and a 7/16 bolt (.4375, probably .005 under) will spin, the hole is probably just about .430 to .432 now, about .010 on a side.

A 29/64 reamer with a good lead would probably open that hole right up by hand without the chance of a drill trying to grab and jump out of the existing hole.

Just as an afterthought, Loctite has a product that will restore threads. You dope up the hole and put the bolt in and leave it for a curing time. I don't know if the shallow surface of the flex-plate would take to it, but you might look into it. I have never used it but have read about it.
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Old 04-16-2005, 08:08 PM
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Biggrin

Quote:
Originally Posted by dwc43
Just drill and tapp to the next size up. We've done that to several converters over the years. You'll have to enlarge the flex plate hole too. Easy to fix that way.
i have done this too. if your worries about balance, scale your bolts, but, when you do, you will realize that the stock ones werent as close as you would think.
dick, have you used the loctite thread maker before? i always though it was a gag.
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Old 04-16-2005, 08:48 PM
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Default J B Weld ?

have you used the loctite thread maker before? i always though it was a gag. [/QUOTE]


Never hurts to try. Loctite thread maker did real good on an aluminum intake we had. We also used it on a stripped header bolt.
Sometimes it doesn't work, you just have to try it.
J-B Weld has some stuff that is just nuts! I have put J-B weld on a broken main saddle in the crank case of a Harley V-Twin, had it remachined and it was just like new. We also used it on a ford tractor block and it still holds. Some stuff it works on and some it don't. It's only a few bucks, so give it a try.
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  #11  
Old 04-16-2005, 10:52 PM
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Default Correct bolt

Dick, thanks for the info about drill/reamer size. I want to go with the 1/2-20 threads as opposed to the loctite thread maker idea.

So where do I get a grade 8 bolt that is 1/2-20 with such a "thin" head? If I take a regular head bolt, and gring down the head to be as thin as needed, have I weakened the bolt due to the heat of the grinding? Probably will help to use lots of cooling water during the head grinding process?

Tim
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  #12  
Old 04-17-2005, 01:35 AM
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A flexplate-to-crank bolt from another make might have a thinner head.............

torch
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  #13  
Old 04-17-2005, 07:44 AM
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Biggrin

Quote:
Originally Posted by eckertt@epri.co
Dick, thanks for the info about drill/reamer size. I want to go with the 1/2-20 threads as opposed to the loctite thread maker idea.

So where do I get a grade 8 bolt that is 1/2-20 with such a "thin" head? If I take a regular head bolt, and gring down the head to be as thin as needed, have I weakened the bolt due to the heat of the grinding? Probably will help to use lots of cooling water during the head grinding process?

Tim
I wouldn't grind it, I would face it off in a lathe with carbide facing tool and coolant. You could grind it but you would have to keep dipping in the coolant can to keep it from getting too hot.

Facing it in a lathe with a carbide tool keeps the heat in the chip if done correctly. Don't try to hold it in a chuck, use a collet instead. That 20 pitch thread is pretty delicate and isn't very deep. Take several facing cuts to make it easier on the tool. You might have to touch the tool up before you are finished, depending on how much you are taking off. The carbide won't be crazy about the interupted cut on the corners and won't like going all the way to center, therefore the edge is probably going to chip a little.
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  #14  
Old 04-17-2005, 08:35 AM
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You most certainly can drill the lug, use a bottoming tap and then cut down a heli-coil to fit. I've done this several times with the converter/trans still in the vehicle. It was a small block though and I did it by the starter mounting area. How your car is may be different.
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  #15  
Old 04-17-2005, 08:44 AM
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Biggrin

Quote:
Originally Posted by dodgetkboy78
i have done this too. if your worries about balance, scale your bolts, but, when you do, you will realize that the stock ones werent as close as you would think.
dick, have you used the loctite thread maker before? i always though it was a gag.
You are correct. It's not enough to worry about. Never caused a balance problem before and one was turned as high as 6800. SO just drill and tap away.
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  #16  
Old 04-17-2005, 10:10 AM
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well at least someone mentioned JB weld before I did. That stuff is great.... the epoxy lovers "duct-tape".
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  #17  
Old 04-18-2005, 01:41 AM
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Quote:
Originally Posted by Dick
I wouldn't grind it, I would face it off in a lathe with carbide facing tool and coolant. You could grind it but you would have to keep dipping in the coolant can to keep it from getting too hot.

Facing it in a lathe with a carbide tool keeps the heat in the chip if done correctly. Don't try to hold it in a chuck, use a collet instead. That 20 pitch thread is pretty delicate and isn't very deep. Take several facing cuts to make it easier on the tool. You might have to touch the tool up before you are finished, depending on how much you are taking off. The carbide won't be crazy about the interupted cut on the corners and won't like going all the way to center, therefore the edge is probably going to chip a little.
Just use flex plate bolts for a HEMI. They are 1/2-20. Dan
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  #18  
Old 04-18-2005, 10:01 AM
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Default hemi flex plate bolt

Dan, good tip.

I have been surfing for 20 minutes looking for a place to buy some 1/2"-20 UNF Grade 8 flex plate to torque converter bolts (I only really need 2) and havn't found a good source yet.

before I spend more more time surfing, does anyone have an idea where I can buy such bolts from?

Tim
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  #19  
Old 04-18-2005, 11:07 AM
Kevin Garceau Kevin Garceau is offline
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I agree, I doubt it will make that much difference in balance.

Heck if you add loctite are you going to put the same amount of grams on each bolt

I always loc-tite my flexplate bolts. ALWAYS, without question.
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  #20  
Old 04-18-2005, 02:04 PM
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Default 1/2-20 GR8 Bolts

www.mcmaster.com has the GR 8 bolts you`re looking for. I buy all my fastening hardware there. They are a huge industrial supply house. Not sure if you are in need of hex head, or hex flange head. They have many different flavors. Not sure if they are available to the general public though.

R/T
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  #21  
Old 04-18-2005, 07:00 PM
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Default Expensive bolt

I had gone to a hardware store and bought a 1/2-20 UNF x 1" bolt grade 8. The guys at the machine shop at work turned the head to the correct thickness, and cut it to length, usung the old 7/16 bolt as a guide. I would hate to know how much this bolt cost "somebody".

I am now armed with many reamers and drill bits and am going under the car to do battle with that darned hole. I also have some high temp Locktite to put on all 4 bolts after I clean them and their little holes.

Thanks to all for the ideas/suggestions.

Tim
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  #22  
Old 04-18-2005, 11:07 PM
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Biggrin

Should have went to your local Advance Auto. You can get stock flex plate bolts from them. I've bought several over the years.
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  #23  
Old 04-18-2005, 11:20 PM
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Default 1/2-20 Bolts

How thick are the heads of the flex plate to crankshaft bolts? They are 1/2-20 and fairly short. Some of them have pretty thin heads and some are a little thicker. If you turn down the heads in a lathe, just screw the bolt into a nut and chuck up the nut. That way you don't mess up the threads and you get a good hold on the bolt. ( Drag race type long lug nuts work real well) Dan
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  #24  
Old 04-18-2005, 11:58 PM
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I had all four bolts loosen on a small block and one eventually hit the back of the block hard enough to tear it out, ruining the thread in the converter before I realised what the ticking noise was. I'd never put them in dry again - Loctite is definitely cheap insurance.
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  #25  
Old 04-20-2005, 02:31 AM
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Wink Funny Noise Gone

The stripped hole has been reamed and tapped to the larger size. The new bolt has been installed. All 4 bolts and bolt holes have been throughly cleaned and Loc-Tite applied. Bolts torqued to 23 ft-lbs.

Ran the 360/904 and the funny noise is GONE!!
Thanks to all for the great advice!

Tim
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  #26  
Old 04-20-2005, 07:26 AM
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Biggrin

Welcome,anytime Tim. Glad you got it fixed.
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