Yield torque test on Torque Converter bolts.

warp2diesel · **Posted:** Tue Jun 15, 2010 4:49 pm

The purpose of this test is to determine the Yield Point of the Torque Converter bolts used to attached the Torque Converter to the Flex plate of the Jeep Liberty CRD. Once the Yield point is reached, the bolt can not generate any more clamping force that helps secure the torque converter properly in place with out shearing off the bolts.
Bolts are 5/16" X 1/2" long 24 TPI Grade 8 with 9/16" heads
Bolts and the threaded mounting tabs on the stock Jeep Torque converter were clean and dry, one drop of Red Loctite was placed onto the bolt threads. To simulate the flex plate that has a hole larger than 5/16" a 5/16" washer was placed onto the mounting tab and the bolt was screwed into the bore and torqued to 270 In-Lbs. After allowing the bolt to rest for two minuets, the bending bar torque wrench was brought up to 270 In-Lbs and the bolt head did not turn. Torque was increased until the torque wrench kept rotating very slowly with out an increase of the torque reading. The torque reading was 350 In-Lbs indicating the bolt was stretching and not capable of generating any more clamping force. The bolt was untorqued and was removed easily with minimal finger effort indicating the bore in the mounting tabs were not damaged even though the bolt was stretched.
Engineering tables recommend 18 Ft-Lbs (216 In-Lbs) for a 5/16" NF Grade 8 bolt. 350 In-Lbs = 29.16 Ft-Lbs.
Conclusion, the Torque Converter bolts used by Jeep for the Liberty CRD application have a torque safety factor of 162% when torqued up with Red Loctite.

This should put to rest any concerns about using Red Loctite on Torque Converter Bolts torqued to 270 In-Lbs. This goes for Original, Euro, SunCoast, or any other well built Torque Converter. This test is no recommendation to exceed the recommended 270 In-Lbs torque on the Torque Converter Bolts and only a determination of the torque safety factor.

tjkj2002 · **Posted:** Tue Jun 15, 2010 4:59 pm

Now you just need to convert the torque to a PSI reading,and just because it threaded out with ease does not mean anything.Some bolts are designed to stretch when torqued properly,after a certain amount of stretch they are considered bad.Cummins uses these types of bolts for there cylinder heads and actually have a little tool(ruler type)to measure bolt stretch.

warp2diesel · **Posted:** Tue Jun 15, 2010 5:45 pm

tjkj2002 wrote:

Now you just need to convert the torque to a PSI reading,and just because it threaded out with ease does not mean anything.Some bolts are designed to stretch when torqued properly,after a certain amount of stretch they are considered bad.Cummins uses these types of bolts for there cylinder heads and actually have a little tool(ruler type)to measure bolt stretch.

Most modern engines use stretch bolts to prolong the life of the Head Gasket.
Want to know the clamping force for a bolt at a given torque, here you go: http://www.engineersedge.com/calculator ... e_calc.htm
Mercedes used to use stretch bolts on their connecting rods where you would measure the waste of the bolt shank to determine if it needed replacement. Others tell you to replace the bolts every time, a good practice.
To put any paranoia to rest, at 270 In-Lbs the tension load on the Torque Converter Bolt is 56,242 PSI.
My point is that Chrysler just went to a chart and grabbed a number that is conservative. The torque converter bolts are capable of more and have conservative Safety Factor when torqued dry. Even at 270 In-Lbs torqued with Red Loctite there is still a safety factor, a good safety factor. Lubricating the threads with oil or Loctite does increase the clamping force and the tension on the bolt, but lets face it 56,242 PSI is less than 130,000 PSI. We still have a good safety factor, plus the bolts will not come loose and fail in shear which some members have had experience with.
An Engineer with a Brain would look at the test results, validate them and have no problems recommending Red Loctite instead of going to larger bolts.
Anyone know what size bolts and how many Torque Converter Bolts the Dodge/ Cummins uses with the 68RFE. SunCoast is putting 800 HP through the 68 RFE with a modified input shaft and clutch pack housing. I know they use Red Loctite.

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

When we received our Euro TCs from Mopar the (4) TC bolts came with a dry blue loctite already on the threads. Did anyone else out there that bought a Euro TC notice blue loctite on the bolts?

warp2diesel · **Posted:** Tue Jun 15, 2010 8:16 pm

GreenDieselEngineering wrote:

When we received our Euro TCs from Mopar the (4) TC bolts came with a dry blue loctite already on the threads. Did anyone else out there that bought a Euro TC notice blue loctite on the bolts?

When I removed my rear drive shaft bolts, they had blue Loctite on them which I refreshed when I assembled and torqued to 85 Ft-Lbs. The Torque Converter Bolts I removed from my Original Torque Converter had no Loctite on them of any kind. They were also installed dry and were dry when I pulled them out.
Good to hear the Chrysler is now using at least Blue Loctite on the Torque Converter Bolts.
Looks like the Torque Converter Bolt Anti Loctite Movement is D.O.A. to put it Politely.

SunCoast calls for Red Loctite, so I used it.

Mountainman · **Posted:** Mon Mar 21, 2016 1:59 pm

How do you bolt experts feel about reusing the old TC bolts? And, how about Zinc Plated Dorman bolts from Summit Racing? I can get a good stock of them of the right size, in grade 8, or would the factory bolts be better?

I guess what I'm really wondering is, are the factory bolts damaged when you remove them, or is the amount of torque to break them loose enough to damage their integrity?

Oh, and would the heads be too thick on the Dorman bolts? There isn't a lot of space in there:/

Thanks for any wisdom on the subject :JEEPIN:

Auberon · **Posted:** Mon Mar 28, 2016 10:53 am

I'd venture to say they should be re-usable as we are dealing with non FAA and rather terrestrial dwelling devices.
Having stated that - I have new ones for my flexplate when the new TC goes in this winter (after fabbing the tranny lift) given they are so cheap for original parts even for me to buy and ship with other parts.
A great read (although it's not exactly light going) is Carroll Smith's Nuts, Fasteners and Plumbing Handbook ISBN-13:978-0-87938-406-7 for Fastener Engineers and others interested.

By the way..Thanks for the reminder it certainly is time I pulled this book and a few others off the shelf and gave them a re-read.
Cheers.

Mountainman · **Posted:** Mon Mar 28, 2016 10:57 am

Many thanks. If my new grade 8's arrive in time I'll use them, otherwise it's the old ones going back in.

Yield torque test on Torque Converter bolts.

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