Torque values

[D&J Edgar]

When I asked my question on torque values I just threw in the cotter pin in as an aside note. While the cotter pin took up a life of it's own in the thread, nobody has commented on the torque values themselves. So I ask again (without cotter pin reference): Who submitted the torque values for XPAG/XPEG engines on our TABC web site Technology page? What source was this info taken from? In looking this over and comparing with other data I have, I am finding variances. In comparing the values from our TABC web site, TD Workshop Manual, Autopress Manual,and data from an reliable MG mechanic I get the following ranges: Rod big end - from 20 to 26 ft. lbs. (our web site shows 25) Main caps - from 55 to 63 ft. lbs. (our web site shows 63 Cylinder head - from 42 to 55 ft. lbs. (our web site shows 50) If you comment on values please indicate your source. What would be the most reliable source? Thank again and now back to the Music Thread , David Edgar, TC 5108 El Cajon, California

[Gene Gillam]

I posted this on the TABC website but got few responses so I want to throw it out to everyone: "I've got a question on the torque values given in the Resource Technical Article file: http://www.mg-tabc.org/library/torque.htm There it says that the 8mm rocker arm assembly bolts are to be torqued to 16 ftlbs. The MG Y-type forum (http://www.mgccyregister.com/node/19016) gives the torque spec as 27 ftlbs. David DuBois (http://homepages.donobi.net/sufuelpumps ... ngines.pdf) gives the torque spec as 19 ftlbs. I also have a question on the 10mm rocker arm assembly bolts...our site tech article gives the torque value as 43 ftlbs. David DuBois concurs, the Y-type forum gives the torque spec as 42 ftlbs but the MG Cars site (http://www.mgcars.org.uk/imgytr/pdf/reassycheck.pdf) lists the torque spec as 30 ftlbs. I'm sure there's other discrepancies throughout the specs but these were the only two I was concerned with today. Can someone verify WHICH is correct...and if our site lists the wrong torque specs please correct it." Tom Wilson responded with this for the immediate questions concerning the 8 and 10mm bolts: "As a general rule I follow both what the MG specs are in combination with modern ISO specifications. More times than not they are comparable. So for an 8mm bolt dry is 19 ft pounds; a 10mm bolt 37 ft pounds. Preferred method (I believe) is lubricated with a light oil - the values are then higher.  http://www.cncexpo.com/MetricBoltTorque.aspx for an example." So, is there a comprehensive torque value guide for our engines that's correct or should I just use Tom's site and forget our Tech Article? Thanks, Gene

[John Seim]

I would go with Tom's values, as that is what I use as well.Tighten, and torque the 10mm bolts first. These are the ones that really hold the assembly to the head.Then, tighten and torque the 8mm bolts. These are to keep the towers stabilized. John SeimIrvine, CA

On Apr 30, 2013, at 4:21 PM, Gene Gillam wrote: I posted this on the TABC website but got few responses so I want to throw it out to everyone: "I've got a question on the torque values given in the Resource Technical Article file: http://www.mg-tabc.org/library/torque.htm There it says that the 8mm rocker arm assembly bolts are to be torqued to 16 ftlbs. The MG Y-type forum (http://www.mgccyregister.com/node/19016) gives the torque spec as 27 ftlbs. David DuBois (http://homepages.donobi.net/sufuelpumps ... ngines.pdf) gives the torque spec as 19 ftlbs. I also have a question on the 10mm rocker arm assembly bolts...our site tech article gives the torque value as 43 ftlbs. David DuBois concurs, the Y-type forum gives the torque spec as 42 ftlbs but the MG Cars site (http://www.mgcars.org.uk/imgytr/pdf/reassycheck.pdf) lists the torque spec as 30 ftlbs. I'm sure there's other discrepancies throughout the specs but these were the only two I was concerned with today. Can someone verify WHICH is correct...and if our site lists the wrong torque specs please correct it." Tom Wilson responded with this for the immediate questions concerning the 8 and 10mm bolts: "As a general rule I follow both what the MG specs are in combination with modern ISO specifications. More times than not they are comparable. So for an 8mm bolt dry is 19 ft pounds; a 10mm bolt 37 ft pounds. Preferred method (I believe) is lubricated with a light oil - the values are then higher.  http://www.cncexpo.com/MetricBoltTorque.aspx for an example." So, is there a comprehensive torque value guide for our engines that's correct or should I just use Tom's site and forget our Tech Article? Thanks, Gene

[Bill Hyatt]

Gene,

 

Whoever 1st started publicizing the engine/chassis fastener torque specs didn’t do anyone a favor. These Torque figures are [b]completely useless[/b] unless the original OEM fastener grade specified is used. & nowhere on these spec. lists is there any mention original OEM grade or reference is to those specs. E.G: [b]Never use an ungraded fastener in a critical location.[/b]

1.) a Chrome Moly 8mm bolt of 170,000/180,000 PSI  UTS  grade takes 24 ft. # of torque to achieve  5800 # of preload,

2.) a 190,00/200,000 psi grade bolt takes 28ft.# to =6580 # of preload clamp

3.) a 220,000/ psi  takes 32 ft.# of torque to =7300 # of preload clamp.

4,) ISO  Grade 8.8, minimum UTS 116,000 psi.; ISO 10.9 = 145,000 PSI min. UTS; ISO 12.9 = 174,000 psi min. & Y.S. are 92800, 130,000,  157,000psi respectively

5.) Grade 8 bolts are suppose to have spec of mol 150,000 psi

 

NOTE that all of the above clamp figures (#1-3) are achieved when fastener is tightened to 75% of yield strength using the particular fastener lube the fastener mfgr. specifies. Torquing a bolt dry is a [b]very bad ideal[/b] as almost all of the torque achieved is just from overcoming friction on threads & under fastener head/nut.. As little as 10-20% of torque is achieving clamp preload required, all the rest of torque being  is used overcoming friction. Friction is an unknown quantity that any quality mfgr. accounts for when advising preferred lube to achieve desired preload at particular torque spec.

So what to do? [b]Only[/b] use a fastener of known grade from a reliable source marked with the appropriate grade for the application!

 

If one has access to ISO marked/graded bolts it is possible to determine both the UTS & Yield Strength of the fastener by its marked grade. E.g. an ISO grade 8.8  has (116,000 UTS, & 9200 psi Yield strength) .This is determined by

Multiplying the digit to left of decimal by 14503.7 (8x14503.7=116,029 rounded off = 116,000psi. The # to the right of the decimal is ratio of Y.S. to UTS, so .8 x 116,00 = Y.S. of 92,800 psi. How does this help us?  The torque to achieve Y.S. can easily be established  by passing a spare fastener of type to be used thru a H/D spacer long enough to add a nut to other side of fastener on opposite side of spacer.

1.) Then just use your preferred fastener lube (ARP Ultra Lube in my case) on threads, under nut & under bolt head on top of hardened washer. Progressively torque nut at least 10 cycles to reach Y.S. 10 cycles is normally enough

      cycles to burnish & smoothen threads to insure friction is no longer a serious factor & that torque reading actually achieved clamp required.

2.) Measure bolt o.a. length with a mic. ,

3.) torque  nut till bolt permanently is stretched by .0005” i.e. .005” longer than 1st reading, i,e, till Y.S. is achieved. [b]Throw bolt away as it has permanently failed.                                                    [/b]

4.) Note torque reading necessary to achieve Y.S.

5.) [b]Example only: [/b]If X torque is needed to achieve Y.S. take 75% of X & use that torque figure to tighten your fasteners with same bolts i.e. if Y.S.is achieved at 100 ft. lb., use 75 ft. lb! This will achieve an acceptable preload clamp of 75% of fastener Y.S. [b]NOTE THAT THIS TECHNIQUE IS ONLY SUITABLE IF Y.S. OF FASTENER IS KNOWN OR CAN BE DETERMINED.[/b]  While Y.S. of any non ISO bolt can be determined using this system, it will only tell one what torque it takes to achieve Y.S.[b] It will not tell one how many P.S.I is achieved or grade of bolt[/b]! This system also works well with studs where “Stretch to Yield” cannot be easily determined w/o drilling hole thru length of stud & measuring stretch with a depth gage.

 

Bill

TC 4926

Odessa, Florida

 

[b]From:[/b] mg-tabc@yahoogroups.com [mailto:mg-tabc@yahoogroups.com] [b]On Behalf Of [/b]Gene Gillam [b]Sent:[/b] Tuesday, April 30, 2013 7:21 PM [b]To:[/b] MG-TABC Shade [b]Subject:[/b] [mg-tabc] Torque Values

 

 

I posted this on the TABC website but got few responses so I want to throw it out to everyone:  

"I've got a question on the torque values given in the Resource Technical Article file: [b]http://www.mg-tabc.org/library/torque.htm[/b] There it says that the 8mm rocker arm assembly bolts are to be torqued to 16 ftlbs. The MG Y-type forum ([b]http://www.mgccyregister.com/node/19016[/b]) gives the torque spec as 27 ftlbs. David DuBois ([b]http://homepages.donobi.net/sufuelpumps ... ngines.pdf[/b]) gives the torque spec as 19 ftlbs. I also have a question on the 10mm rocker arm assembly bolts...our site tech article gives the torque value as 43 ftlbs. David DuBois concurs, the Y-type forum gives the torque spec as 42 ftlbs but the MG Cars site ([b]http://www.mgcars.org.uk/imgytr/pdf/reassycheck.pdf[/b]) lists the torque spec as 30 ftlbs. I'm sure there's other discrepancies throughout the specs but these were the only two I was concerned with today. Can someone verify WHICH is correct...and if our site lists the wrong torque specs please correct it."

 

Tom Wilson responded with this for the immediate questions concerning the 8 and 10mm bolts:

 

"As a general rule I follow both what the MG specs are in combination with modern ISO specifications. More times than not they are comparable. So for an 8mm bolt dry is 19 ft pounds; a 10mm bolt 37 ft pounds. Preferred method (I believe) is lubricated with a light oil - the values are then higher.  [b]http://www.cncexpo.com/MetricBoltTorque.aspx[/b] for an example."

 

 

So, is there a comprehensive torque value guide for our engines that's correct or should I just use Tom's site and forget our Tech Article?

Thanks,

Gene