Connecting Rod Pinch Bolts

[Robert Grunau]

I have used metric fine 8.0 x 1.0 x 30 mm long Allen head pinch bolts for many years on connecting rod little ends. I recently bought a new box of bolts in Metric grade 12.9, these are 170,000 psi strength bolts. I did some testing on the weekend, the grade 12.9 bolts are supposed to be 170,000 psi tensile strength. So I took an old bent XPAG rod and installed a wrist pin and new grade 12.9 bolt and torqued it up. While I torqued it, the overall bolt length was checked for stretch. These are the figure, if you are interested: Bolt torque- ft-lbs Bolt length- inches 1 0 1.692 2 20 1.692 3 25 1.692 4 30 1.692 5 35 1.692 6 40 1.696 7 41 1.694 8 42 1.695 9 43 1.698 10 44 1.705 11 45 1.705 12 45 1.706 13 46 1.713 At this torque I had buggered up the socket hole so could not get more readings. So took a new bolt and torqued it to failure. At 49 ft-lbs it was starting to really stretch, ie lots of torque wrench movement before it finally "clicked" to the 49 ft-lbs . Then at 49.5 ft-lbs the bolt broke. There was some stretch at the failure point but not much. Torque wrench used was a 3/8" drive fairly new click type Snap-On. No doubt you will note the length numbers are not entirely consistent, but that's what I measured with my digital calipers and an error of several thou. is quite possible due to "measuring error". The important part is the general trend, ie no stretch till 40 ft-lbs. So I guess this shows the BOLT would be good for at least 33 ft-lbs on a connecting rod pinch bolt application as recommended by MG Car Co. Bob Grunau.

[Skip Kelsey]

Bob: My machine shop recommended using 25 lbs torque on either the socket headed or the standard pinch bolt. That is what I have used for many years with no problems. Skip............................ At 05:22 PM 5/1/01, Robert Grunau wrote:

>I have used metric fine 8.0 x 1.0 x 30 mm long Allen head pinch bolts for >many years on connecting rod little ends. I recently bought a new box of >bolts in Metric grade 12.9, these are 170,000 psi strength bolts. >I did some testing on the weekend, the grade 12.9 bolts are supposed to be >170,000 psi tensile strength. So I took an old bent XPAG rod and installed a >wrist pin and new grade 12.9 bolt and torqued it up. While I torqued it, the >overall bolt length was checked for stretch. These are the figure, if you >are interested: > Bolt torque- ft-lbs Bolt length- inches >1 0 1.692 >2 20 1.692 >3 25 1.692 >4 30 1.692 >5 35 1.692 >6 40 1.696 >7 41 1.694 >8 42 1.695 >9 43 1.698 >10 44 1.705 >11 45 1.705 >12 45 1.706 >13 46 1.713 >At this torque I had buggered up the socket hole so could not get more >readings. So took a new bolt and torqued it to failure. At 49 ft-lbs it was >starting to really stretch, ie lots of torque wrench movement before it >finally "clicked" to the 49 ft-lbs . Then at 49.5 ft-lbs the bolt broke. >There was some stretch at the failure point but not much. Torque wrench used >was a 3/8" drive fairly new click type Snap-On. >No doubt you will note the length numbers are not entirely consistent, but >that's what I measured with my digital calipers and an error of several >thou. is quite possible due to "measuring error". The important part is the >general trend, ie no stretch till 40 ft-lbs. >So I guess this shows the BOLT would be good for at least 33 ft-lbs on a >connecting rod pinch bolt application as recommended by MG Car Co. >Bob Grunau. > > > > > > >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

[joecurto@aol.com]

This bolt stuff is interesting and we all know that MG and the rest of the British car industry had a lock on "rubber" bolts, and I too am running Allen cap bolts on little end and MGB bolts on big end, but least we not forget that the reason that all this works, ( in all engines) is that most of the forces on the rods are on the beam in compression, and while tension plays a part it, I do not think is the dominant force, When they went to higher revs and added more compression than rod design changed a lot, the pinch bolt disappeared, the rod bolts got stronger and bigger the beam got heavier, so we are back to making a prewar engine do things it was never intended to do. Even MG must have known something was up as I reckon that there are at least 4 different rod sizes, TC being the most spindly and TF 1500 being the strongest(?), just ask anyone who tries to balance a T series engine, I used to send out a set of rods and give another 4 or five to the balancer so he could match rods instead of grinding the pants off of the mismatched set. If we all remember those engines that we disassembled in years past with the cotter pinned nuts where they were stretched beyond belief and the shop manual advice to torque to 25 ft pounds (?) and then go to the next split pin hole well boys if you want to see stretch follow that advice. Joe curto

[plus4moggie54]

Can anyone remind me of the necessary specs for replacing the pinch bolts with Allen screws? I vaguely seem to remember that they are 8x1mm, but don't remember the grade required. Also, does anyone have a source for the small washers? Many thanks. Tom TB0327

[David Lodge]

Does anyone know which way the mirror bits go back together, specifically the mirror/card/bracket thingies that the four screws go into? Regards, Lodge

--- On Sun, 25/10/09, plus4moggie54 tlange@acadia.net> wrote: From: plus4moggie54 tlange@acadia.net> Subject: [mg-tabc] Connecting Rod Pinch Bolts To: mg-tabc@yahoogroups.com Date: Sunday, 25 October, 2009, 2:22 PM Can anyone remind me of the necessary specs for replacing the pinch bolts with Allen screws? I vaguely seem to remember that they are 8x1mm, but don't remember the grade required. Also, does anyone have a source for the small washers? Many thanks. Tom TB0327 [Non-text portions of this message have been removed]

[John Stone]

I don't remember the specs any more but I got mine from Shade Tree motors in California. Be sure to torque them to the proper spec. I have heard that more engines fail because these bolts break or come loose. John Stone TC 2433

[Roger Furneaux]

hi Tom - the thread is indeed 8x1mm, as are most other fixing on the engine which would have been 5/16" BSF on any other British car. The Allen head bolts need to be of 12.9 grade, the highest available. Originals are 32-33mm long with 20-21mm of thread, but a modern Allen head will be 30mm, and you will be very lucky to find any with some plain shank. The washers are standard square section spring washers. I normally stock both, but am currently looking for more bolts. ocTagonally TCRoger Tom Lange wrote:

> Can anyone remind me of the necessary specs for replacing the pinch bolts

with Allen screws? I vaguely seem to remember that they are 8x1mm, but don't remember the grade required. Also, does anyone have a source for the small washers?

[laf48@aol.com]

www.metricmcc.com. They are world wide. Len Fanelli [Non-text portions of this message have been removed]

[Peter Cole]

Roger, Try Non Standard Socket Screws Ltd at http://www.nssocketscrews.com/index.php/html/ They make standard and non-standard cap head screws. Regards Peter. 2009/10/28 Roger Furneaux roger.46tc@virgin.net>

> > > hi Tom - the thread is indeed 8x1mm, as are most other fixing on the engine > which would have been 5/16" BSF on any other British car. > > The Allen head bolts need to be of 12.9 grade, the highest available. > Originals are 32-33mm long with 20-21mm of thread, but a modern Allen head > will be 30mm, and you will be very lucky to find any with some plain shank. > The washers are standard square section spring washers. > > I normally stock both, but am currently looking for more bolts. > > ocTagonally > > TCRoger > > Tom Lange wrote: > > > Can anyone remind me of the necessary specs for replacing the pinch bolts > with Allen screws? I vaguely seem to remember that they are 8x1mm, but > don't remember the grade required. Also, does anyone have a source for the > small washers? > > >

[Non-text portions of this message have been removed]

[JohnM]

I have a set of 8mm x 1 socket head pinch bolts from Bob G. I was wondering how you are safeting yours? Bob? There are the original lockwashers. I suppose red high strength Loctite would work. I doubt the area would get hot enough to soften it. One could drill the top edge of the sockets and use Aviation safety wire. Thanks, John TC6338

--- In mg-tabc@yahoogroups.com, Peter Cole wrote: > > Roger, > > Try Non Standard Socket Screws Ltd at > http://www.nssocketscrews.com/index.php/html/ > > They make standard and non-standard cap head screws. > > Regards > Peter. > > > > 2009/10/28 Roger Furneaux > > > > > > > hi Tom - the thread is indeed 8x1mm, as are most other fixing on the engine > > which would have been 5/16" BSF on any other British car. > > > > The Allen head bolts need to be of 12.9 grade, the highest available. > > Originals are 32-33mm long with 20-21mm of thread, but a modern Allen head > > will be 30mm, and you will be very lucky to find any with some plain shank. > > The washers are standard square section spring washers. > > > > I normally stock both, but am currently looking for more bolts. > > > > ocTagonally > > > > TCRoger > > > > Tom Lange wrote: > > > > > Can anyone remind me of the necessary specs for replacing the pinch bolts > > with Allen screws? I vaguely seem to remember that they are 8x1mm, but > > don't remember the grade required. Also, does anyone have a source for the > > small washers? > > > > > > > > > [Non-text portions of this message have been removed] >