Page 1 of 2
Connecting Rod Pinch Bolts
Posted: Tue May 01, 2001 7:10 pm
by 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.
Re: Connecting Rod Pinch Bolts
Posted: Wed May 02, 2001 7:19 am
by 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/
Re: Connecting Rod Pinch Bolts
Posted: Fri May 04, 2001 5:27 am
by 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
Connecting Rod Pinch Bolts
Posted: Sun Oct 25, 2009 7:22 am
by 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
Re: Connecting Rod Pinch Bolts
Posted: Sun Oct 25, 2009 12:22 pm
by 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]
Connecting Rod Pinch Bolts
Posted: Mon Oct 26, 2009 7:58 am
by 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
Re: Connecting Rod Pinch Bolts
Posted: Wed Oct 28, 2009 3:30 pm
by 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?
Re: Connecting Rod Pinch Bolts
Posted: Thu Oct 29, 2009 3:13 am
by laf48@aol.com
www.metricmcc.com. They are world wide.
Len Fanelli
[Non-text portions of this message have been removed]
Re: Connecting Rod Pinch Bolts
Posted: Thu Oct 29, 2009 6:11 am
by 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]
Re: Connecting Rod Pinch Bolts
Posted: Fri Oct 30, 2009 8:10 am
by 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]
>