Propshaft bolts
Discussion
andyy said:
Whats the 8.8, 10.9, 12.9 mean ???
V8 Animal - does your Chim have the toothed wheel for the speedo clamped between the prop and the diff ??
My Griff does which would make standard length bolts about 5mm too short !!!
1. Its an ISO standard, basically different materials. The tensile strength goes up, as does the hardness. IMHO the harder materials are more likely to fail in shear, hence my general preference.V8 Animal - does your Chim have the toothed wheel for the speedo clamped between the prop and the diff ??
My Griff does which would make standard length bolts about 5mm too short !!!
2. Mine too.
3. standard length bolts?
Dave
8.8, 10.9 and 12.9 are all metric material grades for bolts
Thing is Dave the bolts shouldn't be loaded in shear.
You don't drive the prop though the bolts, its through the friction generated between the clamped surfaces.
Consequently use a high strength bolt like an Unbrako to jeff it all up tight and generate the most clamping.
8.8 can take 830N/mm2
whereas 10.9 will 1000N/mm2 take before yielding
and 12.9 will go 1200N/mm2
see here for useful identification info:
http://www.engineersedge.com/hex_bolt_identificati...
As the bolts are probably imperial look for something with a set of lines on top of the hex, one for each corner is best
These bolts should be TIGHT
Best of luck
Matt
Thing is Dave the bolts shouldn't be loaded in shear.
You don't drive the prop though the bolts, its through the friction generated between the clamped surfaces.
Consequently use a high strength bolt like an Unbrako to jeff it all up tight and generate the most clamping.
8.8 can take 830N/mm2
whereas 10.9 will 1000N/mm2 take before yielding
and 12.9 will go 1200N/mm2
see here for useful identification info:
http://www.engineersedge.com/hex_bolt_identificati...
As the bolts are probably imperial look for something with a set of lines on top of the hex, one for each corner is best
These bolts should be TIGHT
Best of luck
Matt
Edited by 350Matt on Sunday 30th March 12:45
350Matt said:
8.8 can take 830N/mm2
whereas 10.9 will 1000N/mm2 take before yielding
and 12.9 will go 1200N/mm2
Also they correspond to something like C23,C33,C38 Rockwell Hardness test, implying a different crystal structure. In my mind these things are just far more liable to developing stress cracking in use.. whereas 10.9 will 1000N/mm2 take before yielding
and 12.9 will go 1200N/mm2
The figs you quoted are material properties, the bolts are sized according to these properties (830N/mm2 * dia of bolt). If the original spec is an 8.8 bolt, then a smaller bolt dia would have been specced in 12.9. What material spec were the bolts that left the factory?
Dave
The Prop bolts on my last 3 TVR's all had the double lines on top of the Hex ( one line to each corner) this means they are a grade 8 imperial fastener or 10.9 in metric terms
And you only tend to get fatigue / stress cracking in parts which move. Even at a micro-vibration level. I would say a bolt under 12 ton of tension will move less than one at 9 ton of tension. But then you can't tighten an 8.8 bolt to 12 ton.....
Still fit what you like its your car
Matt
And you only tend to get fatigue / stress cracking in parts which move. Even at a micro-vibration level. I would say a bolt under 12 ton of tension will move less than one at 9 ton of tension. But then you can't tighten an 8.8 bolt to 12 ton.....
Still fit what you like its your car
Matt
spend said:
In my mind these things are just far more liable to developing stress cracking in use..
That doesn't make sense to me. Since they're loaded in tension, raising the tensile rating of the bolt is likely to reduce the risk of stress related problems. Stress cracking would only be an issue if the bolt was being overloaded.All very interesting...
Generally as a rule of thumb around these sizes, a 12.9 will only have equivalent tensile strength to the next size of 8.8 I believe. I hear many stories about affects of heat on 10.9/12.9, and complaints that they are very hard to assemble. I just don't see the need for the extra tensile strength (per mm2) unless thats the way it was originally designed / specified
Maybe I'm wrong, but I always view the higher tensile strength along with the extra hardness (Rockwell figures). To me this just suggests that the material will be more brittle.
On a practical note I am not even sure you will find it possible to source much else than common 8.8 in Imperial, never mind fine pitch UNF? unless you have them specially manufactured.
Dave
..but I am an old fart who still believes that pairing weaker nuts with stronger bolts was good practice
Generally as a rule of thumb around these sizes, a 12.9 will only have equivalent tensile strength to the next size of 8.8 I believe. I hear many stories about affects of heat on 10.9/12.9, and complaints that they are very hard to assemble. I just don't see the need for the extra tensile strength (per mm2) unless thats the way it was originally designed / specified
Maybe I'm wrong, but I always view the higher tensile strength along with the extra hardness (Rockwell figures). To me this just suggests that the material will be more brittle.
On a practical note I am not even sure you will find it possible to source much else than common 8.8 in Imperial, never mind fine pitch UNF? unless you have them specially manufactured.
Dave
..but I am an old fart who still believes that pairing weaker nuts with stronger bolts was good practice
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