3.9 Heads Bolt

lollorock · Post by **lollorock** » Wed Jul 23, 2014 7:34 pm

Hi everyone,
Are the head bolts of a 3.9 V8 (RRC MY 90) are in strenght class 10.9 or 12.9?

Thank you!

SuperV8 · Post by **SuperV8** » Thu Jul 24, 2014 9:43 am

The head bolts are imperial (7/16 UNC) and I don't believe the property class 10.9/12,9 applies to imperial bolts!

Tom.

lollorock · Post by **lollorock** » Thu Jul 24, 2014 11:22 am

Are you sure?

I have got some 7/16 UNC bolts with "8.8" on the top

SuperV8 · Post by **SuperV8** » Thu Jul 24, 2014 1:13 pm

Are you sure they're not SAE grade 8? which is different to 8.8
SAE grade 8 is equivalent to 10.9

This link shows the Standard Specification for Carbon and Alloy Steel Externally Threaded Metric Fasteners. It defines mechanical properties for fasteners that range from M1.6 to 100 in diameter
http://en.wikipedia.org/wiki/ASTM_F568M

This link shows 7/16 unc bolts under the heading 8.8 but they are actually grade 5
http://www.margnor-online.co.uk/bolts/8-8bolts/unc?p=3
http://www.imperialnutsandbolts.com/fas ... t_251.html

For an example:
If they were 8.8 then they have a min tensile strength of 116,030psi.
12.9 have min tensile strength of 174,045psi
ARP head bolts for example are rated at 200,000psi
I don't know what the standard head bolts tensile strength is?

Tom.

lollorock · Post by **lollorock** » Thu Jul 24, 2014 3:08 pm

Unfortunately are 8.8

Is dangerous use just one 8.8 (the rest of 13 bolts will be the originals) for few time in the head?

SuperV8 · Post by **SuperV8** » Thu Jul 24, 2014 3:39 pm

For the cost of just one bolt I personally I would just buy a new bolt.

lollorock · Post by **lollorock** » Thu Jul 24, 2014 3:48 pm

yes, absolutely.

The problem is that: I live in Italy and the 7/16 UNC in 10.9/8 class are impossible to find.

I can order it online (i.e, paddockspares) but it is a special order and with the summer the deliver will be to far

And i need to use the RRC for work just few days

SuperV8 · Post by **SuperV8** » Fri Jul 25, 2014 7:48 am

Do you have a local land rover dealer you could check?

One thought, which of the bolts are you missing? If it's one of the shorter outside bolts these are not used on later engines and not required.

Tom.

lollorock · Post by **lollorock** » Fri Jul 25, 2014 11:30 am

SuperV8 wrote:Do you have a local land rover dealer you could check?

Done: 15-20 working days to have it:oops:

SuperV8 wrote: One thought, which of the bolts are you missing? If it's one of the shorter outside bolts these are not used on later engines and not required.
Tom.

Yes, i know about it but unfortunately it is one of the three long