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Rod bolt stretch

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dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 ·

#450393
When using these type of rod bolts, the manufacturer says to check that the free length
of the rod bolt should not change by more than one thou after use.
The two on the right are past their use-by date. You can see that they are thin in the middle from permanent yield.
When tensioned correctly, the bolts will stretch around 6 thou (depending on specific bolt),
but return to its original length when removed....unless it is no good.
The tension to acheive this stretch will vary depending on the thread lubricant,
but the end result for stretch must be within the manufacturers specified stretch tolerance.
These particular bolts are tensioned to 45ftlbs with moly lube to achieve 6 thou stretch.
Normal oil on the thread may require 55ftlbs to get the same 6thou stretch.

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westi wrote:That's mad Alan.

1500S Custom Title Time!

1,418 posts · joined Mar 2005 ·

#450556
Under the head MUST also be lubricated otherwise you will get a false torque reading no matter what lubricant you use on the thread!



[ Edited on 24/1/2006 by 1500S ]

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 ·

#450665
Yes, I should have made that clearer.
Also, no nut or bolt should ever be assembled without some form of lubricant
on the thread and under the clamp face of the nut (or bolt in the above example).
Although that being said I would use lubes very spareingly around the clutch
and flywheel area to stop contamination.
On flywheel to crank assembly, I use lube on the threads and under the head(s) of the fasteners,
and then wash everything after tensioning, and before the clutch is installed.
Perhaps others might like to share some input on this topic.
westi wrote:That's mad Alan.

1500S Custom Title Time!

1,418 posts · joined Mar 2005 ·

#450729
Just thought I'd add that bit for you as over the years, too many think that everything is better clean and dry. We found in prac demonstrations that the most friction seemed to be the contact face of the nut or bolt head with the mating face. Plenty of heads leaking in the past due to reduced torque on head nuts. The @#%!! Ford alloy heads have no seperate washer between the bolt head and head and there is noticeable scoring on some engines where there has been lack of lubrication during assembly. Also, aftermarket bolts have a larger integral washer which can add to the friction in initial torqe sequence.

DH