Big end bolt re-use

[Foxie]

I'd say on about the last half dozen rebuilds I've done on my all-steel 1798 twink, I've used a new set of ARP big end bolts. The directions say to measure each bolt length prior to fitment, to tighten to a specific stretch. Alternatively to tighten to 45 ftlb. (Previously the direction sheet said to tighten to torque 45 ftlbs and relax three times, but it my present rebuild, it only says to do it once)

It says if subsequently reassembling, to measure bolts , and not to re-use if the have permanently stretched over a specific amount.

As I do not trust myself to be able to accurately measure these very small differences, I have always opted for replacing the bolts each time, and using torque tightening.

However on my present rebuild, which I have been able to do without an urgent time deadline, I got to thinking.

If the bolts had stretched, I reasoned the original torque settings would have relaxed. Accordingly, before I unbolted the big ends, I put a torque wrench on each bolt, starting at 30 ftlbs, and working up in 5 ftlb steps.
I was pleasantly surprised to find the torque on every bolt was still 45 ftlbs, leading to the conclusion that none of the bolts had stretched. However, as I had already ordered a new set, I fitted these.

At my age, they may see me out

I would be interested to hear comments on this.

Sean

[rgh0]

Hi Sean

The ARP bolts can be reused if you wish to and normal they don't take a permanent stretch . The torque to release is one indicator of stretch but not a particularly accurate one. Measuring length before installation and re-measuring after removal is best but you do need the measuring tools to do it accurately.

Also best to use a stretch gauge for installation versus torque especially if you are using all the revs that you steel bottom end allows.

You must be doing a lot of miles if you have done 6 rebuilds of this engine

cheers
Rohan

[StressCraxx]

The ARP rod bolts are very, very good. They are much stronger than original. 45lbs/ft with lubricated threads and shoulder should give you 0.005 -.006" stretch. I have reused the ARP bolts in my Elan, using the bolt stretch gage. I recorded the length of each at the initial build, before installation and after. I re-measure during before dis-assembly and after. If they are still at their original length I re-install.

On my FF Kent motor, the rods get new bolts every time because of the amount of time the motor is at 6000rpm+ and my inevitable missed shifts.

I would not re-use the original Ford bolts.

[dougal9887]

Do I understand then that the Ford original bolts should not be reused on a standard road rebuild? How about the big end bolts?
Dougal.

[StressCraxx]

Do I understand then that the Ford original bolts should not be reused on a standard road rebuild? How about the big end bolts?
Dougal.

Hello Dougal,

I was told by both Dave Bean and the engine builder who helped me rebuild my engine many years ago (1982) to replace them. I replaced them with Cosworth rod bolts at the time. The Cosworth bolts were $1 a bolt cheaper than the Ford bolts! The ARP bolts are as good or better than the Cosworth bolts.

If I understand you correctly, the main bearing cap bolts are reusable.

[dougal9887]

Sorry, senior moment! I did intend to ask about the main bearing bolts.
Dougal.