Broke A Connecting Rod Bolt. Really Confused?

Discussion in 'Fox 5.0 Mustang Tech' started by tacomatrx450f, Jun 9, 2013.


  1. tacomatrx450f

    tacomatrx450f Member

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    i just got my lower engine block from the machine shop, and i wanted to make sure they torque down the connecting rod bolts, and the stupid haynes manual said to torque to 45 ft lbs, and i ending up breaking one of the two bolts. im really confused because i have been reading that i have to have them resized now? i dont get why if its just a bolt? cant i just press in another bolt and be done with it? im talking about the bolts that are pressed into the connecting rod. just to make sure. so now, as im crying...... i scratched the crack shaft in the picture shown.. is this something i will need to take to the machine shop now? or how bad is it? can i fly with it?



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  2. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    I wouldnt have thought the bolt would have broken at 45ftlbs however spec on stock rods is 25ftlbs...personally I'd replace them all with ARP bolts the weak link in the stock bottom end is the rod bolts. With overtorquing that rod it may be out of round. I can't see any lube on them in the photo make sure you are using Moly lube or oil on the threads and under the bolt head.
    Yes the proper way is to install the new bolts, tq the cap down and check them for roundness and proper size, if they are round and in range you would be good. If not like most cases the caps are slightly cut and the rods get honed to spec.

    Personally it is not worth the cost of the bolts and machine work to resize that stock rod it will cost you at least $150-200. For a little more you can purchase a stronger aftermarket connecting rod but the balance may need to be adjusted. However in your case that may be overkill.

    If your just trying to do a stock like rebuild talk to your machinist about replacing the bolts. I'd just be skeptical replacing that one of it broke that easy...

    Now as far as the scratch grows if you can feel it with your fingernail it may need some attention otherwise it will be fine or you could polish with some ultra fine crocus cloth



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  3. tacomatrx450f

    tacomatrx450f Member

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    thanks for the help, i was able to polish it out over night, and i think i will go with the arp bolts, i always have the worse luck when torques.

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