Hi all,
I am building up a 1957 motor from parts and am wondering if anyone knows the correct fit for the 5/16" big-end bolts, sorting through my collection of con rods with a set of NOS bolts they range from slack to a tight interference fit, in fact some don't want to know at all, if I need to ream them out I'd rather have the right fit if possible.
Thanks a lot,
cheers,
Niall
The bolts have to be be to…
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On all the twin engines I…
On all the twin engines I have worked on, these bolts have always been a very close fit. But not an interference fit. Usually the end caps have needed a physical nudge to help part them from the rods but nothing drastic. Whenever possible I have reused the orignal bolts and sometimes the nuts as well if they appear to be a good fit on the threads. Always check the bolt threads carefully. If they show any signs of stretching then bin them. Also get a good, accurate torque wrench for tightening downthe nuts. Most car torque wrenches are horribly inaccurate below 30 ft lbs. The smaller twins only need 15 ft lbs.
If you can do so, then watch the engine rebuild video made by John Hudson about Norton twins. He answers most of the questions asked about these items.
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Don't know what happened…
Don't know what happened there. Windows 8. I meant to add as I know there have been some inferior bolts sold in the past.
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Thanks fellas, I was talki…
Thanks fellas,
I was talking about variation in the receiving bore of the conrod, the bolts I was using as a gauge are original Norton ones, unused, one pair of rods would not accept them at all, the pair of bolts in them were .012" less on the major diameter which makes the fit.
So they must have been selectively assembled when new.
I'm just going to ream them out to a very light interference fit at about 20 degrees C
Cheers.
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The bolts have to be be top quality.