Commando Mark 3 big end bolts

I put new big end nuts and bolts in the engine when I first rebuilt the engine. Unfortunately, not long after I got it up and running I had to strip the engine again.

The engine was only running for about 15 minutes but opinion seems to be divided about whether the old bolts are still useable or if new bolts are required.

It's about £30/$45 for a set of bolts which I could use for other items if I didn't need to replace the bolts but I don't want to compromise the next built by cutting corners.

The nuts should be replaced.
The bolts should be fine -if they were good ones when you installed them. Running them for a short time and re-torquing them would be of no concern. Jim

Just to add to the point of replacing the nuts: years ago I sold fasteners and one of our sales tools involved showing customers what happens when you torqued up a bolt and nut. We used a piece of equipment that registered the force exerted by the nut and bolt when torqued properly. Typically we used a 3/8 grade 8 (I think, but it might have been a higher grade) bolt and when torqued correctly it gave a reading of 9,000 psi. Then the nut was loosened and retorqued. It usually gave a reading of about 6,000 psi. If the nut was flipped around and retorqued it again gave a reading of 9,00 psi. This was due to deformation of the thread during the initial torqueing.
Dim memory but I seem to recall that the point of the exercise was to show the importance of using high grade nuts and how thread condition affected torque values. Just an FYI

Thanks. I will order up some new nuts and try and get this engine back together again.

I've always reused the bolts but never the special nuts. If you look closely at them there are 2 slots cut in that spread out a bit in use to help grab and not back off. One time useage.