We had a good example of the law of unintended consequences......
Having made the head brace, it soon became clear that spark-plug access was now impossible! I really didn't want to be taking the tank off to get at the plugs, so drastic action was called for:
Getting the holes in the right place was ummm.. interesting!
Been making a lot of small uninteresting stuff this week, all the head studs & nuts for example:
Made the studs from grade 12.9 allen bolts. Cut the heads off & screwcut 10x1mm threads. I wanted to use fine threads to keep the root size as big as possible, what with cut threads being less good than the rolled (10x1.5) threads, so that the ones I cut were stronger than the factory rolled threads.
I made a few more than needed (bound to lose some nuts
) So I did a bit of testing. drilled & tapped a 10mm thread thru a bit of 1" ally plate, screwed a stud in and with a spacer to replicate the head thickness, I set to with the torque wrench & micrometer.
Interesting; at 20 ft-lbs, the stud stretched .003". At 40 it stretched .005", 48 = .006". And so on every 5 ft-lbs or so stretched it another thou.
Each time, I slackened it off before the next 'pull'. At 60 ft-lbs the stud had permanently stretched half a thou, the point at which ARP fasteners reckon a fastener should be scrapped.
Kept on at it, to try & make it fail. 80 ft lbs pulled the stud .011" but it never made it to 90.
It broke where you'd expect, at the end of the coarse thread. My cut threads came thru OK. At all times, there was only 1xD of thread engagement in the nut.
So; conclusions: the studs are good enough for the job, and to get the optimum stud-stretch, which is 6 thou, a torque of 40-45 ft-lbs is needed. The thermal expansion of the ally head means we should stay on the cautious side.
The head hold-down is now almost finished. RH side yet to complete. Heres the LH:
Got started on the inner timing cover today. A bit time consuming doing all the holes. Here I am doing the hole for the intermediate pinion bush:
