Hi, Can anyone give me a bit of guidance regarding the 11/16th 20 tpi thread that the barrel studs screw into on the crankcase top. On my crankcases they are braking away in sections. The nut will screw in but I am unsure how strong they will be when tightened. I think a thread repair is required but what an odd thread? I cant find a heliciol kit so how have other owners repaired these please. I have found a tap from China at a very reasonable price but of course this can only clean the threads out to assist assembly.
Cheers Staffs
I have sourced normal taps from Tracy tools https://www.tracytools.com/index.php?route=product/product&product_id=1004
cant find a helicoil or insert, maybe have a word with an engineer and if room ap out bigger and fit a plug that can then be drilled and tapped to correct. we used to do under concession on compressors and other ally castings.
Thanks Chaz, I am that engineer and hoped there was a quick fix with a helicoil. I will look at fitting flanged bushes from the underside and either pinning them or welding them in place so they do not turn. Is there a torque setting for the bolts or is it "just tight enough"?
Staffs
when we repair its usually opened out to a bigger thread with a fine (usually 20 or 26tpi) thread, a plug made up to suit then loctited in and a dowel fitted half way through thread and body. then re finished as required. if not on a machined face it could be welded to secure and then blended.
as for torque, I find there are many references to torque values BUT you have to remember that , that was fine on new castings 50 years ago but on a modern day restoration I would use a bit of caution, near should do , it could always be nipped up if needed. todays gaskets and sealers are a bit more forgiving.
we have been helicoiling for years, and I have collected most of the tools and inserts the company had as no longer needed, our main product uses MM threads, Armstron are the original ones used and their download centre has more info including the rivnuts discussed on another thread. https://www.boellhoff.com/gb-en/support/download-centre.php
imperial inserts
https://media.boellhoff.com/files/pdf1/helicoil-plus-imperial-en-0101.pdf
Ive had a look through and closest I could find was 5/8 x 20 UNEF
11/16 x 20tpi is an Admiralty Fine thread. Usually used on pressure gauges and glands. The rear axle on an A10 is the same thread which is why Whitworth, nor AF spanners will fit it. I downloaded a load of data on threads from this site - http://www.oldengine.org/members/diesel/front.htm - which deals with old engines - interesting from an engineering point of view. The site may be able to help with thread cutting gear. Attached pdf of the relevant section of the thread tables (can't post everything as there are 117 pages.
the serious bible for engineers, Ive got 3 copies, covering threads. tapers, gears anything engineering workshop
https://www.ebay.co.uk/itm/Machinerys-Handbook-Eighteenth-Edition/153807965031?hash=item23cfab4b67:g:7kUAAOSwx5VeIhpC
there are a few on the bay , years ago they were a supervisors property and dearer than now
Thank you. I shall spend a bit of time looking at various possibilities, I do like a challenge. If and when I come up with something I will post it here.
Thanks again. Staffs
Hi,
Do you have a parts book? They usually have the thread spec. with the part number. If not, have a look to see if Draganfly have it on their website.
Dave.
Yes got a parts book will check it out thanks Staffs