Norton exhaust port thread 1
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- Опубліковано 25 сер 2024
- The first in a series on repairing the exhaust port threads on a Norton head. In this part the head is bored and re-threaded to 2.1/8 x 16 as an oversize ready to fit an insert. Setup and material options are shown and discussed.
For this particular job and enviroment - the bronze insert every time.
Carry on the good work.
Thanks for watching and commenting, I hope to try this type of repair in bronze soon.
This is a great video with very useful information. I'm in the middle of sorting out this procedure for two Norton Commando cylinder head exhaust port threads (total four ports). The price of the tap is out of the question for me, so I've decided to attempt doing this by mounting the heads fixtured onto the lathe's cross-slide and hold the boring bar/threading tool in the lathe's chuck. I'll machine the inner and outer threads of the inserts (bushings) on the lathe as well. Wish me luck! Keep up the good work, I learn a lot from you!
Many thanks for sharing your ideas and great comments
Sempre in gamba il nostro William, direi perfetto.
Una grande professionalità a disposizione di tutti i Motociclisti. BRAVO
Grazie per i gentili commenti, i migliori auguri, Ade
Face off, run in with an end mill, on a circular interpolation, bottom face, run in with a thread mill, job done. I get the bore welded up, then run the threading programme, works a treat..
More set up than machining, machining takes less than a minute, but thats CNC.
Many thanks for your thoughts and comments, appreciated
as always beautiful art work at your shop
Rahul thank you.
very neat ..... just off to watch the next un
Cheers Andy, thanks for watching.
Hi, Ade. Thank you for this video. It's very nice work you're doing and this repair looks quite sturdy.
I'd like to comment on materials. The Norton cylinder head is made from RR53B alloy. The RR alloys were developed by Rolls Royce for aircraft engine use in the 1930 and contracted to a company "down South" called High Duty Alloys; thus the RR series of special alloys are sometimes called "HiDuminium" alloys.
RR53B was originally designed as a piston alloy. It is a casting alloy, has high strength (after fairly complicated heat treatment post-casting), and is very stable under heat; all these qualities make it very suitable as a cylinder head casting material. After post-heat treatment, it's harder than an Inland Revenue agent's heart, but it's rated as a "moderate difficulty" machining quality alloy. You chose 6061 as your insert material. It is a quite different allow from RR53B, but it's probably a good choice. You chose 6061-spec alloy for the insert -- 6061 is a modern high-strength alloy and there are a number of specialist heat treatments (designated by "T-" suffix numbers).
Here are relative specs for materials for RR53B and 6061.
Composition, R.R.53 B 6061
Aluminium 92.8% 95.8 - 98.6
%
Chromium 0% 0.04 - 0.35
%
Copper 2.5% 0.15 - 0.4
%
Nickel 1.5% 0%
Iron 1.2% Max 0.7
%
Silicon 1.2% 0.4 - 0.8
%
Magnesium 0.8% 0.8 - 1.2%
The things that jump out at me are that total alloying metals in RR53B are about twice as much by %-age as 6061, i.e. 7% total alloying metals for RR53B versus aboout 3.5% for 6061. The copper and magnesium spec for RR53B is right in the middle of the 6061 spec and RR53B calls for more nickel, iron, and silicon.
It seems to me - despite the variations in spec on paper - that the use of 6061 is a good choice. I've also looked at the comparison in strength between the two alloys; taking slight differences in test procedure and nomination between the RR spec and the American 6061 spec, it appears that RR53B has "Max Stress" strength of 52 tonnes and 6061 has "Ultimate Yield Strength" of 44 tons. On paper, that would make RR53B perhaps 20% stronger but I think this is little significance; both are modern, high-specification alloys and I see no reason that they should not be compatible for this use. One small issue is the spec of heat treatment of the 6061; I'd look into specs for the various "T-" numbers and look for suitable strength, brittleness, and ease of machining for the 6061 material used in "production work". (The "Aluminum Association" rates both alloys as 50 on the scale of 1 -100 for ease of machining -- not the easiest to machine but certainly not unreasonably difficult.)
A factor that might be considered is thermal expansion, specs for which I could not find. I would guess (only a guess, mind) that it's likely that 6061 would have slightly more thermal expansion than the RR alloy specifically designed to have low expansion and high thermal stability but the relatively thin wall of the insert makes any difference likely to be insignificant. If the insert were thicker, I'd want to look at the head to check for expansion cracks and the pipe nut for signs of "clamping" during running-in, but I am strongly of the opinion that for the thin insert, there should be no practical effect at all. It also appears to me that there should be no issues with the head expanding away from the insert, causing it to loosen in service.
I agree with your assessment that it would be good to look at the depth seating of the insert and align threads so that the insert sits as firmly in the bottom of the bore in the head as possible but there's the flange on the exhaust pipe there so a small gap should be no issue.
One question that comes to me is "why did the threads strip in the first place?" Were the nuts chronically overtightened, either when first done up or over a service period? Or was the bike run with loose nuts that allowed fretting? Or did dis-similar metal corrosion mean that there was damage to the threads that was exacerbated when the nuts were undone? It would seem to me that it might be good to look at the factors in service on all Norton heads to prevent damage. I'd also consider a high-temperature "anti-seize" compound, such as specified for cylinder head studs or exhaust manifold fittings, on the pipe nuts to prevent corrosion between the metals. Your choice of the bonding material "Loc-Tite" for the insert into the head appears suitable and useful.
Finally, I'd like to commend you on your quality of planning, setup of your machinery, choice of tools, and skill of workmanship. It's a very good job, indeed.
Oh, and the second "Norton Head" video seems to indicate that there's a third in the series but I wasn't able to find it. Is there a followup after the second? Thanks.
Hi, thank you for the comments and research, absolutely brilliant stuff! Norton heads were well known for stripped exhaust threads, likely a combination of the design for the period, vibration, lack of checking by owners during use, the correct C spanner not usually being owned by the rider, thermal cycling and other factors. The 2 videos I did a while ago were the first experiments to see if I had the ability and capability to do this job. When I worked as a motorcycle mechanic in my 20's I was always impressed by some of the repairs the shop had contracted out and it gave me a desire to want to be able to do some of these things myself, some of what you see on my channel is me doing just that. The 3rd instalment has not been done yet, I've had a bit of a hiatus from the channel, we've extended the house, done some much needed repairs and improvements,decorated etc and along the way I have changed jobs (twice) so the time has not been available for UA-cam video's unfortunately. There are some bits and bobs on Instagram (a_g_engineering).I hope that 'normal service' will be resumed shortly! Thanks for watching, commenting etc, regards, Ade.
If you touch the gasket surface floor with the cutter the gasket surface is true.I repair them on my lathe or ON THE BIKE! Bronze is better but very expensive to buy.Norvil have aluminum inserts ,but getting the tap is the trick. 50 yr pro- Sundquist Norton - you tube. 2019
Thanks for watching Dave, I've just started looking through some of your interesting videos. I'd be interested on how to repair exhaust threads on the bike? Best wishes, Ade
Where'd you get that tap?
Probably a boot sale, ebay or auto jumble, just have to search for them and eventually you could find something affordable second hand. Thanks for commenting 👍
👍
Thanks for watching Alan, hope you are well.
Hi there. Do not know enough about materials,but you cut that dry. No fluids of any kind. Is there any cutting agent that would help? If you found a way to mount an old style long door spring on the quill handle,would that then allow you to use both hands turning that massive tap ? Is there an easy homemade two handed tap handle you could create without too much time or grief? Thanks for recording this.
Boring or turning with Korloy AK inserts especially on cast aluminium works fine without lube, and the same with the 6061 used for the inserts in part 2 on the lathe, as we are not after a super fine finish at this stage. I do use lubricant for the tapping process and on the lathe when threading. Maybe a bungee cord or something may come in useful on the quill handle next time, good thought. I've actually got a couple of tap wrenches to suit, just not got round to making shorter handles yet. Thanks for the comments, best wishes, Ade
A G Engineering Appreciate the reply.
how much for you to do one port on a 750 Commando head for me
Thank you for your message. Unfortunately I am unable to assist at this time due to other commitments. Many thanks for watching and commenting, Ade
@@AGEngineering thankyou for your reply, could you perhaps let me know what the correct size tap would be for the internal thread, I know they are quite expensive but after watching your very informative video I feel quite tempted to maybe give it a go, although not the quality of your equipment I do have a Mill and a lathe.
Bear with me, I'll let you know 👍🏼
@@AGEngineering is It a 2'' 14 TPI for the original thread? because if it is I can get one, plus its a thread plug non tapered one, oh lord I asked that question on my daughters youtube account... lol
It's 1-15/16" x 14 tpi uns unfortunately, I bought one from China and it was about £80 all in if memory serves. I think for the external thread it was 2-1/8 x 16. But the external thread depends on the amount of damage to a degree
Too bad a "two stud" system wasn't used instead. A lot less trouble
It can be easier to fix studs when broken for sure. Funny how evolution in design often finds a simpler, sturdier solution.