By continuing to use this site, you agree to our use of cookies. Find out more

Member postings for Jeff Austin 1

Here is a list of all the postings Jeff Austin 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: Boring bar size ?
31/01/2021 19:10:01

Thanks JasonB

Actually I do have a four jaw chuck for my lathe so that is a possibility which I will be looking into, I also like the other suggestion of making a mounting plate for the job, as you point out this could be very useful as I have three to do initially and it may lead to doing more of them or similar jobs so the experience would be worthwhile,

Thread: Air Compressor Warning
31/01/2021 19:04:42

Air receivers should be inspected periodically, obviously not enforced for diy types but a good idea nevertheless,

I have only ever seen the aftermath of one air receiver that exploded and it did explode, it was some years ago and being used in a medium sized car repair garage, the vessel in question was a vertical one stood at the side of a compressor that was feeding into it, this was in the bad old days of piston compressors that were all air cooled and consequently when worked hard they ran at high temperature and as a consequence there was lots of oil carry over as the piston clearances went miles out due to heat, the consequence of all this was that the oil that had accumulated in the vessel actually ignited and the pressure rise was so rapid that the pressure relief valve was rendered useless, the result was literally an explosion, the vessel ripped apart and punched a hole through the floor above,

This is why you should be careful using compressed air and compressors, keep them in good condition and inspect the vessel yourself periodically, the chance of catastrophic failure is very small but you do not want to be around if it happens, the picture of the small veseel that looks like it has peeled open should be enough to warn of the potential for injury to anyone stood near,

Vessels are inspected and can have a retest requested if the condition has worsened, testing is done with water for the simple reason that any failure when pressurised with liquid is far less dangerous due to physics, you cannot compress a liquid so there is very little stored energy, when you compress a gas you are storing energy so when it is released it is all that energy that will harm you,

as always look after your tools and they will look after you

Thread: Boring bar size ?
31/01/2021 18:27:58
Posted by old mart on 12/01/2021 16:28:45:

Jason B recommends a 16mm boring bar, and I think that is the best size. The actual tip height of boring bars is somewhere near half the nominal tool height, so if the toolpost has enough depth to hold the bar, it can fit a lathe that could not manage a 16mm standard tool.

ARC sell a nice bar 16mm which takes CCMT09 type inserts. 060-325-39516

An insert suitable for zinc or aluminium CCGT09T308. 060-326-01938

The ARC site shows the dimensions of the tool. It will be long enough for your carb bore. I would recommend very small cuts and lubrication such as wd40 or ac90.

Back in the sixties, I had a pair of Amal monoblocks bored out to 1 3/16" for a Royal Enfield Constellation. The centre part of the carbs was in place and bored simultaneously. Some time later, one of the central parts failed, the cause was blowholes in the zinc casting.


Been very busy so just got back to looking at this project, I have purchased the above recommended bar and insert,

I have since found out that there may be a problem with boring out this particular carb, it looks like even taking 1mm off (26 to 28mm bore) could be tricky as it may remove material that is shrouding an airway, also been given the information that when other engineers have bored these carbs from 26 to 28mm then they do it by boring them slightly off centre so as to avoid removing material from the bottom part of the carb so that the material shrouding the tiny airway is not removed, that means that I probably cannot do the job myself anyway now, I do have a small milling machine which is a Clarke CMD 300 but I think it is close on height to be able to do the job on this machine and I think that I would probably need some way of mounting the carb at a slight offset or tipped over at a slight angle, it does not need to be much to leave the material alone around the airway but it is getting too complex for me at this time,

Thanks to all

Thread: Motorcycle General Discussion
17/01/2021 08:55:14

Peter Jones,

I worked at A Honda dealers when the F2 was launched, forks were incredibly flimsy and would bend badly enough for seals to leak under heavy breaking (you could see the 'wiper' marks on rear of fork leg about 2" higher than on front)

Well forty years ish have passed since I told friends (probably while having a coffe and a pasty at Squires) that if you cornered reasonably hard (after changing the tyres for Pirelli phantoms) on my Suzuki GT750J that you could actually feel the forks flexing and even on the odd occasion see the flex and having them all sceptical I now have confirmation that the forks on those early jap bikes were so thin and flimsy and that I wasn't making it up !

Lots of coincidences here, I have had lots of bikes including some of the same ones, I now have a Honda CB550K3 with carb issues although hopefully I have addressed the issues this winter,

I have ridden trials myself on lots of different bikes, rode as a junior and then a roughly forty year gap before riding again, cannot remember who posted it but I have also ridden a fair number of Spen valley trials plus Bradford, Horsforth, West Leeds, Ripon, Wetherby, Richmond etc etc and one or two centre trials and the odd national including the Manx trial several times, still have a trials bike which is a genuine Majesty Yamaha 200 built form a new frame up and will hopefully be out riding again in 2021 once the current Covid situation has improved enough to resume normal activities,

Nice to now there are plenty of bikers here, they are the love of my life plus of course family and good friends.



Thread: Boring bar size ?
17/01/2021 08:20:31


Sorry for late reply, as is probably the case with most of the forum members I have been cursed by being a "practical man" so always other things to do, i.e. rcd unit tripping, bathroom to refurb, help friends (?) as in do you know anything about ? well the default answer should be "no idea about anything to do with that" but you tend to say yes don't you ?

Old mart, the 16mm boring bar is a decent option for me as I do odds and sods on the lathe for myself and could help others with the same type of work plus there are not any easy alternatives for bigger carbs, they are a flat slide carb with power jets (internal unusually) and are mounted at around 45 degress so the float chambers have to suit, the only bigger bore alternatives need more modification to fit them than is required to bore from 26 to 28mm, the reason for boring the carbs is engine upgrades, two stroke porting and capacity increase with better expansion chambers means that although the standard carbs will work the bigger bore size with correct jetting helps with a substantial power increase through the rev range,

Oily rag, Martin,

They are not pumper carbs but do have a "power jet" which unusually is internal to the carb, you are probably familiar with most power jet type carbs that have an external mounting on the intake side of the carb with a jet fed from the float chamber via an external tube,

re bell mouth changes, they are pretty good on the intake side with a very nice looking profile to the bell mouth shape, I still haven't had chance to get back on with the good jobs (bike engineering in my garage) due to other more mundane stuff to get out of the way, I could take a picture or two when I have a bit more time.

I agree that the youtube video of the diy boring bar is not a great example, I am of limited experience with turning, boring, milling etc but I do have a motto that there are only two ways to do a job, a right way and a wrong way, well that does not look the right way to me, the execution is poor, I cringed when the drilll bit was clearly off centre when drilling through the bar and as someone else said even the filing of the hole from round to square was a bit iffy, he would not have got his O level (GCE not gcse) metalwork at the school I went to, however the idea seems sound so I might have a go at making my own, it does look like the finished bar would work well for my purpose,

One of the replies mentioned being careful about getting the carbs mounted perfect for the obvious reasons of not getting the machining perfectly concentric, well the good news for me is that the carbs will mount directly into the three jaw chuck on the intake spigot so unless I have a meltdown (imminent) then it should not be a problem,

I will measure up my tool post asap and see if I can get a 20mm bar into it to clamp correctly, if not I will most likely go ahead with a 16mm bar and prcoeed with great care, the carbs that I am boring out are a spare set but as they vary between £200 and £600 a second hand set then I don't want to damage even the spare set,

Thanks for all the input, much appreciated,

Regards Jeff

Edited By Jeff Austin 1 on 17/01/2021 08:24:04

Edited By JasonB on 17/01/2021 12:15:47

12/01/2021 23:05:18

Nigel McBurney,

Re the needing a much larger lathe etc, I am not intending doing all of my own machining just the smaller stuff like the carb boring, spacers etc, I also have a small milling machine which I used to modify a top yoke on a trials bike to remove part of the casting that was the bottom of the handlebar clamps, I machined it flat and then was able to fit normal split handlebar clamps that are directly above the yoke rather than the tiller type that used to be the common thing on trials bikes,

It is just stuff like that I want to do myself and larger jobs like the wheel that I am modifying will be done by someone else,

My work will be repairs / restoration with the necessary sub contract work for larger machining, alloy welding etc which I have contacts for.

Thread: Hello from Yorkshire (another one !)
12/01/2021 22:54:45

Re the locals, I am in Tingley so not far from Wakie either, one of those funny areas where my postcode is a WF one but I pay coucil tax and get my bins emptied by Leeds council,

Thread: Boring bar size ?
12/01/2021 22:50:05


well thanks for the responses ! there are a few of them ! I am unsure which route to take, I have yet to check the material that they are made of, as usual lots of other stuff going on at the same time,

Re what type of carb they are, they are Keihin TA09 carbs and they are spigot mounted, there are no engineers motorcycle or other engineers modifying the carbs other than the removal of a 1mm cut to take them to 28mm, this is done as part of a performance upgrade, the carbs work very well as a standard setup so it is just the bigger choke size / bore that is required,

I would like to go with a 20mm boring bar if my tool post can hold it or if I can modify or replace the tool post or the bar itself, I am thinking that the bar can have flats ground on it to facilitate fitting in the tool post if necessary,

I will repost when I have had chance to look at what my tool post can hold and what material the carbs are, I do not think they are mazak but will check,


12/01/2021 06:18:43


Further to my posting on new member introduction,

I am currently working towards providing classic motorcycle repair and restoration services,

First thing that I have to do on my own test bike is to bore out a set of carbs from 26 to 28mm, I need advice on what size boring bar I should purchase for the job, the carbs are 90mm from front to back so it will be a depth slightly less than that, I am not sure what metal the carbs are made from but they are pretty sophisticated carbs and I think they are aluminium, my lathe is an Axminster C6 (Sieg ?) with the original standard tool post,

I need to know minimum and maximum size boring bar and what type of cutter to use, I guess that it's going to be an indexable type bar that is going to be the best way to go ?

Thanks in anticipation, Jeff

Thread: Hello from Yorkshire (another one !)
12/01/2021 06:06:23


Thanks for the replies,

I understand the need to get a bar as big as possible to eliminate flex and chatter, I wondered what size I can go to before it gets too big to fit inside the bore of the carb which is 26mm so only needs 1mm off and depth to bore through is 90mm maximum, I'll put the question on the beginners questions,

Brian, thanks for your reply,

I think the carbs are alloy but will check, my Lathe is an Axminster C6 which I think is manufactured by Sieg ?

Thanks again

11/01/2021 11:38:52


I am from Leeds area of West Yorkshire and I am mostly carrying out work on Classic motorcycles (Jap crap to the British bike fans),

I have no formal training on machining but went to a decent school (blagged my way in !) that had Lathes, milling machines, welding equipment etc so learned basics at school and then during my early working life was making and reconditioning parts with the above plus other machines like surface grinders,

I now need to start being a bit more proficient with my lathe and milling machine, my first job is to bore out some carburettors from 26 to 28mm and need some advice on boring bar size etc,

Can someone tell me which section to post in for the required advice,

Thanks Jeff


Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Support Our Partners
Rapid RC
Eccentric Engineering
Eccentric July 5 2018
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest