Sunday, 16 August 2015

Enclosed SOHC rockerbox


-JdK- We have had photo's of a replica enclosed rockerbox for the SOHC Carroll engine on the site before. Now Chris has contributed pics of an original, owned by his father Ken, who wrote the words below:

"This is one of the genuine six enclosed rocker boxes made by Norton’s for the factory bikes.

One of the reasons to enclose the valve gear (and there are a few!) was to stop the fine spray of oil which, with wear and working clearances, came from the standard single knocker box through the rockers and could reach the rear tyre. The solution of course was to enclose the valve gear and springs within the head/rocker box casting as already in use on the KSS Velocette. A point to note is that the TT, the North West 200 and the Ulster Grand Prix were all very long races and Norton used hairpin valve springs that could break; but they could be pulled and replaced in less than ten seconds with the correct tongs. You can’t do that with a machine which has hairpins or coil springs inside a cam box.

The principle of valve operation is by established Norton practice of a single camshaft and two timed cams lifting two rockers which press down on the valve stems. The enclosed rocker box works on exactly the same principle but the rockers push on a little pushrod - or pusher - which makes contact with the valve stem, opening the valve. The pusher works in a bronze bush which is screwed into the cam box. Except for the exposed length of the pusher, everything - including the oil - is enclosed within the rocker box.   

A standard rocker has an adjustable tappet working on a collet principle. The enclosed rocker has a fixed tappet which can be ground - or the valve stem can be ground - to give the required tappet clearances. The valve clearances therefore should remain the same no matter how many times the rocker box or head is removed or replaced, providing that the valves are not faced or replaced in which case the pushers should be replaced or ground again.

A cammy Norton is a well designed and manufactured piece of kit, but a works item has to be seen and examined to see the high standard of finish and close fitting of each component. I only wish the photographs could show the high standard of workmanship achieved with simple hand tools which was all to common in our industries. For example, the pushers are hollow for lightness and the tapered nuts are lapped to fit the lid.   

I have seen two of these genuine enclosed rocker boxes working on bikes, one on a special J.A.B.S. that my friend John Wilkinson had and another on a works Norton based near Liverpool. 

Was it the solution that was needed, and did it do the job, but was it too expensive to manufacture for the public? Or was it superseded by the double knocker first used by Nortons in the Leinster 200 in 1937? I hope this article provides some clarity and may be the basis for a good healthy debate."

Saturday, 15 August 2015

1928 Model CS1 Norton


-SG- Alan returned recently from a trip to the Isle of Man - during which he visted the Isle of Man Motor Museum at Jurby and took various photos of a CS1 Norton on display.


A lot of effort has been put into this CS1 restoration but with rather mixed results. Modern control levers are fitted which might make it convenient to ride but rather spoil the overall effect. As good reproduction inverted levers have been available for decades, I feel this is unfortunate. Then there is the routing of the clutch cable - totally 'arse about face!' It should come down from above with the cable nipple in the low level cable stop. The inlet stub is of the later - longer - type with the hexagon. Not that difficult to change it to the original type. The float chamber is a later Mazak type and the carburetter is Amal rather than Binks. It appears to be missing the exhaust valve lifter mechanism on the cambox, and also the correct crankcase breather and sheet metal cover on the front engine plates. Admittedly, all small points! But where it really fails to hit the mark with me is in the fuel tank lining -  too narrow and not in the right place. This is an all too frequent error by professional tank restorers in particular, who seem to ignore all period photos which would show them just how to do it!

Monday, 10 August 2015

Model 25 Norton valves and guides


-Juris- You might be interested to hear how I reconditioned valves and guides in my 1926 Model 25 Norton.

Bare nickel steel valves get scored in chilled cast iron guides very soon, especially the exhaust valves, so I thought I should do something about it. As I did not find any suitable modern replacement valves, I decided to use the old originals. Maybe the whole process is a bit old fashioned and slow, but it gave me immense satisfaction from working with my own tools and not having to rely on other suppliers.


I started with an old original Norton valve made of nickel steel, which had a scored stem. I had it hard chrome plated at a factory in Riga. Around 0.25 mm was deposited on the stem diametre and I then put the valve in my lathe chuck and used a Sunnen external hone to hone/lap the stem down until smooth and within 0.01 mm along its length. This operation took the best part of a working day as I used to stop and let the stem cool when it got too hot. It was of course oiled liberally during the honing process and the feed was minimal as I did not want to score the stem. When the stem was finished the valve was reground in our new centreless “Comec” valve grinder.


The valve guides were made of old camshaft cast iron and these were chilled. To get the necessary valve running clearance - 0.12 mm for the exhaust valve and 0.07 mm for the inlet I used our Goodson diamond valve guide hone. To check the clearance I used a go/no go gauge.


The old chrome -moly- vanadium valve seats I had put in in 2003 had behaved very well and the valve seat width had stayed almost at the width I had cut them to - 1.5 mm.

The Norton liked the newly treated valves and guides and with a new piston it went like a bomb!

Wednesday, 5 August 2015

Now we know the real story!


-SG- Those followers of this site and eBay will perhaps have been amused by the rather weird - only word for it - description which accompanies the photographs of this quite tidy 1923 16H (has a later Amal carb. but it looks all there). Not sure I would want to pay nearly £18.000 for it but it will be interesting to see if it sells.  Here's the text:

"Welcome to my advertisement of the sale of my vintage motorcycle a 1923 Norton Model 16H, 490cc side valve. The Norton name is one of the most well known motorcycle manufacturers and was founded in 1901 by a gentleman named Rem Fowler who established a win in the first ever Isle of Man race on board his v-twin engined Norton. Lessons learned on the race track were passed down to the road going motorcycles in performance, handling and braking improvements making the road going motorcycle steps ahead of the competition. 

In 1911 James Lansdowne Norton entered a 490cc side valve motorcycle into the TT races with no success but the following year with some improvements won the Brooklands TT and set three world records. 

My 1923, Norton 16H is in excellent running condition with lots of history, various old tax disc, old M.O.T.. certificates, original old brown logbook confirming correct engine/frame no's, original registration number, current V5C and old V5, well known to the Norton owners club with lots of history."

As the saying goes, couldn't have put it better myself! Even the Bonham's introductory blurb is a good deal better than this.

Sunday, 2 August 2015

New Zealand Grass Track 1925


-SG- My good friend John has sent the photos attached, taken from 'The Weekly Press and NZ Referee' from 12th March 1925. All the bikes are in usual New Zealand grass-track trim with brakes either removed or disconnected, a subject Peter Thomson informed us about a while back. It's not that easy to see much by way of detail but two of the bikes (4 and 17) have Druid forks and no mechanical oil pump or separate oil tank. These two are probably fairly early examples of Model 18s from '23. The other two (3 and 24) both have Webbs, and Best and Lloyd oil pumps/oil tanks and bearing in mind the date of the publication, would have been '24 models. I note that Number 3 has the sophistication of a Twistgrip, no less. As to who the riders are:


  • Bike #3  is  H. Rowe winner of the Taranaki Middle-Weight championship and the Jockey Clup Handicap at New Plymouth and The Consolation Race at Hawera.
  • Bike #4 is H. H. Moller winner of the Manaia Handicap at Hawera (we have had Henry Moller on the site before but at a different event. He also rode in the TT here on a works Norton in 1926 without success).
  • Bike #17 is W. H. Herbert winner of the Moturoa Handicap at New Plymouth.
  • Bike #24 is J. Crockett winner of the Eltham Handicap at Hawera and the Omata Handicap at New Plymouth.

Wednesday, 29 July 2015

1935 Modell 40 Norton

-SG- Don has sent in photos of his very tidy 1935 Model 40 - which, slightly unusual in this day and age, has all numbers matching with the records. Yes, engine, frame, tank, gearbox and magdyno! It formed part of the late Ken Bills' collection before Don bought  it.


Of specific interest is the gearbox and gear-change, of which Don has taken a couple of close-ups. The box is a four speed Sturmey Archer but the gear change is the Norton version as incorporated into the 'doll's head' box, which the firm started using in '35. Don's initial re-action to this arrangement was that it might have been a tidily executed home modification by a previous owner. But Ken McIntosh in New Zealand tells me there are a couple of Inters in Australia of the same vintage with the self-same gearchange arrangement so it seems very much to be something carried out by the works for a short period. Ken explains ...


The two top studs on the SturmeyArcher box are closer together than on the Norton box, so the top of the Sturmey Archer end cover was cut off and recesses milled to accept the mounting lugs of the doll's head change.

Ken also kindly sent the 1935 Patent Application details for the doll's head change and the comment that, when used on a road bike with a relatively long gear change lever, the lever travel is excessive and  not convenient to use - with which I wholeheartedly agree!


Tuesday, 28 July 2015

1930 Model DT Norton


-SG- Leon is Australia has forwarded this photo of Herb Durkin - about whom there's a fair amount on the Internet, worthy of a quick read - seated on a 1930 DT Norton. The photo is via the Herb Durkin Collection of David Dumble in Melbourne. I was on the point of mentioning that only one DT Norton shows in the records as having been sent to Australia when I had another look at the photo - from which it seems quite likely that it was taken in New Zealand where perhaps Herb was on a visit at some time.  Be that as it may, the photo shows quite clearly the through bolts holding head and barrel to crankcase  and, not quite so clearly, the hexagonal exhaust nuts threaded into the exhaust ports, both features of the production DT Nortons.

Monday, 27 July 2015

E O Blacknell's Dirt bike


-SG- In the recent posting about the VMCC Founder's Day event, I mentioned that I had been offered a snap of E O Blacknell on a Dirt Norton prototype (ca 1929) for a little matter of £45 ... I had seen it before and indeed I now find it featured in a short article from Motorcycle Sport  by Titch Allen back in 1966. Regrettably the photo does not scan too well but it appears to show a Model 18, shorn of such things as brakes and mudguards, wearing a rather handsome small sprint tank.

But appearances can be deceptive and in the accompanying text, Titch relates - seemingly with some surprise at such advanced technology - that the cams were screwed to the shafts and minute adjustments to valve timing could be achieved by placing shims behind them. He was, I guess, unaware that this arrangement came into being with the ES2 engines introduced at the end of 1927 although in all honesty, I have never come across even one Vintage ES2 cam with a shim behind it, and I can tell you they are extremely hard to remove without damaging the cam wheel teeth. However, I accept that the engine of Blackie's bike may have been set up in this way initially. As many home assemblers of Vintage Norton engines have found, getting one cam pretty well spot on by careful use of the three keyways in the timing pinion is one thing but getting the other cam right is quite a different matter!

But all this brings about a further question: if ES2 style cams were fitted then the crankcase must also have been ES2 as the timing chest is different from the regular version with the large base circle cams used by Norton for about twenty years. And that would mean ES2 steel flywheels ... And the timing chest cover with mag drive out front ... I guess this must have been a special although by 1930, when the screw-on cams became standard, any of the 1930 OHV/SV timing covers would have fitted.

With the introduction of purpose built Speedway bikes from Nortons and many others, Blackie's speedy machine (capable of over 100 mph according to him) became obselete, was converted for road use and sold.  Now that would have been a good bike to get hold of ...

Sunday, 26 July 2015

Preparation for racing - Models 30 and 40 International, 30M and 40M


-JdK- Jon and Ian in the UK and Isle of Man apparently both took these original Norton 'tuning notes' for the Models 30 and 40 International, 30M and 40M and copied them 'for the older eyes'; very useful!. A copy and the original notes can be found via this link. The originals came from John Bennett and where he got them from is unknown.

Saturday, 25 July 2015

Racing Norton Sturmey gearbox ??‏


-SG- Last Autumn we received photos from Australia of what at first sight seemed to be one of the early twenties racing CS four stud gearboxes without the usual casting extension holding the kick-start mechanism. Very few of these survive and it appears they were initially fitted with the so-called 'fine pitch gears' (pairs add up to 50 teeth), with first gear in the central position thus giving 'semi positive stop.'


But this has turned out to be a bit of a mystery for the good and simple reason that, despite its early twenties shell, the box is stamped up '1929TT' and the stamping appears old enough actually to date from '29. Further it is fitted with a positive stop footchange, some parts of which are Sturmey and some either home-made or from some other foot change mechanism, mounted on the inverted T bracket used on all Norton CS boxes in '29.


To cut a long story short, the box is now back in UK and I have had a chance to take a look at it and its new owner, a friend of mine, has told me about its internals (he knows more about these boxes than most). Internally the gears and shafts are all as new and of the post 1925 'coarse pitch' type (pairs add up to 42). The sleeve gear is the usual 25T CS item and second gear - in the normal mid position - is also the usual CS close ratio option of 20/22T. But bottom gear is very unusual - with a 19T gear on the mainshaft and 23T on the layshaft. For what it's worth this gear-set will give very close intermediate ratios of - assuming a top gear of 4.5 -1 - 6.03 and 8.01.


The mainshaft incidentally is normal for 1929 too, with splined single spring clutch fitting. The final drive sprocket however is not usual being a flat 5/8 x 1/4 item usually fitted to the pivotal LS boxes used on CJ and JE Models. This sprocket usually lines up with a flat rear wheel sprocket on the 350 models.

So... was it fitted to a Norton at some stage as original equipment? I don't know! I checked through all OHV models shipped out in '29 and early '30 and there was no sign of it in the 'Gearbox Column'.  Then I checked my SA literature and perhaps, just perhaps, there is a slight clue there. A special racing gearbox is listed in the 1930 price list supplement, suitable only for Models 18,19 and 20. The shell and cover part nos. (CS123 and 124) are given but neither of these is stamped on the box from Australia. However, it does show the special high bottom gear of 23/19, but, somewhat irritatingly, this is shown only as being in the mid position rather than in the usual low gear position! So in terms of solving the conundrum, I am not that much further forward. Perhaps it was ordered from Sturmey Archer direct for some sporting purpose (dirt-track??) - who knows? Suggestions more than welcome!


postscript: There's nothing like asking a question and then finding the answer oneself! Looking at my papers re Speedway Nortons, I glanced at a period - and rather retouched - Speedway Norton publicity photo. And the gearbox in it? The same type as the one pictured above - see scan.  However, a double check on gearbox numbers for the production Speedway Nortons showed that all had LS boxes fitted. So this ex- Australia box was perhaps a special order for Speedway use?