Racing Inter Restoration - Part 5: Timing Case and Bevel Assemblies (August 2005-September 2005)

Inner and Outer Timing Case Covers
Both castings supplied with my 1938 engine were standard alloy (International) versions and both were in very good unblemished condition. They had even both been polished and were ready to fit, very tempting as it would save me having to do it!
 

Inter Timing Cover

Standard alloy International inner and outer timing covers that came with the engine

 

Inside of Inner Timing Cover

Here you can see the inside face of the inner timing cover, clearly showing the boss for locating the oil drive gear. It also shows the bigend oilway on the left

   
           

Oil Pump Gear

The oil pump gear, with slots that allow for the pump driving plate. Next to it is the crankshaft drive gear. These are new items, which I now stock

 
The inner timing cover has a large boss, bored its full length fitted with a plain phosphor bronze bearing. This casting is designed primarily to locate and hold the oil pump drive gear, so that it meshes with the corresponding drive gear on the crankshaft. The gear itself has twice the number of teeth to the crankshaft gear, therefore reducing the oil pump to half engine speed. This gear has a dual purpose though, as at the opposite end of the pump gear’s shaft (the outermost facing end) it has a taper that locates the magneto sprocket, the chain of which runs in the ‘well’ of the same casting. Finally, the casting also provides the oil supply to the Big End, using an oilway from the crankcase mating face to a central boss where a steel union is located which holds a sprung loaded bronze quill, providing oil through the timing side mainshaft to the Big End.      
       
                         

Manx Timing Cover Inside

You can see here how the inner timing cover holds the oil pump gear and big end oil feed plunger. Note the pump driving plate sat in the gear slots

                     
 

Overall, when you think about it, what a brilliant and simple piece of design this is, in my opinion probably one of Mr Carroll’s single best pieces of work!! I just love the self contained compactness and simplicity of the casting.
But it is not only the engineering soundness of design that should be admired. When this casting is assembled in conjunction with the distinctive mating timing outer cover, with the famous Norton logo emblazoned on it, it provides the visual centre point of what many would argue is the most famous motorcycle engine ever, definitely a design icon, brilliant!

 
                     
     

Manx and Inter Timing Covers

An interesting comparison, showing the original International cover (above) and the magnesium Manx cover (below)

Well, having gone off at tangent about the design virtues of one of my favourite Norton parts, back to the restoration of this particular engine. As I have already touched upon, I was intending this engine to be a competition engine, and therefore wanted it to be of a close as specification to Manx as possible, and also to have a rev clock fitted if possible.
As it happens, many years previously, one of the choice items I had managed to acquire was a genuine pre-war magnesium racing inner timing case cover, which although identical in construction to the alloy version, is substantially lighter. I would also be the first to admit, that the other reason for wanting to fit it was purely because it was a genuine Manx item! - well at least I can admit my own vanity . . .
     
                           

These timing covers in magnesium are very hard to find, and this one turned up in the most unusual of places. It was towards the end of the time I was actively competing in the early 1990’s, and I was entered in the Lyme sprint up near Chesire (a beautiful location and a nice laid back sprint which unfortunately is no longer ran). However, on this particular occasion there was a small autojumble being held, opposite the track from the pits, which I visited in the lunch break. Expecting to find little of interest, imagine my surprise when sat on the small stall in front of me I found a very dishevelled looking piece of corroded black alloy that on inspection turned out to be a magnesium timing cover. The seller knew its rarity, so it was not cheap – but as is often the case with early Manx parts, the biggest challenge is finding the parts in the first place!
Having cleaned the cover up, and spent some time truing the outer cover mating face on a surface plate, I sent it over to Stu Rogers, so that he could re-chromate it for me.

Again, I will cover this process in detail in a future article, but the black finish found on Norton magnesium castings is produced by a chemical process called Chromating, which is there primarily to protect the bare magnesium from exposure to the atmosphere, in which it quickly corrodes. Actually, for many years I had no idea that this blackish colour was not the natural colour of the bare metal, magnesium information not being terribly common. I had heard of the variety of magnesium used by Norton’s being referred to as Elektron and assumed this was a particular type of magnesium which had a natural black finish! Well actually the the natural finish is not dissimilar to bare aluminium, although it quickly diminishes with exposure to the atmosphere becoming greyish, losing strength to boot, so the chromating process provides a very thin (microns) protective layer.
The timing cover is fitted with a phosper bronze plain bearing which the oil drive gear revolves in. This bearing has a blind scroll inside it (i.e. it does not go all the way to the end of the bearing), to ensure excess oil is not fed into the magneto chain chamber. (Having now run the engine quite a few times, I have noticed that some oil does collect in this chamber, so at some point I think I will probably need to replace this bearing).

Manx Timing Cover Fitted

Freshly re-chromated Manx timing cover fitted. Not e Magneto sprocket fitted to end of oil pump drive gear

 
 
       
The outer cover that came with the engine was, again, in very nice condition and had already been polished. But just like the original inner timing case, it was not ideal for racing, in this case because it did not have a takeoff for a rev clock, which I always like to fit.
The works Nortons were first fitted with rev clocks from 1937, so to provide the drive for it, the outer timing cover was amended to provide a mounting for a rev clock gearbox driven from the lower magneto sprocket, i.e. the oil pump drive spindle. The earliest versions of this amended cover were still of the earlier ‘ribbed’ variety, but by about 1938 this ribbed cover was replaced by a ‘plain’ style with just the Norton logo remaining in the centre.
I had managed to acquire one of these revised covers many years ago, so now was the ideal time to make use of it.
When I came to measure up this new outer cover to the magnesium inner cover though, I found it was not an exact match at the top (leftmost) end, and was slightly short. A small amount of difference is quite normal, but the difference here was a bit too much and did not look very good, so off the cover went to Arthur Sosbe so he could weld a bit more aluminium. You can see a photograph here to show what a neat job he did. It was simply then a case of trial mounting the cover in place, and ensuring the rev clock centre hole is as close to central over the oil pump drive shaft, then scribing off the weld area where it needed to be reduced to. After filing away the excess metal, final flatting of the mating face on a surface plate, all that remained to finish the cover was to give it final rub down and polish and hey presto – a very pretty timing cover, with the provision for a rev clock.
         
   

Outer Timing Cover

Original timing cover above and new timing cover below, which includes fitment for revclock drive gearbox. Note also that at this stage it has been welded at its uppermost point, but not finished to shape

         
                                   
With all the main parts cleaned up and where necessary replaced, it was simply a case of re-assembly. As covered in a previous section, I had already shimmed and fitted the vertical bevel housing as well as the crankshaft oil pump gear. All that was necessary to do was assemble the big end oil union gland to the inner timing case, fit the phosper bronze big end plunger and spring (along with copious amounts of clean mineral oil – I tend not to use castor oil, much as I love the smell) and then fit the inner timing cover to timing case, securing with new cheesehead screws.
Before fitting the inner timing cover I had fitted the oil pump drive gear and within this had located the oil pump drive plate. When fitting the cover, it was just necessary to ensure that this drive plate was engaging correctly with the oil pump drive tang, however this is a relatively simple task. As with all Norton singles, I find it preferable to lay the engine down on its drive side, so the mainshaft is vertical. I then feed a good quantity of fresh oil down the mainshaft oilway before final fitment of the timing case.
Although originally fitted with a paper gasket, I prefer to use modern silicone sealant, although this is down purely to personal preference.
Last job after fitting the inner timing cover is to fit the magneto drive sprocket to the oil pump drive gear. I tend to lightly grind this gear to the taper, using fine grinding paste, before cleaning and final fitment of this gear, which also includes a woodruff key to avoid rotation. The nut securing this gear is a specially made one, which includes a drive tang for the revclock gearbox.
                                   
              Having already fitted the revclock gearbox to the outer timing case, securing it with small lockwired bolts, the timing case could then be provisionally fitted. I did not fit the magneto chain at this point, or final tighten the outer timing case screws, as I would not be fitting the magneto until final assembly. However, as can be seen from the photo alongside, it was beginning to look more like a finished engine, and was certainly both purposeful and pretty!With all the main parts cleaned up and where necessary replaced, it was simply a case of re-assembly. As covered in a previous section, I had already shimmed and fitted the vertical bevel housing as well as the crankshaft oil pump gear. All that was necessary to do was assemble the big end oil union gland to the inner timing case, fit the phosper bronze big end plunger and spring (along with copious amounts of clean mineral oil – I tend not to use castor oil, much as I love the smell) and then fit the inner timing cover to timing case, securing with new cheesehead screws.
Before fitting the inner timing cover I had fitted the oil pump drive gear and within this had located the oil pump drive plate. When fitting the cover, it was just necessary to ensure that this drive plate was engaging correctly with the oil pump drive tang, however this is a relatively simple task. As with all Norton singles, I find it preferable to lay the engine down on its drive side, so the mainshaft is vertical. I then feed a good quantity of fresh oil down the mainshaft oilway before final fitment of the timing case.
Although originally fitted with a paper gasket, I prefer to use modern silicone sealant, although this is down purely to personal preference.
Last job after fitting the inner timing cover is to fit the magneto drive sprocket to the oil pump drive gear. I tend to lightly grind this gear to the taper, using fine grinding paste, before cleaning and final fitment of this gear, which also includes a woodruff key to avoid rotation. The nut securing this gear is a specially made one, which includes a drive tang for the revclock gearbox.
Having already fitted the revclock gearbox to the outer timing case, securing it with small lockwired bolts, the timing case could then be provisionally fitted. I did not fit the magneto chain at this point, or final tighten the outer timing case screws, as I would not be fitting the magneto until final assembly. However, as can be seen from the photo alongside, it was beginning to look more like a finished engine, and was certainly both purposeful and pretty!
 
 

Fitted Timing Cover

Assembled timing case assembly showing magnesium inner cover and outer cover with revclock drive fitted

   
               

By the way, a helpful hint here, I tend not to fit the magneto chain at this point, until I am ready to fit the magneto. The reason for this is that without the second magneto sprocket, the chain collects in the bottom of the timing case well. Not a problem until you forget this is the case, and inadvertently turn the engine over from the crankshaft, often resulting in the magneto chain wrapping around the lower sprocket and damaging the timing case, bugger!


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