Go Back to Homepage

SOHC Norton Catalog
Visit Full
Online Catalog

1937 Norton International Build
Part 4

Click on any photo to see a higher resolution version
                Building Up the Engine - Part 4: Bottom Half Assembly                             Last Updated : 25/07/11        

Current Progress
Before you read this article, go to the bottom of the page and read the last (short) update I did for this build back in July 2010, then come back and read on:

It is now late July 2011 and I have not really worked on the 1937 Inter engine for about a month (cribbed from last article, but still holds true, other than the year has increased by +1 !). That is not to say I have lost interest, far from it, I just have not had the time to play with it, so it has sat on my bench with cloths placed over it (exactly the same as last year!).
However, all is not lost. In the intervening time I have had a lot of new items made - most of which are now up for sale, and the remaining items will be listed in the next two weeks (see my latest Newsletter, due out beginning of August). The reason for the long gap between articles is my day job has meant me working away for most of the last year (Dublin and London) in the week, and the majority of every weekend has been spent doing the Norton business (see seperate update), so I have had precious little time left over to work on my own bikes. I am philosophical about this, I would have liked to have moved further along, and had this bke built and finished by now, but then again, I have done lots of other useful stuff - which has kept the bills paid, and this bike is not going anywhere - it is still there progressing slowly in the background, every time I get a few minutes spare.

Engine sat in large lumps this time last year - July 2010.
Inter Engine July 2011
Ah-haa - So I have done something then!
July 2011: Ok, so the bike is not finished yet, but at least I have got a bit further since this time last year!
Chassis on Stand
Chassis Update: And yes . . . even better news, I have the frame back from a friend after pretty serious work . . . rigid Inter frame in Racing Inter spec. More of this in a future article
        July 2011 Position:
So as you can see from the two photos on the left, although not finished by any means, I have at least made some progress on both the 37 Inter engine build, and even a bit of progress on the chassis as well. I have also switched tac in the last 3 months so I can get the cambox of the 38 Racing Inter sorted (see next article), in an effort to get that running properly again, so I can do a couple of track events in 2011

Now read on to fill in the gaps since July 2010, and catchup on the build steps:
August 2010: Shimming and Assembling the Bottom Half
Mainshaft shims
The arrival of new shims in December (mainshaft drive side above, timing side mainshaft below are examples) enabled me to get on with assembling bottom half
Chassis on Stand
Norton 500 Inter crank, ready to fit, as covered in a previous article
Timing  Caset shims
Crank in Crankcase
Starting the shimming process - place crank in timing side crankcase
Having prepped all the lower end components and fitted bearing and oil pump, by October I was ready to start reassembly. Frankly, I knew I would get to a point with this build where I could not go any further until Ithe new batch of shims I was waiting for were ready, but I got the call just before Xmas that a large batch of laser cutting, including full engine shim sets, was ready for me and coming home from work late one friday night there were 2 large box’s sat in the hallway waiting for me, including the all important shims..
Shimming a cammy Norton engine is quite straight forward; it is just a case of doing it in the right order and being methodical. The first stage is to shim the crankshaft so the con rod is sitting central to the crankcase centre line. As the crankshaft is locked to the timing side crankcase main bearing (for the purpose of securing the bevel gears), therefore, it follows that this side is shimmed first.

measuring conrod width
Measuring width of conrod, so I can work out centre point and therefore half width of conrod
Conrod side play measuring
At least my thumb is in focus . . .
Now working out if crank is central (taking into account Bigend Sidefloat)
Shimming the Crankshaft in the Crankcases
To start I set the crankcases down on a clean work surface and then take a rough guess at what shim will be needed I.e. 20 thou, (if you have a crank that has already come out of an engine, then the shims previously fitted are a good starting point). As this was the case with my engine I picked a shim of the same thickness as originally fitted and slid this onto the timing side mainshaft before dropping the crankshaft down gently into the waiting timing side crankcase. Spin the crankshaft just to see everything is seating ok, then I fit the drive side crankcase over the top and fit approx 3 engines bolts in place, just to loosely clamp the crankcases together. This allows you to bring the crankcases and crank into the vertical position and while pushing the crankshaft up against the timing side bearing, you can check how central the conrod sits relative to the crankcase centre line. You need to remember to take a ‘median’ figure for the conrod, as it will have some sideplay on the Bigend pin, so just slide it one way and the other and ensure you measure the shimming with it sat central. If everything is moving around a bit too much you can temporarily fit the bevel gear, oil pump drive gear and LH crankshaft nut, to pull-up the crankshaft to the bearing.
Fitting final TS shim
Having now worked out with a 'starter shim' how close I am, I fit the correct shims for the timing side crank and fit them up against flywheel
Fitting final TS shim
Placing the drive side crankcase on top for the first time, without drive side shims - if the flywheels lock up at this point, you really do have a problem!
  Once the crankshaft is shimmed central to the centreline, you can then measure the end float on the drive side mainshaft, as the drive side roller bearing will be floating. I am really not sure how critical it is to accurately shim this side, but I don’t like the idea of a the inner roller bearing being able to move up and down excessively on the shaft, so I normally aim to leave at least a couple of thou of remaining end float, to allow for expansion etc. To work out how much end float the engine has at this stage, I turn the crankcases on their side again, timing case down, and temporarily fit an engine sprocket and sprocket nut. I can then use a dial gauge and a large set of tyre levers under the sprocket (using wooden blocks against the crankcase, so as not to mark them) to lift the crankshaft, until it meets the roller bearing, and then let it drop again. With the dial gauge touching the outer face of the engine sprocket this is a very good way of measuring the available end float. In the case of this engine I had about 40 thou remaining, so fitted shims to just leave a few thou remaining, last job after fitting the shims was to repeat the process and just ensure that everything still tallied with shims fitted, and there was just a little bit of positive float remaining – i.e. the crankshaft did not lock up as I tighten the crankcase bolts! (which I have had happen before)
Testing with Tyre Lever
Using a tyre lever to push up the crank to ascertain the amount of end float on the drive side mainshaft, before fitting appropriate shims.
Spot the deliberate photoshoot error - I havent put the magnetic stand and dial gauge on yet . . . just pretend that they are there!
Crankcase on blocks
Same process, from a different angle. using steel blocks to ensure as rigid a surface as possible, with blocks on mating face, not on the dowels
Oiling Bearings
Now, with shims for crankshaft calculated, final oiling of Bearings with Castor oil before final assembly . . .
Final fitting of shims
. . . and fit the final shims on the crankshaft, as well as covering that liberally in oil as well, to protect it from rust (in the event this rebuild takes another 5 years!)
Final Crankcase Assembly
Now the crank shimming is complete I can at last do the final assembly of the crank into the crankcases. I think this is the point of an engine build where you finally feel you have reached a threshold, when you can sit the crankcases upright and be able to spin the crankshaft and see everything moving freely. There is not much to do in preparation for this, other than to give the mating crankcase surfaces a final clean and scrape, to ensure they provide the best chance of an oil tight seal. Incidentally, I use a 1” x 0.5” HSS (High Speed Steel) lathe tool for this job), about 3 inches in length. I ‘wet stone’ it to ensure the edge is keen, but use a very blunt (approx 80 degrees) angle to ensure it does not dig into the alloy too much. On the other end, I wrap Gaffa tape so that I can hold it in reasonable comfort. Although that all sounds very impressive, I actually still think the best tool there is for removing old gasket material is your fingernail, I just always end up breaking them!
At this point, I also have a final inspection of both crankcase half’s and just ensure that everything else looks ok, and nothing has found its way into any oilways or the bolt and screw holes while all the other tasks have been in progress. A good thing to ensure you check is the sump pick-up oilway, as this can very easily pick up solder from the process of soldering over the screw heads when fitting the bearing plates. Another thing is to check all the surrounding holes for the engine bolts, as if these have not all been cleaned and had a bolt put through them as part of the previous operation, they may still have dirt in them, and the final mating of the crankcases may be the point where the dirt gets pushed out, and onto the silicon sealer, on the mating faces

Final assembly
Flywheels going into the crankcase (always timing side first), for the final assembly. Ensure no castor oil goes onto the mating surfaces at this stage
Bolting up Crankcases
A very pretty collection of newly manufactured brass crankcase one-way valves (and probably the first time since Norton last made them you would have seen this many together!)
            Fitting a Breather Valve
At this point I also realised I had not re-fitted a one way breather valve on the drive side crankcase, this is the brass fitting that sits directly above the main bearing housing. This valve is often mistaken by restorers for the very similar straight-through breather which is used elsewhere on this and similar engines (including the pushrod and sidevalve engines). However, the one in this location is most definitely a one way breather valve, and is fitted with the screw in component facing outwards – i.e., so the valve can blow out crankcase pressure, but not suck in.
I am not sure just how vital these one way valves are to the overall breathing behaviour of a cammy engine (or any other of the Norton engines that use similar valves), but I get a lot of enquiries from customers telling me their engine does not seem to be oiling properly, or not breathing properly, or pumping out oil excessively etc, and in all cases, one of the things I ask them to check is; is this valve fitted the right way round? And is it actually a one-way valve, i.e. has the person that built the engine by mistake fitted a straight-through breather instead?
This may sound like obvious stuff, but this valve is now extremely hard to find and if you go round the autojumbles and look at any Norton single engines you may find - look at the number of them where this valve is not present, or is very badly chewed, where someone has tried to remove it and only succeeded in removing the hexagon flats (due to the valve being so closely fitted to the crankcase wall, a special thin spanner is required to get a full grip of it).
At this point I go into my full salesman mode (!) and say that I am pleased to say that I can now supply these one way valves, identical to the original Norton valve in appearance and operation.
Note: Appearence? some may question - werent these valves\breathers dull nickel plated? Well I have seen some of the straight-thru breathers plated, but I have also seen them in plain brass, and definitely the one-way valve is normally in plain bass, so I think this finish is more original.
Of late, I have been experiencing the same issue of not being able to find these valves myself, every time I was rebuilding a new engine I was finding either the valve was badly chewed, or just not present at all – so I have been robbing them from every old crankcase I have, so it has been high up on my manufacturing list for some time.
Therefore, in late Summer 2010 I had commissioned one of my normal manufacturers to make a large batch of the main valve bodies, which were finished by early Winter, along with a smaller batch of the special screw in centres, which turn a normal breather into a one-way valve. If you look at original Norton breathers you will see that many of them are actually the same outer body, complete with internal thread, but do not have the inner body fitted. I made enough outer bodies to be able to offer both types – the one-way valve and the plain breather. In manufacturing the one-way valves I was also careful to use higher quality stainless balls, to ensure that they are less prone to rust and lock up if left for long periods without use.
If you need one of these valves (I am in salesman mode again!) then this link takes you to the item on my online catalog:
Online Catalog: One-Way Valve
So it was nice (and no coincidence!) that I was able to take the first of these newly manufactured one-way valves and fit it, with red fibre washer underneath into the drive side crankcase, which can be seen in the accompanying photograph – and how satisfyingly nice it looked once fitted!
Bolting up Crankcases
Final bolting up of crankcase halfs, having applied silicone gasket sealer before hand. Notice one-way valve now fitted
Camobx Oilfeed detail
As can be seen here, I also used one of the new straight-thru breather unions for the cambox oil feed. Note as well the new stainless barrel oilfeed bolt and lipped nut - also available now on the online catalog, as well as a complete kit
Crankcase sump bolt
And not forgetting the sump screw
      Final Bolt Up and Assembly
So having cleaned the mating surfaces one last time, fitted one-way valve, given the crankshaft a final blow over with an airgun (a great investment if you haven’t got one, look for a small portable electric compressor and fit it under the bench), fit the required shims and then squirt a copious quantity of castor oil over the polished flywheels and spread it all over - to ensure they do not rust . . . in case the engine ends up not being ran for another 2 years (that tip comes knowing my own rebuilds very well!), before carefully dropping the crankshaft into place in the timing crankcase. I smear one mating face with my favourite Threebond gasket sealant (a specialist sealant, used by the trade – not cheap, but the best you can get) and then carefully place the drive side crankcase over the mainshafts and fit all the engine bolts (including engine plates in this case, as I had them to hand) and tcase sump screw.
Crankcase sump bolt
Machining stainless steel Norton engine bolts from Hexagon bar, on my Smart and Brown lathe
Engine Bolts
Ahh, I forgot to mention, as a little diversion to building the engine, I had realised a few weeks before I got to this stage that I would need to make up a full set of engine bolts.

When I had initially embarked on this build I had promised myself I would not get bogged down with a concour’s build - after all, I wanted this bike to be primarily a ‘slave’ bike for testing new bits. But on inspection, although I had found a number of reasonable original Norton engine bolts in my collection, I could not make up a complete set, all of the right length, with heads all matching. Added to this, I also realised that I was no more than an unwilling host to my own compulsive disorders(!), and that a quick build was never really going to happen! In the case of the engine bolts, if I did nothing and used the very second hand looking originals, I would always look at them and be pissed off with myself for them looking crabby. Add to this, although original engine bolts look nice, I would need to get them dull nickel plated (not so easy these days) and I have got used to (and spoilt) by always fitting stainless steel – and not having to worry so much about leaving the bike out in the rain!
So, in the depths of October - as the time had now moved on, I spent a couple of Sunday afternoons machining a complete set of engine bolts from hexagon stainless steel, with the correct Norton style ‘reduced head’ finish (i.e. the ‘across flats’ spanner size on a Norton engine bolt is smaller than would normally be expected for 0.5” shaft diameter. This is a very time consuming process, not to mention being very manual - I do not have any CNC machines in my own workshop – only a very old but accurate Smart and Brown Model A Toolroom lathe of approx 1950’s vintage. It would have been very easy to just take round bar length and thread it both ends – i.e. a stud, and fit a nut on both ends (as was done with the bigger Norton engine bolts). However, I prefer to use bolts, with a fixed head on one end, therefore they have to be machined down from stainless hexagon bar. Admittedly the lathe has an automatic traverse, so I just get each one setup, using a revolving centre to hold it at the end, take smallish cuts and engage the traverse. Then, other than the regular squirt of oil to lubricate the cutting tool, it is a case of just watching while I dream of the finished bike! For threads I ensure I am using the correct thread that Norton would have used for that diameter bolt, either 26 tpi Cycle for the smaller bolts or 20 tpi Cycle for the larger ones. Often I will setup a Coventry Die Head with the correct thread cutters for these bolts, as I have made tooling to fit these devices on my lathe’s cross-slide, but with such a small a quantity as this I ended up using good quality HSS Cycle dies and taps instead. In fact I actually ended up making up two full sets of bolts in the end, so I had a spare set for the next build, but still - that is hardly a ‘production batch’!

Crankcase sump bolt
Machined Norton bolts, along with lasercut Norton International front engine plates (available from my online catalog for both 350 and 500)
Crankcase assembly
Crankcase assembly sat on bench, fully bolted up and ready to commence the next step - bevel case assembly
Bolting up Crankcases
And driveside of the same crankcase, now starting to resemble a proper Norton cammy engine again!
While I think about it, the business of making engine bolts on the lathe makes me think – there is a nice little article - to explain what Coventry Die Heads are, as outside of the commercial engineering industry they are not really known, but are a great tool if you have lots of the same size bolt to make and want very high quality threads. Although a little bit outside the realm of normal motorcycle restoration, if you are interested in what they are and what they do, then take this link to a little article I have just written: Coventry Die Head Article

<-- Previous Article:
Short update only, and getting ready for assembly
'37 Norton Inter Part 3

Next Article -->
Timing Case, Lower Bevel Shimming and Piston
'37 Norton Inter Part 5


Go To Top Of Page