37 Inter Build

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1937 Norton International Build
Part 1

Building the Engine - Part 1:

Last Updated : 07/05/10

Whats the Current Norton Project?
Well, I havent really had much chance to work on my own bikes much in the last few months, work, mail order and visiting friends with illness have taking precedence. That said, since Xmas 2009 I have been very slowly building a 1937 International engine which I am going to be using as a test bed ('Works Hack' I kid myself) for testing new parts, in a rigid Inter roadgoing bike.

Anyway, I had a few days holiday this week, so have managed to do a bit of work on it and having already done the prep work on the main castings, I have now started the rebuild. I had already checked and re-balanced the crank, cleaned up and blasted the crankcase castings, so this week I have taken out the oil pump and given it the once over, and have just finished fitting the new main bearings.
For the engine rebuild, I thought it would be nice to treat myself and spend a morning going through my own stock, to sort out everything I needed - something I very rarely do, but I had to remind myself - this was the main reason I originally setup the spares manufacture - so I would have parts for my own bikes! Anyway, I spent a couple of hours going through all my stock and taking one (or two!) of everything - a bit like Xmas! So the engine will be pretty much fully fresh on the inside and have my full collection of parts in it:

Preperation Work

Inter in a Box!
1937 International engine as it arrived from Aussie

The basis for the engine was a very straight and original 1937 International engine that had come from my good friend Arthur Moore in Australia. As always, Arthur had done a wonderful job of packing all the parts up safely and had even included a little bit of Australian written culture for me to read when I opened up the package - thanks for that Arthur!
As with all Arthurs parts, the engine was lovely and unmolested and exactly as he had described it - very much like it used to be if finding an original engine at an autojumble 30 years ago. Unfortunately nowdays, if an engine ever does come up for sale, it is far more probable it will have been put together in the last 6 months with a collection of non-matching dross.
I don't mean to get all weepy eyed and nostalgic, but when buying parts from Arthur it reminds me what it used to be like when parts were more plentiful here in England, and you could find engines where there was a possibility you were the first person to have looked inside it in the last 40 years, Ahh - them were the days . . .

Having unpacked the engine - which was basically a complete bottom end and barrel + a spare barrel that needed relinering, I carefully stripped it down and inspected it. I found everything pretty much as I hoped to find it. the crankcases were in excellent overall condition and I was very pleased to find that the inner timing case, which is of the 'breathered' variety fitted in the late 1930's, shared the same number as the crankcases - just confirming what I said earlier, that this was an unmolested engine, with matching original parts.

Note: In reference to the inner timing case breathing - there were two variations. Standard 1930's engines have a hole in them, above the oil pump drive bearing, that allows the timing case to 'breathe'. This hole corresponds to a milled away area of the timing case chamber on the timing side crankcase. Later International engines, and magnesium timing covers did not have these holes, as the crankcase timing chamber had a breather union exiting out of the top

Crankcases, with everything stripped, just before blasting.
Notice breather hole in timing case, above lower screw hole

Inside of crankcases, showing the original bearing retainer plates, which I later removed to check the bearings. Bottom bevel housing and gear also visible

The drive side crankcase had a small piece broken off it at the rear, on one of the engine bolt surrounds - a very common problem and not serious at all. I could have got away with leaving this, but I do not like anything like this on an engine I am rebuilding (it would play on me every time I looked at it!), so that and a small cosmetic 'knock' on the timing case were set out for alloy welding. I did initially attempt to carry out this welding myself - using my newish DHC 2000 oxy-acetylene torch, which supposedly makes alloy welding a doddle. Although I had had some success with this new torch (which has much greater heat control than the standard oxy-acetylene torch I have been using for 20 years), I was not successful with the crankcase and eventually had to concede defeat and send the crankcase off to my normal welder in Leicester - Arthur Sosbe.
Once the crankcase was back and cleaned up, I gave them and the timing case a light blasting - having first carefully masked up every orifice. Even so, the light blasting grit gets everywhere, and when removing all the blocking material I had to very carefully wash every oilway and cavity to ensure every spot of grit had been removed.
My original intention was to get this engine\bike up and running as quickly as possible. Although I want it to be mechanically good - I do not want it to be too pristine because its main purpose is to be a 'Works Hack' that can be used to quickly test out any new parts on the road. I have mentioned this to my best mate Andy Phillips and suggested he might like to be a 'test rider' - where I give him the bike for a few days and ask him to go and put a few hundred miles on it!

Anyway, as part of this - 'get it together quick' philosophy, I was hoping I might get away with keeping the original Bigend and Mains bearings in for the moment. On inspection, the Bigend felt good and the crank very true, so that is worth keeping for the moment.
However, although the mains initially felt fine, having gently heated the crankcases up, so I could unsolder the bearing cover plates to inspect the bearings - the timing case bearing virtually dropped out, showing signs it had just started spinning in the crankcase - not brilliant, but not uncommon at all. I carefully inspected the crankcase bearing surround - to see how serious the spinning of the bearing had become. There was just a slight matt greyness, but no bad scoring, indicating that the bearing had only just started to spin when hot - and therefore did not yet warrant the serious remedial surgery of machining the crankcase bearing area to take a sleeve - which is not something you want to do unless you really need to. When there are signs that the bearing is starting to slip though - it really needs to be replaced, to ensure the best chance of full interference tolerence is maintained, with new bearing.
Moving on to the drive side bearings, on heating up the crankcases to remove the bearing retaining plate I found the bearings on that side also came out quite easily, but on close inspection of the roller bearing I found two things:
1. the bearings was not a lipped roller - not strictly necessary if the spacer is correct - but it always should be!
2. the outer cage had corrosion on the bottom, where all the weight had been sat over the years. This effectively made the decision for me, yes the bearings will definitely all need to be changed. (see further down)

Anyway, that made life much simpler, because it meant that I did not have to worry about washing bearings out etc. I had already committed to lightly blasting the cases externally, and had carefully taped every orifice up with double layers of Gaffa tape, but once I had made this decision to change bearings, it removed any doubt about if this taping up had been unsuccessful and eradicated the need to carefully rinse and degrease them afterwards.

Very nice, straight Inter crank, after a few hours cleaning it up. It showed as running true as well

The original driveside roller bearing showed a definite track mark, and the case hardening destroyed in one spot - these would make a hell of a noise if not replaced and would soon fail completely. Note that this bearing is not the lipped variety either - which it should be

Cylinder Head and Barrel

Nice condition standard International cast iron barrel. This is after honing and has just been blasted and high temp painted

The barrel was nice and easy. As part of the deal, Arthur had found two nice straight standard Inter cast iron barrels. Both had all fins on them (an amazing rarity in itself!), one was a good standardish size, just needing a rebore, the other had been bored out until it had gone through the side wall - which meant it would need re-linering, but this second one was just a sweetener for the deal and would provide a good basis for a future restoration.
For this build the first barrel was perfect, so all I needed to do was give it a blast and then send it to my local car factor motor engineers for a rebore, where it was ready for collection within two days - job done!

Delapena Honing machine now installed in my workshop - which means I can hone bigend eyes after pressing them into conrod

Incidentally, this visit to my local auto engineers turned out to be very fortuitous for another reason. They are a sikh family who have been refurbishing car and lorry engines since the late 1960's. I can remember visiting them in the late 1970's when I first started restoring bikes. At one time they employed about 25 people and refurbished hundreds of engines per month for fleets etc. Well now the original father is close to retiring and his lads have other interests as well as the automotive side, so the auto engineering business is much smaller. I mentioned to him that I had been looking for a Delapena honing machine for some time, for honing Bigends. With a wry smile he told me to come round the counter and follow him to the workshops. In a far corner, next to a huge and very expensive vertical borer\honer, was a Delapena Auto Speedhone looking clean, but like it had not been used for some time! It transpired it had gone out of use about 10 years ago when they got the new machine, but that it had had a very expensive service and bearings replaced just before it was decommisioned (he reckons the service had cost well over a £1000). He knew how good the machine was, so he was not going to let it go cheap - but the clincher for me was looking through the tooling that came with it and finding the correct honing bar for Norton bigends in very good condition, plus a brand new 'sizing ring' for same. These two alone to buy seperately I had already found out would cost me approx £350 + VAT. Needless to say, it was not long before a deal was done and the honing machine was stripped down to a point where Andy and I stood a chance of trollying it into the back of my van. Another little bonus on stripping it was finding that it had a tank full of Delapena honing fluid that I was told was brand new when they put the machine out of service - approx 50 litres, or £120 quids worth. Wahhay.

Tank and filter system under Delapena is quite elaborate and holds approx 50 litres of honing fluid

Cylinder Head Removation
As I had already mentioned, the bottom half had come from Australia complete, but that meant the head and cambox needed to come from elsewhere. Well luckily I already had a couple of standard iron heads 'on the shelf', but the better one of the pair was really part of a spare Inter engine which I wanted to keep together, as it was all nice and orginal, with all the main castings in good condition. This I had always considered my 'spare' engine for the Racing Inter.
My other 500 spare head was in nowhere near as good a condition, and I had always considered it as a 'last ditch' spare when I had nothing else left. It had 3 key faults -
1. It had two broken fins surrounding the bevel tube cutaway (not in itself serious)
2. It had the front head steady mount over the exhaust port broken away (serious)
3. A common problem with iron heads - a crack from the spark plug to exhaust valve seat (serious)

If you look carefully you can just make out a hairline crack running from the exhaust port to the valve seat

After some thought, I figured that a little bit of extra work now, might result in turning a sows ear into a silk purse, and mean I dont have to use up the decent head - so I decided it was worth giving this head a go.
To address the simple problem first, I cut up a couple of steel plates to roughly the same shape as the broken fins. I then put these to one side, until I was ready to start brazing.
Secondly I looked at the crack between the spark plug and the exhaust valve seat. I gave a lot of thought as to how to address this. The important consideration was that a new exhaust valve seat had been fitted at some time in the past, and therefore the crack in the cylinder head only extended as far as the new seat. This was important, because as far as I can tell, the most serious issue around such a crack would be that a crack on the valve seat would likely cause a hot spot and maybe burn out the valve.
As it was, after serious thought I have decided not to do anything about this fault at the moment, I will suck it and see. If I do need to do something I will grind out a channel (probably about a centimetre in depth) along the length of the crack (about 7mm) and have it cast iron welded - but this would mean having to remove the valve seat as well and then fit a new one afterwards, quite a radical operation, and maybe unnecessary.
Incidentally, when questioning what causes cracks like this, I am not entirely sure - as it is not uncommon, but I suspect that it is because the valve seat was fitted with an interference fit that was too extreme and it overstressed the iron.

This photo shows head just after being brazed. New fins have been added and exhaust port\heady steady rebuilt

Exhaust Port Repair
The most difficult job was how to restore the exhaust port. It looked like at some point in its life someone had dropped the head and it had landed on one of the head steady posts, the one that sits directly over the exhaust thread, and had completely broken it away. It had been such a serious crack that even a section of the exhaust port itself was missing, complete with thread. However, the good news was that the crack ended just where the threaded area finished, and it did not extend into the port itself, therefore, providing a good exhaust washer was used to give a full seal, then in reality the broken section could 'almost' be considered cosmetic, as there was still a lot of good thread in place to allow the exhaust nut to screw in.

That did not change anything though, I still wanted to effect a repair that would restore the exhaust port to its original state, and once painted would look effectively the same as the original.
To achieve this I had first to re-manufacture the missing piece (or pieces as it turned) of the head steady and exhaust port. Eventually this turned out to be 4 components - the upright threaded 'steady' component, manufactured from round bar on the lathe, then drilled and tapped with the correct thread. 2 small vertical fins that come off the steady, made from plate, and finally a thicker piece of plate which when filed to shape could be wedged into the broken exhaust port and act as a platform to mount all the other 3 parts on, and then build around with brazing filler.
Once I had fabricated the parts, the next job was to braze them to the head. Brazing is perfect for ths kind of job, due to its excellent gap filling qualities, but there are a few tricks to ensuring you get get good results and nice flowing fillets when brazing cast iron.

As can be seen, at this point the braze has completely covered the plate of steel that had been placed inbetween the broken port, and has been directed to fill the remaining gaps

Brazing Cast Iron
First off, it goes without saying that all parts to brazed must be spotlessly clean and have any oxide or dirt removed. To achieve this with cast iron I will normally use a rotary wire brush - but blasting is better.
Probably the most important factor when you are dealing with cast iron (either brazing or welding) is the use of pre and post heat. This is absolutely vital to ensure that you have enough heat in the head so that the braze will melt, instead of the head just absorbing the heat given off the torch. It will also ensure that the head does not crack, which is always a risk with cast iron if it is heated up or allowed to cool too quickly - for this reason the head needs to be post heated and allowed to cool down slowly after the brazing is complete. The kitchen oven is perfect for this task (I am sure your wife wont mind, mine is used to it . . . ), you need to keep it in until the head is 'spit hot', i.e. you can spit on the head and you see the spit immediately bounce off.
Obviously, you need to use proper brazing flux for this job, I normally mix a small amount with water, which I brush on to the areas to be brazed, to protect them from oxidisation and aid flow, but I also dip the brazing rod into the powder. If I remember correctly (from my college welding days) it is also a good idea not to use a strong oxidising flame with cast iron as this increases the chances of cracking, instead a neutral or slightly acetylend flame is best.
Finally, when you commence the braze, it is very important to put the flame to the area to be brazed and let the brazing rod flow to the heat. It can be very disconcerting when brazing cast iron, because of the amount of heat the head absorbs, and a common fault is to place the rod into the flame in vain effort to melt the braze, where it just 'globulises' (not sure if that is a real word, but I like it), but does not adhere to the base metal. If you get it right, the braze should just flow onto the area to be brazed and you can get it to follow the torch, nicely flowing across the base metal as it goes, and building up a pool on the surface (or fillet if desired) as you progress. It is important to remember that brazing does not provide 'penetration' with the base metal, unlike welding, therefore there must be a certain amount of 'pool' over the two pieces of metal to be joined, to ensure strength in the join afterwards. This is important to remember when grinding down the braze of any fins you have had to repair. By the way, it goes without saying that one of the most difficult facets of cast iron (welding) is that it tends to 'collapse' when it gets molten - if that starts to happen when you are brazing it, then you are using too much heat!

Looking down on the re-fabricated head steady from above, you can see the two small fins that were welded to the threaded upright, before the whole unit was brazed in place. I then ensured braze flowed around the full area, to fill any gaps between the fins. Small beads to the right of braze are the remnants of the flux

Completed head with the newly fabricated head steady on the left. On the right is my other spare Inter head, as comparison

Finished head after a first coat of paint. I am pleased to say it is pretty much indistinguishable from the other head

Anyway, so much for the theory . . .
As it happens, in this case the job went reasonably well. Having first got the head suitably spit hot, I was then able to braze in the small wedge of steel into the exhaust port. Once I had got this far I was able to rest the upright head steady post on it (I had already welded the two small upright fins to the post) , and then braze the entire post to the base.

Once I had all the pieces in place, I then very carefully built up the braze pools, first on top of the exhaust port, then turning the head over and working from the thread side, until I was happy that any indents had been filled and the shape was basically flush with the original contours. Normally when brazing I would not be too fussed about building up the braze more than needed, then reshaping with grinder and file afterwards. However, with this job I was aware of how difficult and fiddly it would be too grind down the braze aftewards, so I was more particular to ensure that I kept braze to a minimum and only filled the area as economically as was needed. In this case, luckily things went well and I was soon able to return the head to the oven to let it cool slowly.

With the brazing of the head steady completed, and looking pretty reasonable, the remaining jobs - i.e. fitting new valve guides, cutting the seats and fitting valves will wait until a new batch of valve guides I am having made are ready, which as I write this in mid May, should not be more than a few weeks.

Balancing Crank

Crank balancing tool, ideal for the job

As I mentioned earlier in the article, I had previously checked the crank for trueness, it running within 2 thou (thousandths of an inch) across its full length. The Bigend bearing also felt pretty good, so I decided to leave well alone for the moment – there is no point wasting a perfectly serviceable original Bigend, we will see if it stays good, given the state of the main bearing – although I expect it will last at least a couple of thousand miles, (about 10 years use at my current burn rate).
To measure run out on crankshafts, I had made my own crank balancing frame some time before, and very useful it is too (after many years of using some large steel pillars I have, with vee blocks on top). This frame is fabricated from some very substantial solid 1” square bar I found in my dad’s workshop (thanks dad – I heard you swearing as I ‘borrowed’ it), and I then fitted a round bar assembly, with adjusters for holding a dial gauge. Rather than vee blocks I then made a fabricated assembly for holding 4 ball bearing assemblies, in vee formation, that the crank could sit on. One of these sits slightly higher than the other, as Norton mainshafts are of different diameter. The whole top assembly is adjustable for width, as is the main frame, for dealing with different cranks. It does not take up much room, and is just bolted into the vice when needed. It is well worth making one if you are intending to assemble cranks, or change balance factors (necessary whenever you change piston’s with differing weights).

Calculating Balance Factor
Balance factor for SOHC Norton 500 engines should be approx 66%-68%, erring towards the 68% (although I suppose this depends what revs you intend to run the bike at). Some time ago I was fortunate enough to buy a couple of lovely original Hepolite International (petrol) pistons off that old Norton stalwart, Julian Harvey (Hi Julian if you are reading). One of these pistons would be perfect for this engine, so I measured its weight (with gudgeon pin and circlips), weighed an International conrod, and estimated the top third of its mass (this is considered the reciprocating element of a conrod) and added up the sum of these elements. I then calculated what 67% of that mass would be. I then subtracted the top third weight of the conrod from this final amount (don’t forget that when balancing the conrod weight is already attached to the crankshaft!), and that gave me the final weight I needed to hang from the crankshaft to give a ‘neutral’ balance when balancing – i.e. the crankshaft should not stop in any one spot.
I have a collection of small brass weights I use for this, and a plastic screw top peanut container, with a wire hook which is perfect for hanging on the end of the crankshaft. Initially I hung this from the crankshaft and then placed weights in it until the crankshaft was neutral. I then placed the container on an accurate set of scales, and took a reading, which told me it was 50 grams out from the desired rate – hey presto.

Stage 1: Having cleaned up the crank, I measured it for trueness, on my crank balancing setup - it was within 1.5 thou" along its full length - which is good

Stage 2: To get balance factor to 67% using Hepolite Inter piston, I needed to add 50 gram to bobweight side. I tapped holes (12mm) to take plugs on both flywheels

In this case it was the bobweight side (opposite Bigend) that was light, which did not surprise me, because it looked like this side had had additional lightening holes added at some time in the past. I ‘ummed and ‘aahed for some time on the best way to get round this, but thought in the end the most expedient method would be to drill and tap those holes, so I could add Hex head (i.e. Allen spanner) grub screws of varying lengths. Doing this has the advantage that if I change pistons at some time in the future, adjusting balance factor should simply be a case of changing grub screws.
I decided on a 12mm metric thread, as hex head grub screws in this size are easy to get, and come in a variety of lengths. I bought a 3 piece tap set (course thread) and then it was just a case of carefully tapping each hole – first with the taper tap to ensure the thread started easily, then finally the plug. This is a big thread, so if you try it yourself make sure the flywheels are held firmly in a vice (in the photograph you will see a large screwdriver inserted on the opposite side to stop the flywheel spinning) and use plenty of fluid.
I then measured out 4 plugs that approximately equalled the missing weight and screwed them in, two on each flywheel, one on either side of the mainshaft\Bigend centre line.

Stage 3: Having previously worked out the number of inserts neeeded to get to the required weight - I then screwed these hex plugs into the flywheeels with Loctite

Stage 4: Final task was to centre punch the inserts - I had previously put a nick in the head of each one, for this purpose

Stage 5: As can be seen, with the correct weights hanging from the conrod (in plastic container), the Bigend eye sits almost midway - which equates to 67% balance factor

Before finally screwing the grub screws in, I just attached them temporarily, so I could check the balance factor once again (don’t forget the tapping operation will move a little bit of weight), this was now pretty much spot on – good stuff!
I used Studlock fluid on the grub screws to stop them shifting, but for added security I also ground a couple of nicks in the head of each one, which I centre punched once they were tightened into the flywheels for additional security. I was quite pleased with this in the end, and hope this will provide a relatively smooth engine in use – as always, we will see.

Next Article: -->
Fitting Main Bearings and Oil Pump
'37 Norton Inter Part 2

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