We regular have enquiries from people asking if we can make stainless steel  petrol tanks for their vintage and veteran cars or bikes. Our reply is “of course we can, as long as you supply have a pattern or drawing”.

Manufacturing custom stainless steel products has been at the forefront of Stotfold Engineering’s product turnover. We have been manufacturing stainless steel fabrications, fittings and tanks for food preparation companies for over 40 years of trading, so stainless steel fabrication is not a problem for us.

Stainless Steel Petrol Tanks

Stainless steel petrol tanks have the benefit of not rusting, cracking or having to be cleaned or lined due to internal rusting. A lot of vintage and veteran car and bike fuel tanks were folded and soldered along the seams, together with most of the fittings, such as flanges. After many years of service these soldered joints are liable to leak. Years of servicing, undoing and tightening tight nuts, bolts and fittings placed strain on the soldered joints causing cracks and therefore leaks. Over time these cracks would be patched up with solder, but would evenually give up the ghost and then they would find there way to us for replication in stainless. We have a passion for stainless steel work and welding it. When we receive an order to build a stainless steel fuel tank we will measure it up and take drawings before dismantaling it. It has to be dismantled as to ascertain where any internal fittings are fitted and to discover where the baffle plates lie.

Baffle plates are commonly used in car fuel tanks, these are used to stop fuel from slopping around and to strengthen the overall outer structure they even play an important roll in noise control, i.e. if you had a tank with no baffles and it was only part filled with fuel, the petrol would rush to one side of the tank if you put you brakes on or accelerated. stainless steel petrol tanks have many benefits over their counterparts as they do not corrode, they are more rigid and the weld joints are a lot more resilient and they are resistant to the affects of all fuels. Most costomers perfer originality, particualy if the fuel tank is exposed as on many veteran cars. This is no problem to us as we can fit all of the original brass fittings onto the new stainless steel petrol tanks. The stainless tanks can be painted with no special preperation and they will last you a life time with no servicing.

Dad met and married my mum in the USA. They moved back to England, into Necton Rectory, a massive house with a Victorian kitchen, garden surrounded by walls with trained fruit trees and loads of glass houses. The reason why I mention this bit of history is that I was born in 1962, a year after they came back to the UK from the US and after a year of living in the rectory I could distinctly remember a green bicycle in the wine cellars. I was only a little over a year old and was given the freedom to roam throughout the house. Year’s later we moved to another house in letchworth and dad started up an engineering company and was working all the hours under the sun.

I was nine year’s old at this time and interested in mechanical things such as the push lawnmower. It took several hours to cut the grass around the house. Even at this young age I found it irritating having to lift a heavy sheet of canvass that covered something as we didn’t have a shed or garage to store anything in. The irritating article in question was the Rory O’Brien, it had been abandoned but not forgotten during this period in its life as it was being partially protected under tarpaulin. Years later we moved to a bigger house with a garage. I was heavily into motorbikes at the time, but the Rory O’Brien stood there haunting me with its now rusty patina. “Yikes!” its time for a bike restoration, I thought.

The bicycle was bought out onto the workbench and everything was stripped off of the bike. The frame was sent off to the chrome platers to have the lugs and fork ends plated. The rest of the rusty and rotten aluminium parts were trashed and replaced by the latest up to date circa 1980’s Campagnolo parts. The bicycle, now complete, was spray painted in cream, with it’s lugs resplendent in new chrome and outlined in gold. It was the first and best restoration job I thought I had done. Dad enrolled me in several cycle racing clubs and I became a competitive time trialler. I also took the bike to Austria, tackling some of the steep mountain roads and passes up into the Alps.

After 30 years of use and one fork collapse at Stotfold traffic lights, I thought it was time for a proper period parts restoration. Here the fun starts, as I have become a bit of a perfectionist in all my restoration projects. All of the parts I had thrown away and replaced with Campagnolo parts, now had to be replaced with the original period stuff. This had to be done from memory. EBay came to my rescue in the replacement of original parts. I remember that the seat was Brook’s competition with really big rivets. The gears were three speed Sturmy Archer, which was the fashion at this time. This would be the only compromise that I was willing to make, as there are so many good Derailleur changers and gears in this period of cycling. Dad probably couldn’t afford all of to notch additions at the time. The wheel hubs were manufactured by a company in Birmingham called Harden. The brakes were made by GB as were the levers. The wheels or rims were early Mavic alloy ones.  The handle bars were made by a company called Randonier and the stem was made by GB Hiduminium. The bottom bracket was manufactured by Baylis Wiley, the peddles were Brampton “B8s” and the chain ring gears were simplex double chain ring. Bearing in mind all of these parts had been ditched.

Here is an account of the cost of replacing parts that I had thrown away and replaced with more up to date stuff.

Brook’s competition saddle                              £90.00

Brook’s seat bracket                                            £20.00

Hubs, harden flyweights                                    £155.00

GB break levers                                                      £55.00

GB break callipers                                                 £45.00

Bottom Bracket (hollow spindle)                   £65.00

Peddles Brampton B8s                                        £150.00

Double chain ring simplex                                 £40.00

Derailleur simplex                                                £85.00

Early Christophe toe clips                                 £20.00

Other parts                                                              £150.00

All of these parts were purchased on eBay UK with the exception of the simplex double chain ring, the simplex Derailleur and the Christophe toe clips, these parts were found on eBay France - small ads ,which can’t be found on eBay UK worldwide search. Every part purchased had to go though some sort of restoration, be it a quick polish to a re-chroming job, except for the Brampton peddles that were unused and very greasy in their original box. They were purchased from Hillary Stone, who deals in very fine quality products for the discerning restorer and cyclist.

Another part that I kept in mind was another frame and forks as my forks had been brace repaired. Occasionally I would look on eBay not really expecting anything to crop up. But to all my surprise a frame and forks did appear and I put this on my watch list, it looked exactly the same as mine, curly lugs and all. I eventually won the bidding at £255. On receiving it I first looked at the frame number 189, unbelievably mine was 183. The only differences were the agrati dropouts and the centre pull brakes. Mine were Juy simplex dropouts and the side pull brakes. The fork lugs were slightly different to mine as they were not quite as ornate. I decided to scrape some paint off and see what was underneath, on the seat down tube I noticed some little rust lines, a little probing and poking with a scriber revealed some nasty corrosion.

This is a different frame with nervex proffesional lugs fitted.

This was due to a cork, I found later, having been forced down the seat tube to stop water getting down onto the bottom bracket which had a shrouding of thin metal foil wrapped around it. The corks essentially acted as the base of a moisture pond, hence causing the corrosion. “strange what some people do”, as I did when I threw all the original parts away. The repair was affected by making a tube of steel that could be driven down to the corroded area and then be brazed into place, the braze being run into the rust holes so securing the piece of tube that I had made. After brazing the stem was fettled to produce a completely invisible repair ready for painting. The centre pull brake tubes where then sweated off and a couple of cable brackets were welded on to bring it up to my bikes specification. The whole frame was stripped off paint using nitromors and wrapping of cling film to keep the aggressive fumes of the stripper working on the paint.

With the work completed it was now time to get the frame and forks down to the chrome plater. I use Doug Heath In Baldock for chrome and nickel plating as he has an understanding of how delicate the operation of old lug plating is. A plater can polish the lugs to such a degree that they look great, but have no strength in them and after the bike has had some miles put on it you will soon see the stress fractures in the chrome finish. There is a compromise in as much as “do I chrome the lugs or do I paint?”, if the lugs are quite pitted with rust one has to think about painting them. Once the lugs are weakened you will only have a frame that is only worth looking at, not using. Doug Heath will tell you whether it is platable or not.

1. Fully restored antique umbrella stand.

2. The left stay in the picture is the new replicated one.

Recently we were asked to repair an  umbrella stand. The left hand stay was missing. Replacing parts on cast iron objects can be expensive. To cut down on costs and avoid having to go to a foundry to have the part cast I decided to replicate it in steel. The steel would be then coloured to look like cast iron. 

The missing bit had what looked like crudely turned parts. These were in the shape of flower petals, with a square section holding them together. These turned parts were replicated on  the lathe and the rough flower petal shape was filed using a triangular file. The square section was made from 16mm steel tube with a thickness of 3mm. This square tubing was then creased down the  middle of each flat side, its entire length. This produced a subtle star section that replicated the other side of the stand.

The parts were then TIG welded together to obtain a small unnoticeable weld area. The whole replicated part was then aqua blasted to give the surface a good key for blackening, so as to look like cast iron. The blackening was achieved using Zebo Grate Blackening, which is rubbed on with a rag, left to dry and then buffed up to give it a mildly glossy metallic lustre. As you can see from the photographs the replicated part is almost undetectable.

By Terry Ives

 There are four main types that are used on four stroke motorcycle engines:

1. The  splash or spray system
2. The total loss system
3. The dry sump system
4. The wet sump system

1. The splash or spray system of lubrication: This was employed in the earliest days of engine development. The system comprised a sump or crankcase with a set amount of oil enclosed within it. As the rotating crankshaft and connecting rod dipped into the oil at the bottom of the stroke it picked up and lubricated all of the lower parts of the engine. This type of lubrication under went small design modifications. These included a rod which extended down vertically from the big end bearings, dipping into the oil in the sump and therefore picking up a little more oil. There  were several designs of these. There are also accounts of con-rod and flywheel modifications. These were done for the sole purpose of getting the oil higher up the crankcase. The inherent side effect of this system of lubrication is that the crankshaft was subjected to oil drag as it splashed through the oil in the bottom of the engine.

These early engines employed mainly white metal and plain bronze bearings with crude seals. They were slow revving, being low in performance as well as in crankshaft and gearbox speed. As engines developed, the customer and therefore the manufacturer required more speed and with this came higher revs. The stroke of the latter day engines had to be shortened to attain these revs. With the increase in revolutions came increased performance and higher piston speeds. Basically all the internal workings of the engine were subjected to higher rotating and reciprocating speeds.

Oil development and improvement had crept a long with improved engine designs. The ball type bearing had replaced many of the plain bearings and seals were becoming more effective. A more modern lubrication system was required the keep up with the performance changes.

2. The total loss system: was employed for these more advanced engines. They used a simple oil pump that was hand operated. A typical vintage motorcycle users manual of the day stated that at normal riding speeds (20mph) one pump of oil was needed for every eight to ten miles and at higher speeds (30mph) a pump was required every six miles. The oil for the pump was fed from an oil tank. Before starting one of these engines you had to give it a pump of fresh oil. This topped up the splash lubrication system in the sump, which was still being used, and took care of the bottom half of the engine. Drip feed lubricators were often used in conjunction with hand pumps and were normally set to eight drops of oil per minute.

When using just the manually operated pump, the early motorcyclists sometimes it was found that the engine would run faster if less pumps were given, but only for a short while. This was due to there being less oil drag on the piston and other moving parts. If you were lucky you could flood the engine with a couple of extra pumps to make up for the lost ones that had given you the extra performance that all the early motorcyclists craved for. Oil had to be be more accurately governed and manufacturers decided if this could be done their engines would be more reliable, therefore not leaving a bad reputation for reliability in the hands of  their customers.

3. The dry sump system: was one of the first to be mechanically governed. This system uses two pumps. One feeds oil from an oil reservoir under pressure to lubricate the engine before dropping into the sump. The second pump or scavenge pump then picks up the oil to return it to the reservoir, sometime via the transmission or other parts of the engine that require lubrication. you will find on dry sump engines the scavenge pump is double the size of the feed pump. You should be able top see the scavenge pump working by removing the oil tank filler cap and observing oil being fed back into the tank.

When dry sump engines are laid up for a while there is a tendency for them to back flow on the scavenge side (wet sumping). When you start the engine with a dry sump that has sat for a while and you cannot see any return flow coming into the tank, pour a pint of oil in and wait until you see return flow activity. Then adjust the oil level with a siphon or draining.

4. Wet sump lubrication: was the next development and removed the necessity for an oil tank. It seems to be the most popular system for Japanese motorcycle manufactures. The oil is contained in the crankcase sump, however it is separated or masked from the crankshaft, so as to prevent oil drag and any frictional losses from the oil splash. A pump oils the engines vital components and returns the oil via a filter back to the sump for recirculation.

What types of oil pump are there?

There are four types of oil pumps commonly found on motorcycles. These are:

1. Gear oil pumps
2. Piston oil pumps
3. Centrifugal pumps
4. Trochoidal pumps

1. Gear Pump components

2. Piston pump fitted to a Triumph Tiger 100 being restored here at the workshop.

 

2a. Exploded view of a piston pump.

 4. Trochoidal  pumps work with a star shaped gear attached to the end of a shaft. The gear is rotated within a metal body which has the same star shape cut into it, but bigger. The body of the pump, usually steel, also rotates within another housing, which is usually aluminium and machined into the engine cases. Oil enters the body and is pressurised in between the finely machined faces on the star and is forced around the engine via outlet ports.

4. Trochoidal pump components. This is the most common now for modern motorcycles.

 Oil pump restoration and repair

When repairing oil pumps, whether it be for cars or motorcycles, the first thing that has to be done is t o remove it from where it is fitted. The next thing to do with the pump while it is a complete unit is to look at its overall condition. Are the any knocks or dents that might have occurred while removing it. These dents may cause distortions or bad running clearances on shafts or gears within the their housings. When you look at a pump dents or knocks are not always clearly evident, as the may be black oily residue covering the pump body. These oily residues can usually be scrubbed off with petrol or paraffin. Here at Stotfold engineering we aqua-blast them clean. This helps identify any marks on the pump casings. The pump internals are washed in paraffin and blasted with high pressure air.

A gear pump stripped for restoration.

Prior to aqua-blasting the pump should be stripped down completely. Take notes on how it come to pieces and lay the parts out, so that you recognise them for reassembly. Use a digital camera if you think you will forget. Once all the parts are laid out it is time to clean and inspect them, taking note of wear and running clearances. When we rebuild pumps we always set running clearances to 0.001″. This leaves enough gap for hot oil to get between all of the running and pumping parts. It is worth taking into consideration that if any parts such as spindles or pinions are worn, they can be precision ground to just clean them up. The holes they run in can be then bored out and bushed to suit the new spindle diameter. I have not yet found a pump that could not be restored.

Fully restored oil pump completed by us.

It is now time for reassembly. Each part has been meticulously cleaned and checked. Once reassembled, with any nuts replaced or wired up if necessary, it is time to oil it and run it to see if there are any tight spots. This can be done using a drill on low speed. Then check the it operates freely using  just your hand. It should run freely. You can now reinstall the pump.

By Terry Ives

Carburettors - not that scary, just time and patience

With any carburettor restoration the first thing to do is assess the carburettor and see if it is actually worth restoring. The cost of restoration could be more than buying a new one. However if it is a hard to find one or expensive to replace then its generally worth restoring. Lots of the carburettors I have restored fall into these categories and are usually very rare or very old, therefore worth restoration.

The first step in restoration is to dismantle it. Take detailed notes on the position of all the parts and note the settings, whether they are right or wrong. A digital camera can be used to help make these easier, as a picture can tell a thousand words. The settings you get the carburettor in may not necessarily be right, but they will be a starting point. Lay all the parts out in some order that will recognise or do a sketch with arrows pointing to where parts go. Bare in mind that on old carburettors that common thread sizes were used for many jets in one single carb, so it can be easy to get them fitted in the wrong holes when putting it back together.

The next thing to do is systematically clean all the parts. I always start with the major parts, the float chamber and top half. The kindest way of cleaning and getting a great natural lustre is aqua blasting, whatever the carb is made of, brass on early machines or monkey metal on the later types. Aqua blasting is a non abrasive cleaning system that won’t remove any metal, but restores the metal giving it a durable surface that is very resistant to oxidization. Aqua blasting can be used to clean jets, needles, float valves and pins without destroying surfaces or intial sizes.

When all parts are cleaned, inspection can take place for any wear or manual damage that may have been caused by tinkering. Ignitions are often blamed for poor running, but a spark can be seen or felt. An amount of fuel passing through a carburettor is a little harder to govern.

There are some points to take into consideration regarding weld repairs to carbs if the main body leaks. Early brass carburettors are easy to weld and repair as they are generally made of quite high purity metals. Soft solder or silver is best for these. Some of the later carbs were made from zinc aluminium casting, mazak, or pot metal ( the material they used to make cap guns from). Great care must be exercised when repairing these. If it is an early mazak carb it has probably had a lot of fuel ingress in the metal. You may find that if you try and repair these with aluminium welding, TIG or gas, lumps may explode from them. A good indication of fuel ingress is on gasket faces. If under inspection you find cracks or de-lamination evident, then under no circumstances should it be welded.

Lumiweld is a low melting point alloy and the manufacturers says it can weld anything alloy. This is however not true on old mazak carbs, but is successful on later types of carb that use a little less zinc to aluminium ratio. If it cannot be welded there are some good metal adhesives on the market. I have tried most, but for carbs of the mazak or monkey metal variety I use a dental resin that works admirably well. Even stripped thread can be repaired with it.

Thankfully a lot of the inner workings are of brass. Jets are fixed objects, just controlling petrol flow, and the other bits tend not to wear to much, just needing a re-seating with a fine grinding compound, with a good clean afterwards of course. Remember that cleanliness is paramount in the fuel system governor. Sometimes, not usually, the butterfly valve shafts are worn and let the air ingress messing up the air fuel mixture. These can be remedied using bushes of any resilient material, brass or plastic, but it is very difficult to get things perfectly in line to give a smooth operation.

When all parts are clean and inspected you can start on the reassembly. This is quite simple as long as you have kept your notes, sketches or photos. New seals and gaskets should be considered when reconstructing the carburettor. I always tend to fit thin gaskets, but if thick gaskets are fitted then I would consider they are to take up deficiencies in badly mating surfaces, like trying to stop leaks on the join between the float bowl and carb top. These two surfaces should be perfectly flat. I usually file and then finish the faces on a dead flat surface plate using fine grinding compound to take off the absolute minium material. On old mazak carbs this is OK to do at the machined faces of the float bowl and carb body are usually swollen with petrol ingress. Its best to grind of the two surfaces leaving a slight witness of the old surfaces, thus ensuring you have taken of the minium material. A thin gasket with a little petrol resistant sealant on both surface can now be fitted. When bolts are tightened using thick gaskets it is worth remembering that the bolt head size dictates where the gasket is being compressed. If you had two bolts 1″ apart and you tightened them to a couple of pounds, the intermediate gasket space in between the bolts would seal. If you now applied more poundage on the bolts the more distorted the gasket would become and therefore the less sealing capacity you would have between the bolts. This is why I advocate thin gaskets on carburettors.

by Terry Ives

I stripped the engine and set the bottom crankcase up in a holding jig. I then set the gearbox shafts and gears in their respective positions. Then I ran through all the gear selections up and down the gearbox looking at such things as selector fork barrel position and fork position.

Honda CB750 four gearbox selector

I noticed the selector forks (2, 3, & 4) were not pushing the gears into full driving mesh, with some gears heavily meshing and some only with a shallow mesh. This would cause them to jump out of gear under load. After closer inspection I noticed that the selector forks were tilting or moving poorly under selection with the drum (6). This immediately pointed to the selector fork running shaft (5) being worn or undersized.

I measured the selector fork bores and found them all to be well within tolerance. I then measured the shaft and found it to be .005″ undersize from the selector fork bores. I informed the customer about the poblem and he supplied me with another new shaft. I measured the new shaft to ensure it was correct only to find it too was .005″ smaller than the fork selector bores. When ever I have made fork selectors and shafts from scratch I have a running clearance of .0005″.

I then machined a new selector fork shaft with a .0005″ clearance. This provided a very close push fit into the running holes in the bottom crankcase that supports the shaft. Anyway, when it was all fitted I looked at the selector fork operation and found that all the gears meshed perfectly throughout the gearbox.

My conclusion from all this, is that I wonder if gearbox selection on Honda CB750 four’s was an inherent problem or whether the gear selector shafts had been badly manufactured following poor engineering practice. The shafts I make and made for this particular bike are manufactured from material of the highest specification. They are then case hardened and precision ground.

All our restoration work is carried out at our workshops. We do not farm work out to other engineering companies or other so called bike restorers who simply buy a new part and bolt it on. We pride ourselves on the ability to look at a problem, understand it and provide a solution through skilled and competent engineering.

by Terry Ives