Category Archives: Engineering

Back on track

February 11, 2016 Supersquirrel 1 Comment

I’ve been very busy but two months is a long time since the last post and I shall endeavour to do better.

One of the things that has taken a lot of my spare time in the last months has been teaching myself to draw using a 2D CAD program. I didn’t do technical drawing as an apprentice and I’ve always looked upon drawing as being such a vital skill, especially if you need to be able to get work made out by others. Of course, you can do a lot of things with a simple sketch, but it’s undoubtedly quicker and simpler (once you know how) to make changes and amendments using a digital file.
Also, where clearances are tight, and dimensions are precise, because it shows (of course) a true representation of what you are wanting to produce, it enables you to see more easily any mistakes you may have made in measurement or design. Like pretty much everything I do, 2D CAD is so old hat that on one hand it almost seems ridiculous to talk about it but it’s new to me and I think it’s the most exciting and interesting development in my education for years.

The initial incentive to push myself to learn how to use CAD was that I found myself unable to find a particular component for a Scott engine that I’ve been working on. It’s a mid twenties engine and it had a bearing cup which was both corroded and cracked. Enquiries about a replacement cup with those associated with the rebuilding of the older engines have been fruitless. However, before I go any further I should explain a little about the main bearing assembly of a Scott and why repair or replacement presents more of a challenge than for many other engines.

The Scott engine has its two crank-chambers separated by an external area which houses the central flywheel.

The crank-chambers themselves are very slim by design so as to maximise the crankcase pumping effect and so is therefore the main bearing assembly, crank assembly and big end / rod assembly. The main oil feeds are visible on the picture and are fed direct to the main bearings. These are (generally) fed by a metering unit called a Pilgrim pump (sic) which allows the user to adjust the quantity of oil delivered to each cylinder. The delivery rate in use is defined by the engine speed. The main bearings and big end bearings are roller bearing units, which involve outer and inner races that are made specifically for the Scott. Rollers themselves are fortunately still available (!) but if Scott bearings are damaged, the work to ensure the accuracy and fit of the replacement assembly requires a great deal of precise toolroom work.

A picture is worth a thousand words…

Scott main bearing bearing 'cup' in engine. — Scott main bearing bearing ‘cup’ in engine.

Scott crankcase with bearing'cup' removed — Scott crankcase with bearing’cup’ removed

Two variations of Scott main bearing cup

You can see here the drilling into the outer wall of the crankcase main bearing housing

Crankcase main bearing oil feed drilling

and you can see here the corresponding hole in the outer diameter of a main bearing cup. The groove is to give some rotational tolerance when fitting the cup.

Late Scott main bearing cup (big flange)

Here you can see a cross sectional drawing showing the drilling through the rear of the later cup design:

I will one day go through the operation of the metal to metal sealing arrangement of the crank-chamber, but suffice to say that it is a spring loaded seal that in Scott circles is called a ‘gland’.

but back to the bearings.

The bearing outer is retained in the crankcase with an interference fit. This fit is necessary to provide strength to the bearing ‘cup’ during operation and to mitigate against the differential in thermal expansion between the steel cup and the aluminium crankcase. It also has to ensure the constant seal for the oil feed between the crankcase and the cup.
Even if there is no problem with the bearings themselves this interference fit diminishes over time and the cup can become less well secured. This can become evident by oil leaks noticed in the central flywheel area. Sometimes this can be oil leaking past the gland but sometimes it can be leakage at the connection of the oil feed drillings. It’s also very noticeable when you remove an old cup… often they require very little force to knock out.

The cups when newly fitted have 0.005″ interference between the outer diameter and the bore in which they fit. This means that fitting is done with a cold bearing in a hot crankcase and can be a bit ‘heart in mouth’. It is a real pain if the cup isn’t exactly square going in.

And that’s the start. You then have to make a steel ring that fits in an annular groove in the aluminium around the main bearing. This steel ring (called a shrink ring) is made to have 0.009″ interference between it’s ID and the corresponding diameter of the groove. The shrink ring is then heated until it’s red hot and dropped into position.

After all this, the mouth of the cup which is not supported in the same way as the rear, is compressed so that the bearing track is now tapered. The whole lot must be ground in situ… which is another story.

Anyway, back to my CAD drawing. I had an-usable cup and needed to have one made. Although I have some copies of Scott drawings I don’t have one for this particular component and so I thought I must make a drawing myself. After considerable efforts to get on top of the process, I am really happy with progress.

Hopefully I’ll have it finished by the end of the week.

work in progress. 1925 Scott crankcase cup drawing.

Engineering

Casting video

Video December 12, 2015 Supersquirrel Leave a comment

I thought I’d share this. There are lots of casting videos on you tube but I really like the work that ‘Myfordboy’ does, as he shows the entire process through pattern making, core layout, casting, machining and the final object (normally a model engine of some kind) working. Absolutely brilliant.

Engineering

Early Christmas

December 9, 2015 Supersquirrel 2 Comments

I’ve seen a few possibilities for purchasing potentially very useful tooling recently but for reasons of economics and priorities I’ve not been able to take them all up. One thing I did do though was to buy a number of collets specific to the Smart and Brown lathes made by Crawford collets. They are numbered 2804 and not easy to find… my lathe was probably made somewhere in the 1950’s.
Anyway, a little advance but since I am spending so much time scraping the slideways (almost 0.010″ off the second top slideway now but a lot of alignment work to go), it’s encouraging to be able to improve the possibilities of it’s usefulness when it’s finally rebuilt.

Smart and Brown '2804' collets. — Smart and Brown ‘2804’ collets.

Engineering, New posts, Video

Thinking about castings…

December 9, 2015 Supersquirrel 2 Comments

I went to a 3D printing show with a Scott owning friend a couple of months ago to look at the possibilities of using 3D printed models as part of the casting process for development work with Scott barrels and pistons. It was his idea, not mine but it was fascinating. There are various different possibilities: you can make a 3D CAD drawing and then print a pattern from which you then set up to produce castings in a conventional manner, you could possibly print an exact replica of the component you want out of wax or something similar and then investment cast the item such as they do with jewellery. You can also print the actual sand cores, rather than printing the patterns from which to make them. You can use a 3D scanner, either handheld or one that rotates around the component, which will interpret the image into a 3D image from which a CAD file can be automatically produced. It was very interesting, but it got me thinking about how little I really know about casting.
Roger used to have patterns made regularly, not only for his Scott but also on a far larger scale in the context of the family-run, Leicester-based special purpose machine tool company, ‘Moss Machine Tools’, that he used to be works manager/ managing director for.
That company, details of which you can find if you click the link through to ‘Moss Engineering’ at the top of this page was involved in making complex machines for automotive, MOD and other sectors from 1947 to around 1991 when economic conditions forced it to cease trading. I don’t know whether he’s ever cast anything himself but he has significant understanding through having had to work with foundrys and pattern makers and seeing the issues that have to be overcome within those areas.
I realise that I’ve been looking at all this interesting technology to possibly assist within a casting process but I still haven’t any actual experience of casting of any type. I’ve worked with castings of course, and understand a little of the some of the areas that have to be considered; shrinkage, porosity, premature cooling, incomplete filling of cores but have found myself thinking about it more and more and have gone where any self respecting modern would-be self-improver goes to nowadays… You tube.

I’ve seen several casting videos recently but here’s one that I really liked by a guy called Keith Rucker, because of the thoroughness of the explanation of the process. he’s not setting himself up as an expert but he’s doing it and seeing where it could be better. He’s also using 3D printed patterns to make vintage components! I’m not likely to be attempting to cast any time soon, but it’s all part of learning the language and gaining a better understanding at how a pattern has to be made in order to be able to make up a successful set of core boxes and ultimately a successful casting.

Engineering, New posts

Scraping the night away

November 11, 2015 Supersquirrel 3 Comments

I’ve been trying to sort a problem out with the website which means that I can’t upload photos. Hopefully I’ll get it sorted out soon but in the meantime I’ll just have to do without.

I was brought up with Smart and Brown lathes; my dad has had a Model A for around 50 years and a 1024 VSL for around 20 years. It wasn’t therefore a huge decision what I would look for when I started to put my workshop together a few years ago. The lathe I bought (unseen off ebay) was a Model M Mk2 which was a very nice 4″ swing tool-room lathe from the late 1940’s to the end of the 1950’s.

It looks better blurred... — It looks better blurred…

It was in a pretty poor state and I think it was a long time since it was a cossetted tool-room machine. Undoubtedly shifted to some unswept corner of the maintenance shop to turn spacers on. I made several other posts about the assessment and strip-down but the most significant matter was the slide-way wear. There was 0.010″ over the length which is quite a lot!
I had wondered about grinding and looked into the costs, but it didn’t seem to be a perfect solution. True it would be a lot quicker than scraping but I could see the possibility of knock-on problems. I wanted to keep the original position of the head, which provided the correct clearance arrangements with the feed drive gears at the rear. One grinder I spoke to suggested that they had ‘shaved’ gears to get over this problem. It just didn’t seem like the right answer. Whatever I did I was going to have to re-establish the original height of the saddle once the work had been completed to ensure that the half nuts still centered on the lead-screw, the feed shaft within the apron, and the main traverse gears had the correct clearance with the rack.
So, to cut a long story short, I decided to scrape the slide-ways using a hardened rail sitting on part of the original head location face and the end of the tail-stock slide as a guide. With a clock stand moving along that whilst clocking the front way, I was not only able to see the initial wear but it gave me a basis from which I could start the work, so that I could start to scrape the worst of it out and establish a reasonable state of parallelism before moving to the next stage.
Months of intermittent scraping have followed. A bit here, a bit there. A few weeks ago, I had arrived at the point of being within 0.001″ over the slide-way according to the clock and so I went to blueing the rail and using it directly on the slide-way to establish a better flatness.

Still further hours but at last the front slide is now ‘good enough’ to sit the rail on to start to do the opposite way. There’s a lot of work to come and this is why I haven’t tried to finish the front slide perfectly. When the rear slide is done, then I’ll use a precision level on my datum faces (under the head) to set the bed horizontal and then use some ground V blocks which span the two slide-ways to establish not only the angular alignment to the head face but to ensure, using blue under the v blocks, that the alignment is achieved with faces on the same plane, not just parallel. It’s almost inevitable that after I’ve scraped the rear way, that the two faces will be parallel but not on the same plane. The process to align will mean that at least one of the ways will have to be completely re-scraped again.
Anyway, months of intermittent work ahead but the first stage is complete.

Engineering, Historical posts/ stories, Motorcycles, Scotts

Featherston workshop

June 18, 2015 Supersquirrel Leave a comment

Roger had a recent email exchange with a gentleman in New Zealand, John Stewart, who has had a long history around Scotts. His grandfather was a photographer and captured a wonderful photograph of his father in his workshop in Featherston, New Zealand. John’s son, Scott, repaired the plate glass image and apart from Yowl (the journal of the Scott Owners club), it’s not been published before. He has kindly allowed me to do so. The copyright belongs to John Stewart and I use the image here with his consent.

Enjoy

The attached photograph of my father’s workshop in Featherston may be of interest. This was almost certainly taken by my grandfather, GT Stewart on his glass plate camera (which we still have), sometime during WW1. The garage was established in 1906 as Stewart and Son, Later Stewarts Imperial Garage. The garage provided a wide range of services including maintenance of steam traction engines, motor cars and motor cycles and during the war, repair and servicing of army vehicles for the nearby Featherston army camp.. Two vehicles in the background are almost certainly army truck chassis.

The man at the back is Dick Rowe who was workshop foreman. The lass sitting on the chassis is Miss Freed secretary and the other figures apprentices and tradesmen a couple of whom appear to be working on Model T Ford engines.

The interesting bit is of course the Scott on the right. This I believe is a 1914 model and was the machine that my father, H.H.Stewart raced on the grass track in Featherston with some success. The family left Featherston in the mid 1920’s and dad kept the engine and two speed gear out of the Scott along with the remains of an 1898 De Dion Tricycle and a 1900 Locomobile steam car. He carted these parts round the country during a number of moves until finally settling in Auckland in 1926. The two speed gear was used as a change speed gear on a turret lathe after WW2. The engine I gave to a friend many years ago who had unearthed the remains of his late brother’s 1914 Scott with no engine and the De Dion has been subjected to full restoration over the last 3 years which I finished in Dec. last. It runs superbly.

1932 Flying Squirrel Racer, Engineering, New posts

A morning on the dyno with the Scott

April 23, 2015 Supersquirrel 2 Comments

I really enjoyed taking the Scott to the dyno yesterday. It was the first time I’d ever actually booked a proper set-up rather than a single run. I suppose cost was always an issue but I have realised how useful it is to be able to see the results of the changes you make and a proper session allows you to experiment with many different settings and see how each affects the result. It’s a bloody good way to see what affects your power output, and how. The cost is similar to me going to a trackday, and there’s no way I’d have gained the same information from that.
Of course, you need to have someone who can run the dyno and can interpret results. GT motorcycles of Plymouth have a very interesting division called ‘Performance Engineering‘ that specialise in rebuilding, restoring and tuning Honda racing bikes, and it’s these guys that run the dyno. Steve is highly knowledgeable and experienced in getting the most from an engine on the dyno. I’ve done my previous runs with him, but yesterday he was able to really show me the benefits of a dyno setup. Steves colleague Andy, another two stroke fanatic, was assisting and as the Scott’s engine note became crisper and cleaner they were both obviously enjoying the experience. Ok, so the Scott doesn’t put out the sort of horsepower as an NSR500, but it did sound so very good .. and maybe the 4.5% Castor mixture helps too!

Anyway, I realise that for many people the idea of going on a dyno seems a bit extreme but carburation and ignition set-up problems can persist for years if you don’t seize the opportunity to really get to the bottom of them. I don’t want to spend my time at a race meeting or a track day like the Beezumph constantly messing around with jets , needles and timing just to try and get somewhere close. You’ll always have a certain amount of tweaking.. but at least I feel like I am quite close with what was a completely unknown arrangement.

So, What happened?

I’d fitted the 1″ carbs with 320 main jets for a start. The needle was on the bottom groove, so all the way up. I’d figured that it might be rich but I had no desire to start from the other direction! The timing started at 22BTDC.

It was rich. Our runs followed the following order:

1: down two mainjet sizes to 300
2: down two mainjet sizes to 280
3: drop needle one notch
4: drop needle another notch
5: drop mainjet one size
6: raise mainjet one size
7: change timing to 23.5

You can see the graphs here for the final results compared to the very good curve I produced when I first set up the bike up on methanol.

Torque curve for the Super Squirrel racer.

horsepower curve for Super Squirrel racer

The exhaust temperature sensors were really useful and we were able to monitor for significant changes with any modifications to setup that we made. The final high was around 530°C. Always increasing by about 30°C to 40°C the moment you shut the throttle off… interesting stuff.

Type K thermocouples read by simple meter

You can see that the Torque curve starts later and then increases at a very high rate. It may be that this lost section (around 400 revs) at the beginning is retrievable by playing with cutaways, but the gain in midrange torque is very good indeed. That may be down to the improved gas flow in the head. It loses to the methanol later in the rev range, about 4000rpm. The methanol torque stays high all the way to 5000rpm where it suddenly falls off a cliff. The new curve hits a higher torque figure but tails off more noticeably. However, the fact that suddenly I started to have more revs was a bonus (as long as I can get the 400 back at the beginning!). I think Steve’s attitude was that the extra ‘over rev’ was extremely useful as the engine was able to keep pulling longer because of it.
As far as I understand, the fact that I increased the head volume, lowering the compression ratio might have created the conditions to encourage the engine to keep revving.

As the torque was lower late in the new curve the maximum power is less than before, but I’m not too concerned about that at the moment. It might be that I could do with the shape that I have created in the combustion chambers, but with a high compression ratio. It would be worth experimenting with heads sometime.. but not now. It may even be that the carb size is a little small, and I’ve never done any further tests with the exhausts but short of changing the slides to try a higher cutaway I’m now looking at actually using it! It felt really smooth and sounded great.

So, this afternoon I posted off my entry to the British Historic racing clubs second meeting of the year at Anglesey on the weekend of the 16th and 17th May. Roger is going too. I’ve never ridden Anglesey before but I’m really looking forward to it.

Engineering, New posts, Silk Scott

Dash to the North – the completion of the Silk Scott frame

March 19, 2015 Supersquirrel Leave a comment

I have a whiteboard in my workshop and it generally lists too many tasks that I am a reasonable amount of effort away from achieving. This last week however, I managed to get some significant ‘to do’s’ rubbed off the board.
The Silk Scott frame had been waiting at Alan Noakes’s workshop for me to come up with a plan for the final brazing solution. The lugs had been made to be brazed with a capillary fixing which really needed oxy-acetylene. I must admit that we hadn’t fixed the exact type of brazing material we were going to use and this was all part of the delay. I saw a clear weekend coming up and thought that this was my chance to push to get it finished. So the plan unfurled: first to get oxy/acetylene.
We’d had a plasma cutter at work that we’d bought from machine mart (please no comments). It was around £600 new and lasted a year and a day. The warranty department, were sympathetic but not quite to the point of being reasonable or useful, and I was told (after paying for the service) that it could be repaired for a sum of 500 and something pounds. I declined their kind offer. We’d only used it a handful of times to make register plates for woodburners and other bits and pieces. Normally around 3-4mm thick steel for a machine rated for 10mm. Anyway, since this incident I am resolved not to use them again and so was without any metal cutting equipment at work apart from grinders. So, I figured at £5 each per month for bottle hire, I could justify the oxy/acetylene. My Dad had an old portapak I could have and so I found myself at BOC sorting out an account last week.
I called Alan from the shop and enquired as to whether he’d got any prior arrangements for the weekend, and asked about rods. He didn’t and It didn’t seem that they had anything suitable, so I left with two bottles hoping that I could sort out the rest in the following few days.
I remembered a conversation with a man called Arthur Sosbe not long ago. Arthur, though now mostly retired, is a Leicester welder held in very high regard by my father. He is also a vintage motorcycle enthusiast and I believe used to race a velocette that used to lurk under a cloth in his workshop. I myself have known Arthur for many years and he has repaired many a Scott crankcase, as well as frost damaged barrels and many other fragile vintage parts.
Arthur had said that he’d naturally use silver solder, but when I quoted him a 0.010″ gap, he said that it was too wide and he suggested something else. I remembered this conversation and also that many lugged cycle frames used silver solder and I did a bit of research. A company called ‘Cupalloys’ came up as being suppliers of silver solder to model engineers, so I gave them a ring. I’d since confirmed the gap with Alan as being nearer 0.006″, which was within the capillary range for a 38% silver solder alloy which also apparently had the benefit of melting over a reasonably wide heat range, which gave scope to also create fillets.
I bought two packs of 5 rods, and at over £4 per rod, I hoped this was going to work.
So Friday came and later than I’d hoped, I packed the Moss crankcase destined for the Silk Scott into the van and I headed up country to Leicester to see Roger and to get the portapak and hoses/ regulators I needed to take up to Alan. I didn’t arrive until after 9pm but we gathered all the bits and pieces together, as well as a trophy I’d been awarded by the British Historic Racing club, the ‘Aotearoa Trophy’, gifted once to the club by a New Zealander. I believe it’s supposed to be the best performance of a 1930 and under bike. I won it last year also, and although it’s not that I actually won a race, it’s a beautiful shield with names going back many years.
We chatted, a lot, and eventually I got to bed around 1.30am.
So up and off to Alans, the offside front wheelbearing of my van starting to whine somewhat irritatingly.
I arrived at Alan’s somewhere after 10.30am and had thoughts that I might need to find a B & B for the night, as I didn’t know how fast the job would go with untested equipment and solder. I needn’t have worried because apart from Alan having to adapt some spacers to fit the crankcase, the whole process went very quickly.

Moss Scott crankcase fitted into frame - just to be sure! — Moss Scott crankcase fitted into frame – just to be sure!

we did take a few minutes to try to establish that the frame was straight prior to fixing it, and to that end I took a sight from the rear engine mounting to a straight edge laid over the bottom face of the head stock. This looked spot on, although pretty much every other tube in the middle looked like it was in a slightly different position. I realised that it was simply built this way from new and that as long as the main datum points were correct, the bits in had some ‘tolerance’. That of course is one of the joys of a low production handbuilt machine. Every one is truly different!
So onto the hot work and (making sure the detachable lugs all faced in the correct directions) using a propane torch and the oxy-acetylene, Alan soldered the new cradle assembly into the frame within a few short hours.

I was very grateful for the sandwiches made by Margaret for lunch and delighted with the way the frame came together.
with a thanks and farewell to Alan, after he’d showed me some detailed bits he’d made for Scott TT replica forks,

I shoveled my frame and the bits and pieces back into the van and headed back to Devon. A quick stop in at my dad’s to show him the results, but all in all a great result for the weekend.. and I was home on Saturday night.

Engineering, New posts, Scotts

Scott Iron barrel machining

Gallery February 14, 2015 Supersquirrel Leave a comment

I already posted a picture of an iron barrel my father, Roger, has been machining up from one of his castings but he’s sent me some more pictures as he’s almost finished.

In his email Roger said:

Pics depict a newly manufactured iron block showing inlet tract arrangement where it must be noted that as the “Spectacles” portion of the crankcase will be removed, then this forms the upper ceiling of an enhanced inlet tract.

Note the two 10mm counter bores which are used to enable accurate poisoning on holding fixtures during the metal cutting processes and by using ring dowels (Sleeves) to accurately position the cylinder head which also has such features.

Ports timings are more advanced than standard DPY blocks, but less than the aluminium competition blocks I make to special order which still give much improved torque at low to medium revs.

Dies and piston blanks to make 500cc pistons are currently in manufacture as are another batch of cranks comprising 15 sets of standard long stroke cranks. 5 sets of standard long stroke cranks to be fitted with Tungsten weighting slugs, and finally 5 sets of a special heavy duty crank variant for use with ball bearing main bearings and incorporating heavy metal weighting slugs. These can be used in standard cases after appropriate modification or in the Moss high duty large inlet competition crankcases.

If you are interested then contact him at Moss Engineering.