Speedzilla Forums banner

C3M Gurty

696 Views 7 Replies 2 Participants Last post by  cuti3moto
The urban dictionary defines Gurty as “something that looks so wrong it's right.”
I need a bike to go back for TT23.

This is my how-to guide.

Let me know if you can prove this is your bike.
I have a gift for you.

This is Gurty.
Or, should I say, this is the early stages of Gurty being re-born.

I’ve just contacted the seller about a shipping rate for this turbo.

I’ve just ordered these throttle bodies.

I’ve also just ordered a thirty-litre sonic cleaner.
Safe to say that Gurty will be ugly, but interesting.
See less See more
1 - 8 of 8 Posts
Is that the donor engine and power train it is sitting on? Interesting build, will be watching for sure.
Is that the donor engine and power train it is sitting on? Interesting build, will be watching for sure.
Is that the donor engine and power train it is sitting on? Interesting build, will be watching for sure.
Hi Tinsnips.
Yep - I'll be using the engine pictured, with a chain drive.
The frame, swingarm, and front-end will not be OEM.
  • Like
Reactions: 1
Recent progress on Gurty has been incremental.
After finally getting the shipping sorted out, my whee-bang! showed up.

I’ve eyeballed it in relation to the frame – packaging will be tight, but do-able.

My throttle bodies and secondary injectors showed up – packaging for them in the available space will also be tight, but do-able.

The shippers didn’t put the foil tape on either of these items.
I did that to keep cosmic debris out of the delicate bits.
Once bitten, twice shy.

The main frame down-tube is finished to my satisfaction – it looks simple, but took a little bit of getting right.

The main swingarm is… well, it’s not exactly done, but I’m satisfied that the design in my head can actually exist in the so-called real world.
It’s not a hundred percent perfect, but it meets my original use-case requirements of 300 millimetres of wheel travel with minimal variation on chain tension.

It also has adjustability, because it’s still required.
I could probably get it better, but I’ve tried literally hundreds of different configurations on my test mule, and this is about the best I’ve been able to achieve.
Why 300 mil?

Now it’s just a case of making it in steel, and running it past my tame engineer for his critique and blessing.
Once he’s happy, I’ll re-make it in black steel tube using a jig.
Now I know most of the dimensions, I just have to make sure the orientation is right and hold it steady while I tack and weld it together.

This will be my hold-point – if I think I have enough time, I’ll re-make the final version in a much lighter and stronger material.
If not, I’ll happily run the tube frame for the TT trip – it will be a great way to get some field testing under my belt.
Either way, the engineer can then inspect and certify the final version so I can get a unique frame number issued and get Gurty registered.

The next tricky part is to get the rear suspension design right – I’ve just ordered two cheap shocks to use in the mock-up.
I’m striving for a progressive action based on a structure which is as light and strong as it can be, while still being useable.
Design is one component of that strategy, material is the other.
Once I get the design right, we can play with materials.

While I’m still fascinated by carbon fiber, I’ve gone away from using it.
It strikes me as something that takes a lot of practice to get right – time which I don’t really have for this job.
It also strikes me as something that you really need to be set up for – I don’t have the space or the tooling just now.
So, I’ll be sticking with metals I can cut, shape, and weld – which pretty much means aluminium or titanium for this application.

Aluminium makes more sense from a cost perspective, but money is a great measure of scarcity and a shitty measure of value.
While every project is subject to budgetary constraints, I’m striving to make a statement beyond the decrepit reach of capital.
So, I’m leaning more towards titanium for the final construction, but am well aware that this means more complexity in terms of fabrication.

I’ve been schooling myself in this regard, and, as far as I can tell, it comes down to three things: precise joint fitment, extremely hygienic preparation of the pieces to be welded, and thorough shielding of the weld pool and heat affected zone.

The process I’m describing here is intended to address the first point.
The other two I will tool up for, and address through practice.
See less See more
Time for a quick update.

Thanks to help from various agencies and individuals, we were able to organise mum’s funeral before Christmas. I also managed to get through the eulogy mostly intact. Mostly. It’s funny – the amount of stuff you don’t know about someone you’ve known all your life is quite astounding. The realisation that none of us are perfect, and that we all have inherent flaws and fundamental shortcomings also hits hard.

The good news is that dad is doing okay, all things considered. He’s making plans for the future, and is taking action to bring them to fruition. He has a sale contract on his current place, and has been getting rid of excess clutter in preparation for living a more streamlined lifestyle. This evolution is not without challenges. I spent an hour on the phone yesterday day trying to convince him of the importance of being able to do basic personal admin (e.g. email and banking etc.) online. That conversation somehow ended up focused on how cheque banking is kind-of, but not-really still a thing, which should provide some indication of how long its been since he’s had to do this for himself. Still, we all face little hurdles in life, and none of ours are insurmountable.

Next, the TT23 trip and the land-speed record attempts have both successfully been deferred until next year. So Violatrix is back on the road, and Gurty is back on the bench in preparation for a Simpson Desert crossing in August-September this year (i.e. SD23). I also have a firm plan and budget for the big-wheelie ‘busa, which will be talked about more in forthcoming content. I’ve recently changed my employment circumstances to give me greater freedom and budget to complete these projects, but I will have less time to do the work. It’s a compromise I’m willing to live with in the short-term, as I am serving a revised long-term plan. It’s all about having more time, money, and inclination to do big bike projects and trips.

With regards to Gurty, it’s taken me a while to get my head back in the game, but I have been doing bits and pieces where I can. This has included rechecking all my design assumptions and calculations to make sure I’m happy with them. I went to the extent of making a 1:1 scale mock-up of the frame and swingarm, and testing it to make sure I can get the suspension travel combined with 100% anti-squat through the full range of movement (i.e. 300mm), all with minimal variation in chain tension. I was able to achieve the first two, and an acceptable compromise on the third. All engineering is compromise, so I can live with that. The frame design has evolved to accommodate the swingarm pivot configuration necessary to achieve the desired suspension performance, but that has actually made my life simpler in lots of ways. The front-end design is a lot simpler, and achieves the required suspension performance with minimal fuss. It definitely looks weird though, which highlights the variable importance of form versus function.

As of today, I’m about 75% complete on a 1:1 scale cardboard model of the whole thing that I can video in order to explain what the hell I’m talking about. Me no wordy so good. I’m also planning to get the materials necessary to make a frame jig so I can mock the whole thing up in plastic/PVC, including the bearings and fixings etc. I’m intending to use. This will be used to get feedback from my tame engineer – once he’s happy, I’ll move on to making the first frame out of Chromoly tube, round bar, and plate. I’ve found a local supplier who can deliver at reasonable prices. Moreover, I can bronze weld the frame to minimise heat distortion while maximising durability in both design and function. The titanium frame is still on the agenda, but it will be the second, or possible third iteration. I really want to get some field testing under my belt before I commit to the expense and complexity of building a titanium frame. Hence the SD23 trip.

Taking the turbo requirement into account, I’ve completed the build budget and schedule. In light of my work changes, the timeline is tight, but do-able. Isn’t it always? At this stage, the plan is to have the frame and engine ready for dyno testing late June, or early July this year. That’s four to five months away. For me, that’s 4-5 weeks of actual work time. Hardly a challenge.

I’m also in the process of revising and simplifying my website in particular, and my social media presence in general.

See less See more
I did a thing.
Gurty suspension movement mock-up - designed with 300mm front and rear, minimal change in chain tension, and anti-squat characteristics through the full range of motion.
Time for a quick update.

I spent some of my available time this week building a frame jig. As mentioned previously, the intention is to use it to make a PVC tube mock-up of the cardboard frame design. From there, the plan is to show it to my tame engineer to see what he reckons. Then I can listen to his recommendations and certification requirements, and build any required changes into the design before starting to make things in ChroMo.

Well, that was the plan. Things went wrong when I downloaded the free jig blueprints – the designer’s brief specified 50 x 50 mm box for the main frame, but didn’t mention a thickness. Keen to get started, I raced out and brought the closest suitable steel could find, which turned out to be 50 x 50 x 1.6 mm galvanised tube. I had some old welding rods in stock at home, so elected to stick weld the thing together instead of TIGing it – stick being much quicker in this application.

Anyway, problems were immediately obvious. Gal steel is a pain in the spadgebox to weld, not to mention that the fumes contain lead oxide, which can cause brain cancer and nervous system disorders. I took this into account, and set up a suitable ventilation system prior to starting (check your material safety data sheets kids!). Didn’t matter – it turns out that this steel is far too thin for this application. Despite being clamped and gradually tacked, it moved about a lot during welding. The end result was not as square as I would have liked, and flexed a lot once I’d finished – too much for what I want it for. Also, the combination of old rods, gal coating, and my muppet welding skills meant that the final result ended up looking like arse. I consider the time and money spent on this to be dickhead tax, and will incorporate the lessons learnt into the next version. I’ll make it using heavier material (which I’ve sourced), and will add triangulation to the original design to get rid of any potential for flex.

I’ve also spent some time developing a project budget. In my experience, failing to plan is planning to fail. Also, plans are redundant, but planning is essential – meaning that no plan survives first contact with reality, but considering the what-ifs before starting is a healthy survival strategy. As of today, I reckon that I know where to get about 80% of the parts and material I need for Gurty, and am in a position to start buying bits as my cash flow permits. Two thoughts here – it’s advantageous to base projects on popular/raced engines, as the OEM and after-market parts supply options are much better. For example, the engine in Gurty is thirty years old this year, and I don’t have any real problem buying the OEM parts I need. I do have to shop around, but they are there. There are also many after-market options available for parts and tuning that make my life just a little bit easier in terms of building and tuning for bigly power.

Of course, only time will tell whether the things I can see online can actually be brought and delivered in time. I was torpedoed by this recently when buying tools. I found an online supplier with the things I wanted showing as being in stock, and placed my order. Then waited for delivery. And waited. And waited some more. After reaching out, I was informed that supply was not currently available for all the things I ordered. To which I responded that those things were still showing as stock items on the vendor’s website, and that I’d like a refund. I got my coin back nearly two months later, but what a ball-ache. This brings me to my second point – things almost never, ever go strictly according to plan. Keeping an eye on my project time/cost/quality constraints, and having a plan to mitigate any risk, gives me the best chance of success.

Concurrently, I’ve also done up my budgets for the big wheelie bike, and the two land-speed record (LSR) bikes. Speed Week 2023 starts today at Lake Gairdner, but I obviously won’t be making it given that I’m, typing this from my home office 2,200 km away. However, I have a cunning plan – I’m about 75% on the budgets for these bikes (the remaining 25% is comprised by the unknowns inherent to building a frame from the ground up, and from boosting the engines), and I’m still working on building them. Moreover, I’ve found a place where I can test to my heart’s content without breaking the law or upsetting anyone. The use case for Gurty is pretty simple, and relatively easy to both test and verify. I won’t spoil the story by getting into specifics of that mission just yet, but it simply involves getting from A to B. The mission for the big wheelie bike and the LSR bikes is more complex, and is much harder to both test and verify. Given their intended purpose, the LSR bikes, in particular, are quite difficult to test in anything other than real-world conditions. There are two wind tunnels within 200 km of me – as far as I can tell, neither of them are available for anything other than research and teaching purposes, so my chances of getting access to them are slim. More to the point, it’s debatable as to whether or not such testing would be of any value. So, real-world testing is the only way forward. And I’ve found the place to do it. More on that later.

You may recall that TT24 is back on the agenda. Two updates need to be discussed here. First, my shipper is offering to send my bike to Barcelona in early May-2024, as opposed to sending it straight to the UK. Considering that we originally intended to travel in such a way as to meet up as a family at certain places (i.e. Mrs Wife and kidlets would fly, and I’d ride and meet them), this raises obvious questions around the overall trip plan. I’m still in discussion with Mrs Wife on this one – no doubt she’ll tell me what I think in due course. Right now, my thinking is to take a longer trip, see more of Europe, and take in some of the Irish road racing before heading over to the Isle of Man for the TT. I’ve done this before, and can highly recommend it. It’ll probably cost me some family bribery, but I reckon I can get this approved. The second update is that the accommodation I had for this year was rolled over to 2024. Unfortunately, the owners of the venue had had some family strife, and it is no longer available. I’ve rolled my deposit over to secure whatever digs become available, and don’t anticipate not having a place to stay. Still, even this far out, I’m slightly nervous about not having my TT24 accommodation locked in. Also, Steam Packet ferry tickets for 2024 went on sale on 6th of Mar-2023, so if you want to go, you better get in quick. This is relevant because, based on previous experience, coming to the Isle of Man from the mainland UK via Ireland can be easier than coming direct from the UK mainland. Something to think about.

I had some reader questions from the last update which I’d like to address. First one – why do I need so much suspension travel? Well, I’ll be taking Gurty places where more suspension will be better than less. I chose 300 mm as the arbitrary target for two reasons – it’s more than any stock motorbike I could find/buy, and I wanted to see if I could do it. Second question – why stuff around so much to get the anti-squat and zero chain slack? Well, as per Foale’s comments, the bigger the suspension movement, the bigger the effect that suspension movement has on anti-squat performance and chain slack. So, I had to take this into consideration in my design from the outset. Just copying an existing design would not achieve the benefits I’m looking for, and would likely incur more problems if I just tried forcing more suspension movement into it.

Third question – what will performance of the leading link front suspension be like? Well, in this design, function has determined form. I need the chassis to be light, strong, simple, and able to accommodate the required engine package and suspension movement. Reading Foale’s book led me to the decision that the leading link would be the way to go for the front suspension. I did consider a trailing link setup for some time, but it ended up looking too hard to package it neatly and still be able to maintain the OEM wheel base and engine/radiator position. All design is compromise. The cardboard mock-up video shows that it is at least feasible – I have lingering concerns regarding the strength and rigidity of the leading link, but, so far at least, the idea is do-able.

Further explanation probably requires that you read Foale’s book, as he explains it much better than I can. However, he does note that having the forks attached to the steering stem (as I do) means that braking and suspension forces still go through it. This means that it has to be strong, and likely heavier than alternative designs as a result (as my design probably is). I can live with over-engineering, but I can’t live with a premature failure of a flawed or weak design. It’s also the simplest design combination that I could see, but I’m happy to be proven wrong on that. Foale also talks about the potential benefits of leading links, including much better rigidity, stability, and control than standard forks. Anti-dive can (and will) be built in, and stiction performance is generally better than forks in his estimation. Foale does mention that leading links are generally not ideal where large suspension movements are required due to the larder range of motion of the axle with respect to the link pivot (i.e. the axle moves in a semi-circular arc, not a straight line), but I suspect that this won’t be a major concern considering where I want to take this thing. Foale also talks about the effect that link length can have on angular suspension movement – the shorter the links, the greater the movement, and the less anti-dive effect which can be achieved. I did consider this, and tried to keep the link as long as possible while still keeping it packed in the required space and giving the required suspension movement. Once again, everything is a compromise, and I’m prepared to live with a bit less anti-dive.

Fourth question – how do I understand Foale’s calculations? Well, the short answer is that I don’t – I didn’t even try, because I’m a certified turnip. Instead, I started with the design brief (i.e. 300mm wheel travel front and rear). Next, I decided to try for anti-squat and zero effect on chain slack throughout that range – just because I could. As noted above, I looked at designs that could feasibly achieve this, then looked around for suspension units that I could buy which would let me achieve this range of movement. Once I had all this, I started drawing various designs – lots and lots of drawings. This evolved into cardboard models, and culminated with the video you saw last time. In short, I didn’t have to understand the maths – I just had to know it works. I did this via the video, and will try to validate it with a physical 3D model next. I could try modelling it in some sort of software, but that seems like an extra step – I’m unlikely to learn any more about the design my modelling the thing virtually than I would be actually cutting bits up and gluing them together. Besides, I’m not competent with any of these software packages, and don’t have the time to gain those skills. I can lean on my engineer for finite element analysis when the time comes, so this is the path of least resistance for me.

Apologies if I’ve forgotten any questions. Hit me up, and I’ll answer them next time.

See less See more
Update time.

Apologies for skipping my last update. Just before my last break, I somehow slept wrong, and pinched a nerve in my neck. This is my life now – debilitating injuries from wonky nighty-nights. Hurt like a… well, it hurt a lot – too much to even think about mowing the lawn, let alone getting busy in the shed. Wouldn’t have made any difference anyway – I was busy doing family stuff that week, and didn’t have a lot of tool-time.

I got back to town this break to the shocking news that Quicky from the Quick Bikes channel on YouTube had passed away. I found out first from Matt on Dirty Garage Guy, and Craig over at Doghouse Customs confirmed it when I caught up with his videos later on. I didn’t know the bloke, but I learnt a lot from watching him work – his fabrication and machining skills were far better than mine, and I was really looking forward to seeing Gixit finished. He seemed like a good egg, and I’m sure the world is poorer for his passing. Commiserations must go out to his friends and family – he was obviously a solid family man.

This has motivated me to start recording and posting more of my work online – you never know who it might help out.

In the meantime, the two shocks I ordered have shown up – they’re a bit ratty, but good enough to validate suitability for the task. Refurbishing them for final use shouldn’t be a huge challenge – I’ve verified that all the required parts are available, and as previously mentioned, I intend to build a blast cabinet to allow me to clean everything up prior to final prep/assembly. It’s on my list of things to do – honest.

I also ordered, and received the heavier steel for the frame jig (the old steel got repurposed into a new cover for our pool filter), and have started measuring bits up. I also showed our eldest how to TIG weld, so that’s something. Credit where its due – I’m using a set of free plans (Building A Rotating Motorcycle Chassis Jig) made available by a bloke called James Biggar on his very interesting YouTube channel (
). The plan now is to order some trapezoidal threaded rod for the head stock, and get the whole thing ready to go – including some modifications to suite my circumstances and requirements.

From there, I already have a supply of PVC tube on hand ready to start the next mock-up of the frame. I’ve also been thinking about how to approach the engine rebuild – I know what parts I want, and where to get them. Putting it all together will be as easy or as hard as I make it. First order of business is to get a manual, and read through it to understand the order of operations. I already have a Clymer book of words, and a PDF copy of the OEM manual to compare it against. Then I need to make a frame to allow me to actually work on the thing – from both top and bottom. I have already had a go at building an engine stand – it didn’t work as well as intended, and I need to do better, especially when I consider that I have a few different styles of engine to rebuild. When ordering the steel for the frame jig, it occurred to me that I could, and probably should, use the rotary head of the jig to help spin the engine to allow access to both the crank and head/top end without having to lift the engine by hand every time.

I have a frame that allows me to lift complete engines and bikes if required, but it’s still a mission to shuffle things around in my limited space without doing some manual handling. I’d much rather spend my time on productive things than lugging big heavy things around – this includes Gurty’s engine. I’ll have to put some more thought into that over the next couple of weeks.

In other news, I received a newsletter from the Dry Lake Racers Association around ten days ago. The 2023 event started on the 10th of March, and was scheduled to run for five days. Unfortunately, bad weather meant that they only got 2.5 days of actual racing in – the rest was either washed out, or waiting around to see what the weather would do. There’s always next year, I guess, but I’m glad I didn’t drive two days straight to not even qualify, or get a run in. Credit to the organisers who make that event happen every year – they’re mostly volunteers, and without their love of, and dedication to the sport, it just wouldn’t happen here.

Outside of that, I only have two breaks left before the mid-year school holidays. I’m taking two weeks off with the fam to go on a 6,000 kilometer walkabout, including a trip to my friendly dyno shop. Problem is that I won’t have Gurty ready for that trip, and work-related stuff (not to mention the unseasonally wet weather) is putting the September desert trip in some jeopardy as well. In light of the fact that I need Gurty ready for the TT trip next year, I may be forced to reschedule some of these minor trips.

Sorry – no photos or video for this one, as I’m in a rush getting this out before I have to leave again.
See less See more
1 - 8 of 8 Posts