pfouche's blog

Another GPZ FF - gets a new rear end

pfouche — Tue, 11 Jun 2013 07:16:49 +0000

Last September I had a shake-down run to Monty's place in York, across to Kirby Lonsdale and home. Apart from learning a few things about chain maintenance, that trip reinforced the need to sort the rear end. To make space for the lowered seat, the rear wheel had been moved back. This was done by adding bolt-on swingarm extensions. Extending the swing arm messes with the suspension, so it felt a bit soggy at the back. The effective spring rate changes with a square rule, meaning that the response time to any bump was loooooong.

I could have changed the original coil-over-shock unit, but that wouldn't have addressed the issue of flex in the swing arm. So, as suggested by Jean-Marc and Arthur, I added supplementary units mounted at the rear. The units I chose are from an X9 (or possibly and X8). In themselves they are not big enough, but combined with the existing unit, they seem to be ok.

In addition, I added Royce's 'Hippy Handling Helper' (otherwise known as a rear wishbone) - you can see it in red. This deals with any possibility of the long arms moving independently.

Here are the before and after pictures minus the top box (which obscures all the interesting bits)

Before: After:

Another GPZ FF

pfouche — Sat, 05 Jan 2013 16:20:46 +0000

With the t-max project slowing down and the prospect of another summer coming and going without an FF to ride – and that summer being in the south of France, I decided it was time to build something – anything (with a low COG and seat-back) – to get me on the road.

When we left Ireland and the truck came to take our stuff to France, I had been planning to sell the GPZ that I had been riding while the T-Max was off the road being FFed, but at the last minute there was room for it, so to France it came.

The GPZ has been FF’d (I used the term in it broadest definition) before by several people. Arthur and Bob have both used this as a donor.

The first step is to unbolt everything, stand back and scratch the head.

I started by cutting the top frame rail to make some space to sit. After butchering the airbox I could see that my legs would still need to be too wide, or I would have to sit higher or further back.

I opted to cut away the struts supporting the rear tank mount and fabricate something different. This is the new support system for the rear tank mount. These photos were taken before all the extra metal was removed. In this photo you can see that I partly cut through the rear frame so I could lower it to get the seat height down.

Next I started in the swing arm extensions. Arthur machined his. Bob extended his swing arm. I didn't have a mill and decided against the cost of getting someone to do it for me. To be honest the language barrier also scared me, so I decided to fabricate my own

The slots were made with a hole saw, a plasma cutter and a file

Here you can see how the extensions are made. I fabricated channel by welding angle together. The smaller piece goes inside the end of the swing arm.

Here the extension is being boxed in

Here is the completed unit in position.

The battery box is galv plate pop-rivited together. It hangs inside the swing arm. The high side will act as a front mud-guard

Here you can see the extra bracing that has been added under the frame to replace the support given by the upper brace that has been removed. You can also see the mounting points for the seat back.

With the seat back in position, a seat base is needed. The bottom of the seat base must mate with the frame, so I mocked up the shape in cardboard

... and replicated it in aluminium

Ok so now there is somewhere to sit. The rest of the ergonomics are determined from this position. I decided to work on my hand before my feet. I put my hands in front of me into what I felt was a natural position. The handlebar ends go there. I then needed to support the handlebars there - ie in mid air.

I decided to build a Y shaped support to hold a secondary steering head. It must not cover the fuel cap and must be light, so I opted for aluminium. It must also be easily removable in case the tank has to come off on the side of the road.

Here I am using a hole saw in a pillar drill to notch the tube

Here two of the three tubes are welded in position already. The vertical is a piece of tube I fabricated from plate as I didn't have tube the correct dimension. It is 25mm ID, so I simply belted a piece of aluminium around some inch bar and welded a seam while it was still on the bar. There is no risk of welding the aluminium to the steel and you get a beautiful internal seam. The ends were squared up in the lathe.

The big boss is because this was the only idea that came to mind to join the aluminium Y to the rear steel upright at the rear of the tank. Given its rather sensitive location, I wanted the steel to curve around the tank. I don't want any sharp edges between by legs if I have to stop suddenly.

This is the secondary steering head about to be assembled. I am using an Aheadset from Cane Creek. They don't require any threading. The stem is also off a mountain bike. It is about 20 quid and it is 6061 T6 - which seems to be the cool thing to use. Its light, and cheap, so it will do me.

All those bits go together to look like this.

The beginnings of the handlebar and the drag link. Fortunately there is enough angularity at both ends. The steering pivit at the front is the standard rake angle. At the rear, the pivot it vertical so that the bars to not drop at full lock.

OK, so now I have a piece of straight bar pivoted just forward of where I want my hands. The handlebars on the standard GPZ are stubs that go into risers, so I need to build to attachment points to take these. I turn the attachment points, but need to connect them to the bar. I decided that the bar stubs are to be swept back 20° and down 20°. More would be nice but I was concerned about have the brake master cylinder at too much of an angle.

To connect these pieces I need a short piece of tube with very specific notches. This was one of the few times I resorted to CAD. I placed the pieces where I wanted them in CAD, used them to cut the joint piece then developed the tube.

Inside the development I added a curve 3.4mm smaller. I printed this pattern 1:1.

I suppose I should mention that the distance from the edge of a cut made with my plasma cutter to the edge of the nozzle is 3.4mm

The picture above is filing a piece of scrap aluminium to the shape of the printed pattern to make a template.

Here the template is clamped to the steel ready to cut

and here is the cut piece next to the template showing the actual edge and the 3.4mm offset

Making the tube is a matter of gentle persuasion with a hammer.

Once the seam is welded up the piece matched very nicely. One weld done, one to go.

and voilà!

The completed handlebar in place waiting for the new throttle cables and brake hose. As I was not sure exactly what length I needed, I used a repair kit from Venhill. You get enough sheath and cable to make several cables. I found though that for cables greater than 1m the liner has to be fed in from both ends.

With a seating position sorted and handlebars in place it was possible to feel where my feet should be. I mocked up foot plates in wood to feel the position was right

OK I lied. I used CAD again. This is a rather boring shot of the steel blanks for the new foot peg mounts.

Guide in place ready to cut

5 seconds later

The completed foot-peg mount

and again with the foot peg and gear change in place.

The right peg and brake pedal

The brake cable in place.

The far end of the brake cable connecting to the original brake rod.

To connect the gear pedal to the gear box I needed a redirector, and there was no straight run - the alternator was in the way. It was a good excuse to have some fun on the lathe.

The redirector mounts on the original gear pedal mount. The new connector rod then runs forward to the new pedal location outboard of the alternator housing.

And that is it for the basics. Find a new, low, secure seat position, and move the user interface to match that position.

The project is far from finished at this point. Still to do at this point in the story, was the bodywork and tuning the suspension.

Mallory Approacheth

pfouche — Mon, 02 Jul 2012 11:19:41 +0000

On the last Saturday before the Festival of 1000 Bikes at Mallory Park, this is what the bike looked like. Naked and lying in the sun - a good way to enjoy summer in Provence.

What you can't see is the closed fuel tap. I found that on the main highway.

Somewhere to sit

pfouche — Sun, 19 Jun 2011 12:37:05 +0000

After initially building a seat mock-up to check ergonomics, I designed the seat sub frame in two parts.

The upper seat frame sits on a lower frame which is height adjustable. Both are welded 1.5mm aluminium. The upper frame slides forward and back to accommodate leg length. It also allows the whole seat to be quickly removed to access the engine. The design supports a seat transport much like Royce Creasey's design to allow for a 2 up configuration if required.

As shown the bike weighs 155kg

The seat base started as the original seat base from the car seat. It is from a Fiat Punto. It is an all foam (no springs) base in a steel pan. I removed it from the pan and cut away what I needed to get my legs down.

Next I squeezed the sides together to make the bulge and held it like that with string. It order to permanently hold it, I stitched between the pieces of wire you can see running the length of the seat. They are there in the original configuration to hold the seat fabric in place.

I smoothed the rough cuts on the foam with a surform tool. It is a little slow on flexible PU foam (FPF) but gives a very uniform finish.

Mating Hossack to T-Max Lump

pfouche — Sat, 25 Dec 2010 13:52:47 +0000

Here the Hossack front end it being held up while the first pieces of the frame are fitted between it and the engine. The rear suspension has been disconnected to allow the lump down to ride height un-laden. The engine is supported by four temporary legs with adjustable feet. These allow the lump to be levelled. The bottom of the sump is set level and the ground clearance set to the T-max quoted ride height. As shown the wheel base is exactly as per standard. You can see that there is room to reduce the wheelbase.

The new front end interferes with the standard location on the air-box. You can see is sitting on top of the engine. The radiator is unsupported - the lump of wood fell over.

Actual Progess

pfouche — Sat, 28 Aug 2010 21:31:42 +0000

A lot has happened since my last post. The first thing that happened was that I got actual prices for the billet forks. It turns out that CNC is not that much cheaper in Thailand than in Europe. I guess that makes sense as the point of CNC is to remove most of the labour which is the element that is cheaper in Thailand.

After going through the designs with Royce Creasey and faced with an imminent departure from Thailand, I redesigned the forks from 50 x 25 x 3 mm rectangular section steel.

The approach taken was that all parts could be fabricated with simple tools. Where precision is required, parts should only need a lathe to fabricate them.

Shortly after I returned to Ireland and set about setting up a workshop. I got myself a Colchester Bantam from the UK and started work. Without access to cheap labour I have had to fabricate everything myself. This is good and bad. I have to learn every skill as I go, and with 3 small children and a full time job time is limited, but there is no better way to refine a design than to build it yourself.

Here are the forks ready for welding:

In the above photo, the holes are not yet cut to weld in the turned insets.

The headstock was tricky to turn without a 4 jaw chuck or a steady. The following photo shows how I am still learning how to use the lathe. The finish could be better, but the critical dimensions are within tolerance.

The A-arms are a simple design. Here is a picture of the components waiting for welding.

Since I am welding with TIG, I want accurate notches. I built a tube clamp to fit into the tool post of my lathe. This allows me to accurately hold a piece of tube at any angle and notch it with a hole saw.

Next I have to to the lower A-arm and start welding. Then on to the frame

Ready to cut steel (and aluminium) hopefully!

pfouche — Sun, 05 Apr 2009 13:47:16 +0000

Ok this is the 'final' design - ready to go to the builders. The forks have been pared down to 3.6kg for the pair. They are 6061 – T6 alloy. FEA has been done assuming a 1 G stoppy with a 300kg all up weight all on the front wheel.

With the cross pieces added as well as fixings the weight jumps to 5.3kg. As I don’t have a weight for the wheel, I can’t give a total steered mass for comparison with the standard T-max.

Here are a few different views of the whole assembly mated to a mocked up frame.

Here is some detail on the forks.

Hossack is not always as simple as it looks!

pfouche — Sat, 28 Mar 2009 09:28:04 +0000

My first attempt at a Hossack front end was designed to be built as much as possible out of stock material - tube and box section - as possible. The ball joints were bought from a friendly neighbourhood motor factor for the princely sum of 600 baht (about €12).

The reasoning was that I wanted a reasonably skilled Thai fabricator to be able to build it without needing a well equipped machine shop.

The result was a little complicated to build. Quite a lot of jigging would be required.
The keen eyed amongst you will also notice that the bottom ball joint is in compression. After discussions with Arthur about reducing pre-load, it dawned on me that this type of ball joint was not designed to be loaded in compression. Shock loading it in compression could possibly pop the back out of the ball joint causing the ball joint to come apart.

After talking to my fabricator, I discovered that he was capable of fairly tricky sheet metal work. Here is an example of his work.

I set out to redesign the front end with the same dimensions, the bottom ball joint in tension and a fork fabricated from sheet metal. This is the result

As you can see the location of the ball joint centres is the same. This moves the mounts quite close together. Under braking, the inertia of the bike pushing of the ball joint will tend to twist the shaft of the ball joint, putting considerable force into the bridge of the fork.

This style of ball joint just doesn’t lend itself to this type of design. The risk is also that the stiction in the ball joints will adversely affect steering feel.

I had a meeting with my builder. Being a chopper artist he hated the look of the ball joints. He also pointed out the difficulty of fabricating both the tube fork and the sheet fork. He suggested I consider machining the front fork from solid billet. Once I had scraped myself off the floor and stopped choking, he explained that he had a friend with a CNC machine that could handle Solid Works models. He showed me a part his friend had machined for him for a chopper. It had cost under €20 but was being sold in the chopper catalogues in the US for about $300.

So back to the drawing board I went (there’s an expression that needs updating) and came up with the following rough sketch.

ThaiMax - The story so far - Design Evolution

pfouche — Sat, 28 Mar 2009 06:30:19 +0000

It started with a tape measure. That didn't get me too far, so I got a friend to photograph me on my T-max from as far away as possible with maximum zoom. It wasn't nearly far enough, but the results are acceptable.
Using CAD software, I built up a photo montage of my bike, the naked T-max shot from BikeWeb. I overlaid a 2D sketch of lines to simulate the Hossack geometry. I played around with length of the Hossack arms and the positions until I got the geometry I wanted. By sketching in the anti-dive geometry, I could see the anti-dive locus as I moved the frame up and down to simulate suspension travel. see here
Next I moved on to 3D. I already had wheels modelled from the Burgman project which I re-sized and inserted into the model.
I then built a mock-up frame to connect the rear wheel to the Hossack front end. This allows the model to be manipulated to check geometry is still correct and to check what hits what and when.
Here is a series of screen shots that shows the progression. You will see some details changing throughout the sequence as bad ideas are replaced with (hopefully) better ideas.
Oh I have missed one important step - continued emails to Arthur for his advice, judicious bothering of Royce and the occasional cryptic post to the feet forward group

ThaiMax - The story so far.

pfouche — Fri, 27 Mar 2009 11:09:35 +0000

Since the re-build of BikeWeb has killed my links I am going to build this as a blog, rather than a book

I had been keeping this under my hat until such time as it appeared it would actually going to get off the drawing board.

Arriving in Thailand in February 08 has put my main (Burgman based) project on hold. Faced with the prospect of further delays, the need to commute to work through Bangkok traffic and the prospect of cheap labour, I decided to buy a T-max

I chose the T-max because of all the good work done on the ComfortMax. I initially intended to print of the design, try to borrow the moulds, take it all to a shop and say "make me one of these".

Finding a builder prepared to manage the project rather than just do work to order has been more difficult than I thought, which is frustrating given all the little workshops that do every sort of fabrication imaginable.

After reading about what was learned from the ComfortMax project I decided that I wanted to do things a little differently.

Initially I don't want to cut bodywork until I see if the performance is worth it, but I am happy to ride it is naked form for a while.

I want to position myself in the bike, then adjust the steering position to suit me, then apply bodywork around that position. Hopefully I can re-use existing panels, but with new mounting points.

Anyone who has applied brakes suddenly on a Mark I T-max will tell you that the front forks are not the best. Having experience this for myself, I starting thinking about a Hossack front end.

A conventional frame connects the rear swing arm to the steering head. The T-max has the rear swing arm integral to the engine. The frame connects the engine to the steering head. I however want a Hossack front end and a new handle bar position, so the existing frame does not fulfil this function. The other function of the frame is to mount the seat. I want a new seat and seat position.

In short, the existing frame does nothing that I don't want to change. I decided that I would have a new frame built as well as a Hossack front end.

The plan is to build a Hossack front end, strip the bike of bodywork and frame, and build a new frame to connect the engine to the Hossack. Next my seating position will be mocked up and measured. Then the seat and handlebars can be fabricated.

Once ride-able I plan to test the bike naked (the bike, not me). When and if I get suitable performance, we will commence bodywork. If performance is a failure, I can re-fit the original frame and bodywork and sell the T-max on.