Author Topic: GS500 Classic Trials Project  (Read 15170 times)

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Offline Paul Wheatley

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Re: GS500 Classic Trials Project
« Reply #60 on: October 26, 2019, 07:38:49 am »
I can't help thinking - will the front wheel (+ mudguard) clear the exhaust when the front forks are compressed? I had a problem with my Royal Enfield when I fitted a trials tyre to the front wheel and needed to lift the mudguard just half an inch to get side clearance. It looked fine until I compressed the front springs then tried to steer....the mudguard clouted the exhaust and would lock the forks off to one side.   
PW.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #61 on: October 26, 2019, 04:07:47 pm »
I had the exact same concerns so during the R&D stage, I installed the forks and front wheel in the frame without the springs.  By fully compressing the forks I could deduce where the header pipes could and couldnít go.  All good until, at a later stage, I had to fine tune the position of the engine and extend the header pipes.  However, Iím pretty sure I checked again with the forks fully compressed :-\.  At least, I hope so :-\.  Might be a pretty short mudguard if Iím wrong ;).

As for water-proofing the connections, the standard Suzuki multi-way connectors will be ok with some grease on the pins :-\

Offline Jason Potts

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Re: GS500 Classic Trials Project
« Reply #62 on: October 26, 2019, 05:41:52 pm »
It's looking good Paul, this is by far and away my favourite thread on this site. Keep posting, I can't wait to see this finished.

 8)

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #63 on: October 29, 2019, 05:41:49 pm »
Been tinkering in the garage again.  The OEM throttle cable worked out about 160 mm too short, which is strange as the OEM clutch cable seems to fit ok ???.  Anyway, after dismissing the idea of knocking up some mechanical linkage that would connect the OEM cable to the carburetters, I bought a cable kit from Venhill.  Quality parts and a good price :).  As an example, a brass nipple that costs a few pence from Venhill is charged a couple of quid from sellers on ebay :o.  And cable adjusters are silly money on ebay :o.

In the end, I cut the OEM throttle cable and only used the inner and outer wires and a brass nipple from the kit.  All the adjusters, I re-used from the OEM cable.  I thought Iíd have trouble getting the inner wire through the PTFE liner in the outer cable, but I cut a clean end with no frays and assembled the parts :).  It was so cold in the garage, I soldered the brass nipple onto the inner wire indoors :-\.


Finished throttle cable :)

Next up was installing the front master cylinder and slave cylinder.  Iíve installed new seals and dust seals in both.  Iíve found the only satisfactory method to remove the pistons from the slave cylinder is to pump the brake lever and gently tease the pistons out.  Alright, brake fluid spills out, but stick the cylinder in a tray and itís all good :).  The circlip in the master cylinder was a bit of a problem and involved filing my circlip pliers to make them fit the circlip and the confines of the recess.  It means a new needle file, but canít be helped.

The front brake is a pain in the backside to bleed >:(.  I reckon that's because there is a long loop of hose that rises above the master cylinder, which, I think, traps air that canít be shifted by pumping the brake lever :(.  Thinking ahead, I clamped the master cylinder in the vise, laid the hose and slave cylinder out as horizontal as possible and bled the brake.  Later, I put the slave cylinder on the floor below the master cylinder and left it for a couple of days for any air bubbles to pass into the reservoir and out of the fluid ;).


Master cylinder installed Ė new seals :)


Slave cylinder installed Ė new seals :)

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #64 on: November 13, 2019, 06:10:06 pm »
Been pottering in the garage again.  Been calculating what length rear shocks to fit that will give me a suitable front fork rake and a suitable seat height, hence the wooden shocks in the photo.  Rear shocks at 360 mm eye to eye gives the bike a 29 degree rake and means I can put my feet on the floor (though that is sitting on only 15 mm thickness of towelling).  Ground clearance is approx. 235 mm (9.25 in.)


Paul W, you were correct in your frightening comment on the mudguard, I checked the gaps again with the forks fully compressed.  Yes, the mudguard hits the header pipe :(, which is why the mudguard is missing.  The clearance will be ok if I make a new bracket, or fit the mudguard under the bracket instead of above the bracket.  So, all is not lost :).


I weighed the bike on a set of bathroom scales while it was out.  The front comes in at 70 kg (154 lb); the rear at 80.5 kg (177 lb); total 150.5 kg (331 lb)   Dry weight that is and without the silencer, which is approx.. another 2 kg.  Not too bad, considering thereís not much scope for weight saving ::).

Though the brakes are bled, Iíve got hydraulic fluid weeping from some of the copper washers under pressure.  I think the washers are just crap so theyíll need replacing :(.


The speedometer is mounted so I can still see it with a route box installed on the handlebars.  The panel for the warning LEDs is fabricated and just awaiting the LEDs once Iíve sorted out what wires to solder to each other. 


Any advice on shocks would be appreciated.  Iíve looked at Hagon, Betor and NJB Shocks.  Iím on a budget here so Ohlins and the like are totally out.

Offline Tony Bishop

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Re: GS500 Classic Trials Project
« Reply #65 on: November 14, 2019, 05:01:59 pm »
Hi Paul,

Looks rather tidy if a tiny bit heavy but as you say there is not a lot to be done from that perspective.
NJB shocks have quite a good reputation particularly at the price and would probably work out considerably cheaper than Hagons.
Don't forget that you are checking the seat height with the suspension rigid so allow for some shock compression when you sit on the bike. I would imagine NJB would be able to give you some indication on the amount of compression you would achieve based on your weight.

david@whitepost.me.uk

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Re: GS500 Classic Trials Project
« Reply #66 on: November 14, 2019, 06:28:15 pm »
Have a look at Shock Factory.

They do a range of excellent units from simple emulsion all the way up to remote reservoir.  They'll also make them to your specs too.

http://www.shock-factory.co.uk

Offline Jason Potts

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Re: GS500 Classic Trials Project
« Reply #67 on: November 14, 2019, 08:10:15 pm »
I have a brand new (still in the packaging) pair of JAWA 350 shocks and a brand new (still in packaging) pair of MZ 250 shocks that I wont be using.

will sell for 40 quid per pair plus post.

Jawa are 325mm between centres
MZ are 380mm between centres.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #68 on: November 14, 2019, 10:21:52 pm »
Have a look at Shock Factory.
http://www.shock-factory.co.uk
Thanks David, I did, but they'll blow the budget :o.

I have a brand new (still in the packaging) pair of JAWA 350 shocks and a brand new (still in packaging) pair of MZ 250 shocks that I wont be using.
Jawa are 325mm between centres
MZ are 380mm between centres.
Thanks Jason, but the lengths are unsuitable.  325 mm will probably give a rake of over 30 degrees; 380 mm will mean I'll be on tip toe.  I think there might be problems with the spring poundage as well; those shocks are meant for single cylinder two-strokes and my bike is a twin cylinder 500 four stroke.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #69 on: December 10, 2019, 04:13:26 pm »
Finally made a decision on the rear shocks after an informative phone conversation with Hagon.  Iíve now got 370 mm eye-to-eye shocks with medium damping and 18 kg springs :).  Having settled on that dimension for the rear shocks, I finished the assembly of the forks by tightening each damper-rod Allen bolt and filling with 10W fork oil.

The final fork assembly involved knocking up a couple of tools ::).  The first tool was to hold the damper rod while I tightened the Allen bolt at the base of the fork slider.  The second tool was to measure the oil depth in each leg.  The damper-rod tool was a cut-down bolt (27 mm across the flats) welded to a 3/8 in. drive socket that was no longer any use (cracked it down one side doing something I shouldnít have tried to do ::)).  The oil-depth tool was fabricated from some m4 studding with washers and nuts attached; the bottom nut is set at 164 mm.


Tools worked a treat ;D.

Also finished is the warning lights panel.  Those LEDs are bright so Iíve run some 400 grade carborundum paper across the outside to give a frosted finish.  Hopefully, Iíll keep my night vision when they illuminate :-\.  A couple of diodes are hidden in the loom so I can use one warning light for left and right indicators.


Warning lights panel front view


Warning lights panel rear view

I was going to fit the rear shocks, but gave up because it was so cold in the garage, and raining outside :(.  A cup of tea seemed a better idea ;).

Offline Stephen Bailey

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Re: GS500 Classic Trials Project
« Reply #70 on: December 10, 2019, 08:13:15 pm »
Are you on time fer the Exeter?
Posts by myself are personal posts and in no way are an official expression of the MCC. or the MCC Committee.

https://www.youtube.com/watch?v=6_3KP7X8RQ4

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #71 on: December 13, 2019, 06:13:43 pm »
The project's not on time for anything.  It'll just get finished when it's finished.  I never did put a finish date on the project; too much stress.  I just fit in the work as and when I have the time.  Might be nice to do the MCC Scatter Rally 2020 on it, but that's in June so that seems pretty close.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #72 on: March 07, 2020, 08:04:11 am »
Done some more work on the project; this time fabricating the seat.  Fortunately, the rear sub-frame is flat so I cut a piece of 6 mm thick plywood to shape.  To allow for the rear mudguard, a few layers of plywood are glued to the rear end, then shaped to fit the profile of the mudguard.  The seat foam is from a Suzuki DR650, cut to the shape of the plywood base, then the gaps filled in with offcuts of the foam.  The bread knife and a wood saw worked well for cutting the foam :).



Black vinyl is used for the cover.  I did toy with the idea of stitching pleats in the top of the cover and stitching the corners so asked my 12 year-old granddaughter, who has a sewing machine, if sheíd take the task on.  A pretty firm ĎNo!í on that request :o.  So plan B kicked in.  The foam is glued to the plywood with contact adhesive and the vinyl cover placed over the foam.  The foam does look real grubby, but it is 28 years old.



To attach the vinyl cover, the plan was to use galvanised staples, but the plywood is so hard, it bent the staples :(.  That meant I used contact adhesive and woodscrews.  The bracket at the rear of the base attaches the seat to the frame by two 5 mm screws.



It feels comfortable, though, whether itíll still feel like that after an hour or more is to be seen :-\.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #73 on: March 28, 2020, 10:53:58 am »
Having some time on my hands since Iím self isolating from Covid-19 due to my age, I set out to come up with an answer on how to tune the silencer.  The bikeís fitted with a Supertrapp silencer, part number 358-1719.  For those not familiar with Supertrapp, the silencer is equipped with a stack of 3 inch discs, the quantity of which can be adjusted to affect engine power and noise.  The exhaust gases pass radially across the outer edges of the discs.  To quote the manufacturer, ĎFewer discs reduce sound levels, more discs increase sound levels.  Fewer discs increase low-end torque and richen the fuel mixture.  More discs increase sound levels, increase top-end power and lean out the fuel mixture.í  So there you go ;).

I fitted this silencer on a previous project and managed to reduce the engine power by about 8 BHP (about 15% if I remember correctly) :-[.  There were other factors involved on that project such as using 2 into 1 header pipes, increased header pipe bore.  All a load of guesswork :(.

This time round I decided to be a bit more scientific about it.  Surely, one of the factors in compatibility would be the pressure drop across the two different silencers?  Exhaust gases going in are resisted by the internals of the silencer, consequently, higher pressure in than out.  So if I can measure the pressure drop across the original Nexus silencer, then match the Supertrapp silencer to that pressure drop, I should be reasonably close? ???

I came up with the rig below.  A manometer from plastic hose, containing coloured water, each end plugged into the opposite ends of the silencer.  Compressed air injected through a sealed wooden plug (in the blue hose), then note the differing levels on the water. 



It took a few dummy runs to get the trigger action correct for a sustained reading on the Nexus silencer originally fitted to the engine.  Pull the trigger too fast and the water levels bounced up and down, then the air reservoir ran out of air before the levels became stable.  Did a few runs and came up with a difference of approx. 140 mm between the two water levels.  (Thatís approx. 0.2 psi.)

Substituted the Supertrapp in  the rig and repeated the procedure.  After a few runs and adjusted with six discs and the end disc in place, I got a difference of more or less 140 mm between the water levels ;D.


Factors that affect any useful result are 1) I had no idea what the air flow through the silencers was and 2) Air flow through the silencer dropped off pretty quickly as the reservoir emptied.  Will all this result in an equivalent performance when the engineís pushing the bike along at normal road speeds?  I have absolutely no idea  ???

Everyone take care and stay healthy.

Offline Tim Kingham

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Re: GS500 Classic Trials Project
« Reply #74 on: April 02, 2020, 11:13:40 am »
I dont have a problem with the supertrap discs and as we found out on the Egli Racer its dead easy to fit the disc pack to another silencer bodyhttp://www.oldracer.co.uk/img/gallery-pics/thumbs/pic6.jpg