Author Topic: GS500 Classic Trials Project  (Read 13343 times)

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Offline Stephen Bailey

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Re: GS500 Classic Trials Project
« Reply #15 on: May 24, 2018, 01:16:52 pm »
I have used Suzuki Petrol tanks on two Velocette Trials bikes.. Sprayed the appropriate colour.. and decals... An excellent choice.

Offline Jason Potts

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Re: GS500 Classic Trials Project
« Reply #16 on: May 27, 2018, 07:28:32 pm »
Quote
Still have some questions on what is the optimum ground clearance and optimum front suspension travel for MCC trials  :-\. Anyone got some opinions?
I've chatted with Rick on a few occasions regards what's the best solution for LDT's. The best solution is a light weight modern trail bike like a beta alp or a serow etc. However, like me Paul I think you favour the unusual and more so the home built so it's going to be a compromise. For best stability you want your centre of gravity as close to the centre line of your wheel axles as possible. If your C of G is too high the bike will feel top heavy. If you'd started with a bantam or some other little 2stroke engine then its not too detrimental to stability if this is hoyked up high as it doesn't weigh much. You've chosen a GS lump so I'd get this as low as you dare because it's going to wiegh some. I'm in the same boat as you Paul, I'm about to start a class A project using a 600 sidevalve engine. I'll be using the standard 1953 forks though, not much travel or damping. But as Rick says, we do this for the challenge so where's the fun in making it easy. You have your 400 for that  ;)

Rick keeps telling me, just build it, ride it and then modify it as you go. You won't get it 100% right first time. He told me his bantam got developed over 10 years and I totally respect that.

Offline Stephen Bailey

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Re: GS500 Classic Trials Project
« Reply #17 on: May 28, 2018, 03:47:01 pm »
Only need a few inches of ground clearance for Classic Reliability Trials. I managed OK for quite a few years on a Girder Rigid Velo MAC.

Offline Stephen Bailey

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Re: GS500 Classic Trials Project
« Reply #18 on: May 28, 2018, 03:47:56 pm »
Are you sure you need the engine guards? Looks like it might be getting a tad heavy.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #19 on: May 29, 2018, 07:40:05 am »
For best stability you want your centre of gravity as close to the centre line of your wheel axles as possible.
I've got no alternatives for the position because the engine is so tight in the frame.

I'm about to start a class A project using a 600 sidevalve engine. I'll be using the standard 1953 forks though, not much travel or damping.
You need to start a new thread  ;).

Rick keeps telling me, just build it, ride it and then modify it as you go. You won't get it 100% right first time. He told me his bantam got developed over 10 years and I totally respect that.
10 years! I haven't got that much time.  Or patience  ::).  If I could modify anything at this stage, it would be fit an 18 inch rear wheel without a cush-drive (lighter and will take an MT43) and fit an alloy tank.  But that's not going to happen; yet.

Are you sure you need the engine guards? Looks like it might be getting a tad heavy.
Yes, you do need engine guards for the GS500. It's a very wide engine with thin-wall cases. I've seen posts on the internet where the bike has been dropped, the case damaged, causing the alternator to get chewed up, or even the crankshaft damaged. See the pictures below of the left side of some poor guy's engine  :(.


Fig. 1 Rotor damage due to a GS500 being dropped


Fig.2 Coil damage due to a GS500 being dropped

Offline Jason Potts

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Re: GS500 Classic Trials Project
« Reply #20 on: May 29, 2018, 09:04:11 am »
Hey Paul, I didn't mean change the engine position in your frame. You change the engine position when you fit a 21" wheel, fit longer forks and raise the rear by fitting longer shocks or changing the mount positions etc. This all has the effect of increasing ground clearance but also raises the engine up too. With a light engine this is not too bad but a heavyweight will make your bike feel top heavy.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #21 on: May 29, 2018, 09:32:54 am »
Ah, got you.  That's my motivation in getting as low a ground clearance as I can get away with.  Because the frame is a fixed, i.e. I'm not moving the position of the headstock, I can only lower the bike by shortening the fork suspension travel and/or raising the fork stanchions in the yokes.  Hence the question, what's the optimum suspension travel I can have on an MCC trial? Examples of fork suspension travel are REH forks 165 mm, Ceriani CONV38rev3 (trials) forks 170 mm, XT500 forks 195 mm and RE Bullet 130 mm.

Offline Stephen Bailey

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Re: GS500 Classic Trials Project
« Reply #22 on: May 29, 2018, 10:10:54 am »
 "That's my motivation in getting as low a ground clearance as I can get away with".

Neat.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #23 on: July 11, 2018, 09:44:16 am »
Had a bit of time after the Scatter Rally to work on the project.  Gear change linkage is now sorted and dummied-up.

Fig. 1 Side view of gearchange

The geometry is not strictly correct :(.  The adjustable link should be a tangent with the foot pedal and with the remote lever.  Therefore, an angle of 90 degrees would be formed between the adjustable link and the foot pedal and remote lever. However, when I marked up the holes for drilling, I was hanging over the top of the frame in a confined space (too much junk in the garage).  Ended up with an angle more like 45 degrees.  Anyway, if I'd got it correct, the link would've been too long to fit.  It'll do to change gear so that's all that matters ;).


Fig.2 Aerial view of gearchange

Still got to work out a way to keep the crap off the rose joints.  Perhaps some self-amalgamating rubber tape would do?

Could be a postponement for a while; I've done my sciatic nerve so major discomfort  :-[

Offline Paul Wheatley

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Re: GS500 Classic Trials Project
« Reply #24 on: July 16, 2018, 06:01:05 pm »
PW.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #25 on: July 17, 2018, 11:51:40 am »
Those covers work out too expensive for me; £15.92 plus the postage :o.  The two rose joints only cost me £5.02 including the postage.  I'll see what else I have knocking about in the garage.

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #26 on: July 20, 2018, 10:22:55 am »
Well, I made a start on moving the petrol tap to the rear of the tank from the centre.  What I thought was a steel reinforcing plate at the rear (fig 1), and into which the tap would be installed, turned out to be a copper blanking plate.  After drilling two holes in the copper plate, a difficult look inside revealed weld-nuts on a separate plate. 

Off came the copper blanking plate, which was sealed to the tank with lead, to reveal all.  Bugger!  The two weld-nuts were rusted to hell and were intended for a tap with wider bolt spacing.  No way I can utilise these weld-nuts.  Drilling out two spot welds, released the weld-nuts plate, leaving a mass of holes (fig 2). 

 
Fig 1 Before the truth is revealed                                              Fig 2 After the debacle

Solution?  Fabricate a new steel plate with two rivet-nuts (centres 35 mm apart) to fit inside the tank, then install a 2 mm steel plate on the outside of the tank to create a clean surface for the petrol tap.  The next problem is bonding the outside plate to the tank because the mating surfaces are not perfectly flat and the bonding product must be petrol resistant.

Leading is the obvious solution, but I donít have the skill or facilities for that.  After much internet search and a telephone conversation with a very helpful guy at Loctite I deduced this.  Some anaerobic gaskets are petrol resistant, but need a very flat surface.  Silicon gaskets are not petrol resistant.  Some epoxy bonding products are petrol resistant, but can be brittle.  My conclusion is to experiment with some Chemical Metal, manufactured by Plastic Padding.  If a test piece works out ok, then Chemical Metal it is unless someone can recommend a more suitable product.

Offline Stephen Bailey

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Re: GS500 Classic Trials Project
« Reply #27 on: July 26, 2018, 08:34:42 am »
Why not soft solder or braze a plate on?

Offline Paul K

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Re: GS500 Classic Trials Project
« Reply #28 on: July 27, 2018, 09:08:43 am »
Good point.  The problem is that I don't have the equipment for that process and there's no-one local that I know will put a naked flame to a petrol tank, no matter how clean.  Don't know why not  ;D. So if an alternative is available, I'll go for that.

Offline Stephen Bailey

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Re: GS500 Classic Trials Project
« Reply #29 on: July 27, 2018, 10:32:31 am »
It was clean enough to drill... :)