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I think its important to to take into account what the OP is going to use this bike for and that his age is almost 60, the use is the easy route in UK club trials. I live in the UK and can say that if he is a fairly competent rider then he could have some good rides using a well prepped TWINSHOCK FANTIC or 200 TY YAMAHA a current 200cc mono shock is well on top of the job and if it cannot be coaxed into winning the class of white route in the UK every time out then that is the riders fault not the bikes The white EASY route that the OP is going to ride is not as difficult as this example of UK sections Terrain. https://youtu.be/Ev9FqM0g5hQ?feature=shared

Thank you for your response Konrad , hopefully I have redeemed myself after my public disgrace as regards my previous 'little slip up' .

Hello Konrad , i think there may be a misunderstanding about the position of the O rings. I am talking about the O rings that go on the head bolts not the internal ones that seal the head to the cylinder and cannot be affected by UV light. the ones that i am speaking of are the 8mm I D that are used to seal the head bolts to the head and when in place can have the edges exposed to sunlight in their position. This UV reference based on Technical specifications given by a seal manufacturer regarding their products. Too much detail I suppose but that is the human mind at work , probably my undetected autism is in full swing , who knows. Have a good evening. Alan.

As the saying goes 'You learn something new everyday' , I have to say though In my Ignorance I have been using Copa slip with steel to Aluminium For decades without consequence. and I have certain bikes that I have had for decades. Not a very good excuse of course for not using the correct type of product but it is a fact none the less. I need to stop digging. I never thought I would be judged by Mark Twain in my lifetime so that is something new also. Have a good day.

8mm head bolts with O rings to seal head = 18ft/lbs = 24Nm you need to lubricate the O rings with Silicone grease and lubricate the threads of the bolts to get a proper torque reading , Copper Slip Anti Seize is best to stop future corrosion and so for ease of future removal. 6mm head bolts with 1.5mm thick copper washers to seal head = 9 ft/lbs = 12.2 Nm. Lubricate threads with copper anti seize as above. Anyone looking for O rings you need FKM/VITON ones Nitrile is not as resistant to UV light. These settings are for a Standard GasGas Head. I have had S3 heads on Gas Gas PRO motors an I used standard head Torque settings and had Zero problems If that is bothering you.

@obd I have both , Leonelli magnet plastic red cap actually clips as well as having the magnet to connect it to the black base where the connecter is and so resists separating accidently more than the Apico Type that is connected purely by magnetic attraction , this means that if you are using an elastic tether cord that when you fall off the resistance to seperate in the Leonelli design means that it pings off with greater force than the Apico kill switch and so will sting more if it hits you in the face, I have had no problems with Leonelli magnets falling out of the red plastic cap but have had quite a few come out of the Apico red cap, I now use a pick to pull them out when new and use the rubberised type shock resistant Loctite super glue to refix them and had no problems so far. My prefered type is the Apico one as it clips on easier and pings off with less force during a quick get off but with the glue fix to the magnet obviously. My advice is throw away the metal laceration handlebar clip and use a cable tie to strap it to the bar then hide it along side the clutch master cylinder like the pro riders do , find a closeup image of one of their setups , the way most people fix them on their bikes they must like Accident and Emergency waits. The magnets on the Apico and the Leonelli kill buttons have different polarities as already mentioned so if you need a spare magnet and lanyard you have to use the same brand you cannot mix and match.

https://www.trialscentral.com/forums/topic/46067-what-gearbox-oil-do-you-use/

If it actually is a 163cc then if it is tuned nicely and the piston and cylinder etc is in good order then it will have plenty of power for most mid weight riders , a better bike IMO than the earlier PRO models. Have fun.

@Rob1985 Your Scorpa SY is a rip off of a Bike that Birkett designed and built himself using the TYZ motor he used to make them to order before Scorpa made the SY you can see the obvious similarities https://www.trialscentral.com/forums/uploads/post-12-1077274121.jpg

@Rob1985 Yes Nigel Birkett is a mechanic/engineer and worked for a few Trials bike manufacturers during his earlier career to develop their products including the later TY bikes like the mono, if he cannot sort you with bits for a Yamaha Trials bike then its unlikely any one else would know any better than him . He is your first port of call for your bike and its motor when you need parts/help.

@wayno57 according to that it is a 163cc motor which should be a 1994 JT 160 , or called a 200 by some people , look on the cylinder it may be marked on there although it could have been converted to a 125cc at some stage in its life as those two capacities share the same crank/conrod assembly. If you want to be sure then drain the coolant and take the head off and measure the piston diameter , if its a 163cc it will be 64mm dia , if it is a 54mm it is a 125cc , the gearbox/clutch casings look the same on all the variants so it could have had a complete motor change at some point and be a 250 or larger , as i said you will know by the piston diameter.

Make drawings and take photographs /video when you strip the gearbox to remove it and place it in its order using rubber bands to keep everything held together in their specific order on the different shafts to help you when you put it back btogether again.

@Chrissy1990 This may help https://trialsport.com.au/beta/Manuals/mikuni/

Buy a carb re build kit and new floats with a new needle jet along with a new fuel shut off valve as well then take the carb apart completely and clean it thoroughly , preferably with a ultra sonic cleaning bath and blow all the air passages out with compressed air , set the float height up as per the owners manual and put the recommended jets in for your country. Turn the fuel tap OFF every time you park the bike up to walk the sections and any time the motor is not running to help avoid the flooding problem ,

YAMAHA or SHERCO motor , if its a SHERCO then Splat Shop have 24X58 for £25. If it is a TYZ motor did you call the UK SCORPA importer Birkett Motosport.

@lemurGasGas 80 and Beta 80 versions have senior models that run with full size wheels i.e. 4;00x18" and 2.75 x 21 , they have shortened frames and swing arms with lighter tubing but are close to full size bikes.

@eirik You are very lucky to have a great bike and to be buying your 125 next year , I wish you good luck and hope you enjoy yourself on your bike as much as I enjoy riding mine.

https://youtu.be/V09zf7kfKKA?feature=shared

Here is another www.bjracing.com look under Vintage Trials Yamaha

Here is a starter for you https://www.yamahaty.com/english/tyusineen/majestyen.html

Here is interesting information for comparison Dexron Vl or Dexron 6 is 6.4 @ 100C , While this next one is the big surprise Motorex Trial 75W Gear oil specially developed for the new KTM GasGas GP box / wet clutch has a viscosity of 14.2 @ 100C . I have put the Motorex Trial specific oil in a pre KTM GasGas Pro and the Clutch was a little draggy under normal use with it adjusted correctly with the usual on/ off action. So if you are looking for less drag then Putoline GP 10 would be the best bet in theory.

Hello John good luck with your return , I think your choice of bike is a good one , It was my second trials bike ownership when I was 17 years old and they have a surprising amount of power for such small displacement having said that the Fantic 200 was of course only a 156cc but was a good bike in its time also. It is good to have excitement in life at any age so here is to that . This may be of interest to you http://www.bsaotter.com/nick_draper_the_return_and_ty_yamaha_s.html

Localised heat to inner bearing race of main bearing , oxy acetalene welding torch or use of a case splitter tool home made or ready made ?

As you are used to the Yamaha TYZ motor in the Scorpa I think you may find that the Beta 200 feels equal too it in terms of power output as motors have been developed for more power and better response than back then because of the obsession now with going up great big steps , at 13 stone I think you will find it plenty powerful for your needs /likes . Enjoy whatever you choose.

How much you weigh is a factor if you are choosing an engine size on a trials bike if you weigh 17 stone go for a 250/300 , If you are 12 stone or less 125/200 is plenty of power for riding the easy white route. There have been younger riders that have completed the Scottish 6 Days on 125cc bikes in recent times , 200cc has much more power and torque to do what you need it to do , If you are wanting to do road trials/National events sometime in the near future you might want to consider a 250cc.