dadof2

what actually happens when you try to rev it? Does it just start cutting out or does it misfire with a fair bit of smoke?

ATF is designed for rapid clutch / band brake lock up in automatic transmissions that usually have epicylic gears, a fluid flywheel and jurid coupling You may find a 10w 40 or 5w 30 oil better and gice satisfactory clutch action and it will protect your gearbox better and give smoother gear changes.

#151 I am not deliberately singling out and slating gassers, its just in this area they do seem to have had more than their fair share of problems. Gearbox excepted gassers are probably about on a par with the other makes but unfortunately the recurrent gearbox problems makes them stand out as unreliable. If someone had asked which was the most unreliable bike several years ago it would have been a toss up between gassers and beta because beta were notorious for ignition failure. I know of one mature careful rider who had 2 gassers over about 3 years and during that time he needed 3 gearbox rebuilds and a new ignition system - total cost about £1800. The unfortunate fact is all trials bikes break more than they should because manufacturers have pursued competitiveness and "hopability" at world level rather than producing reliable but heavier clubman bikes. The FIM have made a good start in reversing this trend by setting a 70 kg limit but ideally it needs to be higher, at least 75 and possibly 80 to 85 kg. Getting a bit off topic with the following but take EFI systems, they have many advantages over carbs but if all manufacturers go down their own route it could be storing up problems and expensive out of warranty repairs. Far better if they were standardized and OBD compatable or could be interrogated by standard laptop software. If a standard ECU is appropriate for F1 why does trials need more than that?

Sounds like fuel evaporating from the carb leaving an oily over rich mixture that may be hard to atomize and even clogging the jets. This problem can be made worse by a leaking petrol tap, this continuously re fills the float bowl as the more volatile components (needed for easy starting) evaporate again leaving something akin to diesel oil in the carb.

I am near certain an 06 beta will have a vertex piston and vertex do up to 9 pistons for the same nominal bore although 4 (A to D) is more common. Look at the vertex website / catalog as it gives details of piston to bore clearance, ring end gaps etc and how to measure them.Their site has an email address for more info.

Have a look at #67 by factory on the Montesa forum, New RT 260, whos got one topic. Poor bloke had his lightly built gasser fall to pieces then when he bought his already expensive but heavy and reliable 4RT he had to spend a shedload more to lighten it! If there had been a sensible 75 + kG minimum weight years ago manufacturers would not have needed to go down the too light / road to nowhere route. The gasser probably would not have fallen to pieces and he would not have had to spend money lightening the Montesa. Perhaps I have a different view to those in some parts of UK, but here in the North Pennines sections are mostly rocks and bikes need to be tougher.

# 26 identifies hot spot # 48 identifies worn rings as cause of weakness (lean fuel air mix) # 49 identifies detonation and leaning of mixture due to altitude change. To me the engine looks pretty dirty and worn, with a fair bit of carbon and blowby stains. I suspect there has been some debris / carbon on the head where metal is now missing. These debris will have glowed and acted as a source of ignition as the piston approached TDC. When the spark plug fired the mixture there will have been two flame fronts approaching each other, one from the spark plug and one from the glowing debris. As these flame fronts converge there is a violent increase in combustion chamber pressure that causes something to give way. In the days of aircooled engines with thick heads and cast pistons it was usually the piston crown that gave way and holed. With modern high strength forged pistons, and thin heads due to the water jacket, it is just as likely, possibly more so that the head will give way. The detonation will have been exacerbated or made more frequent due to leaning of mixture due to change of altitude.

I would be inclined to agree with # 32 diagnosis - initiated by gradual coolant loss. Having said the above I also wondered is the combustion chamber is the right shape or has it been machined out (excessively) at some time to reduce compression. Need to compare it to a known standard head. The cylinder head metal looks very thin - manufacturing fault? I have never seen cylinder head metal this thin although I have not seen a broken pro head before. The only time I have seen heads break is by hydraulic pressure when the bike has been dropped in a river or when bits of piston, ring, big end or main bearings have been punched thought it.

Thanks for illustration My guess is the bit across the inside end of the of the cylinder where the arrow points or the parts numbered 13 are kinked.

Dabster you seem to be getting a bit would up over this - its meant to be a friendly forum, not a court of law. You say what I suggest is never going to happen - well it may or may not. Who foresaw the return of no stop and the increase in minimum weight? If you were to ask most trials riders I mix with would they like a heavier bike they would answer no. It you asked the if they would like a stronger more reliable bike they would say yes, If you said would they like bikes to cost less they would say yes If you then added that the previous 2 yeses would mean a heavier bike they would still say yes so long as its not too much. Only one rider I know has changed his bike specifically for a lighter one and that was because of an illness which has weakened him. The reasons most change bike is they fancy something newer, can't be bothered with MOTs, but often the main reason is they are fed up with poor reliability of their old bike and often change make at the same time. With the one exception as above none has cited reduced weight as the reason to change bike. I think the FIM with its raised minimum weight has intervened in the nick of time, As someone posted the works Shercos have to have their frames strengthened. I have seen 2 not very old GG pros where the frame has broken where it bolts on under the gearbox and Betas with cracked frames also. A few extra kGs in the right places and a few lees £s cost wold be a big improvement to the sport.

I don't know if its possible on a pro but on motocrossers I used to link the front of the brake pedal to the frame forward of the pedal with a loop of throttle inner cable or similar.The cable had just enough slack to allow the brake to operate it. The cable stopped bits of brush getting between the pedal and the case and prevented the pedal being bent back if it stuck something hard like a post or other bike Another mod to protect gear levers is to make a triangular deflector with a large base and stick it to the engine / flywheel cover with a good layer of silicone.

Dabster # 129had 5 gassers and never had a chain pawl go or kickstart mech so anecdotal evidence isn't necessarily true? All I can say is that you are careful and / or have been very lucky. Just look at the number of GG gearbox posts and the fact that GG have partially modified them. Jon Stoodley has gone to the effort of GG pro gearbox rebuild videos as the problem is so common. Which as most circular arguments go comes back to WHOSE RULES, and what happens to the thousands and thousands of bikes that are underweight? Please answer this question. Whoose rules ? Many motorsports have minimum weights and detailed component specs to control costs. It would be up to the FIM to introduce them then filter down to National organisations. The problem of current machinery not meeting new rules could be addressed by exemptions for older bikes or bringing in the regulations gradually. For instance if it was now stated that from 2015 new bikes must have non perforated sprockets and discs and from 2017 ALL bikes must comply, manufactures and component makers would have plenty of time to adjust. Minimum weight increase on older bikes could be by adding ballast in specified locations and random use of scales in trials.

On the subject of tax avoidance how many farmers or farmers sons reclaim the VAT on their trials bike as of course its for shepherding etc.

I think we need a bit sharper photo and ideally an arrow (or screwdriver) pointing to the area of concern.

whats light and unreliable on a trials bike anyway? - As a gasgas rider you have presented an open goal - Pro kickstart mechanisms and the little chain link pawls in the gearbox selector mechanism for starters The steel footpegs on my CR500 have done a lot longer than 5 years! If you are so sure heavier is better start up a business selling heavy/reliable/cheaper parts and see what happens? - this is occasionally what happens as per my previous example of Ty ignition cases. However at present trial bike sales volumes hardly justify making anything. I would not try to make anything for the trials market at the moment, there are far better investments such as property. I am not in favour of heaviness for heaviness sake. I just think that increasing the minimum weight by a few kgs gives the manufacturer more scope for robustness and selection of lower cost materials.

Note who the queue jumpers are then when the are just slotting the bike into gear to make their attempt kick a nice big rock into the section or bend a flag inwards where they are likely to hit it.

Frame and swinging arm cracks, particularly near welds. Chrome coming off hub brake surfaces, Loose bearing housing on rear wheel bearing inside brake hub, jumping out of 2nd or 3rd gear under load. Plus usual off road bike faults

If its a Bing carb have you got the plastic bit under or over the throttle needle clip - is should be on top. I once had an intermittent HT coil fault that gave similar symptoms and I know of another bulto owner who had this type of problem for weeks, turned out to be a wiring fault near the points, The fault was hard to see and I can't remember if it was a break or a short.

I had gearbox oil being drawn past transmission side crank oil seal on my CR500 MX and it made no noticeable difference to performance. Oddly enough the ignition seal which runs with less lubrication was not leaking.

Sorry to hear about your problem - I would do some detail checking on the law. Any chance you can post the photographs? Do you know why the original impeller stripped? Higher temperatures would soften plastic I suspect your bike may have had a minor (but significant) underlying fault that came to light under rather extreme riding. For example sometimes coolant hoses can swell with age causing flow restricting kinks where they bend, problems only arise on long steep hill climbs.

The new license system is a right complicated pile of boll---s. I would not let it influence your choice of bike as the training / test centers usually include a bike. Ring up the training / test center and get their advice on the best way to get an appropriate license.

Castor based mineral oil! I knew a grasstracker who had SAE 50 castor oil for his 4 stroke total loss grass tracking engines. He used the same stuff in his 250 Bultaco trials at 25:1. Totally gummed up the engine and the big end failed. Following some lengthy discussion on another thread about oils and mix ratios I contacted 3 oil blenders / manufacturers, all of whom produce mineral, semi and fully synthetic grades of 2t. None gave definitive mix ratios saying follow engine manufacturers / tuners guidance on oil specs and mix ratios. 2 no longer suggest any ratio on their packaging, the other says according to manufacturers (of engine) guidance up to 50:1 2 said semi synthetic was more than adequate for trials and fully synthetic was not required. One was quite adamant on this pointing out their fully synthetic was a racing oil and trials engines were not racing engines. Another pointed out that their semi synthetic was their recommendation for older air cooled MX and trials engines. One pointed out that the additive package and oils specification / approvals was more important than the base oil type.

Cost cutting and weight increase tend to be intertwined. World superbike used to have to use cast iron / steel discs rather than lighter more expensive carbob fibre. MotoGP has increased the minimum weight limit to the point where teams no longer need to use expensive light titanium exhausts = even the M1 works Yam of Jorge Lorenzo uses steel. If its good enough for the highly sponsord classes surely its good enough for the low cost sport of trials.

I would think the last thing you would want on a trials bike is more complex electrics - electricity and water don't mix well. The inboard wet brake is well established on tractors and other off road equipment. An in gearbox wet disc brake on a trials bike wold be relatively simple and probably much longer lasting and more reliable than present systems. Would also reduce unsprung weight and what weight there was would be low and central. The drawback may be legal issues due to chain and possible lack of sensitivity for same reason. Another alternative is to retain the disc on the rear wheel but operate pad movement by a rod or cable linkage and ACME type screws. his does away with hydraulics which can give problems and is hard to fix during an event. A system worth investigating would be to incorporate the reservoir, master and slave cylinders in the same casting on the rear caliper and operate them by rod or cable from the foot pedal. This does away with a lot of components and still provided the self adjusting properties of hydraulic systems

Used to be chrome plated I think, certainly were on the 348s