dadof2

Ham 2 - in answer to your questions More oil = less coke. This is just based on experience of what I see on piston crowns and combustion chamber. More oil conducts more heat put of the piston meaning the temperature is less than that needed to char the oil, the oil therefore remains "fluid" to some extent and its detergents remain active. These lower piston temperatures seem to result in lower head temperatures also. You find that in a bike run at say 32:1 you can usually wash away the deposits with thinners. In an engine run at 60:1 the depostits tend to be burnt on and have to be scraped of. More oil gives better piston ring seaking and greatly reduces blow by to the crank case. You will find much less carbon in the crank case of a bike run at 25:1 than you will in one run at 60:1. Most of the deposits do not come from the oil (which is only a small % of fuel) they come from incomplete combustion of the petrol. It may just be that putting lenty of good quality oil in means there is plenty of detergents to flush away potential deposit forming combustion by products. I do not know what the main factor is in exhaust clogging - I suspect it is oil type, oil quality, running temperature and exhaust design. I know of people who run rich oil mixes like myself and have no clogging, I know of people who run rich mixes and lean mixes who have exhaust clogging. Petrol could be a factor. The following relate to 4 stroke car engines. One had been run on Texaco for years and had significant inlet tract deposits, within a week of switching to Shell (not V power but the standard clean burn stuff) a lot of the deposits in line with the injector spray had been stripped off and the car had an inlet gasket manifold leak (previously sealed by Texaco deposits) A Ford Fiesta lost power a few weeks after switching from Texaco to Shell. Serious loss of compression due to carbon chunks preventing the exhaust valves closing properly. Wnen the head was removed the reason was clear, years of deposits built up using Texaco were being stripped off by the shell, it was like pieces of black fungus coming off. All cleaned out and the car ran perfectly. Cheers

There will never be a definitive answer to this until manufacturers and oil companies publish wear rates and actual lubricating properties. There are too many miths about also. I recently striped a 17 year old gasser engine that had been run at 30 : 1 on Putoilne MX5 and latterly a semi synthetic. No wear and virtually no coke. Also a 348 Mont run at 25:1 on various mineral oils and semi synthetics. Virtually no wear and little coke. I have stripped much newer engines (2007 on) run at 60 :1 to 80:1 on modern synthetics and found they have significant wear and coke build up I belive the folowing to be true: 1) More oil = more power 2) More oil = Less wear. There seems to be a significant increase in wear rates as ratio moves from 32:1 to 40:1 and leaner. 3) More oil = Better piston sealing and lower piston crown temperature = less coke and less detonation 4) The fuel oil ratio is not the main factor in exhaust clogging. Against higher oil ratios, is the cost of oil. When you consider the cost of a piston & replate, possible mains and conrod + gaskets + labour my feeling is more oil is a wise insurance policy.

I have several times advised of this technique on this forum, mainly to check source and trigger coil output and it is a very useful technique. In my experience a battery drill is not powerfull or fast enough as some electronic ignitions are designed not to spark at low RPM (to prevent backfires on start up). I use a 680watt Dewalt variable speed drill. Also you must always earth the plug. If the plug is not earthed the "spark" energy will go somewhere else, possibly through the coil and CDI and quite likely damaging them. Put a few drips of oil in the plug hole to lubricate the bore and make sure there is not much / any petrol in the barrel - I have seen a bloke burn his face and quite a lot of hair off when looking closely for a spark at a plug rested near the plug hole, and the sprayed out petrol fired. Best to remove the carb and reed block as this lowers crank case compression and makes spinning the engine easier. If engine is stiff to turn you can accidentially undo the flywheel nut. Cheers

Depends on the exact grade of magnesium alloy and what else is in the mix. For example a Yamaha TY250 ignition cover will nearly always crack after welding, A Yamaha TYZ 250 cluctch casing is easily welded and is durable. A Honda priamary drive case is unweldable but honda crank cases weld quite easily. I have no experience of SWM to comment. I would have thought that a European bike of the SWM era probably had aluminium cases that are wewldable. Cheers

Telecat, I do not know the situation in Leeds but some other posters down south also feel the 125 limit is a barrier. In this area (N Yorks / Co Durham) the great majority of riders enter the sport after practicing ilegally as I did. When they get a bike they (as you say) know nothing of the ACU etc, they just want to ride bikes and the road is not an option - so its the fells or other unfenced ground. There then comes a time when they see a trial or hear of one through friends or a dealer and fancy a go. It's at this point the 125 limit can cause problems. Whether a 125 teaches you to be a better rider is irrelevant, its the fact that riders are put off or prevented from entering because they can't use the over 125 bike they already have. Breagh "Regardless of capacity, I would welcome restriction in horsepower across the board" What would be the point of a power reduction? Cheers

Its hard to describe in writing but here goes. You want 2 pieces of metal bar about 8m thick, 40mm wide and 50mm longer than the distance from the flywheel nut to the footest. Drill 8mm holes about 10mm in from each end of both bars. Fasten the bars together with an M8 bolt and nut at one end so they form a V. Put M8 bolts through the other holes and tighten nuts on. The heads of the bolts at the open end of the V can then be located in the holes in the flywheel and the other end held or jammed on the footrest. Alternatively a garage with a windy gun should be able to do it. Cheers

Thanks very much for your replies lads. Some comfort to know my (northern) observations are not isolated cases. Telecat #5 "FACT that the rider has to work the Bike not expect the engine to get them out of trouble does mean they ride better" No it means a large proportion in this situation don't ride at ACU events at all, worse still some ride where they should not with all the problems that brings for the sport. Cheers

These do tend to get water in flywheel case, platic cover, wirig gromet do not seal well and the breather pipe exits too low - can suck water in in deep pools. Have a look at the Bradford ignitions website. Your ignitin source coil should have a resistance of 200 to 250 ohms and generate over 20V ac when you kick the engine over. Cheers

If you look at most bike handbooks they will say if you are using mineral oil mix at 25:1 and if you are running fully synthetic mix at 50:1, 60:1 or 75:1 depending on manufacturer and model. Beta does / did recommend Bardahl VBA synthetic. There are some synthetic oils on the market that do not seem to provide good protection when at ratios higher than 30:1. I do not include castrol, shell or putoline in that category. I have seen trials engines that have significant wear after 2 to 3 years use when run on synthetic oils at 75:1. The same maufacturrers engines run on semi synthtic at 25:1 or 30:1 have virtually no wear. If you look at quite a few makes of oil it says mix at manufacturers recomendations up to 50:1 ie the oil company does not expect the product to be used at over 50:1. With a barrel replate and new piston costing near £400 I now recomment running at 30:1 on semi synthetic. Cheers

I have only ever bought 1 tin of air filter oil (silkoline) in my life and that was for motocross. I found it very difficult to wash out thoroughly compared to 20w-50 or 2 stroke oil. I now use 2 stroke, 10w-40 or gear oil and know from the wear (lack of) on my engines they must be doing the job OK. Using Duckhams hypergrade 15w50 (car engine oil) on my Honda CR500 motocross filter I would find that the outside of the filter could be nearly completely clogged by the end of a days racing but non at all had got through to the inside of the filter. I have seen bikes set on fire by using 2 stoke mix or filter oil on the filter and not allowing sufficient time for the petrol or solve to evaporate. Coat the inside of yur air box with oil also. I suspect that frequency and thorougness of cleaning is far more important than type of oil. Cheers

I may be mistaken but my understanding was that the ACU introduced this 125 limit as 250s became more powerfull and the ACU felt this could get younger riders into difficulty. I have come across a few 14 / 15 year olds who have quit or are considering quiting trials because their 125s are "gutless" when ridden clutch always engaged / no stop style as they are having to. One of these lads is over 6ft tall and 14 + stone. There are other 14/15 years olds who have bought 250s or bigger for messing about on the fell or their friends farm who would like to try trialing but are not going to change down to a 125 to do so. In Karting you are alowed diferent power outputs depending on weight to even up performance - this is achieved by inlet restrictors. Back to trials I think there is a lack of suitable bikes for small riders as well schoolboy riders as well. They want a 125 so they have enough poerr but could do with smaller wheels and lower seat height, also lwer rear mudguard so they can get their leg over easier.. Cheers

If you really get stuck then any 4 wire cdi for a 2 stroke will do or even a fixed advance cdi off a 4 stroke honda 90. These can be picked up at breakers for next to nothing. Consider a scooter CDI - the ones with switchable characteristics to get round the 50cc speed restriction. Cheers

Now that trials seem to be moving back towards non stop perhaps it is time to reviw the 125cc restriction. Many lads are adult size by the time thy are 14 and could hapily ride a 250, they are after all permitted to ride motocrossers with much more power, height ad weight than a 250 cc trials bike. 125s do not suit no stop riding and tend to be more expensive and more worn than 250s. Anyone any thoughts? Cheers

""There is little to be gained by going back over the same old ground, but neither is there a lot to be gained by people just jumping once" Is there some hidden implication in the above opening line from yesterdays post? Cheers

Check the ignition source coil behind thre flywheel. Its the large coil with the finer wire windings. You need a digital AC voltmeter - it should give over 20 volts AC when you kick it over with plug out - don't forget to earth plug lead. Check the resistance of this coil - I don't have figure for sherco but typically its 200 to 300 ohms. Any less suspect internal short, any more suspect poor connection or coil windings stating to fail. I doubt if its CDI Can you find someone else whose bike uses same HT coil - try your HT coil on that. Cheers

Hi there - the good new is that expensive wear is easily avoided. 1) Reguarly clean the air filter and soak with sticky oil - whatever you use in the engine usually works fine 2) Wash out the air box now and then 3) Never use a pressure washer and don't put water on a hot engine so it steams the electrics under the tank 4) Regualry grease swink arm bearings, shock bearings, linkage and steering head bearings 5) Change fork oil and brake fluid every year 6) Reguarly change the gearbox oil. You can reuse some of it if you leave it to settle for a couple of weeks and only reuse the clean oil at the top. Check the discoloured oil for bits of metal 7) After washing spray the metal parts and pivots with WD40 or similar (obviously take care near brakes or handlebar grips etc) Cheers.

Looking at the video on Pete_Scorpa3 post "Dougie the 5 that was'nt" which follows my previous post. Had I been observing under no stop rules from the cameramans point I would have given a 5. Dougie clearly moved back after running his front wheel into a rock. The stop could clearly be seen without a slomo replay. If I had been stood at the end of the section (say for punch card marking) having only a head on view I may well having give him the benefit of the doubt and not awarded a five. Cheers

The fact is since stop and hop started bike sales have fallen and presumably that is one reason importers are keen on a return to no stop. Recently I observed at a no stop trial and there were a number of argumemts regarding 5s for stopping. It is going to take some riders a while to change technique. I was observing for near on 5 hours with no break and near continuous small queues for the relatively easy secion. Had it been stop and hop (and the section stiffer as a result) I would probably have taken 6 to 7 hours with longer queues. 6 or 7 hours is too long to obsrerve. 5s should be awarded for even a monentary stop. If not the scores may make the section look too easy and the CoC will then stiffen it up for next year which will bring even more riders to a stop, increase time through the secitions and spoil the enjoyment of many. I admire the skills of the hop and stop riders but really they should have started their own sport rather than hijacking tradittinal reliability trials. Cheers

Difficult one over the internet! Reving up could be a sign of an air leak, crank case gasket, main bearing seals, inlet tract seals etc. These will lower compression and make bike difficult to restart. If it revved hard and ran dry it may have nipped the piston ring by piston dragging in bore - again hard to start due to low compression. It would not explain the revving up but could be break in ignition lead which is only in open circuit when lead is in plug installed postion - try an HT strobe light to see. Try a good dose of easy start direct into plug hole. Being a BETA of that age I would not rule out an ignition fault even if the plug sparks outside the engine. Cheers

Reminds me of the old joke "If I knew you were a virgin I'd have taken more time" - girlfriend reples "If I knew we had more time I'd have taken my tights off" The morale of this story is - don't spoil things by rushing. If the outer part of your seal is metal go very gently with the dremmel - don't want to spoil the housing. A way I have used is to MIG weld an old bolt onto the band. This works well with needle roller races in swing arms as well but you have to shield carefully against MIG spatter damage. If the outer part is just "rubber" a paint stripping hot air gun will soften it. Cheers

You don't say what age your bike is. It could be the caliper seals. It is likely not the seals semselves but corrosion in their grooves. It has to be scraped out carefully then finally poished out with fine steel wool. Is the few minutes you mention riding the bike - if so a bent disc could be pushing the pads too far back. Can air get into the top of your rservoir - see if leaving the cap loose cures the problem Master cylinder - make sure the free play has not been adjusted so that the feed hole is not being properly uncovered when pedal is released. It is possible the master cylinder piston is partially seizing due to sludge and corrosion and not returning fully when pedal is released. Use a good brake fluid such as castrol motorcycle brake fluid, not a universal car type fluid. Cheers

To test your CDI it would be better to put your CDI on a known good bike. Rig up a power drill so you can spin your flywheel with it. Check the out put from the ignition source coil - expect to see over 20 volts AC at over 600 RPM. Does your bike have a trigger coil? if so check its output - typicallly 1.5 to 4.5 volts AC at 600 RPM. Source coil resistance 200 to 300 ohms, trigger coil 1100 to 1300 ohms. Your CDI produces a surge voltage (by discharging its capacitor) through the ignition coil causing the spark at the plug. The switching in your CDI unit should normally determine (in conjunction with a signal from trigger coil or waveform pattern) when this happens. Reverse dischaging your CDI via the kill switch could I suppose also cause a spark. This would suggest the switching circuit on your CDI or the trigger coil is faulty. I have seen both these fault on Gas Gas and betas. Cheers

Before I write anythng else - do you realise the chain is wng side of the tensioner roller, it should be above it. I have seen a couple of these Yams with the modified inlect tract in about 1990 - 91. I don't know who did the mod or if the capacity was inceased. I can't remember the names of the riders but they were decent / occasional win at centre level riders in the North Yorks / Richmond area. The bikes pulled and gripped really well. They seemed able to pull 3rd gear where a standard Pinky could only use second and found grip a lot easier on the clay / limestone sections common in that area. Cheers

Waste of time trying to do it on a lathe. Grinding will quite possibly result in distortion. Follow the advice others have given on getting rid of squeal - copperslip of blue hylomar btwen piston and pad work. Cheers

Try different oils - maybe 10w-40 semi synthetic engine oil, or 75 fully syntheticgear oil. Use good quality hydraulic clutch fluid like Castrol motorcycle brake fluid - there is quite a diffence between this and cheaper fluids or fluids that are intended for cars with ABS. Cheers