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al_Orange Start with looking at the position of the gear lever, if its too high then you will experience difficulty in selection. Is the lever binding on the case at the shaft? Is the lever bent? When did you first experience this problem as its a 2019(?) bike? Is the lever standard...not replaced with a shorter lever. Once on the move most riders ignore using the clutch as ‘dog boxes’ are designed for just such operation, with the exception of some circumstances ie longish downhill sections as an example. Before tearing the thing apart try changing gear 1st to 2nd without using the clutch and be firm in your use of the gear lever. The detent may be a possible cause as this might be creating excess pressure for some reason. You say you have trouble selecting neutral with a cold engine, have you rocked the bike back and forth whilst applying pressure on the lever in either up or down?

Well you could try the internet or have a look at your nearest industrial area and try to find a good aluminium welder. The original Montesa alloy tanks will be very brittle especially in any repair areas. Some people have tried various sealants and plastic metals but they invariably leak fairly quickly. Preparation pre weld will need the tank steam cleaning or filling with exhaust fumes, neither of which are truly safe for welding a petrol tank. I have had race car alloy tanks cut and modified and then re welded....but I went into the next county before any welding action took place. Good luck, I am not too far away from Metmachek who make alloy swing arms, specialist race parts and they welded a Bultaco flywheel cover for me...I coughed when charged £40 for a 1 inch weld..hope you find a reasonable cost.

There are plenty of manufacturers that make to order. Talon Engineering, Bespoke Sprockets, B&C Express and many more, your choice. You can also get sprocket blanks that allow you to get them machined to your specs. Don’t forget I measured the Brake plate to give an approx ID and I could well be out by 2-3 mm?. My measurement of the sprocket bolt holes was also approximate.

Finally after Mondays advertised showing was cancelled, saw the programme yesterday Tuesday. Marc Marquez high-sided after a tremendous push through the pack after taking to the kitty litter big time when leading. It was a miracle he managed to stay upright and rejoin near the back of the pack, so then he proceeds to demolish everyone and fight back to second only to get caught out by himself (tyres were an issue for many riders) a wobble, a twitch and then the kick and way up goes Marc to land on the sand but then gets punted by his bike. After flailing about and rolling a few times his right arm looked to be in a right state. The bike was trashed and Marc looked to be in serious pain....last seen on a stretcher white faced and clearly distressed. Later report stated he had sustained a broken arm and potentially extensive bruising everywhere. It was a nasty incident and could have been a lot worse. Nice to see MGP again.

Measured today, the ID of the rear sprocket and hub flange are 120mm and from sprocket bolt centres 130mm. I did not remove the rear wheel for this so I fiddled about with a steel rule. 60 mm from the centre of the rear wheel spindle to the flange or rear sprocket = 120 mm ID Guess you have definitely got a 348 rear hub, don’t know if the Cappra MX used the same hub. Brake shoes will be available from In Motion in the UK, I suggest a look online there may be shoe dimensions to help. Saw some 348 parts on e-bay a few months back eg wheels, brake plates and pivots etc. Good luck with the project? There are more photos of my 348 on the classified ads section.

At least with your current fan you can tell when its working which is a plus.

1976....will have a measure up Weds and let you know the result.

The hub you show does indeed look exactly like a 348 rear hub. Heres mine for you to compare.

You can see quite clear photographs of the C3 and its alternative roller bearing. Ease of assembly is good with the roller bearing but friction is increased due to greater surface area covered by each individual roller, unlike a ball bearing which has a significantly smaller contact area. If you are going to be stripping the engine down on a regular basis then go for the roller bearing otherwise save some dosh and stick with the C3 type which has designed in free play for sideways movement. As mentioned the reason that the flywheel side (ignition) main bearing usually fails first is that it runs hotter as there is less cooling due to the shrouding action of the timing cover and the fact that the crankshaft can dissipate more heat through the primary gear/chain and of course oil. Too much side play wont do the crank seals any good either, unless you like changing them regularly.

Use two, and get the right size as they are different. Obviously some are made better than others, some just squash the tyre bead against the rim others clamp more positively. Use at least one on the front as well.

Have you thought about the socks that you wear with your trials boots. These may be a cause of your ‘hot feet’. Do you get hot feet when wearing everyday footwear of the non sandal variety? Do your riding trousers tuck inside your boots, maybe try them outside, this will allow some air to circulate. Obviously if you wear those ballet type stretchy material things that most tend to that could be the answer to your problem, as they are a reasonably snug fit they could be causing blood circulation issues or your heart to work overtime, which would then make your tootsies a smidge hot. Are the securing straps too tight? Lastly the boots you wear may be the wrong size and are too restrictive. This could all be wrong but at least it gives you somethings to consider.

Steel toe cap sandals obviously!

Hello Ian, welcome to you.?

Thats the best method to ensure no adverse side loading to a piston running up the bore and down obviously. The main reason that there seems to be so many variables with cranks, rods and spacers was that Bultaco wanted to reduce any friction losses without too many dimensional challenges....a loose engine in other words. You will most probably find that your crank will not be exactly in the centre of the cases when the piston is in the centre of the bore. When you have finished at least you will have an engine that has been assembled properly and not just put together. A few passes through the old main bearings with an abrasive flap or Dremel attachment will give the desired effect, you will need to lock the inner to prevent it spinning, a ‘g’ clamp or mole grips can be used if sited carefully. Every factory trainer that has to show others how to do an assembly job eases the bearings so they never ‘struggle’ with a demo.

Very nice, very nice indeed?

Maybe as you only have experience of two machines perhaps try a few more before spending any money. Its always the same question...machine gun or rifle, big engine, little engine, rip your arms out power or enjoy the ride. 250’s tend to be acceptable for most riders, lets face it theres only between 20 and 40cc’s difference in the capacity so its more about engine state of tune. Some smaller capacity bikes are just as capable and a whole lot less threatening when you take a fistful of throttle. Hope you find a good bike that you like and are not intimidated by.

The big end is normally shimmed on the Bultaco, at least the ones I have done are. But you never know whats gone on before either at the factory or by previous owners. The hole is a breather in my opinion, most people that know about them seal them up and vent elsewhere with some plastic tube to run up out of the way of water etc. As many of the different trials engines were originally intended for road bikes it is likely that the hole you have identified would be perfectly ok for road use but not so good for wading etc and more likely to become clogged up in competition use.

worldtrialchamp....Thats not what I wrote, if you read again you will see I suggest reducing the interference fit....not allow the crank to slide about in the inner sleeve of the bearing.

Very nicely done, brake operating lever looks to be well protected ?

Side stand is in stock location.

Just because there is a circlip in (supposedly) the centre of the main bearing outers this will not stop the crank from moving in either direction when everything gets hot. Certainly it is good engineering practice to have the crank set in the middle of the crankcases but I don't think Bultaco mass production was that accurate. If there was no shims involved when you stripped the engine I would not be putting any shims in. More importantly its better to ensure the crank bearing housings in each case actually are in perfect alignment, or as close as damn it. The crank will move in the bearings (sideways) unless you weld everything in place. Some Bultaco engines have no spacer/shims in the little end to keep the conrod central, others have shims in place. I ended up making some alloy spacers as I was not happy that there was no mechanical control on aligment in the top of the engine (piston) as my engine originally had no shims for the little end and the gudgeon pin bearing (little end was free to slop about, thats how it was meant to be. The alignment was down to the con rod and the big end bearing shims to keep all aligned. If you are using C3 bearings these have a design intended amount of sideways movement to allow for heat expansion and contraction. Should you decide to use a shim to centralise the crank in the case mouth I would gently polish the crank shafts so that the main bearing inners are not such an interference fit. This makes assembly easier and if the crank needs to move when its hot the bearings may allow some slight movement sideways. I would assemble the barrel onto the crankcase without the piston fitted and check that the conrod is in fact central to the bore...such fun! You may well be surprised by what you find when doing this. Incidentally the barrel can move around on the studs an amount you may want to look at a more positive register for the barrel....giving away secrets here. I prefer to have the main bearings in the crankcase halves ( don’t forget the ‘o’ rings that go on the crankshaft ) and then slide the crank assembly (shaft lightly oiled) into the main bearings... only a slight tap required to achieve this. Check everything spins nicely before fitting the crank seals, I fit two to each side the inner goes in backwards and the outer fits in the right way round...one seal keeps crank pressure in and the a*** about face one stops air being drawn in through the seal...good eh! Thats nothing new and many engines are sealed this way. Happy spannering?

Extremely nice looking Ossa, a credit to you?

When a condenser (capacitor) is failing a good tell tale sign is the contact breaker faces show signs of bluing (dark blue) this is due to heat created by arcing. This arcing is more than you would get with a good condenser. The condenser stores electricity when the circuit is made, when the contacts begin to open the circuit is broken....unfortunately the split second the contacts begin to open there is inevitably some sparking and arcing, the condenser’s stored electrical energy provides a ‘back’ emf that helps damp the arcing and more importantly provides a boost to the ht coil. A lot of fledgling apprentices can attest to being given an electric belt from a charged condenser handed to them by a giggling work mate! So when the condenser fails you get misfiring and starting issues. Condensers for Bosch distributors are mounted on the outside of the distributor (on cars) and good old Lucas mounted the condenser inside the distributor....guess which one failed more often than not. Mounting the condenser on the frame ( usually under the tank area) allows the condenser to operate in a more friendly environment, ie less heat and vibration. The engine manufacturers installed the condenser in the flywheel area just for ease of packaging and less wire ( it all adds up to cost and time saving). Most any car type condenser will work on most any trials bike using CB ignition. Personally I use two mounted under the tank but shielded by the frame from exhaust heat and rising engine heat from the cylinder head. You should be able to view the contacts using a thin screwdriver to part the contacts and a torch to illuminate said contact faces, if the condenser is ok the faces will look light grey in colour, if blue then change the condenser.....iffy wiring connections excepted. Pay no more than £4-6.00 or go to a scrap yard and find a few engines with the distributor intact then strike a deal for the condenser’s say £2.00. Wiring...such fun?

Came in a tube then, it was all we were allowed to use, well that and ‘ hold me tight’ or Hermetite red semi hard setting and green hard setting. But we all knew Hylomar was best!

That happens when excess amounts are used, applied sparingly the Hylomar works well without causing oilway and filter clogging. A thin bead in the centre of the mating land will spread when compressed between both mating faces. Too thick a bead and hey presto it squeezes out both sides. Best practice is to apply a thin bead and wait 4-5 minutes before assembly.