section swept

The seal lip should face in towards the crank, any crankcase compression will push against the lip improving the sealing against pressure leakage. As a single seal there will always be a bit of lip movement as in the crankcase there will be a negative pressure before the positive crankcase pressure develops that’s why some engines have back to back seals ( where space permits) to eliminate air being drawn in from the generator side or indeed clutch case oil from the drive side. The first causes a lean mixture...too much air and the second causes too much oil in the combustion process and thus lowered petrol octane and smoky exhausts with poor pick up when the engine is revved up. Main bearings lubed by the gearbox oil under gravity will allow oil to be sucked into the crankcase if the crank oil seal is fitted wrong way round.

Maybe you should put yourself forward as a Brexit advisor, you have probably got more negotiating skills than any Eurocrats due to the experience dealing with DVLA ( doubtful vehicle licensing authority) ?

A 250 might be better for you, although a 200 would do you might find that with your physical size the slightly larger engine will tend to give you more control and not be quite so rev your. Even a 125 could give you a fun time but it depends upon the type of terrain you are riding, wet and boggy you will need a bigger engine. Join a club, make some contacts and possible blag a go in a few different bikes. Talking to club members will provide you with invaluable information and good guidance. You may find that due to your size you gel with a bigger engine say a 300. But try before you invest in the wrong bike, what suits one doesn’t mean it’s fit you.

US market spark arrestor, remove it and the engine might run just a little more crisply. Not sure what the State Troopers reaction might be though.

Oil seal deffo wrong way round

Apart from the bears this could be a forest in Wales, you are so lucky.

You are lucky living in or near to Church Stratton. Stayed a few times at a lovely guest house on the Long Mynd ( not sure if spelt correctly)?

We all make mistakes, most you learn from. Doesn’t look to be much by way of waterproofing around those cases. Have you done anything about that?

Register the bike as a historic/Classic and you can use a black number plate with white or silver numbers. The age of your bike also exempts from mot and road tax. You still need to apply for tax but there should be no charge.

Depends on your lads level of fitness and experience. What was he last riding? A 300 sounds big but in reality when compared to the 250 there’s only approximately 46 cc difference. The torque is the difference and a 300 could be more forgiving in capable hands, one may actually suit your son more so than a 250. Having said that there’s a confidence issue that riding a 250 isn’t quite so threatening. The last Enduro I rode a WR 450 and although a totally different animal that bigger engine lugged away in taller gears leaving you to ride and worry about changing gear when it was more practical. Are you intending any road work, licence laws may affect any decision. Oh to be 17 and 10 stone again, when I was that age my father bought me a new 250 Sprite (£167) power was probably the last consideration made. Hope you get a good bike.?

Bet you’ve got a Fireblade tucked away in the garage, just for when it’s nice and dry to have a blast on?

So if I read your description of the area ?that you ride correctly you’ll need the following. 1 a big hand gun of some sort?say a Magnum and ammunition....for the bears. 2 a very loud screeching horn....for the Wolves. 3 a sat phone like Lone Survivors team used ( Mark Wharlberg) 4 comprehensive first aid kit ?with snake ? bite serum. 5 a good camera? so you can make us all envy where you live with all that scenery. Bottle of water and food.??☕️ If your tail pipe is the genuine Yamaha item made of steel then it should be classed as a spark arrester....to be legal will you not have to comply or are your cops lenient. If your bike is noisy will that in itself drive away any bear of wolf pack, it would be very scary to have to stop and repair your bike only to have a Grissly passing you tools?? and the wolves making camp to watch⛺️

When you ride with throttle shut you restrict petroil mix from the piston and hey presto you get piston nipping and score lines on the piston skirt. The porting photos look like there may have been a weld repair done and then a clean up. The honing marks look a bit course from the photo and what appears to be cleaning rag fluff. The port itself would benefit from a gentle clean up or smoothing.

Here’s a few tips that may help you. Take photos of what you have for reference later or when sourcing parts. Spend some time just looking at and studying pictures/videos of Bultacos and the detail. Get familiar with the model types, you will find that some owners have altered their bikes quite a bit so try to stay with the more authentic builds. Get to notice the frame rail differences as the factory modified and then introduced these changes onto production bikes. Photos of works riders and their bikes can be invaluable when assessing correctness of parts to a model. Now put the frame and cycle parts in separate areas or on shelves but keep them apart. For example front wheel and brake in one location, rear wheel etc in another, frame somewhere else and chain and sprockets in a box. I always start with the engine first, break this down into cylinder, head and piston and store away, now you can strip the engine. If you have not taken an engine apart before, get an old moped engine or similar and practice on that first. A manual is invaluable a Clymer is more superior than Haynes but both are useful. The crankcase halves cab be troublesome to spit but everyone has there own ways to do this. I thoroughly recommend that you watch some of the videos on YouTube for Bultaco, the Spanish ones are good some are crap and not all of the methods used are acceptable so be aware. When you split the engine cases some will say you must use heat on the main bearings, to release them from the cases whereas others including me use other ways....? The gearbox is quite straight forward, but there are booby traps with the selector forks and a ship that goes on the kickstart shaft. Some of the breather holes made at the factory are in some daft places and when you locate these you may be surprised. You will get no end of help from the members on this site and the parts suppliers in the UK are excellent. A few photos to help??

Wheel spindle enters swing arm and brake plate from drive side. No spacer between brake plate and swing arm lug. Non drive side should be speedo drive (if fitted) spacer and additional thin spacer if no speedo or replacement double shouldered spacer. Then you have snail cam and thin washer. Some rear wheel spindles also had a thin washer on the drive side, between the spindle shoulder end and snail cam, this brings the spindle slit pin hole into line more for the castleated nut. Take the chain guard off and use a good straight edge on the rear sprocket and align the gearbox and rear wheel sprocket. Tighten spindle nut and look at exhaust where it is closest to tyre. You may need to adjust the rear silencer if the tyre rubs. It’s more important that the chain is true as this could cause serious wear to the sprocket teeth and possibly take a bit of power away from the engine. As Woody says you may have the tyre inflated too high but if the pressure was reduced to say 4 psi you might have more rubbing issues due to tyre flexing on the rim. There never has been much room for the back wheel in most Bultacos a design issue but then they tend to be slim which helps the rider. A bit of rubbing here and there will always happen when the bike is in action, you may get it all set lovely with no rubbing but after use the alignment fairies with have been busy shifting thing around for you so it all rubs on everything! If you search on this site you’ll find some tips on wheel alignment if you are the fussy sort and must have a perfect bike....and why not! But it wouldn’t be a bad thing to check front forks for correct alignment then check front to rear. 2-3 mm out is not significant ( watch me get pilloried for that comment) as it’s the chain which is important. You will not notice that small measurement when riding unless your an alignment fairy or Toni Bou. I wonder how many frames the works boys throw away after each trial because they’ve been used so hard. Last piece of advice if you are having problems still, then I would either remove the swing arm and get it on a surface plate at a local engineering company to make sure it’s not twisted. That’s fairly easy to sort with a bit of brute force or a hydraulic press. If you can’t go there then again on this site is the pics and info to help you DIY. Hope you get sorted and don’t forget you can always gain a little extra clearance on the exhaust back box by deft use of a......BIG hammer.?? Erm number plates could be covered next time ??

Did you not take any photos prior to dismantling? It’ll be a novel feature having to ride sections in reverse, you could pre select whether you are on a five or maybe a clean!? Seriously you must have created a reverse current to flow somehow. I would go back and re check all of your work very carefully. I’ve not worked on an Osset yet but have on numerous electric motors. This may sound daft but re check battery polarity first. Then it’s down to either workshop manual or tinternet.

Resourceful bike stand?How high can you stack and still support the bike?

They are showing you a method of removal using limited tools and equipment the sort most people might have access to. If they showed the use of specialised tools then that would defeat the object of the exercise. An alternative to the water pump pliers could be a suitable sized expanding rawl bolt.??

There’s quite a lot of useful pictures and information on this website, a little research will equip you with some knowledge and the photos help. On the internet are a great many tutorial type videos, some you need to be aware are not technically correct, others rate as good to excellent. Depending how deep you want to go, but for trials bike maintenance a lot of the work is basic stuff, set up is more involved and experience counts here. Just studying the photos of various bikes gives you plenty to think about. Some of the auto stuff is good to investigate as well. Before you do any work on your bike or anything else you are not sure of take photos before you actually carry out the work. Say you want to remove the back wheel, photo the wheel spindle and in particular any spacers and brackets. Then when you come to refit the wheel you can refer back to the photos.

Dont know how strict your construction and use regulations are or how well they are enforced, your police seem to be very keen, but I’d start there. It’s very easy to make suggestions and be totally wrong which won’t help you. Most older trials bikes had fairly ineffective lights in any case. If you are riding off road in failing light you might consider something else far more efficient that wont upset plod?????

Just measure any part of the frame side rails, the main loop would be good but 20mm or 3/4 in OD ??

Toolroll mounting point???‍?

After a long lay off due to other commitments finally she’s done and started second kick, rode her down the drive and back tested all gears worked, set idle and tested kill switch. Now up for sale as another project in the pipeline.

That tensioner helps keep the primary chain in its ‘torque arc’ the centrifugal effect that makes the chain try to arc upwards as if following the crank sprocket but the clutch drum sprocket pulls it down. As you say smoothing the on off throttle but also helping to slow the wear on sprocket teeth and chain. That whirring sound is the engine humming to itself.....it’s the chain under tension and is normal on nearly all Bultaco with single row chain, the twin row or duplex primary chain is less noise prone.

The frame tube wall thickness is 2.00mm as standard, probably a good reason why the frames are heavy.