DickyM

Hi all, thanks for your replies. Choice of bearing seems to be a matter of personal choice as there doesn't seem to be a consensus point of view. I take on board and acknowledge the different views people have and recognise the merits of the different points of view. But I have now decided and rightly or wrongly, bought a steel caged N205 roller for the ignition side with free float either way. I shall see in due course how it works out. Johnjsy and section swept make the comment that the ignition side bearings tend to go first due to generally running hotter. I wonder if this is also true of the ignition side seals? The outer seal on this side must vertually run dry as well as hot. Any evidence of more failures on this side? Daveys I'm sure your loctite solution will work fine. I have used it in numerous situations in all sorts of applications and personally never known it fail. Thanks again everyone.

Hi again all. Back again so soon. I am literally about to order all the bearings and seals for my 198a and I thought what the heck why not fit a roller bearing to the timing side like many others have already successfully done. An extra £30 or so in percentage terms is not much. So my question is what type of roller bearing to buy? What type have you all fitted? I note that DaveyS posted a similar question back on 26th June and he has used an SKF NJ205 ECP/C3. This type of bearing allows free float in one direction but not in the other and fitted with the flange against the flywheel means that if the crankcase expands more than the crank itself, which it probably does, it is free to float. If for some reason the crank moves more than the cases then the bearing would resist, as a ball bearing would do. Personally I was thinking of an NU205 series which can float in either direction. With the double bearings located with a circlip on the drive side I thought this arrangement gives the most flexibility. Also I note that the P in the designation ECP means that the cage is made from plastic. Reinforced polyamide (Nylon). Is the cage being made out of plastic likely to be an issue or am I fretting about nothing, again. SKF NJ205 ECJ/C3 and NU205 ECJ/C3 with steel cages are available at yet more cost if required. I would be interested to hear your experiences. It never crossed my mind that bearing cages these days could be plastic so maybe plastic cages are being used on ball bearings as well. All the old bearings I removed are steel cages though. As a by the way I had a go at calculating the differential movement between crank and cases just to see how much they can move. Aluminium crankcases will move almost twice as much as the steel crank but with an engine temperature of say 120C from say a 20C ambient the movement is around 0.1mm with the cases moving outwards relative to the crank. (According to my calculations that is) Not much but enough to stress ball bearings. Can't see the crank/cases getting much hotter than 120C otherwise the nitrile crank seals would break down and the gearbox oil would be boiling! I would be grateful if you would let me know your thoughts. Thanks

Well thanks everyone for your advice. Centering the crank. Decided. Centralise the crank to the centre of the bore. Crank assembly. Many and varied varieties out there. There doesn't seem to be a preference for one version over another so will use what's available. Piston. I spent 3 hours last night looking for NOS 71.25mm, etc pistons and there are non easily available that I can find. Need a rebore anyway so decided to go for 72mm. Readily available. Small hole is a breather. Will leave alone. Thanks Lorenzo for the pictures. That does indeed look like my crank and by the way no intention of carrying out any irreversable mods. Wouldn't dream of assuming Bultaco didn't know what they were doing but they sure chopped and changed with their crank designs. Good idea from feet up fun to modify old bearings so room temperature test assemblies can be made. Difficult for me to modify hard bearings so turned up a couple of dummy bearings in aluminium that allow the same thing although cant turn the crankshaft with these though. Thanks again

Thank you all for your replies. Some useful thoughts there. Lorenzo. There are several people on this forum that suggest getting the crank central is important to better running. Not having done a Bultaco before I don't really know. However whilst it's all apart I might as well do the best job I can and might as well centralise the crank, as long as there is no downside. All. I spent time this morning measuring up the parts from my dismantled engine and made a drawing of the drive side crank assembly, just to get it clear in my head. See below. As far as I can see there is little chance of lateral movement whether hot or cold, especially if the crank nut is tightened to 90 lb ft as specified in the manual. That is very tight. Also with this in mind I cannot for the life of me understand why the inner bearing races need to be such a tight fit on the shaft on the drive side. A light friction fit is all that's needed as when all bolted up that is not going to move. Easier assembly too as Section Swept says. Any movement due to heat expansion will happen on the alternator side or be taken up by the C3 bearings. So the way it looks to me is that if I do want to centralise the crank I will have to fit a shim between bearing and crankshaft thrust face, if indeed it is worth doing. I was very interested in Section Swept's comments about the crank/piston assembly. As I understand it you had spacers on the big end and none on the small end and you made up spacers yourself for the small end. So you have spacers on both big and little ends of the con rod. My crank piston assembly is the opposite. Spacers on the small end and none on the big end with side to side play of 3.1mm. (There are spacers in fact but the OD is small enough for the conrod to go over them.) See photo's. Sorry they're a bit blurry. This arrangement relies on only the small end to keep things in line. This all seems original. Bultaco stamped on conrod and original piston. Never been rebored. Replacement conrods available from In Motion or Feked have big end spacers and a wide bearing at the small end and no spacers so that the conrod can float. Neither of these suppliers have a conrod that matches mine either. 24mm crankpin but only 16mm gudgeon pin. I need a new piston as well probably 72mm as the 71mm range does not seem to be available. Not sure what diameter gudgeon pin this would have. Any advice on the way forward with this would be much appreciated. The current bearing seems ok but I'd prefer to replace a 41 year old bearing set up. Finally there is a small hole (approx 2.5mm dia) behind the kickstart mechanism in the gearbox which comes out above the kickstart return spring on the outside. See photo. What's this for? Doesn't it drip all the time? Oil the spring maybe although enough oil gets flung off the rear chain to do that I would have thought. There is an adequate breather system so I don't get what this hole is for. Can anyone enlighten me? Thanks again everyone.

Hi all My Sherpa198a project is moving ahead again after a break for a few summer jobs. Engine stripped and cases split and I am now thinking ahead to assembly. I've read the workshop manual (which doesn't actually cover the 198a), studied the parts manual exploded view and trawled through similar questions/answers on the forum. I am therefore familiar with the two main methods of assembling the main bearings. Fit onto crank and then into crankcases or into crankcases first and then fit crank. But I did notice that quite a few people on the forum talk about the importance of taking care to centralise the crankshaft in the cases as you bolt them up. However although I haven't seen it mentioned anywhere or by anyone my bike has a round section circlip fitted between the two drive side bearings. This means that when the drive side crank nut is fully tightend the right side of the crank pulls up to a fixed position with the drive side double bearings pulled up tight either side of the circlip. I.E. The position of the crank is fixed, determined by the circlip, with no lateral movement for any adjustment. I measured the crank position before I split the cases and there is a gap of 0.7mm between the crankshaft face and the inside of the case on the drive side and a gap of 1.2mm on the alternator side. If I want to centralise this the only way I can see to do it is to fit a 0.25mm shim between the crankshaft face and the inner bearing or between the two bearings. This should then give a gap of 0.95mm either side, Has anyone done this successfully? Or is this a complete waste of time and best to just leave it just as it is? I have a few other things `I need to clarify but I think I will post them separately. One thing at a time is perhaps best. Regards to all and thanks in advance.

Hi Lorenzo, thanks for your comment. I think you're right about the front hub being sleeved with a ferrous liner. It is in good nick anyway. The rear chrome is very good and as you say I will keep until it fails. Both front and rear wheels had galvanised spokes but front had alloy nipples and the rear steel.

Chrome then. Wasn't expecting that but obvious now you've all said. Leave alone and rebuild the wheel then. This bike is full of odd surprises. I'm pretty sure that drums and wheels are original fittings as in fact I think were the tyres. Date codes definitely pre 1990 anyway. So front wheel no sign of chrome plate and a magnet sticks to the liner. Rear brake chrome plate and the liner is completely non magnetic so makes me wonder what they actually put the chrome plate on to. Also front wheel had all aluminium spoke nipples whereas rear wheel all steel. Using up stock as they got towards the end I guess. Picture of front wheel hub posted for comparison. Thanks for all the replies on the subject and to Woody for the paint info.

Hi All Hoping to benefit from your collective experience. Getting on OK restoring my Sherpa 198A and am currently working on the wheels/brakes. Front wheel all sorted and rebuilt. On the back wheel though the steel brake liner pressed into the hub has a highly polished, almost mirror like finish. I thought this should be roughened up a bit with some wet and dry before reassembly. Problem is the surface is beyond glass hard and wet and dry doesn't seem to touch it. I've never personally come across this before. Any ideas on how to get under this hard glazed surface, or should I just leave it as is? The bike was a non runner when aquired so never ridden so no idea if the brake worked properly or not. Brake linings look fine and nothing obviously wrong with them. Whilst I'm asking for the benefit of everyones experience anyone got any recommendations for black paint for the motor? It was originally black so I want to refinish the same. I'm thinking mostly for the barrel and head as obviously they get the hottest. Never had a painted motor before so no experience. Any suggestions welcome. Thanks in advance

Hi Ian T I'm refurbishing a later Sherpa 198A and had exactly the same decision to make a few weeks ago. I got similar costs quoted so I decided to buy new ones from InMotion. These are different to yours as mine have parallel tops. I'm pretty sure they are pattern replacements but that said I thought the quality was excellent. Everything fitted and lined up as expected and they had a quality feel about them. I haven't tested them on the bike yet as that is a long way off but I think the InMotion ones are fine. I'm glad I bought them as eventually I found a nasty crack in one of the originals right down at the bottom where the circlip holds in the damper assembly. Good luck!

Thanks for the replies. Apart from the situation with the new throttle slide that basically answers all my questions. The guys that sold the slide don't know the answer to the question about that either so I will make a new needle retaining disc to my own design. Sorted. Very little wear on the slide bore actually but the slide itself was badly worn so not that keen on originality feetup just trying to keep costs down a bit for the time being. Not sure what I'll find when I take the engine apart but I dare say there will be lots of expenditure. I was originally after a british two stroke for a project but they are very expensive and not many about that I was interested in. Always admired the Sherpa and when I found out the gear change can be arranged on either side (rhs for me) and there were plenty available at reasonable cost I went for it. Cost me £900 but I can see by the time I've finished it would have been far cheaper to have bought one already done up. But where's the fun in that? I have though been quite shocked at the cost of spares, particularly second hand junk on ebay. Cheers.

Hi All Getting on with restoring my Sherpa 198A and currently trying to sort out the carburettor. Stripped it and generally wasn't too bad except for worn throttle slide and a bashed about float chamber. Anyway jets and needle were as specified in the Owners Manual but as general detail is a bit thin I have referred to an Amal Mk2 Technical Manual available off the internet. Totally confused now so I'm hoping forum members can put me right. Attached pdf shows the needle jet, Carb Bits.pdfmain jet holder and main jet taken from my carb. Needle jet is the 2 stroke variety without the bleed hole but according to the Amal Technical Manual (extract on pdf) the main jet holder is a 4 stroke type. Picture in the Owners Manual seems to show this 4 stroke holder but it is not very clear. Is the main jet holder currently fitted the correct one or not?? Owners Manual and the Amal Mk2 Technical Manual both show a main jet 'screen' on their respective exploded views which seems to be a mesh of some sort that fits over the main jet. Is this necessary? I've never seen one before in my life. Spray tube. The one on my carb looks a bit like the one described in the Technical Manual extract as coming from a late Norton 850 with the cutaway facing the engine. Is this correct? Throttle slide was badly worn so bought a new one which appears to be teflon coated. Relationship of cutaway to needle height is identical to the old one but internals where the spring fits is different. See picture on pdf. The needle retaining disc doesn't fit properly into the new slide because of the lug. All shown in the picture. Is there a different type of needle retaining disc available or do I just bash the lug flat and reuse that? Finally I have a problem of my own making. As the float bowl on the original was badly bashed I shopped around and bought a new one at the best price I could find. Problem is in my ignorance I didn't realise there are 2 stroke and 4 stroke versions. I appear to have ended up with a 4 stroke version which comes with a fat float needle and a brass seat with a 3.1mm (.125') bore. The original float bowl has a slimmer needle , a nylon or similar seat and a bore of approximately 2.2mm as near as I can measure. Does anyone know what will happenif the bike was run with this 4 stroke set up? Would it work ok or do I need to faff about sourcing and fitting a new seat, needle etc?? I would be extremely grateful for your advice. Thanks

Thanks for the replies guys. I'll do as you suggest feetupfun and cadge a ride on an earlier bike for comparison when I can. And your thought Greg about downgrading the power output on paper is a very real possibility, one I hadn't considered to be honest. An earlier version of the VW emissions scandal! I'm not at all worried about this power output thing and as I said before the bike will be rebuilt to it's original spec (or as near as I can get it) All I was querying really, admittedly being a bit of an anorak about these things, was to find out what the actual engine differences were. I dare say I'll find out more when I split the engine. Dealing with the cycle parts first. Thanks again.

Thanks you both for yourPower Graphs.pdf comments and your comprehensive reply feetupfun. Could be that the 238cc unit was tested at the back wheel but that would be a big loss through transmission for a chain driven bike and it would be odd to put the 250 and 350 on the same graph, one measured at the back wheel and the other at the crank. Understood all you said feetupfun and you can pick up the torque reading at lower revs from the graphs. Clearly having useful power at lower revs is good for a trials bike. It's just that 14.1 bhp is so low and the 350 doesn't seem to have suffered in the same way. 14.1 is even lower that the 1959 BSA C15 I used to own which was rated at 15 bhp if I remember correctly. For a Bultaco 238cc made 21 years later 14.1 just didn't seem right. Interestingly, to me anyway, I also noticed that the power curve given for the Alpina 250 (again 238cc I believe) in the Workshop Service Manual is almost identical to the 198 graph included in the Owners Manual. I have attached a copy of the power curves in question so you can have a look for yourselves if you like. All the best

Hi All Just joined the forum. I've made plenty of visits as a guest and found it very useful so thought I'd join as I think I'm going to need plenty of advice with my project. Bought a 198A Sherpa T 1979/1980 vintage over the Christmas holiday as a retirement project. It's a bit of a wreck with everything falling into the 3 B's category. Bodged, bent or busted. However that's fine and going well so far. But I have a question that no one seems to know the answer to. So heres hoping. Before I bought the bike I did a bit of online research. I discovered, on this forum somewhere actually, that max power output of a 250 Sherpa was around 20 bhp compared to around 21.5 bhp for the 350 version but with the 350 having much higher torque. As soon as I bought the bike I also bought myself a Workshop Service Manual from In-Motion Trials. This covers all models up to model number 200 but actually excludes the 198 and 199 series. In this manual there are power and torque curve graphs for 250 and 350 Sherpas showing max bhp as 20 and 21.5 respectively and torque as 2.72 and 3.15 M/Kg. Exactly as expected. However the bike came with an owners manual specific to the 198 and 199 model series. This is a proper printed glossy booklet printed in Barcelona in November 1978. When I got round to reading it several weeks after acquiring the bike I found there are power curve graphs shown in this book also. The 350 is much the same with max power shown as 20.8 bhp but with a lower torque of 2.76 M/Kg. The 250 however shows a maximum power of only 14.1 bhp and torque down to 2.04 M/Kg. IE Power down 30% and torque by 25%. These figures are also repeated in the general data section. What goes on? Can anyone shed any light on this? I find it hard to believe that Bultaco, faced with ever increasing competion from Japan, would take a proven bike with impressive history and track record and suddenly decide to lop power by 30% and torque by 25%. It seems that they did but what on earth did they do to the engine? I have not seen any reference to this anywhere and believe me I have dredged the internet. I am aware that the cc of the 250 ws dropped to 236 cc but surely this didn't lead to a 30% drop off in power. The outcome of this is irrelevant to my project bike as I will refurb it as it comes. I'm not chasing power but I like to get under the skin of a bike and I'd just like to know. Does anyone know what happened here and what they did to the motor to strangle the power. Thanks in advance.

Thanks Rich, appreciate it. Hope the guy who has just started trialling has got good knees!

Hi All New member just signed up. I've been using this site as a guest for long enough so thought I ought to sign up. When I retired a few years ago I decided I was too old for bikes so sold bike and all my odds and ends. Few years on and bored I yielded to ebay temptation and bought myself an absolute wreck of a Bultaco 250, 198A for not much money. Having great fun working on it even if by the time I've finished it wont be a cheap option! Always fancied a trials bike, lean and functional that's how I like them. Now we are all on lockdown my wife is even glad to get rid of me for most of the day in the garage. Biggest issue with the bike is undoing the handiwork of previous owners. Some people should be kept away from doing anything mechanical by law in my opinion. Anyway hope to pick the brains of the Bultaco experts on the forum soon as there are a few things I need to sort out. Take care all in these times of the Coronavirus and enjoy your biking, whatever it is.