Daveys

Section Swept. Like your explanation. When I have eventually got everything sorted, which may involve further strip downs, I will return to straight C3s.

DickyM, Hello. I fitted the SKF NJ205 ECP/C3 on the ignition side as you mention, with the flange against the flywheel. I am happy with the arrangement, more from the ease of assembly and disassembly than the other benefits whihi I haven't experienced yet. Johnjsy confirms this ease. When I was reading up on this bearing the main benefit as I saw it was the ability to use some loctite (641) on this side alone as the bearing I took off was a little loose and I figured i would fix it with the loctite and allow the float to take up the movement which had caused the slight wear on the crankshaft in the first place. Apparently this side is prone to such wear. I have retained 2 x C3 on the other side and they are not fixed with any loctite. When I was speaking with Inmotion they did have a bearing which could float in both directions and stated this was for a Mk10 370 Pursang. It is here that Sherpa325's comment has merit and it is clearly for a motocrosser. My bike is a frontera 370 so I'm nearly a motocrosser but I will generally be driving miss daisy when i get it going. If I had been aware of the plastic I would have bought one with a steel cage the reason being if I need to take the bearing out of the crankcase then I have been using a blowtorch which will likely damage the plastic. I had to swap some bearings between clutch baskets and one had a plastic cage which slightly singed when removing it. I will stay away from P in the future. Thanks Daveys

markg, Your question re which side the NJ 205 goes was answered by Lorenzo but it did make me think whether you could use all NJ 205s. This could be an option on cranks which only have one bearing on each side but as mine has 2 on the drive side it would be pointless and an unnecessary cost. Also on rereading Lorenzo's post the drive side sounds like it needs to be fixed for the primary chain alignment and not have the movement which an NJ 205 provides. It easy to overthink this which I can be guilty of doing.

Lorenzo, I worked out why the crankshaft was not going around. The centralising did not work. I had a 1.4mm gap on the drive side and a 0.7 mm on the magneto. When I tightened the cases it was rubbing somewhere. The gasket was also slightly proud inside the crankshaft area but that can be moved over when I reassemble. The centralising technique I used was flawed and missing an important addition. I did not put the oil seal retainer on the RH crankcase side when I heated it and dropped it on the frozen crank where the 2 x C3 bearings sat. I thought my 0.9mm measurement on the other side would be enough and the joining of the crankcases would leave the drive side 2 x 3s in the right position within the crankcase. It didn't work. Perhaps I removed the feeler gauges a bit early and as the magneto crankshaft could move within the NJ205 the whole crankshaft dropped a bit. Most likely it was down to the omission of the oil seal retainer. I decided to see if I could put it right by installing the oil seal retainer on the RH crankcase, use a blow torch to heat around the bearing seat and then with the nut installed on the LH crankshaft hit it with a rubber mallet until moved up to the oil seal retainer. It worked. Crank now central ( roughly 0.9mm one side and 0.8mm the other). I tried tightening the cases without the gasket in place but this caused a slight rub. I then put the gasket on and tightened all 12 nuts and the crank now freely moves. Another Bultaco lesson learned the hardway.

Lorenzo. Thanks for the reply and thanks for the other replies Your suggestion is right. I spoke to In Motion and they suggested the same. Mind you they also said that the original should be the standard C3 and the needle bearing option was just for the Mk10 Pursang. Before I read your reply I removed the needle bearing and put the standard C3 on. I then read your reply and thought I would be brave so removed the C3 and put the inner race on the crankshaft with the flange on the inside so that the outer bearing can just slide on and off. I then put the outer bearing in the freezer for a few hrs before heating the LH crankcase with blowtorch and bearing dropped in. I then put the crank in the freezer again, 2 x C3 on the drive side and the inner race on the magneto side. I then assembled the gearbox put some blue hylomar on the crankcase joints and a new gasket. I has previously measured the gap between the crankcases and crank as 1.8mm so tried to centre it at 0.9mm each side using a dismantled feeler gauge. I placed 2 x 0.9mm gauge combinations on the LH crankcase and dropped the frozen crankshaft into the NJ 205 outer bearing so that it sat on these gauges which were retrievable after the cases were assembled. I then used a blow torch on the bearing seat of the RH crankcase and dropped the case on the awaiting crank and 2 x C3. A slight wiggle of the kickstart shaft and they joined up. All appeared very good so I tightened the 12 or so nuts. After this I tried to rotate the crankshaft and it would hardly move. I was worried but did remember that when I put the gasket on it was slightly proud at the point the crankcase join where the crank sits. I split the cases and recognised the benefit of the NJ 205 as the cases could be split without me having to heat around the bearing seats. I took the gasket off (ripped to shreds in doing so) and put the cases together. The crank turned as it should. I will used another gasket and trim it back so that it does not touch the LH inner crank 1/2 weight. I can definitely see the benefit of the NJ 205 on assembly and disassembly alone. The crankshaft not turning did worry me but thankfully it was simple and I should have trimmed the gasket back.

Hello. I saw some old topics which recommended a NJ 205 ECP/ C3 bearing for the ignition side. This was specific to Bultacos but probably applies to lots of others. I bought an SKF which was pretty pricey at £30 but the benefits of fitting it sold on the outlay. The SKF has a collar/flange on one side and the whole outer bearing can slide off the other uncollared side. When I put the bearing on the crankshaft (370 Frontera Mk10) the bearing inner is up against the slight raised section of weight, as should be, but the bearing outer is free to slide up over this raised section and sit against the weight. My concern is that in on assembly when I drop the crankshaft plus bearings into the LH case this will push the bearing outer up against the weight and it will rub. I could try and put a temporary shim in between the bearing and the weight on assembly so that there is a 1mm gap as per the normal C3s on the other side and then when the case cools down it will grip in in this position. The other option is to reverse the installation so that the collar sits up against the weight (on the slight raised section) and the outer can slide off. This might make assembly tricky with the hot LH case horizontal on bench and the cold crankcase being lowered as the outer bearing will keep falling off. I installed the first way because this would still allow me to see the manufacturing number when installed which I though would be the correct way to do it. The other option is to ditch the NJ 205 ECP/ C3 and use the spare plain C3 I have as installed on the the other side. I feel I am making a simple mistake which could be catastrophic if I get the bike going. I am off to In Motion this morning as they showed me the needle bearing they sell which does flex either way on the inner but does not totally come off one end as per the SKF. I could have bought the wrong type. Any advice gratefully received _

Hello. Similar to many others I have used the site a lot and thought it time to join. I bought my Bultaco Frontera back in 1986 for £100. It was in bad shape but still worked. This was all pre internet days and I was only 21 but I did have enough sense to buy the Haynes competition manual. Other than being very tatty the main problem back then was difficulty in selecting 2nd gear. Luckily I lived near the Len Savage Shop in Farnborough and he put me in touch with an old mechanic who had loads of spares and I got another selector drum. I don't know how we managed it but with some help from friends we changed the drum and it all worked. I got the bike through the MOT without any lights and borrowing some working rear shocks. At the time the rear wheel bub had split, been welded and was split again. I wrapped electricians tape around the bearing and knocked it into the hub which solved the wobble for the MOT. Incredibly stupid but effective in the short term. I rode the bike around for a summer but it ate petrol such that I had to plan any journey via petrol stations. In the end I put it in my mum's garage and then went travelling. I had covered it in grease as I thought she would chuck it outside while I was away. 31 years later COVID arrives, I'm bored and so decide to try and get it going. The renovation has been quite an effort and is still ongoing. I have a lot of pictures and will post some if people are interested. I always knew I was going to do the bike up at one stage and had bought an Akron rear wheel from USA. This fitted very well and it did make me laugh when I saw the remnants of the electricians tape on the old bearing. It was at this stage I started to identify lots of mistakes that the previous owner,and likely me, had made in the past. I bought some used Betor rear shocks as the originals were already not working and were now totally perished. The back end looks pretty good and all seems to work well. I am in the process of reassembling the engine which was in a bit of state. All the main bearings had rusted. I have learnt a lot, have leaned on the good nature of In Motion and still have lots of questions but perhaps can help others as well. Will be posting soon.