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About lorenzo

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    Advanced Member

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  • Bike
    (6X) Bultacos 73-81

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    East Anglia UK
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  1. You can junk the cast bracket and replace with a fabricated steel one, as Bultaco themselves did on later bikes. Bracket should be obtainable new from Inmotion, or possibly secondhand on fleabay, etc. Also check carefully the (cyl.)head steady and fixings.
  2. More information needed, methinks...... Is this a bike you have owned for some while (and had running), or a disparate collection of parts you are trying to assemble ? When did the problem first arise ? What parts have you replaced ?
  3. Time Left: 1 month and 24 days

    • FOR SALE
    • USED

    Dismantled engine (ser. # 21M 3474) semi-complete - with usable cylinder barrel (bore .50mm. o/size) and head. No broken fins. Salvageable mag. and clutch covers . Second earlier engine (ser. 21M1079) - crankcases and clutch / gearbox parts. Can take more pics. if required. Buyer collects.

    75.00 GBP

  4. cyril - Don't want to be too hard on you.........I'm sure we all made stupid mistakes as raw novices - I know I did...... However, "culprit of the nasty noise in the engine" is unlikely to be just a nut that's come undone - that's more likely to be merely a symptom of other damage. As vintagenut has suggested, the woodruff key is probably also sheared, with attendant damage to the tapers of flywheel and shaft. Also, depending on the revs. reached (and for how long) when the bike started w.f.o. you may have damaged the conrod bearings. As misscrabstick and pschrauber have said, engine now needs a total strip and rebuild. Best thing you can do is follow your own admission, and entrust the work to someone who actually knows what he's doing. Be prepared for a sizeable bill...sorry !
  5. Jonboy - Probably nothing more than "barrel" distortion (camera lens). Did notice that the conrod. looks to have been replaced already.........and why two cyl. base gaskets, I wonder ?
  6. lorenzo

    Crank centering

    DickyM - Whatever you decide with your engine, I urge you not to make any non-reversible changes - reducing the interference fit of main bearings "to make assembly" easier would be one such change............you could regret this when your main bearing inner races start to spin on the crankshaft........ Never assume that Bultaco didn't know what they were doing ..... Your con rod assembly looks like :- As far as I can tell replacements ARE available - this is one bought in January and now fitted to one of my cranks:_ (I was quite surprised to find this crank in a mod. 124 engine, which I believe would have had an 18mm. crankpin originally..! ) Also have o/size Mahle 71mm. pistons, although many have said these are "unobtainium". "Seek and ye shall find" ? The availability (or otherwise) of parts is influenced by how soon they are needed, and the depth of your pockets. I have several engines undergoing "the treatment " at the moment and I've not found one that's worked out cheaply so far........
  7. lorenzo

    Crank centering

    DickyM - The small hole pictured is the gearbox breather, the only breather in standard form. It needs to be kept clear - if it becomes blocked it can lead to oil leaks and/or g/box sprocket seal failure. Attempts to provide alternative breathing through the filler plug have had mixed results, according to previous posts on the subject. Over the years Bultaco appear to have experimented with either two or three main bearings / crankpin (and crankwhee)l diameters / conrod location by big-end washers and small-end spacers / location by small-end spacers only. Your conrod/big end bearing with narrow thrust washers is the original type of set up for your engine.
  8. lorenzo

    Crank centering

    But wasn't that was the very reason the circlip was introduced on later engines..? Well............ there you have it...... What are you hoping to achieve by "centre-ing" ?
  9. Daveys - Crankcase gasket must stand proud of cylinder base joint face at assembly, to be trimmed after cases are together and all fixings tightened. This should ensure that there are no leaks at cylinder base. You seem to have taken considerable care to centralise crank within cases ; what happens when driveside nut (for oil seal sleeve and sprocket/weight) is fully tightened ?
  10. Yes............. Crankshaft needs positive location relative to drive side crankcase half to retain primary chain alignment. Using roller bearing on mag. side of crank also makes crank width and axial location of main bearing less critical.
  11. markg - As the inner and outer races of the roller bearing are separate parts, once fitted to crankshaft and crankcase respectively it's then possible to assemble/disassemble the engine without heat.. See above from the o.p.
  12. Daveys - The roler bearing you have has axial location in one direction ( a shoulder on the inner race) - have I got that right ? Why not heat the inner race and fit that to the crank (shoulder to the wheel), heat the crankcase and fit the outer race ("open" side to crank). Inner and outer parts of the bearing are then located independently and you can simply slide the bearing parts together when you assemble crankcase halves. This of course ignores manufacturer's markings........( and I don't know which way they face on SKF bearing, anyway)....... having NJ series bearing also sets up requirement for the crankshaft width between bearing seats to be controlled to avoid negative axial clearance. Or maybe I'm completely off beam here.........
  13. lorenzo


    Model 158 original frame colour was silver.
  14. lorenzo

    Sherpa Brakes

    Front wheel has had a steel/cast iron? (ferrous, anyway..) liner inserted. This is the usual means of salvaging hubs which have suffered deterioration of the chrome plating. Hard chrome originally applied direct to alloy casting. If your chrome is as intact as it looks, keep it unti it fails. Rear spokes stainless butted, or steel galvanised ?
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