1988 bike



  • @oldman If it was running a 3MB and you put a 3BN barrel on it, the stroke will be too long. Is it the crank, is it the rod? I don't know. But the stroke is definitely different. So you will want to make sure you have clearance.



  • Checked fowlers for part no, con rod for 88 listed as separate item, later years checked a(89 and 1990) and shows discontinued with no part nos? Have ordered a genuine 88 one to be sure but any info you have useful? Original barrel was already 1.75 over hence the replacement



  • It's definitely an 88 bike and engine, the barrel was consistent with engine and I did have a spare 3mb barrel but sourced like for like. Cant be sure con rod in engine is correct hence ordering correct one from fowlers. Could be whole crank differs from later bikes but don't know (yet) will check clearances as built, lucky to find a matching barrel to be honest



  • @oldman Yeah this.

    The manual specifies both the bore and stroke for the 3BN, I'm sure. I don't have it to hand.

    It is so minor I doubt it'll be too much of a problem. Powervalves are not interchangeable though.

    As said, doubling up on base gasket will do the trick. My worry is that the con rod is designed to stretch and compress, how close will it be at 12k RPM is anyones guess!



  • Have the original powervalve fortunately, the manual is. 4 or. 04 difference I think from memory, Will be checking when assembling .



  • My understanding is the 1988 has the BN barrel and slightly longer stroke 0.5mm or something. 88 on wards they had slightly bigger bore and shorter stroke. Think if you mix and match parts you can end up with a 135cc or similar.



  • @Calum said in 1988 bike:

    @oldman Yeah this.

    The manual specifies both the bore and stroke for the 3BN, I'm sure. I don't have it to hand.

    It is so minor I doubt it'll be too much of a problem. Powervalves are not interchangeable though.

    As said, doubling up on base gasket will do the trick. My worry is that the con rod is designed to stretch and compress, how close will it be at 12k RPM is anyones guess!

    Hello Calum,What's the difference with the powervalve? Have measured and dry assembled and seems no different than one that came with bike, bar original has no grooves for seals and diamond style pulley shaft on end? Frame back but waiting for rack, grab rail, footrest hangers, suspension spring, etc.



  • @oldman I must be thinking 4FU and 3MB.

    One of them didn't fit.



  • OK, thanks Calum. Replacement shock arrived and it's worse than the one I need to replace sadly. Lower ball joint corroded and worn and corrosion on plunger shaft has damaged the seal, very little damping going on. Will keep looking for a decent one.



  • @oldman FFS 😠



  • @oldman said in 1988 bike:

    OK, thanks Calum. Replacement shock arrived and it's worse than the one I need to replace sadly. Lower ball joint corroded and worn and corrosion on plunger shaft has damaged the seal, very little damping going on. Will keep looking for a decent one.

    look for a shock from a newer bike they have a white spring an fit on the 89 model



  • Finally got a decent shock, waiting for powdercoating to return (have frame back though)so I can start rebuild. Seller of faulty shock not responded yet to return for refund, but covered via PayPal. Looked at getting a new indicator switch gear assembly and they are over £150. Put that on the wish list with everything else. Photos will be posted when there is something to show!



  • Powdercoating back bar 2 items that should be here later this week, now where did I leave the assembly instructions????20190623_231148-460x818.jpg


Log in to reply