New start for Al’s bot­tom end

Crank needs a re­grind and new big end shells, rest of it seems in rea­son­ably good health

Practical Sportsbikes (UK) - - On Our Bench -

Last month saw me in a slough of some de­spond at the re­al­i­sa­tion my 900SS’S big-ends were in an amount of trou­ble. There was a glim­mer of hope, how­ever, in the thought that it had sim­ply spun a shell and that if the crank had sur­vived un­scuffed I might get away with new plain bear­ings.

Hav­ing ini­tially thought I couldn’t get the con­rods off with the cases still in­tact, fur­ther in­spec­tion and a tad more de­ter­mi­na­tion showed that I could. I at­tacked the rod for the ver­ti­cal cylin­der first, as this was the one that had gone stiff on the crank. As it came apart it was quickly ob­vi­ous that the lead lin­ing of the shells had mostly de­parted. I slid the rod for the hor­i­zon­tal pot along the crankpin to where the other one had been and it moved freely enough sug­gest­ing that at least the crank hadn’t been knocked out of round.

At this point all hope of an easy fix evap­o­rated as when I ran a ten­ta­tive fin­ger­nail along the crank pin it picked up just ever so slightly. Nearly got away with it but not quite. Re­grind time. Re­mov­ing the other rod re­vealed its big-end shells to be just as de­void of white me­tal as the other ones. Re­place­ments are in quar­ter and half a mil­lime­tre over­sizes how­ever they’re typ­i­cally more than twice the price of stan­dard ones at around £60 each. Can’t say I fan­cied a £250 bill just for those, plus the crank grind too. A late night trawl of ebay turned up three 0.25 at 39 Eu­ros each at an Ital­ian dealer and one with a UK seller at £30. That was a bit more like it. Fig­ur­ing that the Ital­ian fel­low would strug­gle to find a buyer for an odd num­ber like three I made him an of­fer he im­me­di­ately ac­cepted. There was no such op­tion with the UK ven­dor but I was happy to pay his ask­ing price to net me a set for just around the ton. That was more like it. I or­dered up some new con­rod bolts from Ger­man firm Stein-dinse for 9.81 Eu­ros each.

While that lot was in the post, I turned my at­ten­tions to strip­ping down the rest of the en­gine. The first prob­lem was that hav­ing been so con­fi­dent at the out­set of this de­ba­cle that all I was do­ing was fit­ting my home­brewed big-bore 944cc top-end, I hadn’t even both­ered to drop the oil. There was 35 quids worth of fully-syn­thetic in there and it had only done about 60 miles. There’s a fair amount of heft in a Du­cati bot­tom-end so I dis­missed the


idea of hold­ing it over a bowl while the lube trick­led out. I man­aged to siphon most of the oil out. Al­though once the en­gine’s side cov­ers were off it soon be­came ev­i­dent that I hadn’t been wholly suc­cess­ful in this en­deav­our. A mas­sive slick spread across the bench when I leaned the en­gine a lit­tle to one side to ex­tract the starter mo­tor. There com­menced a cleanup oper­a­tion of epic pro­por­tion. By now I had wasted way more than the price of new oil in time and ef­fort ex­pended. Les­son learnt? Maybe.

It’s a few years since I re­built the en­gine but it was all sur­pris­ingly fa­mil­iar. I re­mem­bered that the pri­mary gear – which is mounted on a taper on the end of the crank – was par­tic­u­larly tricky to ex­tract. Last time I took it to my lo­cal Du­cati spe­cial­ist, St Neots Mo­tor­cy­cles and they used a hy­draulic puller to re­move it. Quite of­ten th­ese gears are so tena­ciously at­tached to their cranks that the me­chan­ics have to wind up the puller and just leave it on there un­til the cog de­cides to let go, usu­ally with a dra­matic bang as it leaves the shaft and clat­ters to the bench. I had no such puller to hand and even a trawl through Pete O’dell of The Mo­tor­cy­cle Works com­pre­hen­sive tool chests failed to un­earth any­thing suited to the task. How­ever one of our neigh­bours is RM Clutch Ser­vices and their line of work re­quires all man­ner of pullers and ex­trac­tors. Pro­pri­etor Richard of­fered me a loan of his Snap-on CJ86-1 two­leg puller. I wasn’t wholly op­ti­mistic about its chances of suc­cess based on past ex­pe­ri­ence but it had the pri­mary gear off in sec­onds. So im­pressed was I that I went straight to ebay and bought a used one from the States. The re­ally clever fea­ture of this par­tic­u­lar puller is that the legs can be braced to­gether to stop them bend­ing and pop­ping out from the gear as pres­sure is ap­plied to the cen­tre screw.

From there the rest of the en­gine strip was a slam dunk. As you might pre­dict the oil strainer had cap­tured some ev­i­dence of the big-end shells’ demise al­though some bits of stray grey gas­ket goo made things look even worse than they were.

Ev­ery oil­way will need blow­ing out prior to re­assem­bly and the oil pump will be com­ing in for par­tic­u­lar at­ten­tion. For now I’m off to get the crank ground. I’ll let you know how that all went next month. Will 0.25mm shells be enough or should I have gone 0.50mm. I can hardly stand the an­tic­i­pa­tion.

Smil­ing through ad­ver­sity as ever (un­til he gets the bill for the crank re­grind)

Valves and guides all checked out OK. A re­lief

Snap-on puller – brace to pre­vent legs splay­ing

Acid etch primer: £14 a tin. But you’ll want it

Af­ter a bit of gen­tle per­sua­sion and in­dus­trial lan­guage

Good for noth­ing now

White me­tal. Yuck.

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