Bolt­ing-up Bologna’s bestest

It’s all plain(ish) sail­ing for Cap­tian See­ley as the 900 lump goes back to­gether again

Practical Sportsbikes (UK) - - On our Bench -

aving got the bot­tom-end of my 1993 Du­cati 900SS en­gine pretty much to­gether last month, I’m now back at the point I hadn’t ex­pected to have to go beyond when I took the en­gine out a cou­ple of months back. That is, I’m now ready to fit the ST2 barrels that will give me a 40cc hike from 904 to 944cc.

Doesn’t sound like much in per­cent­age terms, but hav­ing rid­den a carbed SS that had al­ready had the con­ver­sion done it’s well worth­while. High-comp JE pis­tons will only add to the fun, as will a pair of ST2 camshafts, reck­oned in many quar­ters to be the best choice for the 2V en­gines.

I con­verted the barrels from liq­uid to oil­cooled about three years ago, blank­ing off the wa­ter jack­ets’ con­nec­tions to the wa­ter-cooled ST2 heads and re­open­ing the oil ways. The brand-new pis­tons have been sit­ting on the shelf for a sim­i­lar pe­riod of time.

First up this month was to re­fin­ish the pri­mary and gen­er­a­tor cov­ers. When I got the bike back in 2012, I re­built the en­gine and had all of the cast­ings soda-blasted. They cer­tainly came up a treat but what I failed to do prior to paint­ing was to get all of the soda out of the alu­minium sur­faces by wash­ing with vine­gar then wa­ter. The re­sult was that most of the paint flaked off within weeks. This time around I cleaned and prepped the sur­faces prop­erly prior to a cou­ple of coats of etch primer fol­lowed by an ap­pli­ca­tion of Tech­cote high­temp satin black. Most of the time taken to do that job was in the mask­ing up.

While the paint was dry­ing I set about fit­ting new valve seals, a task akin to get­ting a stan­dard con­dom on an ele­phant. Next up was in­stal­la­tion of the cor­rect open­ing and clos­ing

shims for the valves in the desmod­romic heads. I have a set of shims from EMS Du­cati in the US that are claimed to be bet­ter than Du­cati’s own. I also use MBP re­tain­ing col­lets for the closer shims, also sup­plied by EMS. They’re far su­pe­rior to the OE Du­cati half moon rings. The stan­dard ones tend to com­press and work-harden and have even been know to break. The MBP col­lets are a su­pe­rior de­sign that ex­tends up the valve stems. Valve clear­ances are less prone to go out with these, partly be­cause the don’t tend to com­press like the OE ones and also be­cause with the clos­ing shims bet­ter stay­ing in ad­just­ment, the valves them­selves give their seats less of a hard time so the open­ing clear­ances re­main good for longer too.

Cer­tainly my pre­vi­ous ex­pe­ri­ence of them showed that valve ad­just­ment in­ter­vals had at least dou­bled – good news for any Du­cati owner who has had to fid­dle about with shim swaps, es­pe­cially when the en­gine is still on the bike. At least that was one thing I had mak­ing the task of valve clear­ances eas­ier

– the heads were off the en­gine and on the bench. The prob­lem I did have is that as the kit goes in 0.1mm in­cre­ments, it was just my luck that I was fall­ing on half sizes for three of the four closers which were too wide on one size and too tight on the next one up. I won­dered if they might be close enough on the nar­rower open­ers. The clear­ance you’re aim­ing for on the closers is 0.03mm when the clos­ing arms are pushed against their cam lobes. Mi­nus­cule clear­ances.

So I thought I’d visit my old mate and Du­cati fa­natic Mark Brewin at BSD for a sec­ond opin­ion. He con­firmed that three of the four closers were a lit­tle loose and also sug­gested I go a bit wider than work­shop man­ual specs for the open­ers. “They run hot these air­cooled en­gines,” he said, “as soon as they’re warm clear­ances close up mas­sively so go for 0.15mm in and 0.15-0.20mm ex­haust on the open­ers.” Mark has the same shim set as I do so there was no point ri­fling through his. My only op­tion was to re­turn to the work­shop, swap the closers around a bit to see if I could get closer then maybe take a lit­tle bit off of larger clos­ing shims to get the cor­rect clear­ances.

Af­ter much mess­ing about, con­fus­ing my­self over which shim I’d just taken from where,


and mea­sur­ing both the EMS ones and a few ran­dom OE ones I had kick­ing about, it fi­nally came to pass that I was lack­ing the cor­rect­size shim for just one of the closers. So tak­ing the next size up, I re­paired to Pete O’dell of The Mo­tor­cy­cle Works sur­face ta­ble with sheets of 600 and 1500 grit wet-and-dry and a can of WD40. Work­ing away us­ing a fig­ure-of-eight mo­tion on lu­bri­cated wet-and-dry pa­per on the per­fectly flat sur­face fi­nally saw the few hun­dredths of a mil­lime­tre I needed to get off of the shim dis­ap­pear.

The paint on the pri­mary and gen­er­a­tor cov­ers had dried a treat by then so I put the cover on and re­fit­ted the light­weight EVR clutch from Speedy­com I treated the bike to a few months into my own­er­ship. Just as I was about to ad­dress the is­sue of torquing up the hub cen­tre nut, Fer­ret bounded into the work­shop. Our fave moto-elec­tri­cian had been pass­ing en route from York­shire back home to Sus­sex. His were a wel­come pair of hands when it came to tight­en­ing the nut up to the fac­tory man­ual set­ting of 190Nm.

Feel­ing the sat­is­fac­tion of a de­cent day’s work well done, I de­cided to re­con­vene with the SS en­gine the next day. The JE pis­tons could now go onto their rods. There’s pre­cious lit­tle clear­ance be­tween the bar­rel/head studs mak­ing it hard to squeeze the stiff pis­ton rings enough to slide the barrels over. I do have a compressor plier for the job but that was an un­help­ful 30 miles away at home. More help­ful was Pete O’dell, who helped me get the barrels down. Torquing the heads down is a typ­i­cally odd­ball Du­cati chal­lenge. You can’t get on the nuts with a stan­dard socket. There is a spe­cial tool avail­able that looks like a C-clamp that comes up and over the tim­ing pul­ley hous­ing on the right and cam bear­ing hous­ing on the left and al­lows a torque wrench to be placed con­cen­tric with the nuts. How­ever I have an al­ter­na­tive, a flat span­ner of the cor­rect length so if the torque wrench is kept at right angles to it and your arm is kept at right angles to that, the forces bal­ance out. The nuts are tight­ened in three stages, 15Nm then 30Nm and fi­nally 42Nm. Th studs are long, so you can feel them twist­ing against the force on the fi­nal stage, al­most to the point that you fear they might snap. Thank­fully they don’t.

Next I bolted on the tim­ing pul­leys and fit­ted a new set of belts, ten­sion­ing them with a spring bal­ance and cup tool bought from Tony Bran­cato many years ago. Back on with the gen­er­a­tor cover and there we have it; the en­gine can at last go back into the bike.


Alan See­ley

That’s Alan do­ing a lot of torque-ing (as per usual)

Mask­ing tape be­fore paint­ing. Lovely old job

Black gaffer tape mask be­fore bead-blast­ing

Left side cover all blasted and keyed for paint

He’s just back from his hol­i­days in Dundee, hence the shades

Desmo heads are not beyond the scope of any­one with their head screwed on

Lovely new Vi­ton valve stem seal in place

Looks com­pli­cated, but isn’t

Tight slid­ing fit

Knack­ered old Vi­ton valve stem seal

ALAN’S TOP TIP Gas­ket goo should be used spar­ingly. It’s only ap­plied to make up for im­per­fec­tions in the mat­ing sur­faces ei­ther side of the gas­ket. If too much oozes out on the out­side, imag­ine the same thing on the in­side. That’s po­ten­tial en­gine dam­age if it clogs oil­ways. Louis XIV drops in for a cup of tea

Funky spring bal­ance to check cam­belt ten­sions

Rock­ing the cam to set­tle shim be­fore mea­sur­ing

Verniers (very nears) good enough for shim­stack

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