Bolting-up Bologna’s bestest
It’s all plain(ish) sailing for Captian Seeley as the 900 lump goes back together again
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,
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
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.
WORKING AWAY IN A FIGURE-OF-EIGHT MOTION ON LUBRICATED WET-AND-DRY PAPER ON THE PERFECTLY FLAT SURFACE FINALLY SAW THE FEW HUNDREDTHS OF A MILLIMETRE OFF THE SHIM
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