Just a thought, on the 996 engines the crank has a radius where the shafts meet the web. If yours is the same, you cant use the dial gauge method without having smaller shims fitted or the radii jam on the bearings and give an incorrect reading. Ducati do give another method of measuring preload, this involves measuring the amount of wobble on the output shaft after the cases are tightened. Doing this bends the crank slightly and causes the shaft to run out of true.
Probably out of the scope of most home mechanics and even dealers, but it wouldn't be too hard with the right equipment to measure the overall dimensions of the shoulders of the crankshaft, and then using a surface table measure the crankcase half's independently to determine the internal dimensions ,which would enable the pre-load ,or lack of it to be determined.
I'm with Mr R on this. The Haynes book recommends applying preload when building up the bottom end. Unavailability of Ducati gaskets that go between the crank case halfs that were fitted to the earlier SS motors leads the intrepid home mechanic into extensive re-shimming to achieve the correct result. I've built a couple of engines from scratch, using the preload figures from the Haynes manual, and haven't experienced any problems in about 25k miles, post rebuilds. I can also report that time spent paying attention to these specs pays dividends, with respect to gear change smoothness, and feel.
I'm back and here's what I did in the end. I replaced the mains bearings when I spilt the engine, so as the bearings are new you have to preload them by 0.15mm. If the bearings are not new there is no need to preload them. As it was the first time I split an engine, when I split the crankcase many months ago some of the contents "fell" out. I had 3 crank shims which seemed very odd as I thought the crank should be shimmed evenly. I managed to buy a NOS gasket set for my 750ss engine on eBay so I didn't have to worry about reshimming and gluing the cases. The gasket thinkness is 0.3mm. Today I got round to building the engine back up and when It came to installing the crank with 2 shims, the end float was way more than it should have been, so I measured the crankcase depth from a parallel placed on the mating face, to the inner bearing race. The crank cases had different depths, which would explain an extra shim on one side. I added the 3rd shim on the deeper side which sorted it all out. In the end the crank had almost no endplay, the gearbox shafts had 0.15mm and the gearbox drum had 0.25mm, just like the workshop manual says.
The problem with having no preload on radial main bearings that pretty much all Ducati's use is when the engine gets hot everything expands and the crank will be too loose and you may end up with killing the bearing in the alternator cover etc this is why they quote the preload figures
As this is the first engine I have built, I am going to be taking it to a friend who runs a ducati garage. I'm going to get him to check it all over to make sure I've not done anything wrong so far. I'll update with news after he has checked it out.
Which is in complete opposition to the SS workshop manual.......But I see the point being made, but if Haynes came up with it, I would be loathe to take notice. As an aside, while the OP has the engine apart, I recommend he checks and / or replaces the oil galley plugs.
I took the engine to my local Ducati mechanic yesterday, and he said everything felt spot on. If he's happy, I'm happy. Thanks to everyone for your input.
There's a general belief that a lot of these motors are over preloaded at the factory. My 851 LHS main is fuc3ed as you can see. the bearings are not just ball races but angular contact bearings. The preload is a cold figure. The cases are alloy and the crank steel. alloy expands more than steel, so if you set them with 0 preload cold they will run too loose when hot. As someone mentioned you can measure the run out on the crank as you bolt up the cases, if it starts to run out you have too much preload and the crank is actually starting to bend. So preloaded correctly and when warm the preload should just be very slightly Another good reason to allow your motor to warm up nicely before working it hard!
I'm no expert by any means, but all I can add is that the ST4 I had with less than 10k on it knackered the main bearings. When Rich at Louigi Moto stripped it he told me it had been preloaded by 0.2mm and that this was the cause of the bearings failing. From the type of gasket sealant, he was able to tell that this must have been done at the factory, as there were no signs that the engine had ever been apart. When he removed them for replacement, one of them literally fell apart . . . I'd suggest you seek confirmation from one of the independent experts such as JHP, Louigi Moto etc., as has already been mentioned. Look at it this way, you really only want to do it once, you'd kick yourself if you get it wrong and have to strip the thing down again later . . .
......and of course, the great omission.............don't preload used bearings, only new ones.......... ...according to the Haynes manual.............. a statement which makes a mockery of the expansion issues already raised. Probably the Ducati workshop manual assumes the bearings aren't renewed, which is why they don't indicate any preload........
