I think the factory preload of .3 is considered high. .15 might be a better value. @Steve Robins can advise.
So just over 0.1mm? OK, that's quite a difference. Any risk to much lower preload - bearings spinning in cases or on the crank when they warm up?
Many years ago now I was advised by John Hackett to use 4 thou, I've NEVER had any problems using this preload. Steve R
This might be below your skill level but have you wartched Desmowerx on youtube, he has done all manner of 2 and 4 valve engine rebuilds, he builds to the Ducati spec for the pre-load on the bearings. Useful reference point if you forget where a shim goes
Thanks for all the input, everyone. Shims now ordered for a reduced preload value vs Service Manual. I'm still a bit worried about the 7g difference between brand new pistons, I've double checked and it's not measurement error - the values are repeatable. I'm not convinced that I can safely remove 7g from the heavy piston. Is such a high part-to-part variation normal?
I'm 100% sure that you can remove close to the amount that you need by reducing the skirt/underside of the piston. Just take it a bit at a time and keep weighing the heavier piston until you get to your target weight, 1 or 2 grams one way or another will make cock all difference to a road motor.* I've done this many times with good results. *The best dynamic balancers allow 25 grams for the oil in the cranks, they don't weigh the oil they just use 25 grams as a "Guesstimate"...Those last 1 or 2 grams make very little difference to the smoothness of the motor. Steve R
Have had a go at lightening the heavy piston this evening - I have got it down to 4g difference between them, by gradually removing material from the webs and skirt - and comparing local thicknesses so I don't go too far. The strange thing is that I can't measure any significant difference between them dimensionally, with the caveat that I haven't been able to check crown thickness. It is extremely frustrating, as I used to build Ford Kent Crossflows for racing, and even with Fords' 1960s cast pistons made by worn-out tooling getting to within 0.5g was very easy! I'm really surprised at the part-to-part variation of these.
OK, so while the barrels are away for replating, I've received the shims I ordered for the crank, input shaft and output shaft. The crank and input shaft are behaving as expected, the new shims fit a treat and give me preload (crank) and a better endfloat value (input shaft). Where I'm struggling is the gearbox output shaft. I had an end float value of 0.83mm with the original shims (which measure 0.92 and 1.63mm). I've put two new shims of 1.0mm and 2.2mm, and still got an end float of 0.75mm - which doesn't work in my head. By the latest numbers I would need a combined shim thickness of 3.82mm to get to the maximum book figure of 0.15mm, which isn't possible according to the parts manual I have using one shim on each end of the shaft. Is stacking shims to get to the numbers I need acceptable? Is it usually required? I had a look through Desmoworx's Youtube channel but it doesn't appear he details a gearbox strip other than shaft endfloat check. You guys & girls must all be thinking I'm making a meal of this - I know I am!
Did some more checking on this this afternoon. First of all checked that the bearings I had installed into the crankcases are the correct ones - MotoRapido confirmed that the bearings on the parts list are the same as the ones I have installed, and the ones I took out match those I put back in:- I put the old output shaft back in and I get the same endfloat with the new shims, so I'm going to swap the single 1.00mm LH shim for two 0.8s and see where we go from there. To cheer myself up and feel like I'm making some progress- I re-installed the bungs back into the crank now that my ThreeBond has turned up, and cleaned and rebuilt the flywheel/alternator/sprag assembly. The inside of the alternator rotor has a wicked sharp edge on it!
Where did you source your bearings? Thought the mains were only available from Ducati, due to the contact angle
Mains I did indeed get from Ducati, and have no issues with crank shimming. Gearbox needle rollers are genuine SKF from Simplybearings - both those I took out and what I put back in are SKF NJ 203 ECP / C3s.
Little update, have started on assembly of the vertical head. I refitted the vertical head's cams back into the bearing holders with new washers and locknuts. After that I spent far too long trying to get the closer rocker springs back in, with much stabbing of oneself in the hand, and much blue language. Many bad words were said about Ducati and Cosworth, and how you didn't get this hassle with a H@&!a. So today, following a bit of work-time Google searching and help from this thread:- https://www.ducatiforum.co.uk/threads/closer-rocker-install.46637/ I butchered modified a screwdriver to suit, which seems to work. A top tip seems to be compressing the spring part of the way and then using an old rocker shaft to stop it extending back again. Which gets me to here:- Have also measured the shims I removed, to start figuring out the closing shims I need. The opening rockers are away for refurbishment so cannot measure anything on opening side yet.
Managed to get all of the closing rockers back in to the heads, and the horizontal cams back into their bearings. Measured up for closing shims, and was pleasantly surprised that even with hand-cut valve seats the differences in shim required for all the valves are small. Horizontal head - Inlets 2.95 & 2.95 - Exhausts 3.15 & 3.05 Vertical Head - Inlets 2.95 & 2.90 - Exhausts 3.25 & 3.20 The bent screwdriver worked a treat to get the other closer springs back in position, I couldn't believe the difference from yesterday's attempt! Took some reference pictures of the process, as there doesn't seem to be much visual stuff on the 'net about getting these pesky closer springs back into place, and the manual practically uses the well-worn Haynes phrase of "re-assembly is the reverse of removal". Step 1) Put spring, rocker and rocker shaft back into the head. Make sure end of spring is engaged in hole in rocker. Step 2) Using a suitable lever, or in some cases a finger, compress the free end of the spring far enough to allow an old rocker shaft to be slid into the head. This stops the spring extending too far if you slip off it during Step 3. Use an old one so if it gets scratched it doesn't matter. If no old one is available, make do with something else that won't damage the head. That gets us to here:- Step 3) Working from the opposite side of the head, using the bent screwdriver and levering against the side of the head or the rocker, move the end of the spring towards the centre of the head (towards the spark plug) and down past the retaining lug/tab. I found you can go pretty slowly to avoid sudden movements.
The cylinder barrels have come back from plating, really fast turnaround and they're bang on size. The bores were full of honing dirt, which I fully expected and have no problem with - repeated rinsing and cleaning with thinners until the cloth comes out clean means they're now ready to go. What I wasn't to pleased with was the head gasket surfaces were badly scratched from what looks like the cleaning process. I've refinished them using wet and dry on a surface plate. I found a small patch of what looks like corrosion that's been removed through blasting, but has left a hollow on the surface. Does anyone think this will be a problem? It seems to be close to where the two layers of the head gasket meet with the pressed bead.
Decided to procrastinate and feel like I was making progress. So replaced the nose bearing (6002Z) and shaft seal (24 x 15 x 5) in the starter motor, which I'd repainted. Then, as mentioned before I started out with the crank balancing. I'd already measured the components involved - big ends of both rods, bearing shells, pistons, rings, gudgeon pins and worked out what the counterweight should be. So, a big piece of EN3 bright mild has been hacked about on my old lathe, and then split to fit around the crankpin. And fixed to the big end with a special adjustable high-tensile polymer retaining device. OK, a cable tie or two. The crank balancer is essentially 2 roller v-blocks that can move along tracks. The out-of-balance force causes the blocks to move two DTIs mounted to the frame, controlled by a pair of springs. The crank can be spun (by hand in this case) and weight (Play-Doh) added in various places to try to find the right location and amount. Once the right amount and location is found, the same amount of weight can be removed 180° from the addition. I added the primary drive gear, alternator rotor and flywheel and they made no difference to the balance results. With a bit of luck, and a following wind, I should be able to finish the balancing tomorrow, and start to build the bottom end.
Had a good day at the rebuild today - finally after what seems like an age of preparation and generally d*cking about I have managed to nail some parts together. I started with the crank and rods, so put the bearing shells into the rods and caps, and torqued to spec. As the torque spec is a pre-torque + angle, I needed a gauge. I have a Laser one, which is rubbish, so I 3D printed one that just slips over the 10mm socket. So with that done, parts were assembled into the RH casing, following the service manual. Then finally, the cases were together and we were onto the engine stand! Primary drive gear on and torqued, then clutch cover, and finally clutch hub and basket brings us up to date. I found there were a couple of issues with the ST4s service manual. First off it mentions some M6 x 80 bolts in the crankcase RH side near the jackshaft, which in my cases are actually M8 x 75. Also, it mentions a spacer behind the primary gear, which isn't there in the parts manual. Tomorrow I hope to get the alternator side built, put all the gallery and inspection plugs in, and perhaps get to measuring the deck heights to figure out what base gaskets I need to set the squish!
