A friend who worked for a main dealership had a strange 749s that was difficult to start and kept stalling. Everything was tried and everything had failed (new tps, new throttles, cam timing, pc3 dyno the lot.
However 3 years later being the other month the engine eventually came apart. The crank would not turn over without huge force from a big spanner.
Nearly 0.40mm was taken off the crank preload to make it spin nicely. The bike has not stalled since and starts on the button.
Its a total joke how tight it was. The cases obviously had to be forced together on assembly ((
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I had the same problem with my 03 749s. I was lucky that my dealership found the problem while the bike was having a valve adjust, and ended up getting the engine rebuilt under warranty. Lucky because the bike was going off warranty the next month. The dealer also found one of the cams moving around in its bore, so I got a new cylinder head as well. I was told some of the engines had too much pre-load on the crank by the dealer, but your story is the first I've heard of since mine in late '06.
Out of the 30 to 40 cranks we see a year during blueprinting, 90% are .15 to .25mm over pre-loaded, when you get over that then the stalling and bearing damage starts and will throw the crank ends out of true (measurable run out). Not to mention the too tight rod bearing clearances.
they increased the preload spec around '03 i think when they added another ball to the lh main, up to 0.30mm. which was where they were before that anyway. every engine we did (not many) we used to take 0.15 or so out of the shims. to the point where we had a heap of s/h 2.20 - 2.35mm shims in stock. and always seemed to be replacing them with 2.05 - 2.15.
i'd never thought of it impacting the stalling, but some of them were noticably hard to turn oever when grabbing the end of the crank with everything else removed.
i had this "over preloaded" discussing with our importer rep many times.
they increased the preload spec around '03 i think when they added another ball to the lh main, up to 0.30mm. which was where they were before that anyway. every engine we did (not many) we used to take 0.15 or so out of the shims. to the point where we had a heap of s/h 2.20 - 2.35mm shims in stock. and always seemed to be replacing them with 2.05 - 2.15.
i'd never thought of it impacting the stalling, but some of them were noticably hard to turn oever when grabbing the end of the crank with everything else removed.
i had this "over preloaded" discussing with our importer rep many times.
I hear you, the Ducati class instructor was stuck on setting them at .30
When we get a bunch of thick shims saved up we have them surfaced ground in the 2.10 range.
When my 996 broke the first time, the reason was the steel case insert cracked in half and walked outward, probably partially due to crank preload (I guess?). I'll never know what it was set to or what actually caused that.
I have the 1999 service manual and when I went to set the preload the dealer told me to basically double the value !!!
No f'in way I'm thinking... If I remember correct (notes are not here with me), we set it to about .009" (coming up on .2 mm) and left it.
On these engines that were physically hard to turn by hand, has anyone tested that at full operating temperature, or somewhere near?
I understand why you don't want any play, but it seems like the spec is way, way too tight.
So I'm wondering if anyone has an official story on why they set it so tight? And is this still how they are setting them to this day?
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i think bruce meyers check a set of cases once in a tub of near boiling water and the preload went from 0.15 to pretty much zero. so if it was assembled at 0.30mm it would be 0.15mm hot, that was the general gist of it.
i think bruce meyers check a set of cases once in a tub of near boiling water and the preload went from 0.15 to pretty much zero. so if it was assembled at 0.30mm it would be 0.15mm hot, that was the general gist of it.
may be better asking bruce.
A few years ago when I built my 851 engine Bruce told me to set preload at .004" with used bearings, .006" with new bearings. I set at .004" with used, still running after 20K miles (hard miles).
Guess I had better pull my S4RS engine apart and check! I wanted an excuse to put Carrillos in (thanks Brad), 749 trans, set squish anyway!
A few years ago when I built my 851 engine Bruce told me to set preload at .004" with used bearings, .006" with new bearings. I set at .004" with used, still running after 20K miles (hard miles).
Guess I had better pull my S4RS engine apart and check! I wanted an excuse to put Carrillos in (thanks Brad), 749 trans, set squish anyway!
Does any one know at what preload the crank start to have a serious runout ( is that correct word for it)?
If it is no runout and the crank rotates freely and at the same time dont have any backlash I dont see any reason to worry to much or am i wrong?
Just interested as I have a 996 engine going in my 851. I could split the engine now and check it but it is a bit of work that I realy dont have the time for right now.
Jocke.............
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Does any one know at what preload the crank start to have a serious runout ( is that correct word for it)?
If it is no runout and the crank rotates freely and at the same time dont have any backlash I dont see any reason to worry to much or am i wrong?
Just interested as I have a 996 engine going in my 851. I could split the engine now and check it but it is a bit of work that I realy dont have the time for right now.
Jocke.............
I just re-read my Factory 851 Manual:
"the crank should turn freely with no axial play" (pretty precise directions!!)
hehe...let me chime in with my story.....
Had a customer come into the shop with his 749...ran, but always seemed to stall, had problems charging the battery, and always had a slight, intermittent whinning sound. I looked over the bike SEVERAL times, but couldn't quite put my finger on the problem....checked belt tension, checked the power output from the stator, checked the waterpump and bearings.... but the problem was never consistent. Anyway, the customer decided to take a long roadtrip (against my reccomendations) only to have the motor HAND GRENADE leaving him straded in Canada. Well, upon splitting the cases, found the crank preload was excessive (set at almost .50mm of preload!!!) causing excessive runout on the nose bearing of the water pump side cover. The bearing finally failed, and let loose into the entire motor. The good however is Ducati stood behind their products with a good faith waranty, paid for all parts and even covered someof the labor. (even thought the bike had been out of warranty for several years!)
749s crank preload stalling story
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