You need to WATCH OUT that you get bearings of the correct contact angle. As I recall the Duc bearings are a lower contact angle that typical off the shelf bearing house angular contact bearings. I don't believe that SKF makes the proper contact angle.
Also the brass bearing cages aren't as good as the nylon (TN9) cages.
You might want to rethink your crank main bearings....
Having bought the same style bearing from SKF, also with the thought of saving a few dollars, I can tell you it's a very questionable replacement choice.
Numerous phone calls to SKF after the bearings failed at 3000 miles, resulted in them advising me to use the Ducati OEM bearings and NOT the SKF supplied by the bearing house.
The SKF bearing has a 15 degree contact angle (thrust bearing), the Ducati bearing has a 40 degree contact angle. SKF does have a "precision" bearing available in that size, but will cost you 2-1/2 times more than the Ducati OEM piece.
They came from a local bearing supply, but seem to be identical to what was in the motor, same numbers and country of origin, and saved me about $50 just for the two crank bearings.
Well I just spent almost an hour talking with the bearing nerds down at the supply house. The bearings that I installed do have a 40degree contact angle, and the brass cage is much better at dealing with vibration than the plastic, according to the nerds. They said that a "precision" bearing with a small contact angle (10 degrees) is only used in servos etc., where minimal drag is more important than robustness. I want robustness, and feel reassured that these bearings are the right ones for the job. I did tell them what application I was using these for when I ordered them.
Thanks for the input, I like understanding all the variables, and it always feels good to have confidence in the parts that you're putting together.
I may have gotten the information reversed, nonetheless, the tech department at SKF told me specifically this was not the correct bearing for that application. Even though everyone at the bearing house told me it was OK.
It's your call, it's your labor that will be required to do it all over again.
I also spoke with a Ducati race motor builder who was using the same SKF aftermarket bearings. He was getting 2500 miles average before going back to the OEM units. I got 3000 miles out of mine before I had to split the cases again..............
You're right that the bearing nerds are not infallible, but I stayed there until I understood the factors, maybe. From what I understand at this point, the greater contact angle between the balls and the race creates more drag but can tolerate more load. What was the failure in the short lived bearings that you mention, was it overheating (maybe from the higher angle of contact?) or...?
What it comes down to at this point, is that those bearings are in the case and measured. That makes them really good ****ing bearings in my opinion. The $50 savings feels pretty small relative to the criticality of the part, replacing all the rockers put me into cost saving mode and $50 dollars will pay for the two crank shims that I need, etc. I will be pissed if those bearings or anything else fails within 3000 miles, but the first time is always the hardest, so if I do have to replace these bearings over the winter that is worth the risk. Now, if they end up damaging my crank or something, I'm sure to be bitchin.
The inner race galled and flaked off when it failed. It started as a small tick that I could feel at the bar end, it worsened to a groan and labored motor sound. When I changed the oil it was full of shiny flakes.
Pulled the left side cover and moved the crank up and down a millimeter or so, not good news. As I stated before, an engine builder here has used them and experienced the same failure problem.
The SKF is a slightly smaller ball size and 1 more in the cage than OEM Ducati. There is far more axial play in the SKF versus OEM. Again, it's your call, but I will not take the chance again, it's simply too much work to go in and keep splitting the cases.
As for shims, you can get a 19 piece assortment "Precision Brand" Arbor shims - UPC No. 25280 - 1-3/8 x 1-7/8 for less than $20. If you give me the thickness you need in MM I'll check to see what I have as extras.
As a side note, my crank was balanced at 52%, pistons and conrods static and dynamically balanced as well as flywheel. So everything was done, there was no reason otherwise.
Didn't keep the pics I sent to SKF tech dept., but they will not warranty anything if it goes bad, informing me it's the wrong bearing for that application. YMMV.....
I'm wondering if the .15mm preload is to tight for these higher contact angle bearings, is that what you set yours at? I need 2.217mm and a 2.264mm shims to get to .15, if you have any shims that size or larger, I'd love to make you a deal. I thought about setting the preload a little looser, maybe .1 or .12. What do you think about this?
The original shims are 2.053 and 2.1mm, they gave me an endfloat of .1778mm, so I added .15mm to that and get +.1639mm per shim to get to the 2.217 and 2.264mm new ones, erring on the fat side so I can lap them down suit. That 3.2 you have would need almost 1mm taken off, that might be too much for my patience. Let me see if I can find that shim kit you mentioned first. Can you recommend a vendor for that?
As to reducing the pre-load, I understand that too loose is bad, I just was wondering if reducing the contact pressure would have any positive effect with this 40 degree bearing. I'm assuming that the problem is with the rotation speed in this application. At the very least if I'm going to knowingly repeat a mistake, the best thing to do is change one of the variables and note the effect, for the sake of the science.
I wish that I would have had this conversation a while back, I would have gladly spent the extra $50. Well... the good thing is that the pressure is off, I can just assume that I'll be getting back in the case at some point, like I said the second time is always so much easier. Plus I can tell already that I'll always be working on this bike, it's incredible, I feel lucky to be digging into it.
Thanks for the link, I see that you included the company name in your previous post, I missed that.
Well that kit wouldn't leave me any better with the size that I need, maybe I have a special corse narrow crank If you would be willing to sell me the two large shims that you have that would be great. Shoot me a pm if you're interested.
-Josh
Well, I've decided that I need to spend the ~$210 for new OEM crank bearings. It doesn't make sense to close up these cases with a problem inside. The money sucks, but the time is even worse. I assume this is going to put me another couple of weeks out
I was checking out the original crank bearings, and noticed that I was wrong earlier when I stated that they had the same # and came from the same country. They are RHP from England, one less ball, etc. After doing some research it seems that this is an RPM issue. The fewer number of larger balls, and the small angle of contact are better suited to 10k+. I tried to rationalize that my 996 motor with 6 over on the rear sprocket, will live most of it's life granny shifted at<8500, but that's just stupid to build a motor with a major component that is not rated for the application.
Plus, if I ever want to sell this bike, what do I tell the person?- don't use this engine to it's full potential, or, if the crank bearing fails I promise that I'll fix it. That's ridiculous.
Thanks for the honest input guys, I know that it's not easy to tell people bad news, but the truth is best. This is just engineering and nothing for me to get emotional about.
So if any of you kind souls can recommend a quick source for the two crank bearings in a 1999 996, I would be much obliged. Otherwise I'll ask Jeremy if he will call up Bologna and have them send me some bearings before the August nap.
916duc we're still on for those shims, I figure that I should be able to use those or my originals with bearing set #3. Thanks again.
This is one of the original bearings that had some kind of spalling on one of the balls, it was still turning fine, but you can definitely feel this when you spin it. These had 16k miles on them.
Back to the pre-load figure, at the beginning of this article-BikeBoy.org - Ducati 996 Setting The Squish,
he says, "I still do check and re-shim every crank I get to, however, and usually remove around 0.20 to 0.30 from the preload. After which they spin just nice, with a little noticeable drag".
I assume this is a typo, and he meant .02 to .03mm?
Finally you wake up and smell the coffee...... That will be one less thing you'll need to worry about, especially as this motor design is tough on crank bearings anyway.
GP Cycles in San Diego generally has them call Ian.
Thanks 916duc for the suggestion of GP cycles, I talked to them, but they only had one of them in stock, so I ended up getting These from Boulder Motor Sports they had both in stock and are only a couple hundred miles away, so they got here the next day. Their price was a few dollars more, but that's fine at this point.
RHP made in England. These do feel better than the SKF's, I have to admit.
This is called a pipe bender, but it should be called a pipe kinker or a pipe folder. I have been planning on turning this into a press for quite some time, now I have the motivation, these bearings are too precious to drive in.
Thanks again 916duc and desmo11.
I wanted to ask you desmo11, what is the benefit of the nylon cage vs metal?
Freeze the bearings and with a torch warm the bearing bores to 300 degrees F. They'll drop right in.
Check for a metallurgical supply house in your area. Get a bottle of 300 degree Tempilaq. This is a paint that you brush a few dabs around the OUTSIDE of the bearing bore on the case and let it dry. When you heat the bore the paint re melts and presto you are assured of the correct temperature. It's accurate within 1-2 degrees. Don't hit the paint with the torch or you'll have to start over with new Tempilaq.
We all know what can happen if we press something in that is not perfectly aligned. The bearing will be cocked and do a nice job of skiving aluminum off the bearing bore. The bearing may be seated but it is not square in the bore. I had techs working for me that actually cracked cases doing this.
Here's the rationale on the critical temperatures.
Ball and roller bearings are made from 52100 spherodized alloy. Never heat a bearing over 350 degrees F as the alloy will begin tempering. (losing hardness) Ever heat a bearing to get it off of a shaft? Throw it out!
Nonetheless, bearings with plastic cages must not be heated much above 250. I've heated cases higher than 300 for some stupid tight interference fits then dropped bearings in. As soon as they shrink I have doused them in water to prevent heat soak into the bearing and plastic cages.
If you would be willing to sell me the two large shims that you have that would be great. Shoot me a pm if you're interested.
That will be one less thing you'll need to worry about, especially as this motor design is tough on crank bearings anyway.
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