DUCATI TT and F1 FORUM
 
It is currently Sun Feb 25, 2018 9:58 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 14 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Pantah main bearings
PostPosted: Sun Dec 10, 2017 1:45 am 
Offline

Joined: Wed Nov 17, 2010 5:45 am
Posts: 212
I have a simple question. Why do pantah engines need a angular thrust main bearings? I could understand it with a old roundcase bevel to keep the gear train in correct mesh. But a pantah engine has no such need. Boucher.


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Sun Dec 10, 2017 10:49 pm 
Offline

Joined: Thu Oct 14, 2010 11:23 am
Posts: 1183
Maybe Cranky will chime in on this. If we should change the trans big bearings from ball to roller on straight-cut transmission gears why not the one for the cranks when using straight-cut primaries? MikeV


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Mon Dec 11, 2017 4:57 am 
Offline
User avatar

Joined: Wed Sep 11, 2013 7:13 am
Posts: 173
When I found my 750 SS, some PO had fitted a roller bearing on the bevel side and that was destroying itself.
Had to replace the bottom bevels because they were too damaged to (safely) use.
Roller bearings are very prone to failure when the load aplied is alternating or changing, like a crank spinning around AND flexing.
No problem in a self-aligning bearingholder on a transmissionshaft.
The rollers easily get overloaded when the become point-contacts and selfdistruct.

I guess that when a straight primary is fitted, You could calculate the sidethrust from the cam-chain gear (Leftside) and check it on the bearing charts to see if it is within the parameters of a ordinary ball bearing, together with load and speed index.
And assemble very carefull not to shim it too tight.

ciao
ducadini

_________________
Nego i ricordi peggiori, richiamo i migliori pensieri


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Mon Dec 11, 2017 2:31 pm 
Offline

Joined: Wed Nov 17, 2010 5:45 am
Posts: 212
Hi, why asked the question, I visited a mate on the weekend and while discussing his tt2/tt1 race bikes he announced that he runs c3/11 ball bearings as main bearings. 2thou endfloat. Never had a problem. He told me that the angular contact bearings were a throw back to the roundcase bevels where the gear meshing on the end of the crank couldn't float about. Boucher


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Mon Dec 11, 2017 9:38 pm 
Offline

Joined: Thu Oct 14, 2010 11:23 am
Posts: 1183
C’mon Cranky. Chime in on this! MikeV


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Tue Dec 12, 2017 6:29 am 
Offline

Joined: Wed Mar 21, 2012 9:56 am
Posts: 112
A roller race acts just the same as a sprag clutch when the crank flexes, momentarily locks up the whole plot and spins the outer bearing race in the cases. The wider the roller, the more easily it will lock up at speed.- or explode !
For some reason Ducati changed the Corsa crankcases in 92 and sent them out fitted with a pair of roller bearings. How you'd shim this arrangement with any success i've no idea. I bought a set of cases from Steve for my own 888 but swapped the rollers out for the regular angular contact bearings. After a discussion between us trying to find some merit in the rollers, Steve kept them in to try them out in one of his engines - with predicatably disatrous results. Funny isn't it that Ducati haven't done it again since 92.

I use a couple of thou pre-load which clears as the cases expand to running temp. Having said that, I've stripped several later 4 valve engines with rumbling mains to find the cases spring apart with up to 2mm of pre-load from the factory. I suppose thats exactly why they eventually died.

I'm old enough to remember Norton used their own 'super-blend' main bearings on the Commando which used a slightly barreled roller to get around this issue.


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Tue Dec 12, 2017 7:45 am 
Offline

Joined: Tue Oct 05, 2010 9:21 am
Posts: 223
Images: 0
OK OK....IM awake now. So the question was why did Ducati use an angular contact ball type bearing for the Mains?
The answer is load capacity. A properly preloaded set of bearings will take the dynamic loads of the crank. The more preload on these bearings the more load capacity they will have.....providing the structures... that is the cases and crank.... can take the preload. Case in point....all the motors used the same bearing at least on the drive side...right through those water-cooled super-duper bikes. what triple the HP of the original pantah? Stiffer cases and crank with more preload allowed for the increase. Its always the magic question of how much preload is needed for a given application. Imagine preloading a bevel (pressed up type) crank with the later spec .3 mm preload. Things would get angry and probably unpress themselves! Then again running a big superbike motor with minimal preload is a fast motor..... for a few races.
What I use for preload in inches
Bevel Street .001" Race .002" (unless plain bearing crank)
pantah .003" street race .004"
851-916 .004" street race .005"
All set with used bearings that have been run in.
-Cranky-


Top
 Profile Personal album  
 
 Post subject: Re: Pantah main bearings
PostPosted: Wed Dec 13, 2017 6:16 am 
Offline

Joined: Wed Nov 17, 2010 5:45 am
Posts: 212
Thanks for clearing that one up. Boucher.


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Wed Dec 13, 2017 11:59 am 
Offline

Joined: Thu Oct 14, 2010 11:23 am
Posts: 1183
For that reply we should give Cranky the Kevin Cameron award for 2017. With some others close behind.
MikeV


Top
 Profile  
 
 Post subject: Re: Pantah main bearings
PostPosted: Fri Dec 15, 2017 8:24 pm 
Offline

Joined: Wed Mar 21, 2012 9:56 am
Posts: 112
Angular contact bearings don't simply become somehow stronger by pre-loading the axial thrust. Dynamic load is catered for within the design by the bearing thrust angle.
The commonl Ducati crank fitment is 7207X2 and 7307X2. These are both an RHP designation with a 15 degree thrust line measured from the bearing face towards the axial line.
There are two contact (load) angles available. 15 degree (smaller side load/greater axial load) and 25 degree angular contact (less axial/greater side load). 18 degrees is also available but in a limited size range.

Measure the bearing outer faces set in some cases accurately at room temp, then put them in the oven for an hour at 130 degrees and measure them again. Do the same to a crank and note the difference in growth.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 14 posts ]  Go to page 1, 2  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Template made by DEVPPL