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Steering Head Bearings

 
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DB1 860



Joined: 23 Mar 2014
Posts: 177
Location: Sydney

PostPosted: Sat Dec 28, 2019 12:24 am    Post subject: Steering Head Bearings Reply with quote

Over the last 4 months I've had the job of replacing the steering head bearings in 4 of my bikes... 2 Ducati's and 2 Bimota's... Its a big job as you need to pull the whole front end out... it certainly helps having the right stands.

Ducati's top nut is relatively easy to remove and torque up if you have the right tool...but the Bimota's have a threaded top hat that they call a dust cover... yeah it does that but it also holds the bearings in place so it goes back on more than finger tight... as the cover is completely round a spanner cant be used.

I wonder what the factory use as I ended up using a pipe wrench which as you can guess marked the alloy cover.

Has anyone else had a go at replacing/tightening the bearings and come up with an idea on how to tighten the cover? I had thought of getting two sides machined out of it so I could use a large spanner.


Last edited by DB1 860 on Sat Dec 28, 2019 11:47 pm; edited 1 time in total
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Evilchicken0



Joined: 12 May 2010
Posts: 2996
Location: London

PostPosted: Sat Dec 28, 2019 1:33 am    Post subject: Reply with quote

You could cut a slot in it and use a C-spanner or hook spanner.
Or put some rubber around it then use the pipe wrench
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PaulDB2



Joined: 26 Apr 2014
Posts: 316
Location: Manchester

PostPosted: Sat Dec 28, 2019 1:33 am    Post subject: Reply with quote

I just did mine by hand as tight as I could to remove any play. It is then locked in place with the grub screw, but do not overtighten it or the dust cover will develop a crack. After the yokes and the fork have been assembled, check again for play. Of my Bimotas two have arrived with cracked top-hat dust covers and I have seen it on others.
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Bimota DB1, Bimota YB5, Bimota YB6 Exup, Bimota YB9 SR, Ducati NCR Replica, Moto Guzzi 750 S3, Honda CR750 race replica, Seeley-Suzuki TR500
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DB1 860



Joined: 23 Mar 2014
Posts: 177
Location: Sydney

PostPosted: Sat Dec 28, 2019 11:45 pm    Post subject: Reply with quote

Thanks for the reply's, So Paul were the cracks that you saw running from the center out or around the circumference pretty close to bearing size?

The recommended torque for the Ducati bearings is 30nm... so the resistance I felt in the steering i then duplicated that in the Bimotas as they run the same bearings... so thats more than finger tight. I did for a completely different reason put two shims on top before the top hat they are about bearing size... which looking at it now will help spread the load...were the bearing contacts the cover its only about 3mm wide.

I will keep an eye on the top hat ... meanwhile I better order another one.
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Jonny B Bad



Joined: 05 Dec 2009
Posts: 555
Location: NE London

PostPosted: Sun Jan 12, 2020 9:52 am    Post subject: Steering bearings Reply with quote

I thought the bearings are an interference fit on the stem head and would need to be tensioned as they are installed on the stem head? Then the top hat would be just a dust seal?
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DB1 860



Joined: 23 Mar 2014
Posts: 177
Location: Sydney

PostPosted: Mon Jan 13, 2020 6:49 am    Post subject: Re: Steering bearings Reply with quote

Jonny B Bad wrote:
I thought the bearings are an interference fit on the stem head and would need to be tensioned as they are installed on the stem head? Then the top hat would be just a dust seal?


Yes you would think that there would be a nut to tighten down on to the bearings... but no you use the dust cover to do the tensioning... thats for the DB1/4 and the yb5... im guessing a lot more models have the same system.

Been thinking of having a more substantial nut/cover made... especially since they are prone to cracking as Pauldb2 mentioned.
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PaulDB2



Joined: 26 Apr 2014
Posts: 316
Location: Manchester

PostPosted: Mon Jan 13, 2020 5:50 pm    Post subject: Reply with quote

Mine had cracked along the brim of the dust cover, about 2.5 cm long, I suspect due to over-tightening of the pinch bolt in the past. The cover on my YB9 also has a similar crack in it. To eliminate any play on assembly, use sash or G-clamps to pull the top and bottom yoke together snugly before tightening the pinch bolt and the fork clamp bolts.
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Bimota DB1, Bimota YB5, Bimota YB6 Exup, Bimota YB9 SR, Ducati NCR Replica, Moto Guzzi 750 S3, Honda CR750 race replica, Seeley-Suzuki TR500
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