Tapered Steering Bearing Polini
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Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Fri Sep 18, 2020 1:29 pm quote
Picked up the Polini steering bearing set with hopes of installing it onto the Bajaj Chetak. The set is the lower 0502657 and upper 0502658. Both use the same two piece SKF bearing with Polini proprietary stamped metal race retainer cup which looks like goes in place of original bearing races.

The SKF outer race has an interference fit with the Polini stamped cup. My thoughts are install the race into the cup first then install the cup into the frame.

Looks like the lower bearing will slide/press onto the fork after the supplied dust cup.

The upper bearing and nut with the sleeve have an interference fit. Seems like fit bearing onto sleeve nut first then run onto fork thread to tension.

See any compatibility issues?

69A358D1-9567-4CC8-BD3D-A0038FF9598A.jpeg

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lower bearing arrangement

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interference fit SKF race Polini cup

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dust cup lower bearing

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upper bearing arrangement

534FED4C-D41B-44B5-A64A-AC7D39869A76.jpeg
interference fit SKF bearing upper Polini steering nut



Last edited by hibbert on Fri Sep 18, 2020 4:33 pm; edited 1 time in total
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1778
Location: california
Fri Sep 18, 2020 3:26 pm quote
Never seen this - but like the concept a lot.
Interested to follow.
Please post pics once you have the portion mounted on your "fork" and the parts put in to the frame - wanna understand how it fits up a bit better.
Cool.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Fri Sep 18, 2020 4:28 pm quote
Was on the fence on the Pinasco bearing SIP has a set as well as BGM when Ginch posted the Polini I bit the bullet it is slightly less expensive. Any tips on installation Lynn noticed you did it recently.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Fri Sep 18, 2020 4:32 pm quote
hibbert wrote:
Was on the fence on the Pinasco bearing SIP has a set as well as BGM when Ginch posted the Polini I bit the bullet it is slightly less expensive. Any tips on installation Lynn noticed you did it recently.
I put the new races in but just the standard bearings. Did you pop out the old races yet?
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Fri Sep 18, 2020 4:39 pm quote
Haven't taken anything apart yet still in the planning stage. When I replaced the upper loose balls it was a PITA and it seemed the Bajaj headset was more temperamental than other Vespa's I worked on before getting the bolt back into the headset was problematic. Knowing that want to have scooter elevated preferably on a lift so fork can came down without nuisance. Seeking guidance from others that have more experience.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Fri Sep 18, 2020 5:12 pm quote
hibbert wrote:
Haven't taken anything apart yet still in the planning stage. When I replaced the upper loose balls it was a PITA and it seemed the Bajaj headset was more temperamental than other Vespa's I worked on before getting the bolt back into the headset was problematic. Knowing that want to have scooter elevated preferably on a lift so fork can came down without nuisance. Seeking guidance from others that have more experience.
I will say I had mine up on a milk crate butted up against the front of the stand and the rear wheel touching the ground , the headset I had a hook in the ceiling from hanging the frame to paint it and I used a soft strap and ratchet strap to hold it up off the fork, I also at first had it simply wrapped in a towel and taped up with electrical tape so no damage. I put a cardboard on the floor under the fork with wheel removed ( wheel removed gave enough extra clearance). Loosen fork nuts and drop it down and pull out of way, have something ready to lay it down on. A propane bottle ( yellow one ) will be needed to heat fork race off , youll probably have to heat race and knock on the dust shield to knock race off. I used a long enough 3/8 threaded rod to knock out the races , first downward just catching the edge and then upward, this is why you want to pick the correct length for hitting upward because you have only so much clearance down below hitting upward , I think a nut then a wider flat washer and then another nut to sandwhich the washer would work so you could more easily catch the edge of the race for hitting downward and upward. I'm not sure how tight of a fit the new races will be , I seen a guy did it and had to actually cut part of the top race frame area , wait to see though. If the race is tight going in you can use that same threaded rod to pull the bottom and top into there seats using a big socket on bottom and I used a washer up top, just don't want to do what I did and pull so hard you pull the top race seat downward.
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Sat Sep 19, 2020 12:44 pm quote
I set the SKF races into the Polini cups went in like butta.

Set the UPPER bearing onto the sleeve NUT packing with grease under the the dust cover before tapping it home felt so good guys!

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so good

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9F3F04AD-580D-4FFC-981B-1A24A33E0736.jpeg
holes intended for? easy to remove race.

A95D6272-8474-4559-8D7C-7139B4DB193C.jpeg
lower bearing set

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starting upper bearing onto sleeve NUT

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packed

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Sat Sep 19, 2020 1:01 pm quote
I can only imagine the fork is going to be so much more solid and smooth turning. When's the real install?
Ossessionato
Joined: 26 Oct 2015
Posts: 2685

Sat Sep 19, 2020 2:59 pm quote
Installing the bearings is the exact same process as installing front wheel bearings in a car or truck. I installed new bearings in the headset of my KTM a couple weeks ago. No rocket science involved, just start assembling everything. You were probably just overthinking it. Just remember, make sure that you never pound or press on the bearing cages (which you shouldn't ever have to). Also heat and a freezer makes intalling everything easier. A bearing grease packer tool works the best for lubing all the rollers, but you can still do a decent enough job by hand. Make sure to give us a ride report when you have it up and going!
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Sat Sep 19, 2020 3:19 pm quote
hibbert where did you buy them? I've done about as much as I could do to stabilize this 8" wheeled bike and if its going to help me from getting hemroids from the 60 mph ass puckering , I'm in.
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Sun Sep 20, 2020 5:40 am quote
Hey Lynn I ordered from Scooter Speed P0502657 and P0502658. If they work it might be an option for you too.
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Sun Sep 20, 2020 1:34 pm quote
Dropped the Bajaj fork and looked things over.

The lower Polini bearing appears 6mm taller compared alongside original. Not sure what this means. Does it mean there will be a 6mm larger gap between the fender and frame clearance? Does it mean there might be 6mm less thread on top? Does it create tolerance issue with headset bolt? Does it create tolerance issue with steering lock?

The top bearing looks problematic might not work on this scooter.
Bearing cup diameter so large obstructs cables and wiring coming through the chassis and into headset.

Not sure how to proceed need to sleep on it.

DC3A9DB8-7FB6-481F-A792-103E069DA544.jpeg

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old race

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original vs. Polini lower

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original

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Polini



Last edited by hibbert on Sun Sep 20, 2020 2:00 pm; edited 3 times in total
Addicted
'64 Motovespa 150S (177) , '66 Allstate SF, '64 VBB, '66 180SS
Joined: 27 Mar 2013
Posts: 744
Location: S.Salem, NY
Sun Sep 20, 2020 1:55 pm quote
Is this really going to be an improvement over a good standard set properly adjusted ? Also, all the weight is on the lower bearing so you might just use the tapered one there but I never thought tapered bearings were load-bearing, axially speaking.
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Sun Sep 20, 2020 2:04 pm quote
Moto64 wrote:
Is this really going to be an improvement over a good standard set properly adjusted ? Also, all the weight is on the lower bearing so you might just use the tapered one there but I never thought tapered bearings were load-bearing, axially speaking.
Don't know still learning. Biggest complaint is the slack that is released after the impact and rise, when the space finds it's way back down.
Hooked
64 V90 survivor, 75 V90 graffiti
Joined: 30 May 2018
Posts: 247
Location: Madison WI
Sun Sep 20, 2020 2:20 pm quote
Used these in my 64 smallframe. https://www.sip-scootershop.com/en/products/steering+head+bearing+set+_90126000
Required opening up the top of the frame for cable clearance. Also used blue loctite on top adjuster since no room for stock tabbed washer and lock ring.

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1&3 top and bottom races 2 bottom bearing. 4 top bearing with adjuster built in

Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Sun Sep 20, 2020 2:43 pm quote
Muchas Gracias Mayor mucho needed. Is that a 77 stamp? Like your improvement.

Suspect the SIP/BGM and Pinasco lower fork bearing might be dimensionally closer to original than Polini.

Suspect upper bearing more challenging than payoff.

Lifting many stein tonight
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Sun Sep 20, 2020 3:57 pm quote
Yep what ExMayor did is what I seen in a fb group.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Sun Sep 20, 2020 4:00 pm quote
Moto64 wrote:
Is this really going to be an improvement over a good standard set properly adjusted ? Also, all the weight is on the lower bearing so you might just use the tapered one there but I never thought tapered bearings were load-bearing, axially speaking.
I had heard from a guy that did this that its suppose to be a very good improvement over the stock caged bearing setup, I'm interested to see how it goes with hibbert because I've snugged up my bearings 3 times and although it is better than when I snugged them up the 2nd time, out today i'm back to getting a bit of knocking from the fork.
Addicted
'64 Motovespa 150S (177) , '66 Allstate SF, '64 VBB, '66 180SS
Joined: 27 Mar 2013
Posts: 744
Location: S.Salem, NY
Mon Sep 21, 2020 4:00 pm quote
Lynn, is it possible that after you crushed the top of the steering collar and then pounded it back up it is relaxing back down from tightening the bearing nuts ?
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Mon Sep 21, 2020 4:39 pm quote
Moto64 wrote:
Lynn, is it possible that after you crushed the top of the steering collar and then pounded it back up it is relaxing back down from tightening the bearing nuts ?
Well I certainly have learned that anything is possible. Our roads here really are pretty rough. I will pull the headset tomorrow and check, it did look good the last round of tightening and of course I don't have the experience to know when tight is tight enough. The steering certainly isn't binding up.
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Sat Oct 17, 2020 6:21 am quote
The Polini bearings do not fit. Can only blame myself for not doing my homework. Will follow up on the Bajaj build thread.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7954
Location: Victoria, Australia
Sat Oct 17, 2020 4:51 pm quote
hibbert wrote:
The Polini bearings do not fit. Can only blame myself for not doing my homework. Will follow up on the Bajaj build thread.
Hibbert can you elaborate please? And if you put up something relevant to the Polini bearings can you link to it here, or just repeat here?

Not sure if you mean top or bottom bearings.
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 2852
Location: Nashville
Sun Oct 18, 2020 5:20 am quote
Since I'm seeing steering bearing replacement on my VBB in the near future, I'll probably go this route for exploratory purposes.

I'm going to do something slightly heretical, though, and simply find tapered bearings with the same dimensions as the legacy bearings.

My boat trailer uses tapered bearings. The entire replacement set (two seals, two bearings, two cups) was about $20 US.

I've found (and mentioned in other threads) where if you just figure out the spec's of a part, you can usually find high quality replacements at a fraction of the price. O-Rings and gaskets, too.

I don't mind buying sets of things to support the scooter shops, but there are some cases where I get pretty irritated seeing SIP charge me $50 for something that I can source myself for $10 or less after spending a few minutes with my calipers.

caveat: I know that this option doesn't exist for many people, and for many years, I lacked those skills, too. But I've also gotten pretty tired of paying a premium to order parts based on the "fits Model X" and having them not fit.
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1183
Location: California
Sun Oct 18, 2020 6:57 am quote
The Polini bearings came with an SKF bearing and a steel retaining cup that holds the race which goes into the frame and dust shields.

The upper Polini bearing retaining cup was huge 62mm OD which essentially eliminated space for the cables to pass. The SIP version has a 49mm OD on the upper bearing which was workable with modification to the frame and headset.

The lower Polini bearing is 8-10mm taller than the original. My thinking suggested fork would be slightly lower, gap between fender and frame larger and less threads up top.

I used a BGM7939KT. Might be same producer as SIP. The upper bearing OD is 49mm and the lower is slightly taller than original. Additionally I went back to the lower Polini to potentially use the dust shield. This is when I discovered another discrepancy the bore size is less than 32mm Bajaj fork is 34mm...

I modified a standard dust shield to eliminate interference. Dust shield is smaller OD and shorter now but still provides some protection and grease retention.

Anyone building a chopper and wants nice fork bearings the Polini might work!

0B6E9C45-B3A1-407B-9343-01986C0A8B85.jpeg
Upper Race
Stock left Polini right

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Lower bearing assembly
Stock left Polini right

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BGM bearing - modified dust shield - stock shield

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Lower Polini bearing less than 32mm ID

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Upper BGM bearing left with stock race sitting inside BGM race/cup

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Upper stock race inside Polini

Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
Posts: 1525
Location: Siam
Sun Oct 18, 2020 3:48 pm quote
The first thing that came to my mind was that the overall bearing stack height is too high, thus the fork tube on a stock bike will not be long enough.
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