Steering Head Bearing inner size

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Anthony
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Steering Head Bearing inner size

Postby Anthony » Sun Sep 10, 2017 8:57 pm

Hi

Now that the bike is starting to go back together I have a query about bearing sizes.

The steering head is getting new bearings and having purchased some 32028 bearings (Koyo 320/28JR) the inner dimensions seem a bit on the small side measuring 27.91mm. The steering stem bearing lands measure 28.31 lower and 28.01 upper. I know that the stem to bearing fit is an interference fit but the lower bearing will not slide easily over the upper land making future adjustment and lower bearing regreasing rather problematical.

Would you knowledgeable chaps reckon that the bearings inner dimension should be 28mm near as damn it?

Many Thanks

Anthony

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bwprice100
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Re: Steering Head Bearing inner size

Postby bwprice100 » Mon Sep 11, 2017 7:47 am

Did you use a digital calliper to do the measurements?

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Re: Steering Head Bearing inner size

Postby barryh » Mon Sep 11, 2017 9:43 am

Without looking up the exact bearing tolerances in thr manufacturers tables, I would have expected the bearing ID to typically be 28 mm + .000 -0.01 In other words it should not exceed 28 mm and be no smaller than 27.99 mm

27.91 mm is far too much of an interference fit.

Anthony
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Re: Steering Head Bearing inner size

Postby Anthony » Tue Sep 12, 2017 6:25 pm

Measured the inner bearing inside diameter with a digital vernier.

I have ordered and received some head bearings from Motorworks and they are the same measuring 27.94.

So I am off to the lockup to retrieve the old bearing lower and an old upper for comparison.

Think I might have to take them to an engineering firm to get reamed out to exactly 28.00 or maybe 28.01 seeing how the upper is a sliding fit rather than the lowers interference fit.

All I can say at this point is #@?&%.

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bwprice100
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Re: Steering Head Bearing inner size

Postby bwprice100 » Tue Sep 12, 2017 7:37 pm

Digital callipers will tend to under measure, the smaller the bore the more the error will be.

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1958 R26, (not so many bits now)
1978 R75/7, (a project bike)
1981 R80, (was a TIC)
1995 R1100RT, (speeding ticket the first day I rode it) (Sold)
http://www.eBolt.co.uk
http://www.ToolroomChucks.co.uk

Anthony
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Re: Steering Head Bearing inner size

Postby Anthony » Tue Sep 12, 2017 7:46 pm

Digital callipers will tend to under measure, the smaller the bore the more the error will be.


Any suggestions on the way forward? I have not managed to get to the lockup as it is pee-ing it down and I don't want to get wet.

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bwprice100
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Re: Steering Head Bearing inner size

Postby bwprice100 » Tue Sep 12, 2017 8:16 pm

Hi Anthony

I think the bearings you have are fine as the digital callipers are not accurate enough to get a true size for the bore of the bearings and even measuring outside diameters can be problamatic.
Before fitting the bearings just make sure the steering stem is clean and free of dings and burrs and everything should be ok.

I hope this helps

Brian

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1958 R26, (not so many bits now)
1978 R75/7, (a project bike)
1981 R80, (was a TIC)
1995 R1100RT, (speeding ticket the first day I rode it) (Sold)
http://www.eBolt.co.uk
http://www.ToolroomChucks.co.uk

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Re: Steering Head Bearing inner size

Postby PhilO » Tue Sep 12, 2017 9:42 pm

Put the steering stem in a plastic bag and stick it in your freezer for a couple of hours. Put the bearing in a plastic bag and in a pot of freshly boiled water for five minutes before assembly and they will drop in to place or need very little tapping. Don't forget to place the tin grease retainer first.
Verneer calipers are no good for accurately measuring inside diameters due to their flat contact face. Perhaps some one could manufacture them with convex jaws for this purpose. A knife edge would do it but they would be vulnerable to damage. Since they are so cheap now it could be worth modiying a pair.

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Re: Steering Head Bearing inner size

Postby Anthony » Mon Sep 25, 2017 6:59 pm

This has now been resolved.

It took a while but I needed to eat a space in the freezer - for the bottom yoke, although I have yet to find all the raspberries.

The bottom bearing went into the oven at about 100C not sure how long. Then the bearing once past the upper bearing land literally fell into place thankfully I remembered the grease retainer.

Many thanks for all the useful hints tips and advice much appreciated.


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