Confused about headset bearings

paulbnix

I have a Planet X Spitfire and the info I have is that the lower bearing is a TH MR127 1 1/8TH 36X45.
I bought one of these and it does not fit as it leaves the fork too close to the headtube so it binds slightly.
The original bearing is

and the new one that does not fit is


I am just wondering what the original bearing actually is as there is no visible text on it.

laurentian

I haven't really got an answer for you but I was trying to replace the headset bearings on my commuter/winter bike (Specialized Allez) and having real problems trying to get a definitive answer on which bearing to buy.

Realising the limits of my knowledge (and perhaps ability), I took it to my LBS who replaced the bearings. c.£40 supplied and fitted. For the work done and the aggravation prevented at my end, I thought this great value for money.

trevor.hall12

What width is it ?

There should be 3 dimensions and an angle
The angle on the new one looks too big it will be sitting too deep in the frame ,looks like a 45° the one that came out looks like a 36° or there abouts
You need to measure the old one
Internal diameter
External diameter
Width ( height )

paulbnix

Both bearings are 51.9 OD and 40 ID.
Comparing the slant with a 45 deg line and they both look to be 45 deg.
However the dimensions are different as I attempt to show here.
The new bearing has TH MR127 1.5 36x45 H 9 on it.
Planet X say it should be that type of bearing but don't state the H9 bit.

paulbnix

I've had a look at various bearings on offer and the nearest I can find is a ACB 4545 150 (1-1/2") Headset Bearing 40x52x7 45x45 deg from Wych Bearings.

This is not the one that Planet X specify.

Strange.

trevor.hall12

Is it measured with a vernier caliper ,not to sound like a pedant

Here's what I have in my workshop box

P16 - 40x52x7 45°/45
ACB4051KK - 40x51 x6.5 36x36°
P25k 40x52x6.5 36/45°
ACB518K - 40x51.8x8 36/45°


Looks to me like it's P16

masjer

The joy of headset bearings.

It looks like you’ve got an FSA Orbit ITA headset.
https://support.planetx.co.uk/hc/en-gb/articles/360018490680-Spitfire-Tech-Specs-and-Components

If so (from the FSA website) you’ll need a 40x51.8x7mm 36/45, which tallies with your own measurements.
It’s called an ACB3645-40B (still check measurements).

masjer

https://bearingsrus.co.uk/acb3645-40brs-zen

paulbnix

masjer said:

The joy of headset bearings.

It looks like you’ve got an FSA Orbit ITA headset.
https://support.planetx.co.uk/hc/en-gb/articles/360018490680-Spitfire-Tech-Specs-and-Components

If so (from the FSA website) you’ll need a 40x51.8x7mm 36/45, which tallies with your own measurements.
It’s called an ACB3645-40B (still check measurements).

Thanks for that. Looks like the correct one.

The problem was that the Planet X description of the lower bearing as a TH MR127 1 1/8TH 36X45 did not seem to lead to the one you quoted.

I'll order one and see.

masjer

paulbnix said:

masjer said:

The joy of headset bearings.

It looks like you’ve got an FSA Orbit ITA headset.
https://support.planetx.co.uk/hc/en-gb/articles/360018490680-Spitfire-Tech-Specs-and-Components

If so (from the FSA website) you’ll need a 40x51.8x7mm 36/45, which tallies with your own measurements.
It’s called an ACB3645-40B (still check measurements).

Thanks for that. Looks like the correct one.

The problem was that the Planet X description of the lower bearing as a TH MR127 1 1/8TH 36X45 did not seem to lead to the one you quoted.

I'll order one and see.

Fingers crossed.

paulbnix

I've just had a look at my other bike, Px Hurricane, and the new bearing I bought matches that so if the new one is correct for the Spitfire I've not wasted money ☺

paulbnix

New and Old bearing look to be a perfect match.
Thanks