Associated B74.2 steering block bearing problem

[Lumikko]

I was doing some bearing maintenance on my B74.2 and found the 5 x 10 x 4 mm bearings in the steering block (#92171, common for the B74 series) to feel gritty and indexed.

I pulled the bearing and gave it a clean and lube, the spinning seemed fine so I pressed it back in. The gritty feel was gone but the bearing felt indexed again. Pulled it out, thinking I would replace it with a new one, but once removed, the bearing felt fine again.

Suspecting that the recess in the steering block for the bearing is oval, I took out my calipers and measured the diameters to be 9.94 mm minor and 10.1 mm major. That’s a 0.16 mm difference, not acceptable at all with this bearing size.

I bought a new pair of steering blocks but they are the same. Both the left and right side are affected.

This seems like a poor moulding job, just like with the front arms which must be reamed to eliminate binding on the hinge pin.

I don’t have a 10 mm reamer on hand so I’m looking for alternative ways to fix this. Has anyone else noticed this and managed to solve the problem?

 

[DavidB1126]

I have the B74.1 and I felt no issue/s.
Using stock included kit steering parts.
Don't have a caliper so can't measure the diameter. If I do measure it and it is the same as yours, I guess both .2 and .1 cars have the same issue. The OG B74 likely has the same part and part number so that car might have the same issue too.

 

[Lumikko]

I have the B74.1 and I felt no issue/s.
Using stock included kit steering parts.
Don't have a caliper so can't measure the diameter. If I do measure it and it is the same as yours, I guess both .2 and .1 cars have the same issue. The OG B74 likely has the same part and part number so that car might have the same issue too.

Yes it’s the same part number for all three versions.

The issue was not immediately obvious, it’s easy to miss. Next time when you rebuild the front, see if the inner race of the bearing spins smoothly even at a slow speed.

 

[Lumikko]

Here’s the minor diameter:

And here’s the major diameter:

What a lucky coincidence: the base nuts of a Schrader valve are knurled and out of the three, I found exactly the right size! I put the nut on the valve stem, pressed in, and rotated a few times.

Lo and behold, the size is right! The bearing still requires a deliberate press to install so it’s not a loose fit. But it spins beautifully!

I’m rather relieved this was so easy to fix.

 

[WickedFog]

Likely not so much of a molding issue as it is just inherent in the design that when that part comes out of the mold it collapses a bit in that direction. With that, I would think pressing the bearing in would spring the part back into its molded position. You could verify this by measuring between the kingpin bosses of the knuckle before and after the bearing is installed.

I would be curious to know if you tried a new bearing? If the bearing wears it might allow that much deformity in the journal to squeeze the bearing out of round. But a new bearing shouldn't do that I wouldn't think.

I would grab some aluminum steering knuckles if it were me. Or maybe see if RPM makes a steering knuckle for it.

Nice calipers

 

[Lumikko]

Likely not so much of a molding issue as it is just inherent in the design that when that part comes out of the mold it collapses a bit in that direction. With that, I would think pressing the bearing in would spring the part back into its molded position. You could verify this by measuring between the kingpin bosses of the knuckle before and after the bearing is installed.

I would be curious to know if you tried a new bearing? If the bearing wears it might allow that much deformity in the journal to squeeze the bearing out of round. But a new bearing shouldn't do that I wouldn't think.

That’s the definition of a molding issue I think. The molds and process should be designed to account for shrinkage and other deformations to get a good end result. The B74.2 front arms had to be reamed to have the hinge pins not bind – the rear arms did not require this. So it can be done better.

The outer races of these bearings don’t have a lot of wall thickness and can be deformed quite easily. They don’t wear enough to make a significant difference in this regard. Very often cartridge bearings of any size depend on a bearing cup to support retaining the shape.

The distance between the kingpin bosses might extend slightly with a bearing installed. I’m not sure if calipers are precise enough to measure that but a micrometer would do the job.

I tried new and used bearings and new and used steering blocks, all combinations pointed toward the same issue: the hole is not round and deforms the bearing when installed.

Anyway, the issue is now fixed and I’m happy.

 

[WickedFog]

That’s the definition of a molding issue I think. The molds and process should be designed to account for shrinkage and other deformations to get a good end result.

Well, technically, molding and design are two different things But yeah, they could have redesigned it for shrinkage. They probably never thought it was that big of a problem to worry about redesigning it, and spending the money to machine new molds I'm guessing. Seeing as that is probably part of a multi-part mold, it would likely cost a good bit.

What you can try if this problem comes up again would be to heat the part in boiling water, install the bearing, and run it under cold water. I have done this before with plastic parts where it was hard to install the bearing due to warpage of the bearing journal.

Anyway, glad you got it fixed.

 

[Lumikko]

You’re right it’s a problem with the mold design, not necessarily the process itself. Doing the molds over would be crazy expensive considering the parts work well enough.

The bearings are too flimsy to change the shape but I found a bit driver that fits the hole as tightly as the bearing does. I tried boiling for 90 seconds without much of an effect. Maybe a longer boiling time would help but reaming did the trick this time.