Question about wheel bearing tightness

[Tidybuoy]

I've got new struts coming and so I plan to install new wheel bearings at the same time.

My question: I normally have adjusted the tightness with the calipers on (and so some friction from pads) - this time I will install on the bench with no brakes. How tight should I be adjusting?

Any advice would be appreciated.

[E Sully]

The front wheel bearings are tightened and then backed off till you can just move the washer. Brake calipers will have no effect on that.

[FinallyGotOne]

Well I turned mine by hand using the allen wrench and rotor turning method until I could not turn by hand anymore, then I undid a 1/2 turn put the wheel on and got wheel wobble, so I tightened it 1/4 of a rotation, and that was perfect. Don't really get any play in the washer tho. when I did it had too much wheel wobble.

[Reiver]

Originally Posted by FinallyGotOne

Well I turned mine by hand using the allen wrench and rotor turning method until I could not turn by hand anymore, then I undid a 1/2 turn put the wheel on and got wheel wobble, so I tightened it 1/4 of a rotation, and that was perfect. Don't really get any play in the washer tho. when I did it had too much wheel wobble.

My experience too.
I always count the flats, or in our case, turns of the fastener when removing then replicate and work from there.
Mine are too tight to move the notched washer.....thousands of miles and no issues.
No bluing in the bearing races either.

[Alfa68]

Hi guys just done my first wheel bearing - lots of different views on the tightness of the tab washer. I used the spinning wheel method but when I tighten to get minimal movement in the tab washer I can feel the resistance to rotation- do you only tighten till it free wheels or should there be some resistance.

It also feels like when you tighten the Allen screw it tightens further than when loose.

I still have a little play north-south but less than before (I think)

As a newby I don't want to cook them but I'd rather that than have a wheel off !

Thks

[dannobee]

There should be no resistance. Tighten the nut then back off until you can move the washer, just like it says in the service manual. The looseness is there for a reason; it allows the rotor to cock ever so slightly and push the caliper pistons in to reduce friction. There should be barely any play when you wiggle the wheel.

[Walt Fricke]

This is a new explanation for front wheel play. I had always understood the need for some play to have to do with the type of bearing. The rear axle (and 964 and newer) bearings require being very strongly compressed to work properly. The front, not. But maybe zero play isn't, by itself, tight enough to accelerate bearing wear?

The "move the washer" approach has worked for me, as far as I can tell. There is a factory torque spec in inch pounds, but I don't know if anyone uses that. You'd have to fashion a sort of socket to grab the clamp.

[Alfa68]

Yeah the tab moves quite easily what I am saying though is at that point I can feel resistance to rotation of the hub as I spin it - question is that too tight ?.

All a bit subjective for my liking

Thks

[Walt Fricke]

A bit subjective? Yes. Going to cause trouble? No. This isn't connecting rod ovality specs, or other fairly tight tolerances.

[Reiver]

It is subjective.
The illustration in Bentley's shows the screwdriver attempting to move the washer by applying pressure on its face...if you can move it that way it is too loose.
Tighten and apply pressure on the washer from the edge to get it to move....and it shouldn't move without pressure...but it should move.
Trial and error actually and it took me a bit to get the 'feel'.

[rnln]

no one follow 1.5 turns anymore? With wheel on, the wheel can be able to turn freely for, people says 1 turn, but I like it at least 1.5 turns.

[911obgyn]

If you can move the washer by hand its too loose, if you cannot move it with a screwdriver its too tight. I tighten till it is moveable wedging it with a screwdriver.

[manbridge 74]

At Porsche Classic training it was also brought up that guys tracking the cars could conceivably get the aluminum hub hot enough to cause expansion. You want to use the factory method if you apply heavy loads/high temps to the hubs. Even more so if you have a pre 74 911 which used forged hubs made by Fuchs. Cast version made for 74 and up. As most car guys know forged aluminum pistons due expand more than cast pistons.

[Walt Fricke]

I wouldn't have thought the coefficient of expansion for an element would differ depending on forging or casting. Forged is denser, so expands more per temperature change? High school physics didn't cover in that detail.

Plus I have two styles of hubs in my inventory. From my '68 I noticed the cover cap was an "innie" (cap fits inside hole in hub), while my '77 has an "outie". Does the style difference correspond with a forged/cast change?

[Alfa68]

Originally Posted by rnln

no one follow 1.5 turns anymore? With wheel on, the wheel can be able to turn freely for, people says 1 turn, but I like it at least 1.5 turns.

Thanks for the replies- washer doesnt move by hand but will using the edge as suggested but that does involve some rotational hindrance. I will try with the wheel on and see how many turns it spins I like that suggestion as it involves some numeracy !

[Alfa68]

Had a run with her this morning and all good -no detectable heating of the dust cover. Feels more positive on turn in and just a tiny amount of give compared to before. Will check them after a few more miles thanks for your help.

Oh BTW- Tried bleeding the brakes -who vents an overflow to the great outdoors ! -wowsers.

[manbridge 74]

I imagine the expansion thing is not a big concern here where cars aren’t maintaining Autobahn speeds for any length of time. I do think you can’t go wrong following the manual. A properly adjusted wheel should spin easily with caliper installed.

[spuggy]

Originally Posted by Walt Fricke

I wouldn't have thought the coefficient of expansion for an element would differ depending on forging or casting.

Well, aluminium isn't an element; composition of the alloy causes differences... Also, even if it were an element, the molecular arrangement certainly matters as well.

Originally Posted by Walt Fricke

Forged is denser, so expands more per temperature change?

Yeh, think so; aftermarket forged pistons should come with a spec sheet giving the correct fitted clearance. But don't take my word for it , Wiseco say:

Cast pistons with an integral expansion strut were commonplace for many years and they still provide very reliable service in low-power, low-rpm situations. Close to a century ago, the addition of 12 percent silicon as an alloying constituent was found to significantly stabilize the expansion of aluminum components, such as pistons.

Known as eutectic-aluminum-silicon alloy, it permitted the development of cast, high-silicon pistons with up to 20 percent silicon alloy. These are known as hypereutectic pistons and their chief advantage is a very low expansion rate. They can be installed with as little as 0.0005-inch piston-to-wall clearance on the major diameter.

Interestingly, when a modern forged piston with more initial cold clearance reaches operating temperature, the difference in running clearance is less than might be surmised. For example, Wiseco uses 2618 and 4032 alloys for all its forgings. While the expansion rates are different for each alloy, Wiseco has made pistons from each alloy for the same engine operate successfully at nearly the same running clearance. The higher-expanding 2618 piston may have a larger initial clearance than a 4032 piston, but once the engine reaches operating temperature, both pistons will have similar running clearances.

Piston-To-Wall Clearance: Myths, Mysteries, and Misconceptions Explained

[dannobee]

Comparing expansion rates of cast pistons vs forged pistons isn't accurate as cast pistons have steel expansion struts cast in place to keep the expansion rate low. This fact, above anything else, allows tighter piston to wall clearances to be run in production engines. Forged pistons, on the other hand, lack these struts, and expand more than cast pistons.