Wheel nut torque March 87C

[R. Pare]

One common issue that causes wheels to come loose is interference between the wheel and the radius at the base of the hub center snout, usually because the radius from the wheel center hole to the mounting face is not large enough. When this happens, the centerlock nut is actually clamping the wheel against that radius instead of the hub face, allowing the wheel to wiggle slightly, which in turn loosens the nut.

[provamo]

who built the car?

[stownsen914]

Thanks for the continued input on this. To respond in summary:

• Re: torque, from what I've heard, 125 ft-lbs may be way too low. I've been using 350 ft-lbs after getting input from various sources.
• Interesting point about the hubs/bearings. Not sure I'd heard that before, but it makes sense. I believe the torque of the wheelnut may keep the wheel bearings tight with this design?
• The car was built by Fabcar in the early 1990s using March 87C uprights and hubs.
• I'll check the taper on the ID at the inner face of the wheel. I think I looked at that before but will confirm. I can see why that would be a problem.

Any thoughts on what would be acceptable tolerance for wobble of the wheel nut when loosely sitting on the threaded portion of the hub?

Scott

[R. Pare]

Hate to be the bearer of bad news...

Finally looked closer at the upright picture - that is NOT a March 87C rear upright! Not even close.

Here's the March drawing of the 87C rear upright assembly:

[stownsen914]

Hate to be the bearer of bad news...

Finally looked closer at the upright picture - that is NOT a March 87C rear upright! Not even close.

Here's the March drawing of the 87C rear upright assembly:

Thanks for that. If you are looking at the pic in post #13, that isn't from my car. I'd posted that to show examples of different types of wheelnut retaining clips. I think my rear uprights do look like the diagrams you posted, actually.

[stownsen914]

Today I fitted one of the wheels to the car, and was able to confirm that there isn't any interference between the radius on the ID of the wheel with the hub mounting face. And to make sure I'm not crazy, I confirmed that the uprights are indeed March 87C pieces. In addition to visually matching the diagram posted above, a spare set I have still has tags with the March part numbers.

I'm taking the car out in a couple weeks. I'll be using the retaining clips on the hub snouts. I'm also going to put some shims between the clips and the wheel nuts to minimize the amount they can turn in case they lose torque. At least until I can confirm that they hold torque, or figure out what's going on in case they still don't.

Scott

[DanW]

If you want to confirm your wheel nuts aren't backing off, mark with a paint pen on the nut and the wheel face.

[mark elder]

I think the two word post above got overlooked. You need to go and buy this stuff (or similar)

https://www.amazon.com/Permatex-8003.../dp/B000HBM86Q

It is a blue colour (its not engineers blue for marking up) and you put it on, say, the hub and then fit the wheel tight, then undo it. It will tell you what parts of the hub are touching what. If there is a mismatch with the tapers or the radius etc etc, it will show. You then fix the issue, clean it up and repeat the prussian blue assessment. Repeat until perfect.

Just because you are lead to believe your wheels and hubs were previously all OK, don't. Its an old race car. Bits get swapped all the time. And we have all spoken to previous owners of all sorts of stuff and they end up saying "now you mention it, it used to do that to me too. Never sorted that one out."

[stownsen914]

I actually did buy the Prussian blue and apparently neglected to do the test, so thank you for the reminder! So I think I get the point about checking the contact pattern between the inner face of the wheel and contact points on the hub. What would be the proper way to check the wheelnut contact pattern with the wheel using Prussian blue?

[mark elder]

I would clean up the nut and its mating surface (brake clean etc), then somehow hold the wheel firmly against the hub without the nut. I would try a ratchet tie down from the chassis, across the wheel and back to the chassis. Maybe 2 tie downs straddling the nut area (you need the wheel firmly in its mounted position but you need to get the nut on and off; maybe there is enough gap under just one central strap). Paint Prussian Blue on one surface (maybe the nut), then wind the nut on; torque up and remove. Inspect.

Fix.

Report back

[stownsen914]

Thanks. I'll start with making sure the wheel and hub mating surfaces are flat, and fix as needed. If I am picturing this correctly, I think checking the wheelnut contact pattern using the process mentioned above might not yield valid results if the wheel isn't completely flat against the hub.

[stownsen914]

Something just occurred to me ... not sure if I heard it here or maybe somewhere else. I had the damaged inner wheel face repaired by having it machined flat. Well, it turns out it's not supposed to be flat. I just spoke with a BBS engineer. The inner face is supposed to be tapered by .05mm (.002") from the center to the outside of the inner wheel face (concave as you look at the inner face).

And he confirmed the drive pins are intended to keep the wheel from rotating back and forth from repeated acceleration/braking events, not just to locate the wheel. Clearance between pins and bores should be a few thousandths of an inch max.

[R. Pare]

Yes, wheel faces need to have that taper in order to more evenly spread the centerlock nut load across the face. Without the taper, the load is concentrated directly in line with the nut.

[stownsen914]

I did a trial fitting of the repaired wheel with Prussian blue. I put it on the inner wheel face where it mates with the hub, and also on the wheelnut where it mates with the wheel. Pics below showing what transferred to the hub (technically the brake rotor hat), and to the wheelnut surface on the wheel (sorry, the pics rotated, gotta love Apple).

A couple notes:
1. I noticed what appears to be fretting on the rotor hat where the wheel sits. I assume this is a result of the repeated acceleration/braking events causing the wheel to rotate slightly back and forth. The fretted area is a little rough to the touch, but the hat did not appear to be gouged and I didn't detect any obvious high spots.
2. The Prussian blue didn't transfer to the hub / rotor hat as much as I expected, but did seem somewhat evenly distributed. Could it be that I didn't use enough Prussian blue? I smeared a very thin layer with my finger to the inner face of the wheel.
3. The wheelnut contact pattern looks like I thought it should. The dark ring in the pic of the wheel is the Prussian blue on the wheelnut contact area of the wheel. I'll be curious what others think.

[stownsen914]

Wanted to report back on the latest, and have one more question.

I had the car out a couple weeks ago. No problems with loosening wheels this time! I retorqued a few times during the weekend (after letting things cool), and no loosening detected. A quick summary of changes I've made:

• I'm more careful to make sure all mating surfaces and the wheelnut threads (male and female) are clean.
• After noticing that the slots in the wheels for the drive/locating pins were a bit hogged out (up to .060" larger than the pins), so I had some sleeves made to take up that slack so the wheels don't rock back and forth with repeated braking/acceleration cycles.
• I lube the threads lightly. I saw opinions all over the place about what to do with that. I tried graphite spray initially but noticed the hub snouts oxidized lightly in a couple spots sitting over the winter, and decided an oil based lube might be better. I tried a light coating of WD40 this time.
• I used the safety clips on the rear wheels. Being a bit anal probably, I also put some shims to take up the space between the wheelnuts and the clips.
• I'm torquing to 400 ft-lbs now.

I'm happy with the results.

One question - I noticed on the front hubs (rotor hats, actually) have what appears to be a friction material sprayed on the face where it contacts the wheel, possibly to minimize the wheel rocking back and forth. See the black ring near the drive pins in the pic below. It feels rough to the touch, and appears to be probably a few thousandths thick. Maybe similar to "flame spray" or similar like people sometimes use on clutch friction surfaces. I see remnants of this on the rear hubs / rotor hats as well, but it's more worn off there. I think these remnants is the "fretting" that I thought I felt on the rear mounting face. Anyone know what this stuff is?

Thanks as always for sharing your thoughts/experience.

Scott

[stownsen914]

Bumping this for input on whether there should be a friction coating on the inner face of the center lock wheels, and also on he corresponding contact face on the brake rotor hats. Presumably to help resist rotation between the wheel and hub/rotor. It's on the front wheels/rotors and also the rears. It looks mostly worn off on the rear, I assume due to repeated back and forth rocking of the wheel due to cycles of braking and acceleration.

The friction material applied to the wheels and rotors contact faces looks like a painted on textured material. See the black ring on the rotor in the pic in the post above (this is one of the fronts, where it's not worn off).

Thanks for any input on this!

[Charles Warner]

[QUOTE=stownsen914;584236]

• I used the safety clips on the rear wheels. Being a bit anal probably, I also put some shims to take up the space between the wheelnuts and the clips.

Can't speak to the friction material, but this is an excellent practice for all wheels. This will prevent the wallowing of the wheel by the axle in the case the nut tries to loosen.