Knock-On Alloy Wheel Drive Pegs

[bcmc33]

I am embarrassed, as a so-called, experienced engineer by my ineptness. The so, so obvious is a password in hindsight ? of which I have a PhD. So a cautionary tale for the unwary.

While driving home two nights ago from carrying out 25 running-in cycles (as per Rohan?s advice) on my overhauled engine, I had a rumble from the rear LH wheel. I stopped expecting a flat tyre ? no flat tyre but the wheel was at an angle highlighted by the tyre being about an inch outside the line of the wheel arch. Pushing the wheel to the upright position I held the spinner which fell off in my hand.
Jacked the suspension up to get wheel off to find three of the drive pegs driven through the hub so that the chamfers only were showing and one missing. I carefully put the steel spare wheel on and drove the mile home.
On examination next morning in full daylight the location holes in the wheel were damaged for about 3mm into the holes with some rubbing on the location face.
Then the ?penny dropped?. I measured the depth of the drive peg holes in the wheel at 16.5mm. The drive pegs in the hub are 7mm of which 4mm is the camfer ? perfect for steel wheels, of course.

Now the bright ones among you will say ?why wasn?t longer drive pegs fitted ? he must be a right prat?, and I agree, hence the first line of this thread.

I now know that the usual suspects sell longer drive pegs, but not long enough in my opinion so I?ve bought a length of EN8 bar to make a complete car set with a wheel drive engagement of 11mm.

So the purpose of this message is for those with knock-on alloys and standard steel wheel drive pegs to take notice and do something about it.

Now why the wheel came loose is another matter. I?m putting that down to ME not doing the tightening job properly ? even though I?m sure I did.
For the smart arses out there ? the spinners are on the correct side.

BTW, the running-in cycles appeared to me to be somewhat savage and good fun, i.e. full throttle from 3,000 to 5,000 rpm in third gear, to best serve the fuel injected 1594 engine with a new QED 420 head. I don?t know what the power and torque is yet as I wanted to complete the 50 cycle running-in before getting it on the rolling road. If the QED data is to be believed the torque at 5,000 rpm is just over 130 lbs ft so it?s quite likely that this was too much for marginal drive peg location on the rear wheels.

[gerrym]

Brian, the too short drive pegs...is this because you have fitted non spec alloy wheels to a Sprint which as it left the factory, only ever had steel weheels fitted?

Also, are your spinner threads completely dry or do they have any lubricant. Did you torque them up or hammer them tight? (no right answers, just curious)

Regards
Gerry

[bcmc33]

Brian, the too short drive pegs...is this because you have fitted non spec alloy wheels to a Sprint which as it left the factory, only ever had steel wheels fitted?

That's exactly what I said.

Also, are your spinner threads completely dry or do they have any lubricant. Did you torque them up or hammer them tight? (no right answers, just curious)

My standard practice is to torque to 225 lbft (my weight at 13") plus two belts with the copper mallet.
The threads are as lightly lubricated as is reasonable.

[AussieJohn]

Thanks for highlighting this Brian, never ever gave it a minutes thought. I wonder how many owners have been caught out after replacing a hub with a second-hand one and not checking the peg length, cheers, John.

[gerrym]

Brian, thanks for your replies. I guessing that .... the drive pins caused the wheel holes to enlarge (fail in compression/shear of the soft alloy). Then the sharp acceleration (and braking?) caused the wheels to fret back and forth across the hub. This transferred torque back to the spinner / hub thread and thus loosened the spinner.

So root cause is the inadequacy of the drive peg dimensions, as you have already identified. Solve this, solve the whole problem right?

Regards
Gerry

[bcmc33]

Thanks for highlighting this Brian, never ever gave it a minutes thought. I wonder how many owners have been caught out after replacing a hub with a second-hand one and not checking the peg length, cheers, John.

John,

That's why I thought sod the public embarrassment - get the message out.

[bcmc33]

So root cause is the inadequacy of the drive peg dimensions, as you have already identified. Solve this, solve the whole problem right?

Regards
Gerry

Gerry,

Fingers crossed!!!!!!!

[RichardS]

[The threads are as lightly lubricated as is reasonable.

Brian

Very interested in your observations as I followed your example with Minilites. I will check mine asap.

When I first put my Sprint back on the road last year I had tightened the spinners [with the original steel wheels] up firmly with the traditional lead hammer - went out for a test drive and after a couple of miles stopped to check things over - and a couple of the spinners had gone from hammer tight to finger tight! Transpired that the spinner threads and hub threads were mucky from 20 years of standing. Cleaned up the threads with some petrol and have kept them "dry" since and no further problems.

So [and I am no engineer!] is it possible that even light lubrication may have been enough for the spinner to loosen and cause the damage?

Richard

[bcmc33]

So [and I am no engineer!] is it possible that even light lubrication may have been enough for the spinner to loosen and cause the damage?

As an engineer it has been my teaching and practice that no screw thread fastening should be done without the relevant level of lubrication.

Applying a load on dry threads would be potentially very dangerous as the torque loading would be taken up trying to overcome the high friction levels of dry surface to surface contact and not necessarily creating the correct clamping loads that the torque setting suggests. This would be particularly more severe on large diameter threads like that in the hub and spinner.

I have had the practice of having what I think is the minimum amount of lubrication on the hub threads. However, writing this I can see a contradiction in my thinking as I have never lubricated the spinner/wheel interface. So in conclusion, I have to accept that some of the applied torque is being absorbed to overcome the spinner to wheel friction at the expense of the clamp load.

[twincamman]

great reason to use bolt on wheels -- ---ed

[summerinmaine]

Just went out to measure my drive pegs, even though I'm currently running steel wheels, because my car came with a set of Panasports and I might decide to fit them with some new rubber when I finish the resurrection. My pegs are 11mm, of which 4mm are the chamfers. Should I think about custom making some longer pegs or are these already longer than OEM?

[summerinmaine]

[The threads are as lightly lubricated as is reasonable.

When I first put my Sprint back on the road last year I had tightened the spinners [with the original steel wheels] up firmly with the traditional lead hammer - went out for a test drive and after a couple of miles stopped to check things over - and a couple of the spinners had gone from hammer tight to finger tight! Transpired that the spinner threads and hub threads were mucky from 20 years of standing. Cleaned up the threads with some petrol and have kept them "dry" since and no further problems.

So [and I am no engineer!] is it possible that even light lubrication may have been enough for the spinner to loosen and cause the damage?

Richard

Now I'm getting a bit confused. My understanding was that the "handedness" of the hub/spinner threads was to result in the spinner tightening under wheel rotation.

Is this not correct, and if it is, why should the spinners have loosened on your car?

[bcmc33]

Now I'm getting a bit confused. My understanding was that the "handedness" of the hub/spinner threads was to result in the spinner tightening under wheel rotation.

Is this not correct, and if it is, why should the spinners have loosened on your car?

That's why I said I put it down to me not doing the tightening properly.

However, wheel rotation is not the really the issue, it is the rotational force applied by the wheel from the hub. In acceleration and braking the rotational forces are in opposite directions.
On my running-in cycles the acceleration force was much greater than the retardation force as there was no braking taking place.
As I see it, in acceleration the hub is trying to undo the spinner, and in braking, the hub is trying to tighten the spinner.
Maybe it is a reasonable conclusion to assume that had I braked as hard as the acceleration instead of letting the car slow down from 5000 rpm to 3000 rpm under normal momentum, the spinner may not have come loose. We will never know.

On the remaining 30 running-in cycles still to do, I shall check both rear spinners each time after 10 cycles.

But I have to make the longer pegs first - sometime over the weekend.

[bcmc33]

great reason to use bolt on wheels -- ---ed to

I won't argue with that.

[bcmc33]

Just went out to measure my drive pegs, even though I'm currently running steel wheels, because my car came with a set of Panasports and I might decide to fit them with some new rubber when I finish the resurrection. My pegs are 11mm, of which 4mm are the chamfers. Should I think about custom making some longer pegs or are these already longer than OEM?

Your pegs have a 7mm drive length in the wheel - more that double the 3mm I have. I would have thought that will be OK.

To make even longer pegs may be ideal but what is the depth of the holes in the Panasports? As I said, the holes in the Minilites are 16.5mm deep, so I shall make new pegs at 15mm with a 4mm chamfer to give 11mm drive.