Chip & Gerry:
There are two places where disc wheels "normally" crack, one at the lug
nuts and the other is at the hub cap stud.
The cracks at the lug nuts is not caused by over tightening the lug nuts,
but rather by the stress induced to the wheel by the stiff sliding pillar
suspension under racing conditions. The factory also introduces stresses
at this location by stamping the wheel to provide full purchase for the
sloped shape of the wheel lug nuts. Wheel stresses are also magnified by
the fact that these wheels have only four lug nuts, a 5% increased
loading factor over normal five studded wheels.
The crack at the hub cap studs is due to the factory induced stress when
the curved portion of the wheel is flattened for insertion of the hub cap
stud. These cracks then radiate to the ventilation holes in the wheel. I
have experienced both types of cracks under racing conditions and is the
first thing any Morgan driver checks when they pull into the pits.
My solution was to have flat plates 1/8" thickness welded to the back
side of the wheel with appropriate holes for the lug nuts and the center
hub. Never had the cracking problem again.
John
.
On Fri, 7 Aug 1998 12:45:13 -0700 "Willburn, Gerry"
<Gerry.Willburn@trw.com> writes:
>Chip,
>
>I have never seen a disk wheel (MORGAN) crack around the hubcap
>rivets.
>That is very unusual. The usual place for cracking is from the lug
>nut
>holes. This is usually caused by over-tightening the lug nuts. The
>loss of a wheel by a couple of competitors led to the MORGAN being
>banned from racing for a couple of months in California in the 1950s.
>
>The solution was (is) a safety plate of 3/16 steel between the lug
>nuts
>and the wheel. this distributes the load around the mounting area and
>keeps one from inducing cracks by over-tightening the lug nuts. Works
>well. MORGANs were re-instated and went on to forge a great
>competition
>history.
>
>All the best,
>
>Gerry
>
>
>> -----Original Message-----
>> From: Ernest(Chip) Brown [SMTP:ebrown@ms.com]
>> Sent: Friday, August 07, 1998 11:59 AM
>> To: Graeme Sutherland
>> Cc: Steve Moore; morgans@autox.team.net
>> Subject: Re: disk to wire
>>
>> The wheel issue is becoming serious for some of us. I have a 57 Plus
>> four with
>> 16" wheels and have been looking for better than two years for spare
>> wheels for
>> same. Now I have two of the five wheels with the car that are
>cracked,
>> and
>> another which is suspect. All are cracking in the same exact spot:
>> There are
>> three rivets on each wheel that are designed to hold the hubcap on.
>> Around each
>> rivet is a flattened section of the wheel crown, designed I suppose
>so
>> the tire
>> changer could get a screwdriver underneath to pop off the cap, or
>> maybe designed
>> to give the hub cap a better "purchase" around the rivet.. About
>3/4"
>> wide, with
>> the rivet in the middle.
>>
>> On each of the two wheels the crack starts at the edge of this
>> flattened
>> section, then propagates down to one of the ventilation holes. The
>> third wheel
>> has a crack at the flattened section, but it hasn't spread yet. One
>> crack
>> appeared at Pittsburgh GP after a hard Saturday run and made me
>scrub
>> the car
>> and come home.
>>
> -----
>>
>> Regards to all
>>
>> Chip Brown
>>
>>
>
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