Licence plate cracking

bosco659

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After only 3-400 miles, my licence plate has cracked at the mounting holes due to vibration. Anyone have a good solution to prevent this? Maybe a reinforcement plate, mounted with all four bolt holes? FF2CDBF9-8E1C-4461-B307-56A0A582D04D.jpeg
 
256 crank with lead weights. Almost 7000 smiles and no signs of a crack.
I'm sure others will be along with better suggestions:whistle:.
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There are many good ways to do it. I like simple. For simple, go to the hardware store and buy two rubber grommets. Take the plate in with you because I don't remember the size and it might be different than Georgia or Mississippi. Make sure the grommet fits in the plate and your standard mount bolt fits in the grommet. Mount as normal. The grommets will take up the vibration. I haven't lost a plate since I started doing this many years ago. This method works and is fully compliant with the KISS principle.
 
If you're set up with fiberglass, it will work. That's what I did. Lay a couple of thicknesses of glass cloth on the back, saturate with resin, wait 24 hours.
 
I make backing plates out of aluminum plate. I put rubber sheet between the backing plate and the license plate, and 4 bolt it as you mentioned. This is the plate on my '78 and it's been holding up fine since 2005 .....

on4m0BX.jpg


The plate for my "new to me" '83 got the same treatment .....

ADeSV6h.jpg


ASiTMma.jpg
 
Thx lots of great ideas. My plate is damaged so I’ll go get a replacement and rig up a reinforcing plate and maybe add grommets too.
 
I make backing plates out of aluminum plate. I put rubber sheet between the backing plate and the license plate, and 4 bolt it as you mentioned. This is the plate on my '78 and it's been holding up fine since 2005 .....

on4m0BX.jpg


The plate for my "new to me" '83 got the same treatment .....

ADeSV6h.jpg


ASiTMma.jpg
Is that 1/4” plate?
 
No, it's more like 1/8". It's very easy to cut with a saber saw, and easy to drill.
 
ADeSV6h.jpg
On the upper mounting hardware, I would use bigger/fender washers to spread the load to a bigger area.
 
Can’t find a piece of aluminum that size. Wonder if my wife would notice if one of her cookie sheets disappeared or became shorter?
 
Being a cheapskate, I use washers cut from old inner tube with scissors. Placed between the number plate and the mounting lugs.
 
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On my ride to work outfit I did like 5twins did but I had a piece of scrap 1/4 inch Plexiglas instead of the aluminum plate.

Almost hard to believe that the 1988 Sportster with over 100,000 miles on it never had the same problem as the XS650 that seldom made over a one mile commute. Must be something to do with frequency and amplitude or the fact that nothing on the Sportster is rubber mounted.

However the Sportster did manage to destroy a Speedometer and two tachs!
 
It's not the vibrations of the bike so much as the very thin metal the plate is made from. When mounted by just the two upper holes the plate vibrates, this flexes the plate next to the mount bolts. As with any metal if it flexes enough times it break.
Adding a stiffer backing plate and mounting with 4 bolts stops the flexing.
Most hardware stores sell metal in many sizes of flat, angle, rod and tube as well as flat sheets.
1/8" thick is about right. Buy the piece, cut to match the plate, drill holes to match the holes in the plate and mount with four bolts.
No need for grommets and rubber washers.
Leo
 
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