Author Topic: Plunger bump-stop?  (Read 271 times)

Online Greybeard

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Plunger bump-stop?
« on: 31.05. 2019 19:00 »
Are you aware of anyone inventing some kind of bump-stop for plunger suspension?

Offline Swarfcut

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Re: Plunger bump-stop?
« Reply #1 on: 31.05. 2019 19:18 »
GB...I am thinking you have found the disadvantage of a single sprung saddle. Namely a small dent in the rear mudguard where the rear of the seat frame has smacked into the guard. You need a bump stop on the single saddle. This could be done with extended vertical rods, topped with a buffer, within the saddle support springs. The plunger design is very compact, and putting a rubber sleeve around the springs as a damper or stop is impossible, there is just  not enough room. If the coils were interleaved with a spiral of rubber, this would give some sort of buffer, but obviously restrict suspension movement.

 Swarfy.

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Re: Plunger bump-stop?
« Reply #2 on: 31.05. 2019 19:55 »
No Swarfy, I was thinking about the Plunger columns. I've often wondered about putting some sort of buffer in the tube to take the shock of full compression.

Offline muskrat

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Re: Plunger bump-stop?
« Reply #3 on: 31.05. 2019 20:53 »
G'day GB.
As Swarfy said there ain't much room in there. You know how hard it is to get the springs in normally. To put a rubber on top of the spring you would need to shorten the spring by the same amount. The rubber would need to be fairly firm eg conveyor belt, so wouldn't offer much cushion.
Plunger suspension is just a bit (not much) better than a rigid. Better springs in the seat or loose weight might be the answer  *grins*
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Online Rex

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Re: Plunger bump-stop?
« Reply #4 on: 31.05. 2019 22:09 »
I'm actually impressed by how compliant the rear end is on my single-saddled 1951.
Very comfy, although all my other bikes are either rigid or plunger too..

Online Greybeard

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Re: Plunger bump-stop?
« Reply #5 on: 31.05. 2019 23:22 »
When I'm riding solo, it's not such a problem, but when carrying my camping kit, or a pillion the rear suspension bottoms with a CLANG when I haven't managed to avoid one of the frequent holes in our roads.

Offline Swarfcut

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Re: Plunger bump-stop?
« Reply #6 on: 01.06. 2019 07:36 »
GB  The motorcycling press were less than impressed with the performance of the plunger system, and cited poor road holding as the sliders would tend to bind. Compared to the rigid frame, there was little benefit, they said, as the spring movement is small.

 Substituting a steel tube for the top spring would effectively turn it into a rigid frame, and you could  alter the ride height by altering the tube length. It would not clank over the bumps, but you might be going to Central Wheel a bit more often.

 What makes the clank? The clank must come when the spring gets coil bound, or is it when the inner slider hits the top spring mount? Either way some sort of cushioning to restrict movement would do, say a pile of rubber washers or a slice of  thick walled rubber reinforced hydraulic  hose around the inner column, to match the slider OD.  It fits inside the spring, cut to a length that still offers some movement, but prevents the spring binding or the inner slider hitting the spring mount. Crude, effective, cheap, looks standard. You can bet someone has already done it, necessity, mothers, invention e.t.c.

 I did notice that some washers are available, not official parts, which I thought were grease seals. These may do as buffers so worth researching.

 Save the anguish, just avoid the pot holes.

 Swarfy

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Re: Plunger bump-stop?
« Reply #7 on: 01.06. 2019 08:38 »
Quote
Save the anguish, just dodge the potholes.
I try!

Offline duTch

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Re: Plunger bump-stop?
« Reply #8 on: 01.06. 2019 09:42 »

 I pondered this a bit for a while, but put it on the back burner....short of having custom springs made(thinner wire/less coils), and incorporating some kind of cam type spring pre-load adjuster, it's a bit of a challenge...Mine is not a stock setup, and only have about 50mm of travel but don't have a huge problem- except when the custom made standard pot holes appear unexpectedly (and them're on the 'good' roads)

 PS- I also don't usually cart a half ton of camping gear *eek*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online bsa-bill

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Re: Plunger bump-stop?
« Reply #9 on: 01.06. 2019 09:54 »
Quote
Save the anguish, just dodge the potholes.

mmmmm - those of us in rural areas know how many holes it takes to fill the Albert Hall *cry*
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco