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Rear Sprocket Plastic Fin.

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Hi folks,

 

What is the plastic fin directly in front of the rear sprocket for?

And is it really necessary?

 

I see some bikes with it and some without it.

I don't think any twin shockers have them, do they?

 

I have recently broken mine on rocks and haven't found or made a replacement yet.

It is fairly flexible plastic and when it broke the sprocket and chain must have taken the impact with out any really visible damage.

 

Am I risking damaging something if I choose to run without it?

Or is it a requirement for modern trials?

 

Any knowledge appreciated...

 

 

 

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That is your chain guide. You don't see them on twin shockers because they have less suspension travel and the chain can have more tension. Your bike, if reasonably modern, needs a little chain slack for suspension travel so there is some potential for your chain derailing at the sprocket without running a guide. 

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Is it really?

That surprises me, I thought that was taken care of by the chain tensioner / guide. The sprung runner a little nearer the engine.

I assumed it was a protector of some sort, but was wondering how a flimsy piece of plastic was supposed to protect the hard chain and sprocket.

 

I risk a derail then without it?

 

 

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It's to stop your fingers being cut off if you fall off the bike on to the rear wheel or someone tries to catch the bike.

It is not for guiding the chain, they are fitted to mx & enduro bikes.

Edited by twinshocktosser
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It's to stop your fingers being cut off if you fall off the bike on to the rear wheel or someone tries to catch the bike.

It is not for guiding the chain, they are fitted to mx and enduro bikes.

 

Exactly, and over here ALL trials bikes are required to be fitted with them (and the gearbox sprocket under some circumstances. The Motorcycling Australia Rule book specifically lists them and checked every trial by the scrutineer. I am aware of two amputations from the rear sprocket, one at the SSDT a couple of years ago when the shark fin went missing during the trial.

They are a really good investment.

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Everything that can help to save some fingers should be fitted imo. The new sprocket rules etc, I know already 3 people with fingers suverly hurt or missing!

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Exactly, and over here ALL trials bikes are required to be fitted with them (and the gearbox sprocket under some circumstances. The Motorcycling Australia Rule book specifically lists them and checked every trial by the scrutineer. I am aware of two amputations from the rear sprocket, one at the SSDT a couple of years ago when the shark fin went missing during the trial.

They are a really good investment.

 

 

Everything that can help to save some fingers should be fitted imo. The new sprocket rules etc, I know already 3 people with fingers suverly hurt or missing!

 

 

Yikes!

 

I will "pull my finger out" (LOL) and get it sorted.

 

Thanks chaps.

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Just wanted to show off my shark fin I fitted to my 1984 Fantic 300, as oz thumper stated this is mandatory here in Australia for competition use. It's a right sided modern Beta fin bolted to a 5mm alloy bracket I made which has been Tig welded to the existing alloy Fantic rear brake stay. It almost looks like it's meant to be there. This is what we have to do in Australia.

post-14580-0-41081500-1459852637_thumb.jpg

 

 

Edited by fourex
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Without being pedantic, what's to stop a finger going in above the swingarm, still could do a lot of damage.

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There are always places to hurt yourself, but more protection is better..

 

A finger underneath is instant gone...

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Keep it down b40rt, don't make it too obvious that any form of motorsport is dangerous. The next step will be 'Speedway' type fully enclosed wheels leading on eventually to fully enclosed 'Egg' bodywork and the sections being caged in with F1/NASCAR style debris protection fencing.

Most of us learned as kids that things spinning fast should be left alone until they stop.

 

The old addage of 'Common sense prevails' just get overruled sometimes by someone trying to help and that's the saddest part.

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B40rt, usually the wheel rotates forward, you would have to be very unlucky to get your fingers in there whilst travelling backwards! B)

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Here's a pic of the actual finished product on the Fantic with top guard on, but as others have said, this does not seem to be a problem due to the rotation. Even the modern day GG/Beta/Sherco have little to no guarding on top of the chain, but all have some form of protection on the bottom chain rung leading into the sprocket. Most of us here in Oz simply use something like that kitchen nylon cutting board stuff cable tied to the swingarm or brake stay and that seems to keep the scrutineers happy, we're simply doing what our rule book stipulates.

post-14580-0-72462000-1459862216_thumb.jpg

 

 

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B40rt, usually the wheel rotates forward, you would have to be very unlucky to get your fingers in there whilst travelling backwards! B)

Unless it's a Bultaco, which seem happy to run in either direction .....

Edited by b40rt
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