Noise Regulations

Hi All Racers current and future...
Note the BHR forum is discussing noise regulations which also apply to bantams... As I find 105 Db difficult I will be doing some development on noise reduction on my own machine, last test I went through, I barely scraped in! Given assistance by Tom Miller on this I will be changing the outside of my silencer body to a "soft" aluminium material which helps considerably to deaden the noise, This has been tested on a couple of other bikes by me, and I must say it helps a lot, the rest of my silencers are simple sound absorption arrangement with "Rock Wool" wadding.
I have now accepted that I must change the sound wadding very second meeting, and I keep a good amount in the van just in case I forget! but I am now looking at the very likely possibility of adding a second fold back silencer as the sound men are getting more aggressive every year!
This is good advice from Tom... If you have any more advice on how to reduce the sound levels then please use the forum and let everyone know as it will kill the sport in the long term if we do not reduce our sound levels.
It matters!!!!! Any help or opinions gratefully received.
Alan

Hi Alan
had my two bikes tested at brands back in april.
My bike came out at 96 db
and the one michael is riding came out at 100db
They have the tom miller type end cans yes I can say they work very well

This is a section from the final instructions you will receive with your tickets;-

"Noise. As you are all aware MSV circuits require 100% noise testing of all machines before they enter the circuit. Noise testing will be available from mid afternoon until 7.00 pm on the Saturday next to the scrutineering bay, and from 8.00am on race day in the assembly area. Please approach from normal side of the assembly area on the instructions of the marshal. The machine may be bump started down the hill.
Because of strict noise restrictions; any motorcycle found to be over the noise limit will be excluded from the meeting."

There is an endurance race on at Cadwell on the Saturday before us, so if we can get access to the assembly area we will noise test in there. We are hoping to have three noise testing teams, so we should be able to get through the majority before we start pratice.
When you have been tested you will have a sticker placed on your bike similar in style to the ones that were at Brands Hatch, no sticker no race!

Kim

Hi All,
Because the noise restrictions are getting much harder to meet, I will be doing as much as possible to ensure I meet the targets.
I have repacked the silencer ready for action, and I am looking at some sort of exterior sock arrangement to keep noise coming from the side of the exhaust down... worth a try. If I find it difficult then I will just have to attempt a fold back silencer similar to the type seen on scooters.
I wonder if carb/induction noise adds a db or 2 to the picture?
Anyone any ideas?
Alan

hello, ive duck taped a pepsi max can filled with an oily rag on the tail pipe of my finally running bike, not sure what the db levels are but the neighbours are talking to me again!..... result!

Hi Nobby,
when are you likely to get out to a race meeting?
Alan

with my bike god knows, if it hadnt been raining so much last meeting i would have made an appearance..... ( mallory park not to far away).. sadly the 4 months struggling for work after chistmas has knocked me back , but things seem to be picking up . had hoped to get racing this year but still not sure... bikes almost there, fitted gear lever linkage off rgv 250 last week end .. nighmare.. still not sure if ive got all the gears in the right places... got a flat slide mikuni on its way.. been running it with 34mm mikuni off rgv but its obviously not right.. trying to organise a 54 tooth or 52 tooth rear sprocket this week via rex caunt , noticed mr powells bike on the testing day with 52tooth rear sprocket lying half on half off ..hopefully its all moving in the right direction. still trying to find out the cc value for my piston crown / dome to get the insert made for the head, even wiseco cant tell me the value. looks like im going to have to buy a burette after all.... happy days..

Hi all
Having spent many years re stuffing silencers for road bikes, (I'm a motorcycle mechanic) hear are a few tips.
Rock wool / loft insulation materials are not suitable. They do not alow the exaust gas to penitrait deep enough in to the silencer.
Proper silencer packing meterial is readaly avalable and can be found at any motorcross dealers. It comes in two types. Sheet form is used when your siencer outer sleave is removable and rapped around the inner perferated tube befor the outer tube is replaced. Loose fill is used when you have a silencer with a removable end cap (when both inner and outer tubes remain atached to the expansion chamber).
The silenser packing is quite cheep and one pack will do two silencers. Once packed a silenser will do about two seasons racing. It lookes a bit like glassfibre, do not be temted to use glassfiber it is not the same thing.
The outside diameter of the silencer has an efect on its eficancy, (most silencers on bantams are too small in diameter) but larger diameters are a law of deminishing returns.
When packin a silencer it is vitaly important to get the dencity corect. Packing that is to loose or to tight will make excesive noise. In my experiance 75% of people over pack and 20% under pack. Loose fill should be lightly tamped in and sheet should be lightly rapped. Over filling a silencer is the seme as no silencer atall.

Keep it quiet and keep it rubberside down.

Mick

My usual problem of not having any time and resources meant that in desperation i did a permanent job on the last silencer. a) to stop it dropping off b) was in a hurry and did not have time to think about removable options. Would have been happy to fit a shop bought silencer but past debate has pointed out that where the tail pipe starts becomes a weak point unless the outer sleeve can be attached to the expansion chamber itself. There is no danger of mine dropping off but i am worried that i might not be able to get through this time. my measures, like the original job, will be desperate ... as the silencer is welded shut i will poke around the inside with sharp scriber and loosen up old caked material around the drillings and maybe try a deflector of some kind.
my tip is disconnect rev counter and say it is not charged!
any ideas about using a deflector of some kind on the end, to direct sound waves to the tarmac?

Having read Mick's post I went in search of some wadding on EBAY, and ended up just round the corner.

Anyway the guy was extremely helpful and his measures are generous so I thought I would give him a plug.

http://www.dynoflow.co.uk/

He has a full online shop and offers various grades of wadding, worth a call

James

Mick- what do you think is the ideal diametre off the silencer? 60~80mm and length? as long as you can accomadate?? Interested in your thoughts...

James- good local stuffing find!

James Cook wrote:

Having read Mick's post I went in search of some wadding on EBAY, and ended up just round the corner.

Anyway the guy was extremely helpful and his measures are generous so I thought I would give him a plug.

http://www.dynoflow.co.uk/

He has a full online shop and offers various grades of wadding, worth a call

James

Have they got parsley and tyne stuiffing for my Bantam?

Hi Mike
I sugest a minimum thickness of 25mm for the wadding. therfore a centaral perfarated tube of 20 mm resultes in a 70 mm outer tube. Aneything over 40mm (ie 100 mm OD) will not have any decernable efect.
The longer you can make the inner tube the better as you increase the number of perferations that the gas can escape by.
Tom is quite correct in sugesting a soft outer skin, carbon fibre is even quiter than ally. But there is no good reason why you cant lag a silencer from the outside to stop it resonating.
Packing a silencer is a black art I can show aneyone how to do it but it is dificult to describe.
If your outer tube is not wellded to your expansion chamber it MUST have a suport strap or it WILL brake.

Hope this is usfull to everyone.
Hope to see you all at Lyden.

Best wisses Mick

Thanks Mick ... see you at Lydden..

Hey Mick!
Dunn any of you know the answer to my question of earlier?
The D1 bore was 52mm and the stroke 58mm right? What was the con-rode length centre-to-centre?

...I need it for calculating piston velocity, acceleration and `pulse rate´...

..."Do you know that without gravity we´d go on travelling through space for ever and ever---"
PIP.***

***My missus dressed in `Pretty In Pink´ ....!