"Excessive exhaust noise" - MoT failure point

....well that would be because the XV750SE cans are little more than a
widening in a bit of pipe - which is nevertheless marked with a BS
number. The previous owner obviously had a more tame mechanic than I but
this one helpfully suggested the use of wire wool as a pipe stuffer.

Anyone any experience of this technique? How much do I need and what is
to stop it landing on the bonnet of the first cage I excellerate away
(explosively) from? (Terribly sorry officer, I wondered where my brillo
pads had gone....)

Alternative suggestions welcome [1]

Chris D
[1] provided they don't involve excessive cash or throwing the whole
bike in the skip etc. [2]
[2] humorous is okay

 

I had a little Z200 with a megaphone pipe on it many moons ago and it was
just too loud. I found an old twos stroke baffle from one of the many
pipes I had lying around at the time and literally just hammered it into
the end of the pipe. (It was a SLIGHTLY bigger diameter).

IIRC I then screwed a self tapping screw into the end to hold it there.
Worked a treat a shut it up a good bit. Never affected what little
performance there was.

 

Thanks for that. Unfortunately I only have morris minor and sherpa van
exhausts lying around but I had wondered about fitting a short piece of
blanked off pipe in from the open end with lots of holes drilled in the
sides equivalent to the total bore. I used to have a two cylinder Lister
diesel engine which had this sort of thing fitted on as standard - but
wasn't sure how boat technology would adapt to two wheels

Chris D

 

<snip>

Many years ago I remember wandering into Moto Vecchia, whose mechanic
Jeff Porter spannered Team Bike's then Honda CB900F endurance racer.

They'd flogged the bike to someone on the magazine as they were going
the V4 route. Hell of a CB900 it was, too - well, it managed a fifth at
Le Mans.

Anyway, there was the matter of getting it through an MOT when its
silencer was probably better described as an amplifier.

The workshop staff were down on the ground hammering old Coke cans up
the gaping end can. With each can added they fired it up, listened to
it, and then hammered in the next until the decibel level had been
brought down below "bleeding ears" level.

Then they got an aerosol of black exhaust paint and sprayed it up the
can until all the cans were coated and, effectively, invisible. Job
done. And a spike-onna-stick would hoick them all out after the
MOT.

 

Thus spake Chris Deuchar unto the assembled multitudes:

Yes! I tried wire wool stuffed into a 'silencer' (I use the term *very*
loosely) of a C15 many moons ago. It made a small difference, until on
the blat home from the pub one night with the throttle wide open the wire
wool caught fire. My mates behind were treated to a spectacular and
hilarious firework show. It had all burned out by the time I got home. I
didn't bother using it again

 

<makes notes for next Guzzi MOT>

 

I used to have VW beetle baffles in my bike fixed like these. one was
fine and never moved. the other had a habit of falling out. my
brother, following me on his bike, had to duck when I opened it up a
little too enthusiastically )

--
Adie
(replace spam with nickname to reply)

UKRM FAQ: http://www.ukrm.net/faq/

Triumph 955iSS / GSF1200 bandit / CG125
MRO#11 BOTAFOF#7 BOTAFOT#130 DIAABTCOD#17 MIB#24 YTC#16 BOB#15 ex-UKRMMA#22 BOMB#11

 

Do folk remember the Supertrap silencers with the disk stack at the
muffler end? It was perfect for MOT situations.
<quick google>
Bloody hell it's still available 25 years on!
http://www.supertrapp.com/product_sections/motorcycle/index.asp

Pair of them might go very nicely on the R100RS

'Hog

 

My SOBoxer has a pair of cigar-shaped straight-through cans intended, IIRC,
for a BSA A65. They're not quiet. Also runs larger than standard main jets
and a pair of K&N-style filters.

 

Aye, I had one on an XT500 back in 1981 or so, and took the spare
disks along to the MOT, where it passed with them all fitted.

Sadly, I neglected to correctly tighten the locking nut afterwards, so
a day later they were all spat out somewhere on the A52 between Long
Eaton and Derby.

--
_______
..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2
`\|/`
`

 

*Ding*

'Hog

 

Spooky - I had one on an XT250 around the same time. A plod pulled me
once because the silencer "looked a bit strange" & he wanted a closer
look. I was bricking myself as I had a small tankbag on it stuffed with
shrooms...

 

Hmmmm.... that would be just up the road - probably not worth looking in
the verges after after 20+ years

The latest on the saga is that I removed the cans and found that they
had a single baffle in the middle (Type 'Hi-Level' e11 - anybody know
about these? Google doesn't. They look more Harley than Yammy). I
stuffed the upstream end with wadding and took it back to Mr MoT man -
who was still not happy. Bstrd

Now on plan B - with the bit of pipe stuffed in the back end as
previously discussed ^

Chris D

 

could always try a different MOT place. How loud is it, if you're honest?

 

Gives me ringing in the ears after a couple of miles ride...


Seriously, it has to be admitted it is cringingly blatty rather than
pleasantly thumpy.

If plan B doesn't work I guess I shall be crawling the scrappies.

Chris D

 

Could I suggest Plan C?

I have had considerable success in all sorts of exhausts by inserting
a 'splitter'. It seems to work by redirecting the exhaust gases and
I'd assume the sound waves too, so that they collide with each other
and "muffle" the sound. The wonder of it is that you can easily see a
reduction of 6dB(A), which is apparent, and annoying tonal components
are removed as well. Additionally it is easily removable, not to
mention cheap, so that if it doesn't work as well as expected or you
don't like the look of it you can heave it out and away.

Take a piece of thin mild steel - 18 gauge or so. Measure the
internal diameter of your exhaust and cut a strip to fit snugly
against the sides. Length - as long as you can get it, but eight to
ten inches is ideal. Take two pairs of pliers, grip your strip at
each end and twist them against each other. What you want to achieve
is a regular smooth twist of 180 degrees over the length - a flat bit
at either end doesn't matter.

Drill a small hole in the end of the twisted splitter, then slip your
strip into your exhaust. Secure to the exhaust outlet with a long,
small-diameter bolt or lockwire. Start it up and listen - it will
(fingers crossed) be noticeably quieter and much of the 'annoying'
component will have gone.

It is one of those things that I don't know how it works, it just does
- and as long as I go on believing that, it will continue to work. A
grand old boy, racing a Bugatti at the age of 85 gave me the idea -
when he took his splitters out of his open pipes the difference was
astonishing.

 

coo. Might try that on my SOBoxer, which is rather loud and harsh with the
straight-throughs on - they seem to let a lot of HF noise though.

does it make any difference to perfomance, and if so, what?

 

Nothing noticeable. It presents no obstruction to the gases, bar
swirling them about a bit.

Give it a go and let us know, Austin.

 

Coo, interesting.

That is effectively what Mark Hill (of MHP Exhausts, and jolly nice
chap) is proposing to do to our 'spare' exhaust system in order to get
the noise level down to 98db for Brands Hatch - he reckons putting
something in the link pipe will lose the noise without affecting the
power, whereas as putting it in the 'silencer' will significantly
effect the horsepower.

And he's a chap wot knows, so sounds like your theory/experience is
bang on.

 

Cool. An empty can will only act as a resonance chamber, so will be
worth packing with proper absorptive material.

Having said that - how many tests will there be? IME, they can only
test before the "competing vehicle enters the circuit for the first
time" - usually a check prior to scrutineering: the bike must pass or
it fails scrutineering iyswim.
Therefore, as long as it passes scruting it should be good to
go. There should not be any official testing after the start, as it
is acknowledged that flybys are not accurate and that packing material
degrades during use.

If the above is accurate then all you need is a can that will pass the
98dB(A) limit *once*, no matter how the bike runs. Unless it is
sealed to the bike and must finish the race with it, then we'd be free
to stealthily change the can before the start and run what we want.
It's not like your bike is the loudest on the circuit any more, in nay
case - there will be other targets that come up before yours.