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trials silencer

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trials silencer

Post  andy-s on Sun Apr 10, 2016 5:38 pm

Hello , can anyone recommend a road legal trials type silencer for a falcon 74 with a 8e. I would like to use the bike for some road work as well as pre65 trials . The one fitted at the moment rattles the windows ! Its ok off road but the bike is going to be registered for road use and I don't get stopped every time I take it out.
Andy

ps thanks to the dating officer for dating it so quickly
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Re: trials silencer

Post  peter@dunfordconstruction on Mon Apr 11, 2016 10:59 am

Hi Andy,

Armours do a 2stroke removable end ed also with a turned out exit pipe suitable for on road use. You may need a sleeve if the inlet pipe into silencer is not 1 3/4". Looks like the silencers used on the F/B trials 92? See Arthur Gent' s book.

Peter
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trials silencer

Post  andy-s on Mon Apr 11, 2016 6:40 pm

Thanks Peter , will take a look.
Andy
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trials silencer

Post  andy-s on Sat Apr 30, 2016 8:30 pm

I have now fitted the silencer from armours. The bike now looks the biz , road legal with new reg . The only thing is it has now caused the bike to back fire . Its more of a poof than a big gun shot sound . It seems to happen when the throttle is opened after low revs . Well I think its caused by the silencer because I haven't changed any think else . Is it a case of changing the carb setup or the timing ?
Andy
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Trials Silencer

Post  peter@dunfordconstruction on Mon May 02, 2016 9:38 am

Hi Andy,

I have the same problem! Just Fired up my Trials 83 which is updated to a Trials 92 spec with Villiers 32a Engine
& fitted with a Armour Silencer that appears to be the same as Mick Ransoms works bike, but with an Amal 626 Carb fitted. All items are as new. The Amal instructions say it is probably weakness but I have tried screwing in the pilot air adjusting screw but this has not cured the problem!

Peter
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Re: trials silencer

Post  Ted Snook on Mon May 02, 2016 9:48 am

Most likely (but not inevitably) you have an air leak in a joint somewhere. Take the Silencer and Pipe off and remake the joints using Silicon. Most people don't realise that the exhaust system is part of the breathing side of the engine and air leaks at joints are important, because there is a 'suck' part of the combustion cycle that will pull air in, diluting any burnable gas left behind, making for a weak residual mixture for a cycle or two.
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silencer causing backfire

Post  piston 197 on Mon May 02, 2016 10:36 am

I endorse what Ted says above, but may also be a back pressure problem, try restricting the outlet end of the silencer and see if this improves the matter.
For town work and trials work, Bill Lomas used the FB type silencer with the exhaust exiting though a slide slit, he made a tube to go over the end with a brazed on nut and a thumb screw to tighten it, he could then slide the sleeve to expose a bigger or smaller slit, to quieten it in town, but be less restrictive off road when opened up.
If you have the slit exit type silencer you can experiment with a sleeve to restrict the outlet size and increase back pressure to see if this makes any difference ??
JH
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trials silencer

Post  andy-s on Mon May 02, 2016 6:14 pm

Thanks John & Ted, I know J H Goddard says the engine will "wuffle" and four stroke as the throttle is opened if the mixture is too rich. The setting was fine when I had a straight trough silencer just no good for the road . The new armours silencer has a small removable angled tail pipe at the end . When I fitted it I made sure the front pipe joint was good , didn't even give the removable end a thought . I know some gas is getting by this joint because of staining . I will make off all joints again and hope its that simple .
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trials silencer

Post  peter@dunfordconstruction on Tue May 03, 2016 8:42 am

Hi Andy John & Ted,
Thank you for suggestions.
I have tried and resealed all possible air inlet points on my silencer and carb joints & stubs to no avail . I think it is quite ironic that two of us have the same problem with 2 different engines but same Silencers????? The inside baffles are a very simple affair of a rod that is bolted to a removable rear outlet with a 1" pipe with
90o/o bend , there are 3 number baffles welded to the rod equidistant with simple 5/8th cuts in outer edges with just the corners bent over to form a triangular hole in the baffle for the gases to escape. What one would think a simple easy to clean/ decoke , but maybe to much back pressure??? Does anyone have an actual original silencer that could throw some light on the baffles etc?? I wondered if they had a similar system of internal pipe as per other F/ Barnett ones?

Peter
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armours silencers

Post  piston 197 on Tue May 03, 2016 10:41 am

Have had varied experience of Armours silencers, they generally are well made and nicely finished, but do not seem to accurately reproduce the performance/silencing of the originals.
A friend of mines son had a Panther with Siamese pipes and a Villiers 2T type silencer made by Armours, the performance was poor and it would not achieve much over 45MPH, he asked me to try it, and it was strangled to death, we fitted his original rusty silencer onto the Armours front pipes, ( well cobbled it on as the pipe was too long to align the brackets so wired it to the pillion footrest) with the old silencer on , it was noticeably quieter and was achieving close to 70MPH on the bypass.
I do think back pressure is the problem and most likely it is too much ?
JH
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Re: trials silencer

Post  peter@dunfordconstruction on Tue May 03, 2016 10:47 am

Hi John,

Thanks for info. I think I will experiment a bit and make anotheraperture on the opposite sides of each of the baffles and see if it is any better! I can easily flatten it back out if it does not work!

Peter
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trials silencer

Post  andy-s on Tue May 03, 2016 8:05 pm

Hi Peter, yes I think it to much of a coincidence that we both have the same problem. I have today re-made all the joints . While I was at it gave the carb a good clean out , it did have a lot of crud in it even past the banjo union filter . I will fire it up tomorrow and see how it goes . I did notice the baffle set up ,thought it looked a bit strange . If you try the mod can you let me know how it goes?
Andy
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Re: trials silencer

Post  Ted Snook on Wed May 04, 2016 10:11 am

The function of the 'baffles' in a silencer of this type is guide the gas in and out of the pipe, and as such the they have to be positioned correctly along the pipe. It is not a pipe with a can containing baffles, but an assembly where the pipe is the other half of the silencer. I don't know whether the original drawings are available still, but many of the offerings today seem to be made just to look shiny and really don't function that well.
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Trials Silencer

Post  peter@dunfordconstruction on Wed May 04, 2016 11:04 am

Hi Ted,

I could not agree more. But who might have the original drawings? Regrettably no one has come forward so far. If only someone would we could get some proper innards made?
The Armours silencers do not have a pipe just a central rod with 3No baffles welded to the rod with a slit in each the rod bolts onto a plate across the inlet side of the silencer and has the removable outlet and tail pipe welded to that.

Peter
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Silencers

Post  kerabo on Wed May 04, 2016 3:27 pm

Can you post a picture please showing your new silencer. I converted my Trials AMC to Villiers but kept the special Original silencer and made a hockey stick front pipe.

Regards Ken
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trials silencer

Post  andy-s on Wed May 04, 2016 7:22 pm

Hi Peter,
Tried the bike with re-made joints to exhaust system , no difference . Tried the pilot adjuster in to enrich this should of made the situation worse but I was going to start from scratch! no more back fire . After a bit more adjustment and the motor not sounding too bad I went for a test run .The bike went ok I think . This is the first time out on the road and with a trials type small front and large rear sprocket got to about 30mph with no back fires (and nothing fell off) . I think I will try some fine tuning of the carb setup seems to be working . I wasn't looking forward to chopping the new baffles .
Andy


Last edited by andy-s on Tue Jun 21, 2016 7:07 pm; edited 1 time in total (Reason for editing : wrong name sorry)
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trials silencer

Post  andy-s on Tue Jun 21, 2016 7:05 pm

Hi David , did you ever get your bike to run ok? I have now used my falcon off road and realised the power is very much less than with this exhaust . I think the air screw is so far in to stop the backfire its strangling the engine. I am now thinking of opening the baffle plates up to see if it will run smoother .Any suggestions welcome Please.
Andy
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Trials silencer

Post  piston 197 on Tue Jun 21, 2016 7:13 pm

My general rule of thumb for a 197cc 8E engine trials bike is
24" pipe before the silencer of at least 1 5/8" pipe, silencer to be between 6 and 7 times the cylinder capacity ( 1200cc to 1400cc) and free flowing, outlet of silencer to be 1/3 the area of inlet diameter with at least 3" of tail pipe, and secondary DEP or WES type end can .
JH
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Trials Silencer

Post  peter@dunfordconstruction on Wed Jun 22, 2016 8:16 am

Hi John & Others,

Thanks for formula I will don my mortarboard measure all up and see where I am at with the silencers. It did get little better once I opened up the baffles a bit but it certainly is not right! I do think the whole design of the insides needs sorting out. Most other F/B pipes seem to have a properly designed pipe/ Baffle with holes and inner baffle also between the holes in the pipe

Regards

Peter
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trials silencer

Post  andy-s on Wed Jun 22, 2016 6:44 pm

John, if your formula is correct ( I have no reason to disbelieve it) then the Armours silencer is too small . I know I only used school boy maffs but I make the volume around 800-900cc. The front pipe is bang on 24". I think I will try taking out the baffles and going from there This will put me in the same position I started from in the beginning of this thread. Oh well and all that.
Andy
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Trials Silencer

Post  peter@dunfordconstruction on Thu Jun 23, 2016 8:30 pm

Hi Andy & John,

Very interesting about the size of the silencers from Armours. If you look in Arthur Gent book on pages 28/9 &176 it shows very clearly that the works 92's used by Mick Ransom successfully used 12/13" with 13/4" pipes going in an outlet of about 1 to 11/4" diameter silencer looks 3" diameter
with curved out tailpipes similar to the Armours ones. This leads me to believe that it is the innards that are not correct on the Armours product?

Peter
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exhaust length

Post  piston 197 on Thu Jun 23, 2016 8:45 pm

Peter have anther look at the front pipe in the pictures you mention, it is a lot longer than 12/13", it comes out of a l/hand port goes down about 6" turns with a right angle across the front tube come up again for about another 6" and then travels back to the silencer, Think 24" would be nearer to the length than 12/13" ?? The outlet from the silencer appears to be around 1" diameter ?
JH
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trials Silencer

Post  peter@dunfordconstruction on Thu Jun 23, 2016 8:55 pm

Hi John,

I meant the silencer is 12"to 13" in the main barrel obviously plus the inlet pipe & the outlet pipe. I sort of checked this by measuring the silencer shown on the 92 on page 176 then comparing it with the 18" rear wheel, if that makes sense? All three of my bikes have the looped down & up exhaust pipe as you describe plus the Armour silencers. Non of which runs well!

Peter
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Silencer

Post  piston 197 on Fri Jun 24, 2016 6:59 am

Peter, the 1954/55 ISDT bikes ( see my avatar) use a silencer with a 3" diameter barrel with 1 3/4" inlet that is 16 1/2" long and a tail pipe of 6 1/2" long with slit side entry, it has concentric baffles inside and is used with a baffled inner pipe that is the same as on the roadster exhaust baffle, We had 4 of these silencers made at Technical tubes an exact copy of the only remaining original silencer. These have been fitted to the 3 ISDT bikes and all work well, these silencers cost 60 each to make and I have one spare one, un-plated if you want it ,at cost to see if it makes any difference, but you would need to fit a baffle tube from a cruiser to your down pipe.
Bare in mind it is some 6" longer than your silencer and may need modification to fit your machine ?, but might solve the running issues.
I will be away for a few days , but you can contact me by phone
JH
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Trials Silencer

Post  peter@dunfordconstruction on Fri Jun 24, 2016 7:39 am

Hi John,

Thanks for info I will be intouch

Peter
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Re: trials silencer

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