The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: alanp on 19.06. 2011 14:43

Title: Twittering Silencers?
Post by: alanp on 19.06. 2011 14:43
Does anyone know who sells Goldie type silencers which twitter?
I know of 4 different silencer internals in Goldie silencers and from experimenting with two of them on two 500 singles, one twittered and the other didn't,
We have been discussing this in Chat & Diverse topic Rocket Gold Star if you want to catch up.
Cheers
Alan
Title: Re: Twittering Silencers?
Post by: bsa-bill on 19.06. 2011 15:57
From another thread Alan

Quote
Mine don't and it's almost  RGS engine spec.
I was told by a Goldie owner the twitter is down to valve overlap on the single, doesn't appear the same on a twin
Title: Re: Twittering Silencers?
Post by: townsends20 on 19.06. 2011 17:35
A few years ago a friend of mine decided to tune his goldie by opening out the inlet port on doing so filed down the step inside, guess what! no more twitter and it never went the same after.   
          steve.
Title: Re: Twittering Silencers?
Post by: Triton Thrasher on 19.06. 2011 18:00
A few years ago a friend of mine decided to tune his goldie by opening out the inlet port on doing so filed down the step inside, guess what! no more twitter and it never went the same after.   
          steve.

Some genius who rationally deduced that it was under-tuned and required to be "ported."
Title: Re: Twittering Silencers?
Post by: groily on 19.06. 2011 18:33
Give a bloke a Dremel for Christmas - and the next owner is guaranteed years of fun discovering where he had his wicked way . . .
Title: Re: Twittering Silencers?
Post by: townsends20 on 19.06. 2011 21:57
yep someone should have re-ported him! *sad2*
Title: Re: Twittering Silencers?
Post by: chaterlea25 on 19.06. 2011 22:02
Hi ALL,
The Stainless "goldie" type silencer on my SR came from Armours, Its like a songbird! *smile*

On the "tuning" escapades on Gold Stars, I was recently told by a reliable source, that increasing the inlet port on a big fin ( DBD)  only slowed the bike  ???? ????
His reasoning is that the 1 1/2in. carb is actually too big for the engine, ???? ????
Opening up the port further actualls slows the gas speed, and undoes the turbulence caused by the lip??

Cheers
John
Title: Re: Twittering Silencers?
Post by: alanp on 20.06. 2011 09:04
Hi ALL,
The Stainless "goldie" type silencer on my SR came from Armours, Its like a songbird! *smile*

On the "tuning" escapades on Gold Stars, I was recently told by a reliable source, that increasing the inlet port on a big fin ( DBD)  only slowed the bike  ???? ????
His reasoning is that the 1 1/2in. carb is actually too big for the engine, ???? ????
Opening up the port further actualls slows the gas speed, and undoes the turbulence caused by the lip??
Thanks for the Armours information.
The Gold Star 1 1/2" GP carb and appropriate matching inlet port and valves were there to provide good cylinder filling at high revs on the DB34GS and DBD34GS, a job which it did well. The downside is that at lower revs the intake air speed is not optimised for good cylinder filling and hence torque at the lower end of the rev range was sacrificed. However, for the purpose it was developed, i.e. clubman racing, it was ideal. For scrambling, where good bottom end torque is/was required, the head is different with a smaller bore carb, inlet port and valve. Carbs of 1 1/8" and 1 5/32" were fitted to 1955 and 1956 DB34/DBD34GS scrambles spec engines which produce a higher air speed at lower revs for good bottom end filling, which incidentally is ideal for coping with modern city traffic conditions.
The RRT2 gearbox ratios for the clubman version were designed to keep the engine revs in the optimum torque range since a standard box lets the revs drop too far out of the 'fat' part of the torque curve, but can be a real pain in city traffic combined with a big GP carb..
As far as the turbulence caused by the lip is concerned, there should not be a lip. If someone has a lip then the head is not correct for the carb bore. It's either a modern poor quality repro head which are around or someone has been mucking about with a scrambles head or more likely someone has fitted a 1 1/2" GP carb on a pre 1956 head e.g. the CB34GS had either a 1 3/16" TT carb or 1 7/32" GP carb. Those heads were not cast to suit 1 1/2" bore carbs.
On the open road bikes like Bonnevilles and RGSs will initially leave the Goldie behind but they are usually pulled back in when the Goldie gets in its stride with revs in the upper reaches of the rev counter and can sustain it as long as you like, while the others are wondering about holing their pistons.
Boy, have our crowd seen a lot of Triumph pistons with holes in the top!
Alan
Title: Re: Twittering Silencers?
Post by: wilko on 20.06. 2011 19:07
There goes the stepped port myth then!!
Title: Re: Twittering Silencers?
Post by: chaterlea25 on 20.06. 2011 21:38
Hi Alan and All,
My source is a well known and respected "goldie" guy. He makes his living from them, rebuilding engines and building "New" ones. He machines all his own castings and supplies the trade as well!
He had a load of new heads and cylinders in production when I was in his workshop
He has repaired a B33 alternator bottom end for one of my customers bike, it broke the crankpin and damaged the flywheels *sad2*
I was relaying his words

Regards
John
Title: Re: Twittering Silencers?
Post by: cus on 21.06. 2011 00:09
G'day Everyone,
Hopefully not too much off topic, & more for Australian readers,
does anyone know what the law is regarding exhaust noise.
Harley's go past my place costantly, & shake the glasses,
most of them run straight thru pipes, I'm thinking of keeping
my '63 straight thru, it's loud, but not nearly as loud as the Harley's.
Do they measure it with a noise metre at rego check?

regards, Cus
Title: Re: Twittering Silencers?
Post by: Brian on 21.06. 2011 00:25
I guess the laws are different in every state but when it comes to bikes I work on the theory, and I suspect Muskrat also lives by this theory, it aint illegal until you get caught !

If you stick to country roads and dont go flogging up and down the main street you should be right. If you are subject to yearly inspections you will be made to fit mufflers. If you intend to ride any distance you will need mufflers, a bit of noise might be fun for a quick flog but after some time on a trip it gets really annoying.

There is a big difference between a bike that sounds nice and one thats just plain loud.
Title: Re: Twittering Silencers?
Post by: Flatboy 1950 on 21.06. 2011 05:40
Years ago I had a Ducati SS Darmah & had a 2 into 1 exhaust system made leading into a Goldie style "silencer".
The stainless steel silencer was locally made to a Goldie drawing.
Wow !! That "silencer" was in fact an amplifier .... twittered beautifully , could raise the dead & certainly focussed the attention of the traffic cops on me ... Big Time !!!

Regards , Flatboy
Title: Re: Twittering Silencers?
Post by: muskrat on 21.06. 2011 08:11
G'day Cus,
              Yep Brian got it in one.
Down here it's 85db at 10 meters at 45 degrees I think (my wife farts louder). 95db for racing. Most people (police) expect old bikes to be a little loud. None of my bikes have baffles, but I'm the local classic bike inspector  ;)
Cheers
Title: Re: Twittering Silencers?
Post by: alanp on 21.06. 2011 08:16
Hi Alan and All,
My source is a well known and respected "goldie" guy. He makes his living from them, rebuilding engines and building "New" ones. He machines all his own castings and supplies the trade as well!
He had a load of new heads and cylinders in production when I was in his workshop
He has repaired a B33 alternator bottom end for one of my customers bike, it broke the crankpin and damaged the flywheels *sad2*
I was relaying his words
Regards
John

Understood John. I bought one of those modern cast heads and it left a lot to be desired not to mention re-machining in 3 different places and it eventually dropped an exhaust valve seat. Come back BSA all is forgiven.
Cheers
Alan
Title: Re: Twittering Silencers?
Post by: bsa-bill on 09.07. 2011 11:46
Had the Project out yesterday for a run on Bosch plugs (colder plugs as I thought to eliminate pre ignition from the list of causes) it did run well and I stopped three times to try hot starting, started every time, I am beginning to get a bit windy about the volume of the Goldie silencers though, glorious it is but loud.
Now I reckon it would be toned down a bit if siamesed (wishful thinking?) and I wonder if it would twitter if Siamesed more or better than with twin pipes
Title: Re: Twittering Silencers?
Post by: muskrat on 09.07. 2011 13:56
Bill, you know the old saying. "If it's too loud your too old". At least if the tintops can't see you they will hear you.
Cheers
Title: Re: Twittering Silencers?
Post by: wilko on 10.07. 2011 00:39
I have a plain sausage shaped silencer on my  old Matchy out of stainless steel that twitters on the over run, go figure. I keep back off just to listen to it. (http://i244.photobucket.com/albums/gg3/takka22/000_0689.jpg)
Title: Re: Twittering Silencers?
Post by: terryk on 10.07. 2011 14:18
Hey Wilko can you email me some more pics of your Matchy please. I have a mate with one the same that he wants to chase parts for and restore. What year is that and when did they go to tele forks?
cheers Terry
gflash11@hotmail.com
Title: Re: Twittering Silencers?
Post by: wilko on 10.07. 2011 22:42
Mines a mockery of a sham. It's mostly 1949 with '39 girders which are a straight swap!
Title: Re: Twittering Silencers?
Post by: terryk on 11.07. 2011 13:49
No worries Wilko his has girders to maybe its a bitsa as well.