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Heavy twins Exhaust pipes and port angles.

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Heavy twins Exhaust pipes and port angles.

Posted by robert_tuck at October 12. 2018

I'm making space and selling stuff I will never use. I have a set of NOS 88/99 pipes that I innocently bought for my  1960 99  25 years ago.  Of course the port angle was wrong as the suppliers did not know their stuff.(is it likely to be better now??,I dont think so).The pipes had a narrower angle than I needed,I assume they would be for an earlier bike. I can imagine that this sort of problem comes up regularly. Does someone have a collection of heads that we can check and measure the port angles ?,This would make it possible to both order the correct parts  (by quoting the head angle) and also  identify what parts we have lying around.I don't want to sell my pipes with the wrong description.

Re: Heavy twins Exhaust pipes and port angles.

Posted by howard_robinson at October 12. 2018

As far as i know there are only two different exhaust head angles.  The shallow one is for all Dominator heads up until the inception of the 650SS (Manxman in US).  These later heads were known as semi-downdraught types and had a steeper exhaust angle.  The included angle is 80 degrees. From then on this angle was utilised on the 88SS, 650SS, Atlas, Mercury and Commando but not the 99SS.  Of course there are people out there with semi-downdraught heads on 99SS's and standard Dominators.  However it was not a standard fit on the 99's, 88's and Nomads.  It gets further complicated with the pipe diameter sizes.    Good luck, Howard

Re: Heavy twins Exhaust pipes and port angles.

Posted by david_comeau at October 12. 2018
Previously robert_tuck wrote:

I'm making space and selling stuff I will never use. I have a set of NOS 88/99 pipes that I innocently bought for my  1960 99  25 years ago.  Of course the port angle was wrong as the suppliers did not know their stuff.(is it likely to be better now??,I dont think so).The pipes had a narrower angle than I needed,I assume they would be for an earlier bike. I can imagine that this sort of problem comes up regularly. Does someone have a collection of heads that we can check and measure the port angles ?,This would make it possible to both order the correct parts  (by quoting the head angle) and also  identify what parts we have lying around.I don't want to sell my pipes with the wrong description.

Long held secret since August of 2000 with Phil Hannam being a valued contributor http://atlanticgreen.com/nhth.htm

Re: Heavy twins Exhaust pipes and port angles.

Posted by robert_tuck at October 12. 2018

Hi Howard, If that is the case then my NOS pipes are just scrap .  I was under the impression that the 59/60 head had a wider splay than the earlier ones.

Re: Heavy twins Exhaust pipes and port angles.

Posted by howard_robinson at October 12. 2018

Yep Robert - If they don't fit your big valve head and don't fit the semi-downdraught head then they will not fit any Dominators even Model 7.  Even the AMC Hybrid Atlas varieties used the 80 degree angle.  Maybe they were 'old stock' simply because they did not fit anything ??   Triton or NorBSA perhaps.   A bit of heat and you'll bend them to fit so long as the chrome doesn't matter.  Cheers, Howard

Re: Heavy twins Exhaust pipes and port angles.

Posted by robert_tuck at October 12. 2018

Hi Howard, These were bought not as NEW OLD stock but as current replacements over 25 years ago, Even then aftermarket replacements were not to be trusted. I doubt things have improved.  I agree that the best thing to do with them now would be to get them bent to fit and properly plated.  That would ensure you finish up with a good job.

Re: Heavy twins Exhaust pipes and port angles.

Posted by philip_hannam at October 13. 2018

Howard / Robert...........if these exhaust pipes were purchased from a well known south coast region supplier, then the chances are that they would not fit any of the Norton Twin (or Hybrid) cylinder heads suggested.

pic NE1 shows the poor bend angles of my Swept-back SS set. You got the choice of the pipe rubbing on the primary case or fouling the brake lever. With the other pipe, the rev counter drive got a battering or the kickstart lever removed chunks when operated. These pipes were returned.

The Standard Exhaust set  purchased was little better. This needing minor adjustments on each side for similar reasons. You can see the blue marks on the RH pipe caused by the blowlamp. You can bend the pipes cold but this often leads to the Chrome plating cracking. Great choice ........blue or rusty brown patches.

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