Welcome to the Access Norton Forum. Login as a VIP member to remove the advertising banners.


Desmodromic 4 valve Manx

Norton Models (not Commando or P11)

Re: Desmodromic 4 valve Manx

Postby Triton Thrasher » Thu Apr 13, 2017 10:41 pm

acotrel wrote:Phil Irving.... - perhaps he had never worked with titanium ?



You say some odd things.

Have you voiced your concerns to the people who sell titanium conrods?
User avatar

Triton Thrasher
Posts: 985
Joined: Tue Feb 10, 2009 7:27 am
Location: Thurso, Scotland

Re: Desmodromic 4 valve Manx

Postby Rohan » Fri Apr 14, 2017 1:00 am

Triton Thrasher wrote:You say some odd things.


N'er a truer word was ever spake !!!

Even if Alan doesn't have a clue on a subject, he will venture in head first..
Last edited by Rohan on Fri Apr 14, 2017 1:05 am, edited 1 time in total.

Rohan
Posts: 8068
Joined: Thu Aug 26, 2010 5:30 pm

Re: Desmodromic 4 valve Manx

Postby Rohan » Fri Apr 14, 2017 1:04 am

acotrel wrote:It is common practice to fit the main bearings into Manx crankcases using steel sleeves


Its not only common practice, it was factory practice - they were built like that !

Thats because MAGNESIUM cases, camboxes etc expand with heat - quite a bit.
If they weren't encased in steel top-hats, the bearings could well just fall out...

You make it sound like a biblical revelation....

Rohan
Posts: 8068
Joined: Thu Aug 26, 2010 5:30 pm

Re: Desmodromic 4 valve Manx

Postby Snotzo » Fri Apr 14, 2017 2:15 am

When Nortons began to experiment with titanium conrods is not known, but they were used for dyno testing as evidenced in the last dyno book that was saved following the factory's close down. This was after Joe Craig had left the company, so whether he had experimented with such conrods I cannot say, but he certainly turned down Harry Weslake's 4 valve head offer -possibly because it was not his own idea ?

Re a Summerfield G50 there is no such thing. Summerfields specialise in their version of 2 valve Manx Nortons only, it's Andy Molnar who manufactures 4 valve versions of both G50 and Manx

Snotzo
Posts: 191
Joined: Tue Mar 12, 2013 3:47 am

Re: Desmodromic 4 valve Manx

Postby Rohan » Fri Apr 14, 2017 2:49 pm

Snotzo wrote: but he certainly turned down Harry Weslake's 4 valve head offer


When was this ?
How ye know such things ?
Are there details of this anywhere.

4 valve heads would have been uncommon in the Joe Craig era,
only Rudge and Excelsior (openly) used such things (all prewar.)(?).

Rohan
Posts: 8068
Joined: Thu Aug 26, 2010 5:30 pm

Re: Desmodromic 4 valve Manx

Postby Snotzo » Sat Apr 15, 2017 12:07 am

Rohan wrote:
Snotzo wrote: but he certainly turned down Harry Weslake's 4 valve head offer


When was this ?
How ye know such things ?
Are there details of this anywhere.

4 valve heads would have been uncommon in the Joe Craig era,
only Rudge and Excelsior (openly) used such things (all prewar.)(?).


The above information may be found in Vic Willoughby's book, Classic Motorcycle Engines, in the chapter about the outside flywheel Norton.
The article also contains a comparison flow chart of the 2 and 4 valve arrangements as shown to Willoughby during his interview with Weslake.

Snotzo
Posts: 191
Joined: Tue Mar 12, 2013 3:47 am

Re: Desmodromic 4 valve Manx

Postby acotrel » Sat Apr 15, 2017 2:27 pm

A question - are the guys who are using titanium conrods running plain bearing big ends or roller big ends ?
I do know this. A friend of mine gave Kevin Magee his start on Ducatis in the 70s. One of his earliest bikes was a 250 Ducati single which had as much done to it as possible - high comp. methanol fuel GP carb., factory race cams etc. At most meetings, it was very fast at first, then it always slowed. When the bike was stripped the only thing he could ever find was too much clearance on the roller big end. If the conrod is titanium and it starts to get hammered, the rod dimensions will probably change.
In Australia we have a couple of guys with grossly oversize G50s - they are not very good. The bigger motor delivers more torque, but the bikes seem to stop being nimble.
I still believe that a 500cc single cylinder motor is probably very limited in how much further it can be developed, than Joe Craig achieved with the Manx. Obviously the Molnar Manx is better than the 1962 Manx, however it is still only marginal.
The simple fact is that oversize motors destroy the whole object of the exercise - the playing field is not level. 4-valve might not be so bad, but if it comes to having the big bill every time you race just to be competitive, it can kill the race class.
User avatar

acotrel
Posts: 5607
- Images: 0
Joined: Sat Jun 30, 2012 5:39 am
Location: Benalla, Australia

Re: Desmodromic 4 valve Manx

Postby Snotzo » Tue Apr 18, 2017 12:20 am

acotrel wrote:A question - are the guys who are using titanium conrods running plain bearing big ends or roller big ends ?
I do know this. A friend of mine gave Kevin Magee his start on Ducatis in the 70s. One of his earliest bikes was a 250 Ducati single which had as much done to it as possible - high comp. methanol fuel GP carb., factory race cams etc. At most meetings, it was very fast at first, then it always slowed. When the bike was stripped the only thing he could ever find was too much clearance on the roller big end. If the conrod is titanium and it starts to get hammered, the rod dimensions will probably change.
In Australia we have a couple of guys with grossly oversize G50s - they are not very good. The bigger motor delivers more torque, but the bikes seem to stop being nimble.
I still believe that a 500cc single cylinder motor is probably very limited in how much further it can be developed, than Joe Craig achieved with the Manx. Obviously the Molnar Manx is better than the 1962 Manx, however it is still only marginal.
The simple fact is that oversize motors destroy the whole object of the exercise - the playing field is not level. 4-valve might not be so bad, but if it comes to having the big bill every time you race just to be competitive, it can kill the race class.


Acotrel, your post is so far off my original, you have effectively killed this topic stone dead!
I will however take you up on one point in your post.
The Joe Craig Manx engines at best were making 52 crankshaft horsepower, and very good horsepower it was for the period in which his engines were raced. The Molnar 2 valve re creation Manx engines are regularly seeing better than 55 rear wheel horsepower. Crankshaft compared to rear wheel, that cannot under any circumstances be considered as a 'marginal' improvement.

Snotzo
Posts: 191
Joined: Tue Mar 12, 2013 3:47 am

Re: Desmodromic 4 valve Manx

Postby Rohan » Tue Apr 18, 2017 10:12 am

And Carillo etc have been supplying Ti conrods for quite some years now,
and if there was a problem someone would have noticed by now !
Next, Alan will be telling us that the alloy Commando rods aren't up to the job... ?!!

Rohan
Posts: 8068
Joined: Thu Aug 26, 2010 5:30 pm

Re: Desmodromic 4 valve Manx

Postby acotrel » Tue Apr 18, 2017 2:45 pm

Aren't Carillo rods used with plain bearings rather than roller bearing big ends ? My comment about titanium rods possibly changing dimension due to hammering was about roller bearing big ends as used in most Manx Nortons and G50s in the old days. I've had titanium bolts neck down when holding brackets and have come loose. It is amazing how quickly it happens. If you destroyed a roller big end in a Manx with a titanium rod, the result might be extremely expensive. Do Molnar Manxes run high pressure pumps and plain bearing big ends ?
User avatar

acotrel
Posts: 5607
- Images: 0
Joined: Sat Jun 30, 2012 5:39 am
Location: Benalla, Australia

Previous

Return to Other Nortons

Who is online

Users browsing this forum: No registered users and 19 guests