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What alloy and heat treatment was used for Girdraulics? 2

Diogenes

Well Known and Active Forum Website User
Non-VOC Member
"Reviving a post from over four years ago, does anyone have additional information on the precise alloy and heat treatment used for the Girdraulics? The above composition doesn't correspond to any standard alloy. However, testing companies can be remarkably far off in the compositions they quote, even to the extent of reporting significant quantities of elements that aren't even present."

Material used was BS L40 or the almost identical RR56, depending on which source you read.

Details of those material specs are given in the Materials folder in the Files section of

http://groups.yahoo.com/neo/groups/stevenageworld/info

To see the contents, you need to first join that YAHOO Group - though that is no sweat as it is free to join or to leave.

That Group also contains many other hard-to-get Vincent related articles.

[ If you wonder why I started a 'new' topic, it is the only way I could get the web site to work for me.]
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
Thank you very much (although having the BS specifications available at that site has just put a reference librarian out of a job...).
 

Diogenes

Well Known and Active Forum Website User
Non-VOC Member
Some additional materials references for Girdraulic fork blades.

'The Motor Cycle', 4 Sep 1952, page 259, "Vincent Range for 1953".
"Front forks are of the Vincent Girdraulic pattern which incorporates the features - and advantages - of both link and telescopic forks.
The blades are massive L.40 Duralumin forgings."

'TWO WHEELS', July 1973, page 40, "The Black Shadow Story" by P E Irving.
"The girders or blades were forgings in RR56 aluminium alloy as were the top and bottom links ...."
Clearly the mention of the bottom link being made of the same material as the top link is an error.
See the 'Light Metals' 1950 article, also by PEI, where L40 is the stated material for the blades and top link, but steel is stated as the bottom link material.

PEI Autobiography page 369 states "The legs and the top link were were forged in RR56 in aluminium alloy by Thomas Smiths Stampings …"


There has been some discussion about L40 versus RR56.
In practice it is common for materials to be supplied with 'dual certification' meaning that the test certificates etc show compliance with both the mentioned specifications.
So it is doubtful if there is any need for concern.
When looking for a modern equivalent, it might be prudent to try for compliance with both specifications.
 

vibrac

Well Known and Active Forum Website User
VOC Member
Now that new blades are being CAD machined from a special alloy bars with a new heat treatment and composition while the originals have been age hardened for sixty odd years can this be little more than historical interest?
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
...can this be little more than historical interest?
Really? It's a little puzzling that someone could own a motorcycle that hasn't even been made for nearly 60 years and write that some piece of information about them is only of historical interest. Almost by definition much of what is written on this Forum is only of historical interest. Much of which I find of interest nonetheless. I hope this doesn't come across as harsh, because I don't mean it to.
 

vibrac

Well Known and Active Forum Website User
VOC Member
Hmmm what I was trying to say perhaps imprecisely is that whatever the original specs its 60 years on and things especially alloys don't stay the same.
and with reference to the new blades being made nor do specifications or manufacturing methods
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
Hmmm what I was trying to say perhaps imprecisely is that whatever the original specs its 60 years on and things especially alloys don't stay the same...
Duly noted. Also, the imprecision that afflicts us all when dashing off something on the internet is why I wrote that I didn't intend my reply to come across as harsh.

The history of the development of the motorcycle is directly linked to the history of advances of materials technology over the past century. Shortly after a better material is developed some of the first applications have been found in airplanes and in motorcycles in ways that improved their performance. As better materials are developed they quickly displace whatever was used previously (e.g. Co steel > W steel > Alnico > SmFeCo > ...). The Al alloys available today have improved properties over the Duralumins of 60 years ago. Still, even though better-than-OEM Girdraulics can be made today using these alloys and CNC machining, I still enjoy having information about what those old alloys were and how the blades were forged.
 

highbury731

Well Known and Active Forum Website User
VOC Member
If new Girdraulic blades are being CNC machined from bar stock, how about making some with the upper fork link bosses a bit closer to the lower link ones? That would reduce the excessive anti-dive and give a more linear wheel movement.
 

vibrac

Well Known and Active Forum Website User
VOC Member
Made to original specification to official drawings what else?
apart from the scandle of non standard parts the US lawyers would see to that little departure from acceptability
You can always fit teles or get an alloy bar and get filing
 

Martyn Goodwin

Well Known and Active Forum Website User
VOC Member
The following has been reproduced from the December 2013 edition of 998, with the approval of the editor of 998.

If you ever find yourself with bent Girdraulic fork blades that require straightening you might be interested in the following information provided by Dave Large, of the Victoria Section.


“The fork blades, part FF40 are made from L40 alloy material which is an old British specification superseded by HE15 which is similar to AS1866-1977 grade 2014.


For straightening or welding first anneal at 360 to 400 degrees centigrade. Solution heat treat at 505 to 515 degrees centigrade for 2 hours. Quench in boiling water then straighten within 30 minutes.


Precipitation harden at 155 to 185 degrees centigrade for 5 hours and furnace cool. This will restore the original hardness of 72 Rockwell B.”


Dave bolted both of his blades together for the process and did not have any problems with distortion.
 
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