F: Frame F106 Dimensions
- Thread starter Howard
- Start date
Howard,
The Factory used DTD 424 for the material of the original. I found it difficult to machine an F106, which I cast, to fit my BAR gearbox because there is no obvious reference mark on the casting. Thus, it is difficult to start by machining one dimension. I had to machine a bit on the timing side and then do the same on the drive side. Then look at it and see if the machining looked even with the casting.
I used a spare F106 to put on the mill and measure in order to get the dimensions straight. I was not able to get the 1/2" bolt holes in exactly the same place despite careful planning. I should have mounted it on its side on the mill and used the DRO to place the 1/2' holes. No harm done as the special F106 would not be interchangeable with the original, because I was using a different gearbox. That would probably not work well for you.
Additionally, you have to figure out where the shrinkage is on the casting you have. I worked from the bottom up and cast the top mount to be very tall. This allowed me to compensate for the shrinkage. It was also tall enough to raise up the back of the UFM and steepen the rake, which worked out quite well.
David
The Factory used DTD 424 for the material of the original. I found it difficult to machine an F106, which I cast, to fit my BAR gearbox because there is no obvious reference mark on the casting. Thus, it is difficult to start by machining one dimension. I had to machine a bit on the timing side and then do the same on the drive side. Then look at it and see if the machining looked even with the casting.
I used a spare F106 to put on the mill and measure in order to get the dimensions straight. I was not able to get the 1/2" bolt holes in exactly the same place despite careful planning. I should have mounted it on its side on the mill and used the DRO to place the 1/2' holes. No harm done as the special F106 would not be interchangeable with the original, because I was using a different gearbox. That would probably not work well for you.
Additionally, you have to figure out where the shrinkage is on the casting you have. I worked from the bottom up and cast the top mount to be very tall. This allowed me to compensate for the shrinkage. It was also tall enough to raise up the back of the UFM and steepen the rake, which worked out quite well.
David
Thanks David. Maybe a fabrication would be a better option. Some thought needed.
I seem to recall the first Grey Flash had a fabricated steel F106, and a BAR type gearbox. My memory is unclear on this. Can anyone enlighten us please? Good period photographs on racingvincent.co.uk WARNING: from time to time on Greedybay there are parts made by chancers that are nothing more than backyard castings from original items put in sand moulds. They are therefore too small, not heat- treated and are not trustworthy as to strength or composition. On a critical part such as this I would go warily. Some years back, before I departed the fold, a bloke in the U.K. had a good article in "M.P.H." detailing an alloy fabricated F106. He appeared to have thought it out methodically.
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I do believe that the F106 and F106/1 can be very highly stressed in service. Generally, they are not put to hard work except in racers or sidecar machines. If the plates on either side of the F106 are not well-designed or improved, the item will crack in several places. This is unlikely to occur on a street bike, but if you are planning to use the bike in competition, it is a concern.
The Stilltime photos of the Grey Flash prototype show steel tubes used instead of the F016.
This set-up would not be very rigid, but considering the tire technology and the track conditions at the time, it appeared to be a suitable choice.
I think steel could be a good choice if fabricating an F106 is necessary and sidecar or competition work is contemplated. Using a light steel box construction would appear to be a good choice if something special is desired. Grade 8 bolts seem to be mandatory. The 6061 plates seem to work fine, but I use 3/8" width, not the original 5/16". I use 7075 on the primary plate.
Weakness in this area can cause chassis wind-up, rear damper breakage, F106 breakage, RFM twisting, and gearbox shell damage. All of this is easy to prevent through a more robust design, but it does add some weight. I have always believed that this is the best area on a Comet to be overweight. The twin does not have this problem as it is unit construction.
David
The Stilltime photos of the Grey Flash prototype show steel tubes used instead of the F016.
This set-up would not be very rigid, but considering the tire technology and the track conditions at the time, it appeared to be a suitable choice.
I think steel could be a good choice if fabricating an F106 is necessary and sidecar or competition work is contemplated. Using a light steel box construction would appear to be a good choice if something special is desired. Grade 8 bolts seem to be mandatory. The 6061 plates seem to work fine, but I use 3/8" width, not the original 5/16". I use 7075 on the primary plate.
Weakness in this area can cause chassis wind-up, rear damper breakage, F106 breakage, RFM twisting, and gearbox shell damage. All of this is easy to prevent through a more robust design, but it does add some weight. I have always believed that this is the best area on a Comet to be overweight. The twin does not have this problem as it is unit construction.
David
We have machined F106 in stock.
The owner says they're too expensive - sorry, not my decision to make.
What dimensions do you require ?
If he has spent that much then I would have thought that an extra £231 would be worth it to get the bike built.I'll have to discuss it with the owner. At the moment he's got a rebuilt engine and a lot of shiny frame parts that are short of the bit that holds the middle together.