E: Engine Comet for the 2020's

[davidd]

Interesting bit in MPH this month, Dai Davies says AVO do a special shorter rear Coilover for the Comet Because the wheel base on the Comet is about 1/2" shorter than a Twin, Always thought it, But never got round to checking.
I have shortened the wheel base on my "D" Comet "hobby horse workshop frame ", To get it nearer what it should be, And the rear "D" spring unit does not look right to me !, The spring angle looks not steep enough, I did run a "D" Comet before, But that was with Norton forks and the steering felt QUICK ! ( Trail ? ), I wonder if I should make the F106 a little taller. Cheers Bill.

The shorter damper for the Comet rear might be an answer to a problem nobody had. I think the Comet has a 3/4" shorter wheelbase with the Type 2 RFM. When looking at the design I could not see a reason why the wheelbase should not be shorter or longer. The Phils certainly had the opportunity to mount the swing arm on the Comet further back, but chose not to do so. They could have also used the spring eyes to adjust the Comet suspension differently than the twins. They did not do so. I assumed that they were happy withe the Comet wheelbase and the length of the springs and dampers. That is still not a very satisfying answer.

In fooling around with the rear suspension I have found it to be pretty forgiving. I have used the Reg Bolton mod to jack up, or lengthen the effective damper/spring length dramatically. I have mounted the damper/springs to the side car hole, which is considerably lower and makes the damper/spring almost parallel to the ground. I also ran the racer with a Type 1 swing arm, which is 1/2" shorter than the Type 2. The handling seems unfazed by these changes. I might make the argument that the Comet has better handling with the longest damper/spring combination available, which steepens the rake and provides more ground clearance.

On the upcoming racer I used a UFM that had the attachments snipped of the back. I installed a plate and welded a shock mount to it for a coil over.

The blue Sharpie pen shows where the original mount would have been. I thought this to be a low risk mod because the hole can always be moved forward.

For the F106, when I cast it up I did elongate the top so I could move the mounting hole upwards.

I should have made it much longer. With the UFM holes lined up as marked I got the steering head one degree steeper, which is not much, but every little bit seems to help.

David

 

[vibrac]

Ah indeed the USA is the land of the free..... Free to make modifications to the basic design without the scrutineers banning you from racing because you deviated from the standard design.

 

[davidd]

AHRMA, WERA, SCTA, ECTA and LTA all let you remove or move brackets as long as you are not in a stock Production class. AHRMA states in its rules that Monoshocks are not allowed, except for Vincent Grey Flash (which they apply to all of the post war singles by the "like design" rule.) It is nice to be mentioned by name in the rule book. In AHRMA they don't seem to get to upset with mods unless there is some type of unfair advantage. Tom Kerr (owner of the Flomet) has an Ariel Red hunter with a later swing arm. They won't let him run in Class C because it was only eligible in Class C with the original rigid frame. So he must run in Classic 60's instead. Carleton and I used to bump up to Classic 60's and run with the Manxes and and Gold Stars, but it is nice to run in Class C where the Vincent has a great handling advantage.

David

 

[Bill Thomas]

The shorter damper for the Comet rear might be an answer to a problem nobody had. I think the Comet has a 3/4" shorter wheelbase with the Type 2 RFM. When looking at the design I could not see a reason why the wheelbase should not be shorter or longer. The Phils certainly had the opportunity to mount the swing arm on the Comet further back, but chose not to do so. They could have also used the spring eyes to adjust the Comet suspension differently than the twins. They did not do so. I assumed that they were happy withe the Comet wheelbase and the length of the springs and dampers. That is still not a very satisfying answer.

In fooling around with the rear suspension I have found it to be pretty forgiving. I have used the Reg Bolton mod to jack up, or lengthen the effective damper/spring length dramatically. I have mounted the damper/springs to the side car hole, which is considerably lower and makes the damper/spring almost parallel to the ground. I also ran the racer with a Type 1 swing arm, which is 1/2" shorter than the Type 2. The handling seems unfazed by these changes. I might make the argument that the Comet has better handling with the longest damper/spring combination available, which steepens the rake and provides more ground clearance.

On the upcoming racer I used a UFM that had the attachments snipped of the back. I installed a plate and welded a shock mount to it for a coil over.

View attachment 17851

The blue Sharpie pen shows where the original mount would have been. I thought this to be a low risk mod because the hole can always be moved forward.

For the F106, when I cast it up I did elongate the top so I could move the mounting hole upwards.

View attachment 17852

I should have made it much longer. With the UFM holes lined up as marked I got the steering head one degree steeper, which is not much, but every little bit seems to help.

David

I will have to do some tests to see that there is enough swing on the top "D" unit, On the "D" top frame, Looks a bit tight, Might sleep with a Hydraulic steering damper under my pillow tonight !!. Cheers Bill.

 

[vibrac]

Next 'problem' I have is carburation I am a dedicated Mikuni fan for Comet use my cooking Comet on a V28 (28mm) Mikuni was exceptional from the box with one pilot jet change. Now I have a 90 bore engine the Compression ratio has gone up from my estimate to a tad over 8:1 (mainly because the HD decompressor is full length 14mm) and the head is 32mm at the port I was intending to fit the 28mm Mikuni again and was planning on belling out to 32mm over the Et32/21 inlet adaptor length and was wondering what changes in settings I would need, My alternative is to get a 32mm carb - I think that would necessitate a special 32mm inlet adaptor and a whole new set of settings which I guess Allens (UK) would help with but wouldn't be out of the box like the 28 and really for touring use might be a lot of effort for small return. Comments and setting suggestions welcome

 

[Bill Thomas]

Didn't Ben have mk2 amals on the Egli ?, I am happy with a 30mm mk2, On my worn out Comet with Flash spec, but a rear head, Nice choke and slow running, With most power I have had with a rear head. Cheers Bill.

 

[vibrac]

Didn't Ben have mk2 amals on the Egli ?, I am happy with a 30mm mk2, On my worn out Comet with Flash spec, but a rear head, Nice choke and slow running, With most power I have had with a rear head. Cheers Bill.

Yes but that was to do with the scrutineers, its not my choice of carby for the road and a kick start (carby! Woops getting a bit AU there)

 

[timetraveller]

Tim, if you really want a 32 mm carb adaptor in either aluminium or bronze then contact me. I designed the casting so that they can be machined to take either a clip fitting, a flange fitting or a Mikuni/late Amal rubber adaptor. These are copies of the original Grey Flash and Lightning carb adaptors. I put photographs in MPH a year or two back so that you can see whether they would be suitable.

 

[vibrac]

Well the lack of data on 32mm mikunis seems to indicate I should stick to the vm28 for the moment and perhaps try a bigger carb later, performance at the top end not being a top priority. I will blend in the adaptor and go up a jet size and try that. I also had some trouble holding the pancake filter on the carb with the cooking comet it needed care with the tension of the jubilee clip too much or too little and it popped off is there a different carb end fitting? My thoughts are to go to a cone filter

 

[timetraveller]

Tim, when I ordered a set of 32 mm Mikunis and specified they were for a Vincent the suppliers told me that they knew what settings were required. Have you tried asking them?