Misc: Everything Else Standard Comet Special

Michael Vane-Hunt

Well Known and Active Forum User
VOC Member
I find it not easy to measure spot on, Can you tell us how you did it. Cheers Bill.
20171017_103044.jpg
20171017_103021.jpg
20171017_102909.jpg
 

timetraveller

Well Known and Active Forum User
VOC Member
Oh, I like that. Once I started playing about with cam design I came to the conclusion that something like that would be a good idea. My concept was a little different as I had not considered tapping the holes, Rather I thought of a bronze 'skull' supported under the top face of the timing chest, which would take two curve based rectangular follower which would be hollowed out to take the bottom of the pushrods by spark erosion. I think it would be possible to make those very light to cut down on reciprocating weight. Something like the bucket followers on OHC engines. The only force on the top of the timing cover would be lateral as the holes in the 'skull' would be made to support the followers through the whole of their movement. So many ideas and so little time!!
 

Oldhaven

Well Known and Active Forum User
VOC Member
I guess it has been a while since I posted here, but some progress has been made with sorting out gearbox mounting and the lack of an F106. Since I will be mounting the seat as a cantilever and there will be no tubing connection to the RFM as in an Egli frame I had to come up with a good way to hold the rear of the UFM and engine together. Based on comments that the rake could be varied by using different distances for a F106 substitute, I decided to use adjustable linages with rod ends. Not too unlike the original Grey Flash arrangement with just bent tubing with flattened ends, and that seemed to work out fine. The center link is a LH/RH threaded arrangement for adjustability and the outside links will mount to the outside of the rear UFM mount. I also figured out one of the 10,000 ways to mount a Commando gearbox and went for an adjustable fixing even though I will be using a Newby belt drive. Those"dogbones" holding the adjusters are slotted to allow variation in bolt angles as adjustment is made. The F102 substitute is fairly conventional as these things go. The bolts, rods and plates are not in final form yet, but this is the general idea. It seems pretty solid with all tightened up.

IMG_1029.jpg
IMG_1045.jpg
IMG_1046.jpg
IMG_1049.jpg
 

Chris Launders

Well Known and Active Forum User
VOC Member
Hmm, I think I can see a potential lack of side to side stiffness there, why not use an A frame with eccentrics at one end.
 

Oldhaven

Well Known and Active Forum User
VOC Member
I take your point, if you mean the links and not the gearbox, though the links are amazingly stiff even when the UFM is not bolted up. The original F106 seems to be a bit of an afterthought as it is and these pictures of an early Flash and a modern one used for racing seem to indicate that something like this may be sufficient, if a bit unusual looking. That picture of George Brown with flattened bent tubes seems to make your point, but I guess it worked. I know the links are not going to break but will have to see if it flexes under cornering.
 

Attachments

  • Dell NJ 2018 01.jpg
    Dell NJ 2018 01.jpg
    467.7 KB · Views: 79
  • George-Brown-Epynt-1949-Grey-Flash.jpg
    George-Brown-Epynt-1949-Grey-Flash.jpg
    143 KB · Views: 85
  • Works Grey Flash Left.GIF
    Works Grey Flash Left.GIF
    244.7 KB · Views: 84
Last edited:

RonandLinda

VOC Membership Secretary
VOC Member
VOC Forum Administrator
No, of course it's not! I own one! :p

Check your Vincent history. From memory about 40 "Comet Specials" left the HRD-Vincent factory around 1935-1937. They were also designated TTC. They were basically road-going Series A Comets but fitted with slightly de-tuned TT Replica racing engines with bronze heads, TT Carbs, TT Forks, TT Brakes, etc. Customers could tweak the spec as they wished, but when each left the factory it was a factory standard "Comet Special". :cool:

http://thevincent.com/vinprod.html

Peter B
Bristol, UK.
TTC 20 - Comet Special.
Hi Peter, just as a matter of interest my very first Vin. was a Series 'A' Comet special, TTC19 and I have a photo of it in a magazine being raced. By the time I got it there was nothing special left about it !
Thanks for your help last Saturday. Ron.
 

Oldhaven

Well Known and Active Forum User
VOC Member
Today I bored out the crankcase mouth to accept the TPV 600cc liner. One of those finicky jobs that takes far longer to set up than to do, especially when I have a small milling machine and the boring head and bar just fit under the quill with 1/4 inch to spare below the tool. I machined the CC mouth to 3.814" as per instructions and the liner fits nicely, but as you can see there is a small breakthrough into one of the front stud tunnels. My question is whether anyone else with a TP big bore kit on a Comet has had this problem? Terry's instructions say that the depth of machining should be no greater than 66 mm to prevent this, and I guess for a twin this makes a difference but maybe not a Comet? Now I have to come up with some arrangement to prevent oil leaks along the CC stud.

IMG_1091.jpg
IMG_1097.jpg
IMG_1100.jpg
 

Cyborg

Well Known and Active Forum User
VOC Member
You could just use a flange nut on that stud with the appropriate washer. On some Honda engines, they use a copper plated steel washer under the cylinder stud flange nuts in order to keep the oil in. You could likely get away with a copper washer or an aluminum one if you don't want the copper reminding you.....
The other end of the stud is in the timing chest, so no worries there.

I was going to make a smart ass comment about you buying a riser, and then had another look at the photo of your mill.
 
Last edited:

Oldhaven

Well Known and Active Forum User
VOC Member
That holiday in the stud tunnel will be covered by the liner with just .0005" clearance, so I may just put some permatex or the like there when I slide things together permanently. Good idea about a flange nut, or someone recently mentioned a slight chamfer at the hole and using a tapered washer and sealant or an o-ring. I guess I will get by with something even if I have to fill the stud tunnel with sealant.

I installed the liner in the muff today. At 200C the muff dropped right on the frozen liner. Despite putting some pressure on the assembly while it cooled the liner crept up a few thou. I reheated to 200C after clamping it with four bolts tightened through the stud holes and a big plate placed on the liner flange. That did it. (believe it or not, I still don't have a hydraulic press after all these years.) I was pleased that the cylinder assembly slid right into the rebored case mouth on the tight fitting two piece cylinder studs, so I guess I did the setup correctly.

I have done some interesting things in the past 35 years with that little 3/4 horse Rockwell. It doesn't take up half the shop and runs on 120V. The 10" rotary table kind of dwarfs it, but it worked for this job since it can be placed vertically. I normally use a smaller 8".
 
Top