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Newbie

th4neuk

New Website User
Non-VOC Member
Hi all,

My first post so hello to everyone.

I guess I have some simple questions really.

What is the availability of the 500cc Comet engine and what kind of price do they go for.

Second one is if they are upgraded to 'Grey Flash' state of tune what kind of relible power outputs can be expected.

Many thanks for any help

Cheers

Alan
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Hi Alan , welcome to our world !!! Can't help with your queries though , outside my experience , although I will say I haven't seen many Comet engines for sale anywhere , even fleabay !!!
 

BlackLightning998

Well Known and Active Website User
VOC Member
Try this....

Hi Alan,

Welcome aboard.

Here are a few thoughts to try and help:

1 - Comet Engine
Try Russ at VinParts - they advertise on this site - his father recently had a box of bits Comet that might still be for sale.

2 - Value ? Mmmmmm
Pretty much they are worth what someone is prepared to pay for them.

Some recent ones I have actually seen sold:

Comet box of bits - all there for the full bike but needed total bottom up restoration with no idea what mechanical work (expensive) needed on the engine - sold for £5000 in April of this year.

Nice Comet - at auction they seem to go for about £7 for a complete and sometimes running bike at the low end to beyond £10 for a nice one. Like everything at auction, all it takes is two people who want it and the achieved price sets a new record. Problem then that lots of other people then believe that that is what one is "worth" - both unfortunate and potentially wrong.

3 - Engine Only
Seen a couple go on ebay over the last year - about £3.5 to £4.5K from memory - you might be able to so an ebay search of past items to find them.
My best advice is to join the VOC, £28 for a year, you get the super MPH magazine monthly where members advertise to buy and sell, occasionally you'll see a Comet engine. There are lots of them under people's benches where they have used the cycle parts for the basis of a Twin. Being a member of the club may put you in touch with someone who'll let you have one.

You'll also get the benefit of full access to this Forum site - including all the members only sections which incorporates the buying and selling section - so you could place your advert and also watch iin case someone posts one for sale. If you're serious about a Comet engine then surely the £28 is a worthwhile investment.

4 - Performance
I am no expert but you can bore them out to 600cc plus - there are many knowledgeable sections members in the VOC who have a lot of experience in race tuning the Comet, again a good reason to join. There is a specific Grey Flash section and they may be able to help you with more specific detail.

5 - Join the club - another reason
Not everyone in the world is a decent type whether in the club or not, joining the club gives you access to the machine register and researcher too, they can check numbers for you - you may not be particularly interested in getting an engine with matching crankcase halves and associated parts that were on the bike when new - but it has been known for people to "clone" Vincent engines and it may be unhelpful for you to spend a load of money on the engine only to find it is a duplicate and you get in a mess with the DVLA, the Police or the Classic race scene - some circuits are now checking numbers and more - even worse would be to buy a stolen engine, they are out there. Joining the club and using the services available won't prevent you from falling into these traps, but they might just help you avoid them.

If we can help with anything else - just ask.

Regards

Stuart

Hi Alan , welcome to our world !!! Can't help with your queries though , outside my experience , although I will say I haven't seen many Comet engines for sale anywhere , even fleabay !!!
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Just thinking about power outputs , 35-40 reliable BHP should be easily achieved as this is half what a twin will comfortably produce with medium tuning. Off course much more could be liberated but then the durability will decline.
 

Comet Rider

Well Known and Active Website User
VOC Member
Comet power outputs

I beleive that if you have a 636cc engine done by Bob Dunn you can expect 48 snarling horses at the back wheel:D

Same as a Rapide!!

Neil

PS
Just dyno'd my 580cc Comet and got 38.6 NP at 47.3 ft/lb torque
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Horsepower

I was 11th at Chimay behind 5 Patons, an MV3, and 4 short stroke Manx Nortons, 90, 92, or 95, whatever, on my (as Norton made them) 86 bore. The bike was pulling 146 mph on the back part of the circuit, 8300 rpm. This means a quick bike, because the rider will never see 65 again.
According to the dyno on which I set up ignition timing, and benchmarked fueling, it was developing 43.6 bhp at its peak, 7200 rpm. This was measured at the rear wheel on an eddy current dyno. An inertia dyno (e.g. Dynajet) would have shown a lot more. A dyno is a comparator, showing how various states of tune work. The figures from different dynos are not comparable.
(It is well known that if one wants to sell a bike to the hard of thinking as super-tuned, then there are certain dynos that give far better figures than others. This is not to suggest that big bore Comets won't pull up tree stumps, but if Bob Dunn Comets are to be compared with, say, Ben Kingham's Comet, it has to be on the same dyno.)
Anyone who thinks that I only know this by reading Graham Bell's invaluable and highly recommended book on four stroke engine tuning is exactly right. And it doesn't set off even the most sensitive bullsh*t detector......
(Dick Linton is the doyen of Aermacchi tuners. He's fond of quoting an American tuner who said "Horsepower sells motorcycles: torque wins races...."
 
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vibrac

Well Known and Active Website User
VOC Member
Tom is so right the dyno we use to tune the Comet shows 39bhp at the back wheel thats on methanol and 13:5 to 1 it could easily show 45 on some dynos
the interesting bit is the efficency of transmission on modern bikes and the loss incured by that thrashing primary thats my next port of call for next season. ;)
Toms mention of Tourqe being the winner is also true especialy with our big bore twin so many twin racers have lost out by over tuning you cannot out handle a lighter bike even with an Egli frame but you sure as hell can out drag em.:D
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Torque

What MAY have made a difference at Chimay was a change of technique. Now I had a torque curve: about 35 at 5200, dropping to 32 at 7200, then falling off much more rapidly thereafter. Ah ha!! There was obviously no point in revving to the mechanical limit, since the grunt was rapidly diminishing. So I shifted at about 6500-7000, only letting it run in top. (The other lesson was that an old fashioned Peel Mountain Mile fairing with a high screen pays off handsomely over 120 mph. I'm damned if I can think of any other reason it should have gone much faster than nominally quicker short-strokes.)
Apropos transmission: I use a belt drive, Newby clutch, and a Schaffleitner replica six speed running (as were the five and four speed that preceded it) on ATF.
Tom is so right the dyno we use to tune the Comet shows 39bhp at the back wheel thats on methanol and 13:5 to 1 it could easily show 45 on some dynos
the interesting bit is the efficency of transmission on modern bikes and the loss incured by that thrashing primary thats my next port of call for next season. ;)
Toms mention of Tourqe being the winner is also true especialy with our big bore twin so many twin racers have lost out by over tuning you cannot out handle a lighter bike even with an Egli frame but you sure as hell can out drag em.:D
 

timetraveller

Well Known and Active Website User
VOC Member
Nice to see a little reality creeping into this discussion on BHP. Our newby is likely to be seriously disapointed if he believes some of the earler figures. For example, Roy Roberston's Egli produces almost exactly 100 BHP at the rear wheel but that is a 1275 cc engine with bore up to 90mm and stroke increased. You would not want to ride Roy's bike in traffic. Increasing the stroke is interesting in that the ratio of the length of a Vincent con rod to its stroke is so extreme that it is not even on the table of what is recommended in modern tuning books. See Tom Gaynor's comments for a good book to start with. When the stroke is increased a shorter con rod can be used to keep the cylinder height the same and this in turn makes the con rod to stroke ratio better. There is one well known club member, who I will not name as he might not want his details publicised, who has progressivley shortened the length of his con rods over the years and they are now half to three quarters of an inch shorter than originals. His 500 engine regularly outperforms all other similar sized engines in the type of competitions he enters. If torque is required then shorter con rods are the answer. In discussions with a professional car engine tuner several years ago about this matter he seemed surprised that this was even a topic of discussion. It seems that in the car racing world there is sufficient money to have engines built with different length conrods and the engines are matched to the requirements of the cicuit to be raced on. So far as I know the only Vincent to be producing 100 BHP from 1,000 ccs on petrol, as opposed to dope, is that of Steve Hammel whos cylinder head modifications were mentioned in this forum some months ago. He has done a seriously large amount of work to obtain that figure and should be heartily congratulated. Most of us are not gong to get that kind of figure out of our bikes.
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
I'm heavily involved in the car tuning world and the motto there is , the head is where the power is !! Simple matter of volumetric efficiency. The head and chamber design of Vincents (post war) was probably near state of the art when introduced , but fuel quality was terrible hence the low CR's. I'm happy with some mild porting work , bigger carbs and increased CR on my Rapide as my preference is for originality and the twin has impressive power & torque even in standard spec. However , for a significant increase in power the head and chamber would need serious modification , requiring a full weld up and re-machine. Then more revs would be required and I'm not sure the standard lubrication system could cope. Also , the mag would probably run into problems with high revs so a modern igntion system would be required.
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Speed and how to obtain it

Hey, good title for a book, no?
While eny fule noe that the Guzzi Gambalunga (literally "leg long") is named for its very long stroke, fewer people know what its bore and stroke were. They were 84 and 90 respectively. Of course if the Vincent had a shorter stroke, the heads wouldn't reach the UFM.........

(Some text from the previous message deleted here) ;6450]I'm heavily involved in the car tuning world and the motto there is , the head is where the power is !! Simple matter of volumetric efficiency. The head and chamber design of Vincents (post war) was probably near state of the art when introduced , but fuel quality was terrible hence the low CR's. I'm happy with some mild porting work , bigger carbs and increased CR on my Rapide as my preference is for originality and the twin has impressive power & torque even in standard spec. However , for a significant increase in power the head and chamber would need serious modification , requiring a full weld up and re-machine. Then more revs would be required and I'm not sure the standard lubrication system could cope. Also , the mag would probably run into problems with high revs so a modern igntion system would be required.[/quote]
 
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th4neuk

New Website User
Non-VOC Member
Thanks for all the replies guys.

The reason why I'm asking is that I have a 1951 formula 3 racing car. You may recall the coopers as the well known name from this time.

Anyway mine is a JP racing car from scotland and it originally had a grey flash engine. The chassis and engine were separated in the late 50's early 60's and the engine is now in a VOC members comet.

As I'm unlikely to ever find a grey flash engine I was looking at maybe using a comet 500cc engine to retain the Vincent heritage of the car.

It originally ran with an Abion TT gearbox but I'm likely to use a norton box as the spares are more available.

I was asking about power as it will be running against JAP and Manx Norton engined machines and I was wondering how close I can get to them.

Obviously being a race car I have to stick to certain tuning guidelines to stay in the regs but I'll look into those in more detail.

Once again cheers for the help.

Alan
 

tonythecat

Well Known and Active Website User
Non-VOC Member
Comet Engine

Hi Alan,
There is a shop in Newcastle, not too far from you, on the famous Westagate Road, called Classic Motorcycles tel:01912614246.

On the shop counter there is a Comet engine, it has been there for more years than I care to remember, it may be for sale? anyhow no harm in giving the guy a ring, best of luck.

Tony
 

Tom Gaynor

Well Known and Active Website User
VOC Member
JP

And JP is of course Joe Potts, sponsor of Bob MacIntyre, and whom I knew quite well. He was also very keen on vintage Sunbeams, particularly Model 90's. A very shy man, Joe tended to allow the light to fall on others, but in fact he was the "tuning genius". There was a time when it seemed that a large part of Glaswegian engineering talent was contributing, possibly unknowingly, to the Potts pursuit of faster bikes and cars......including a desmodromic motor.
Next to me in the paddock at Chimay was Richard Adams, who had an F3 racing car (JAP engined) in a trailer for an event elsewhere. Richard has an article in the current issue of The Classic Motorcycle (which seduced me by having a picture of the first Black Shadow, JRO 122, on its cover). Richard might well be a good start if you were looking for what can and can't be done. I have his email address and telephone number should you decide to pursue this route.
 

th4neuk

New Website User
Non-VOC Member
Hi Guys thanks for that, I'll give the Newcastle Shop a call.

Yep it is indeed a Joe Potts Car. It is one of the early ones which was designed for either a 500 or 1000cc engine. It is the same design as the Ron Flockhart car from that period. I'm guessing if you know of the JP's then you will have come across Sean and Ben Waters? 2 Fabulous guys that are helping me with the restoration.

Cheers

Alan
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Hi Alan,
There is a shop in Newcastle, not too far from you, on the famous Westagate Road, called Classic Motorcycles tel:01912614246.

On the shop counter there is a Comet engine, it has been there for more years than I care to remember, it may be for sale? anyhow no harm in giving the guy a ring, best of luck.

Tony

Now that is truly amazing !! I used to live up in Geordie land too !!
 

timetraveller

Well Known and Active Website User
VOC Member
Hi Alan, you should contact Bob Culver, who manufactures many Vincent parts and who knows more about Vincent history than any one else I know of. He and his son race Vincent 500cc engined cars and as I understand it his son has been national champion in his class for several years while Bob has been up there in the top ten as well. If you do not know how to contact him then contact me privately enw07@btinternet.com and I can send you his phone number.
 

th4neuk

New Website User
Non-VOC Member
Unfortunately the Guy in Newcastle had no info on an engine. I could have had a complete bike though lol.

Cheers

Alan
 

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