E: Engine Big bore Comet

[davidd]

Radar gun on a long straight with a 600 engine in a racer yielded 105 mph. 500 racer clocked 95 mph. This was decades ago. The 500 racers will now do nearly as well as that 600, but the highest timing slip for the 500 is 100.6 mph, which set a record at ECTA. This is using 7000 as a redline. Coburn Benson used 8000 as a redline on the Flash and clocked 113.7 mph to qualify at Daytona in 1968. I have the original timing sheet, which Ben was smart enough to grab. The bike did have a faring.

On a road racing track with a flying start into the straight, I think 105 mph is the best one can do on a 500 racing Comet. I would usually select a rear sprocket that would turn 105 mph on the straight as I hit 7000 rpm on the tachometer. Assuming that gearing worked well in the other corners, I would stick with it.

I don't think the 600 street Comets go very fast as that is an rpm thing. I suspect many are all done around 80 mph, but they should have very good torque, which is what street riding is all about.

Bill's time sounds spot on. I did 98.75 mph at Bonneville, which was 6 mph above the AMA record. The bike would not rev above 6200 because one of the aluminum head nuts broke and let out the compression at the higher revs.

David

 

[Bill Thomas]

Mine was standard gearing 48 sprocket, I never worked out the rev's,
I would think it was about 6200 ??, And I used 100 octane petrol, Which you could buy at the road pumps in the late 1970s. I had a nice tail wind , But I was 6 foot 3 inches, So not built for speed.
Shame that I am too old now, So if I ever get my long stroke 560cc engine built, I will still never know if it would be quicker.
All Good Fun, Cheers Bill.

 

[Monkeypants]

We saw lots of Comets in the UK.
They work great on the B roads.
Here in western North America a standard Comet has to work awfully hard to climb those long mountain passes. 40-45 mph solo is about it on an 8% grade.
A big bore Comet should be able to come close to maintaining the speed limit while climbing, provided it doesn't seize.
The TP top end with its increased cooling should help with this problem.
But it needs to start on Old Guy power.
Perhaps the new Alton Comet estart is made to handle the oversized engines?

Glen

 

[vibrac]

We saw lots of Comets in the UK.
They work great on the B roads.
Here in western North America a standard Comet has to work awfully hard to climb those long mountain passes. 40-45 mph solo is about it on an 8% grade.
A big bore Comet should be able to come close to maintaining the speed limit while climbing, provided it doesn't seize.
The TP top end with its increased cooling should help with this problem.
But it needs to start on Old Guy power.
Perhaps the new Alton Comet estart is made to handle the oversized engines?

Glen

Well my Alton turns my big job on a 12Ah battery (and its supposed to have an 18Ah) with not a massive CR say 8.5:1
So far it seems a much sturdier product to the one on the twin
I will get a new battery with more capacity to cope with the inevitable multiple restarts when traffic or other problems intervene but its all money.

 

[Gene Nehring]

We saw lots of Comets in the UK.
They work great on the B roads.
Here in western North America a standard Comet has to work awfully hard to climb those long mountain passes. 40-45 mph solo is about it on an 8% grade.
A big bore Comet should be able to come close to maintaining the speed limit while climbing, provided it doesn't seize.
The TP top end with its increased cooling should help with this problem.
But it needs to start on Old Guy power.
Perhaps the new Alton Comet estart is made to handle the oversized engines?

Glen

Glen,

I agree completely having ridden my 500 comet from Vancouver to Montana and back (Like riding from london to Edinburgh 4 times). As you were aware on the return leg its not all that great at keeping up with modern bikes or rapides. Its much more fun plodding around down here on the coast roads in nz.
I have to confess that the solo ride at slower speeds out to Montana was more enjoyable. If its a B road with not too much traffic then life is grand. The moment you get the cars going silly around you like I had sometimes on the number 3 to Grand Forks its not fun to be on a Comet.

E.

 

[Bill Thomas]

I love my Comet and my ex L/ning, What we need is one of those modern Switches that changes Power !,
So we can potter around or Give it one !! .

 

[Chris Launders]

Bill, I have one of them on my Brough, it's a LH twistgrip ADV/RET, as they run tight wire advance you just roll them both back to potter along or wind both on to go,

 

[Bill Thomas]

I have one on my Comet , But when I go Full advance, It's not like the L/ning.

 

[Nulli Secundus]

I think we have wandered off topic now for quite a while. The starting question for this thread is copied below. Thanks.

I have a 600cc Comet. The engine was built by Bob Dunn. It has Pazon ignition for big bore, Mikuni carb and AMC gearbox. I can’t kickstart it for love nor money. It starts immediately on the rollers, runs lovely and ticks over like a clock. Anybody got any ideas? Or is it a matter of lowering the compression or fitting an electric starter?

 

[vibrac]

I think we have wandered off topic now for quite a while.

I think that the answer is 5 posts back #54 get a starter. I am willing to bet a few hundred miles on the beast and the kickstarter will become more effective. The more I read of problems on here, the more I think about the typical original owner in 1960 wheeling his ten year old bike out every weekday morning and riding off to work no sumping problems no starting problems no magneto problems it got him 30 odd miles to work every day in fine style, good value just as fast as the 'modern' unit twins. The basic solution is: Ride it dont hide it, we dont, (and I include myself in this) ride them enough