E: Engine Damaged quill

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Gene Nehring

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Comets are very reiable if you ask me. They need to be set up correctly and with care. I have about 5000 miles on a recent rebuild. This includes as a ride to Montana and back from Vancouver BC approx. 2500KM. In the last two weeks commuting to work I have put on 300 miles.

As for the timing I use 34 degrees with a degree wheel. I set the timing like its written in Know thy Beast and the Vincent Service book. I can set it very accurately. I would suggest if you are having trouble timing have a friend assist on one side of the bike. I know its not easy setting the points gap and locking the ATD at the same time. Some people choose to use an aircraft magneto timing unit.

I have an Omega 8:1 piston with Total seal top piston ring (Good top rings are important) and Mark 1 cam. Lucas Magneto and Lucas Generator. All Standard Vincent stuff.
 
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Bill Thomas

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Another trick I was told many years ago, Say if you have been going at a steady 70 mph for a long time, Roll the throttle off every now and again, It brings the oil up to the top of the engine, Don't know how or why ?.
But on my Knackered old Comet, If a car is too close behind, I roll it off and on and cover them in Smoke, They soon back off. Cheers Bill.
 

everiman

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Plug is an NGK B7EV, nice tan color, no sign of blistering, or tiny shiny spheres :)
So far the Comet has returned home on the back of my truck anytime I attempted a ride that was longer than 10 miles. I now realize the first time it stopped it must have seized, although it was free when I stopped, and started up again after it cooled off. The second time there was no doubt about what happened, that was mile 126 of my ownership. I am now at mile 205, new piston (7.3:1 diecast VOC part) and cylinder, and nervous about riding any distance.
I timed it with a degree wheel and the head removed, the tricky bit is making sure it does not move when tightening the atd. Next time I will make a piston stop out of an old spark plug. All my other bikes have points except my 07 Guzzi, many years ago I had an Atlas with a magneto. They were all much easier to set. Interesting factoid, I have a Chrysler 9.9 hp two cylinder water cooled outboard motor, the speed control twist grip moves the timing plate, a lot, not the carburetor. My first outboard, so I don't know if this is normal or unusual. It will empty the gas tank without blowing up as will all my other bikes.
 

Bill Thomas

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The 7 Ngk should be OK, Some of us have had fouling trouble with NGK, I like Champion N5c, But some people are OK with Ngk.
When doing the timing, If you get it where you want it, Then put a socket over the bolt head and give the socket a light tap with a hammer, Which should knock the ATD taper on to the Mag' taper, Then do it up.
I like to clean the oil out of the taper before I put it together. Cheers Bill.
 

davidd

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It sounds like your taper is worn out. I have never done what Bill suggested, but focusing on getting the taper on quick and tight is a good think and that may do the trick.

The Comet is pretty robust and reliable. There seems to be a powerful inclination to build Comet engines with too little clearance in the pistons and small end. If you talk with the long term Comet riders you might have a hard time finding one who seized and engine. I have never had a holed piston or a piston seizure. I think of Glenn Bewley, who is not a delicate little flower and the thousands of fast mile he has put on his Comet. I also think of all the racers over the past twenty years running in AHRMA and I don't remember any of them seizing a piston. In the past two weeks David Tompkins raced his Comet with a new piston and cylinder because he wanted more compression and a Nicasil liner. He came home with two firsts and two seconds, while spending most of his time at full throttle. The bike ran great.

David
 

Bill Thomas

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David, You can add me to the list, I used my Comet on the road, Did sprinting/Drag racing and road racing.
But I have run Specialloid Pistons with race clearance, 9 or 10 thou at the skirt, Only changed 1 piston/Barrel,
Since the 70s.
Because it burnt too much oil, Like it's doing now !, I will see if I can get another year out of it.
I don't think you can count Tony Cording, His is a Special 600cc ? thingy. Cheers Bill.
 

oexing

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Looking at the diagram above I was a bit shocked at these timings: It cannot possibly be right to have full advance at only 2700 rpm with the best combination of springs and bobweights. I invite you to do some Googling for ignition advance diagrams and I believe you will find all sorts of figures showing full advance at over 4000 rpm up to 5000 rpm. On my bikes I´d go for full advance not before 3500 rpm or higher. Don´t you think that might be a factor for hot running engines when you don´t deal with mild side valve or prewar low comp tractors ? I suspect Lucas was mentally still stuck in olden ages when they finally arrived at the atd idea after their old manual lever settings looked long outdated in early fifties. So maybe a bit more of fiddling with the atd springs for more preload would get you better readings and a smoother ride as well when you have no chance of noticing the pinking in the engine that rattles anyway for other reasons. A Comet is just no low comp old banger where too much advance would not matter.
As for accurate timing, I would definitely mill slots into the Lucas mag casting mounting holes for fine adjustments, makes one´s life a lot easier. When they do that on aircraft mags so it should be allright on old bike stuff.

Vic
P1030710.JPG
 

Garth Robinson

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David, You can add me to the list, I used my Comet on the road, Did sprinting/Drag racing and road racing.
But I have run Specialloid Pistons with race clearance, 9 or 10 thou at the skirt, Only changed 1 piston/Barrel,
Since the 70s.
Because it burnt too much oil, Like it's doing now !, I will see if I can get another year out of it.
I don't think you can count Tony Cording, His is a Special 600cc ? thingy. Cheers Bill.
I have always liked Specialloids,pity new ones are a bit hard to find now.I reckon the urge to run low clearance pistons and sealed valve guides causes a lot of our overheating problems.A nice cloud of smoke lets you know the oil is getting to where it is needed!
 

Gene Nehring

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It sounds like your taper is worn out. I have never done what Bill suggested, but focusing on getting the taper on quick and tight is a good think and that may do the trick.

The Comet is pretty robust and reliable. There seems to be a powerful inclination to build Comet engines with too little clearance in the pistons and small end. If you talk with the long term Comet riders you might have a hard time finding one who seized and engine. I have never had a holed piston or a piston seizure. I think of Glenn Bewley, who is not a delicate little flower and the thousands of fast mile he has put on his Comet. I also think of all the racers over the past twenty years running in AHRMA and I don't remember any of them seizing a piston. In the past two weeks David Tompkins raced his Comet with a new piston and cylinder because he wanted more compression and a Nicasil liner. He came home with two firsts and two seconds, while spending most of his time at full throttle. The bike ran great.

David
David and Co,

You are on to something with the taper in the end of the magneto. Everman this is a real issue with standard lucas magnetos, the taper is a press fit into the armature housing and often is loose enough to create erratic spark. I had this happen to me early on with my bike. Armiture repaired the problem with timing and spark went away. The lucas racing units were a one piece and not pressed like the standard items. I do not understand for the life me why.

Also the guys here in Vancouver, Dan, Dale and Robert all run more robust ATD springs. Which is where I got mine.


Best,

Eugene.
 
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greg brillus

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The steel shaft on the standard armatures has a square end at the opposite end of the taper and is cast into the brass housing. These do come loose which is irreparable, unless you replace this end housing. The racing ones were machined from one piece in stainless steel and give no trouble. The main issue with reliability or unreliability of any of these engines many time comes down to the after market components fitted, mostly ignition and carburretion. If you get either of these wrong, the engine will suffer, and given it is air cooled the effects will show up quicker than a liquid cooled modern engine. Because so many of these items were not installed at the factory, then the test pilot is you. I agree that it is entirely possible that the advance on these engines comes in too soon. If you look at the BT-H type advance unit, they get to full advance way too early. I had a later model Venom that would ping very easily due to the engine going to full advance way too soon, and I had to rework the clock-spring to slow the advance down, this definitely helped and the engine was far happier for it.
 
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