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Comet ignition timing for 8:1 comp. #555069
07/26/14 8:45 pm
07/26/14 8:45 pm
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
57nortonmodel77 Offline OP
BritBike Forum member
57nortonmodel77  Offline OP
BritBike Forum member
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
Hi all,
a friend dropped off his Comet to get the mag replaced & I will of course need to set the timing after the install. He has no manuals , or specs on the timing. It currently has 8:1 compression.
Can anyone recommend the correct ignition timing either in degrees, or inches before top dead center?

Thank you in advance,

Skip


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Re: Comet ignition timing for 8:1 comp. [Re: 57nortonmodel77] #555187
07/27/14 4:08 pm
07/27/14 4:08 pm
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
57nortonmodel77 Offline OP
BritBike Forum member
57nortonmodel77  Offline OP
BritBike Forum member
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
I am thinking about 1/2" BTDC ?
Thoughts?


Magneto & Dynamo restorations & supplies

My Bikes
1948 Norton 500T Trials bike
1950 Norton Model 7
1952 Norton ES2
1957 Norton Model 77
1960 Norton Nomad 600cc Desert sled
1961 Norton ES2 (slimline)
1964 Norton Atlas Scrambler
1972 Bultaco Alpina
Re: Comet ignition timing for 8:1 comp. [Re: 57nortonmodel77] #555189
07/27/14 4:26 pm
07/27/14 4:26 pm
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
57nortonmodel77 Offline OP
BritBike Forum member
57nortonmodel77  Offline OP
BritBike Forum member
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
I am thinking about 1/2" BTDC ?
Thoughts?


Magneto & Dynamo restorations & supplies

My Bikes
1948 Norton 500T Trials bike
1950 Norton Model 7
1952 Norton ES2
1957 Norton Model 77
1960 Norton Nomad 600cc Desert sled
1961 Norton ES2 (slimline)
1964 Norton Atlas Scrambler
1972 Bultaco Alpina
Re: Comet ignition timing for 8:1 comp. [Re: 57nortonmodel77] #555460
07/28/14 11:23 pm
07/28/14 11:23 pm
Joined: Aug 2010
Posts: 318
New Hampshire, USA
David Dunfey Offline
BritBike Forum member
David Dunfey  Offline
BritBike Forum member
Joined: Aug 2010
Posts: 318
New Hampshire, USA
Originally Posted By: 57nortonmodel77
Hi all,
a friend dropped off his Comet to get the mag replaced & I will of course need to set the timing after the install. He has no manuals , or specs on the timing. It currently has 8:1 compression.
Can anyone recommend the correct ignition timing either in degrees, or inches before top dead center?

Thank you in advance,

Skip


Skip,

With the ATD spring weights open to full advance it should be 36 degrees BTDC for a single plug ignition.

David

Re: Comet ignition timing for 8:1 comp. [Re: David Dunfey] #555500
07/29/14 7:54 am
07/29/14 7:54 am
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
57nortonmodel77 Offline OP
BritBike Forum member
57nortonmodel77  Offline OP
BritBike Forum member
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
Thanks David,

So 36 degrees BTDC would be .414" BTDC.
I have already set it at 1/2" and all seems well, but i'll reset at .414 & see how it does.

It has high compression pistons installed giving 8:1 comp., would I still use .414"BTDC ?

Thank you in advance,

Skip


Magneto & Dynamo restorations & supplies

My Bikes
1948 Norton 500T Trials bike
1950 Norton Model 7
1952 Norton ES2
1957 Norton Model 77
1960 Norton Nomad 600cc Desert sled
1961 Norton ES2 (slimline)
1964 Norton Atlas Scrambler
1972 Bultaco Alpina
Re: Comet ignition timing for 8:1 comp. [Re: 57nortonmodel77] #555532
07/29/14 10:42 am
07/29/14 10:42 am
Joined: Aug 2010
Posts: 318
New Hampshire, USA
David Dunfey Offline
BritBike Forum member
David Dunfey  Offline
BritBike Forum member
Joined: Aug 2010
Posts: 318
New Hampshire, USA
Skip,

That is why I always used degrees, but I would think 1/2" is fine. It is only important if there are other things that are off, because you start second guessing your own work.

If you want to do degrees, because you find something else is wrong, you can make a spindle out of threaded rod and grind the end to fit in the crank shaft oil passage. You can access the crank by removing the brass nut at the bottom center of the timing cover. It is actually not a nut, but a quill delivering oil to the crank bearings. Cut the threaded rod long enough to clear the exhaust pipes and use two nuts to secure the degree wheel. There is a brass nut, or a decorative nut on the timing cover at the top center. I usually put a piece of wire under it as a pointer. Just make sure that whatever goes in the end of the crank is clean and you will be all set.

David

Re: Comet ignition timing for 8:1 comp. [Re: David Dunfey] #555678
07/30/14 10:41 am
07/30/14 10:41 am
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
57nortonmodel77 Offline OP
BritBike Forum member
57nortonmodel77  Offline OP
BritBike Forum member
Joined: Jan 2008
Posts: 324
Concord Township, Ohio
Thanks David,
The only reason I guess I was questioning the degrees was because this engine has higher than standard compression pistons & wanted to be sure I has the timing adjusted for that.
I prefer to use a degree wheel, but in this case I had planned on using my spark plug hole tool simply to simplify the process.

Yesterday I used the 1/2" (40 degree) setting as a test. No pinging under a load & the performance seems very good. I may reset it at 36 degrees (.414) and compare the two settings.

Thank you for the advice on the degree wheel mounting!

All the best,

Skip


Magneto & Dynamo restorations & supplies

My Bikes
1948 Norton 500T Trials bike
1950 Norton Model 7
1952 Norton ES2
1957 Norton Model 77
1960 Norton Nomad 600cc Desert sled
1961 Norton ES2 (slimline)
1964 Norton Atlas Scrambler
1972 Bultaco Alpina

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