E: Engine Comet for the 2020's

[vibrac]

After a long time playing with these engines to obtain speed type performance I find myself a little bemused with my latest engine its a 90 bore Comet and my calculations have got me very near 7.3:1 compression ratio which I guess is about right for a light weight touring machine for long term use (with a nod to the fact my kick will get weaker and the speed limits more policed by electronics and I expect drones). Also amongst all my MK2 and 105 degree cams and exotic stuff I have found a set of MK3's
My thoughts are I should just set the Lucas mag (which has given good service and is quite fresh) at 4-6 degrees BTDC with bob weights closed and let the devil take the fully advanced position (holding a blob of weld in reserve if the advance proves to great). Anyway that is the summation that I have gleaned from sources (including here) comments please

 

[Bill Thomas]

After a long time playing with these engines to obtain speed type performance I find myself a little bemused with my latest engine its a 90 bore Comet and my calculations have got me very near 7.3:1 compression ratio which I guess is about right for a light weight touring machine for long term use (with a nod to the fact my kick will get weaker and the speed limits more policed by electronics and I expect drones). Also amongst all my MK2 and 105 degree cams and exotic stuff I have found a set of MK3's
My thoughts are I should just set the Lucas mag (which has given good service and is quite fresh) at 4-6 degrees BTDC with bob weights closed and let the devil take the fully advanced position (holding a blob of weld in reserve if the advance proves to great). Anyway that is the summation that I have gleaned from sources (including here) comments please

You are right , That's the way to go, A nice soft bike, But I can't bring myself to do the same !, So it's Mk2 cam, Big piston, Big Carb' etc, There is no hope for me !. Cheers Bill.

 

[nkt267]

You are right , That's the way to go, A nice soft bike, But I can't bring myself to do the same !, So it's Mk2 cam, Big piston, Big Carb' etc, There is no hope for me !. Cheers Bill.

And plenty of right hand to keep it in the band.

 

[Martyn Goodwin]

After a long time playing with these engines to obtain speed type performance I find myself a little bemused with my latest engine its a 90 bore Comet and my calculations have got me very near 7.3:1 compression ratio which I guess is about right for a light weight touring machine for long term use (with a nod to the fact my kick will get weaker and the speed limits more policed by electronics and I expect drones). Also amongst all my MK2 and 105 degree cams and exotic stuff I have found a set of MK3's
My thoughts are I should just set the Lucas mag (which has given good service and is quite fresh) at 4-6 degrees BTDC with bob weights closed and let the devil take the fully advanced position (holding a blob of weld in reserve if the advance proves to great). Anyway that is the summation that I have gleaned from sources (including here) comments please

If your advance goes past 36 BTDC AND you have extended runs of 65 MPH + then you WILL end up with a destroyed piston at worst or collapsed ring grooves at best. See OVR Sept 2017 on how to tune the ATD - its not difficult. Aim for retarded @ 4 BTDC and Advanced @ 34 BTDC

M

 

[greg brillus]

Yes if you set up the ATD so it has 15 degrees of travel then you are pretty right, originals have 17 plus if they are worn, too much for modern fuel...........

 

[Martyn Goodwin]

After a long time playing with these engines to obtain speed type performance I find myself a little bemused with my latest engine its a 90 bore Comet and my calculations have got me very near 7.3:1 compression ratio which I guess is about right for a light weight touring machine for long term use (with a nod to the fact my kick will get weaker and the speed limits more policed by electronics and I expect drones). Also amongst all my MK2 and 105 degree cams and exotic stuff I have found a set of MK3's
My thoughts are I should just set the Lucas mag (which has given good service and is quite fresh) at 4-6 degrees BTDC with bob weights closed and let the devil take the fully advanced position (holding a blob of weld in reserve if the advance proves to great). Anyway that is the summation that I have gleaned from sources (including here) comments please

If you change to a lower viscosity multi grade oil such as 10W-30 or 10W-40 you will find it much easirt to kick over. Even PEI recommended lighter oil not heavier

 

[vibrac]

I know that the old refurbisher who died who's name escapes me was starting to reduce the throw from 17 degrees at the end and the table on bright sparks web site gives 47505A/D Lucas for Vincent as 16 to 18 degrees so that seems to tie in. So a bit of weld blobbing would seem in order.

 

[Simon Dinsdale]

When an ATD wears it's in all the pins & links etc and not usually the stops. This makes it sloppy and is usually the reason it refuses to fully return to full retard when you have one in your hand. It's as if the springs are too weak. To overcome this when I have reduced the advance by a bead of weld I have always done it on the retard stops so the springs are working all the time and the slack is taken up when fully retarded. Then retime the bike. Probably doesn't make much difference to the running operation, but just feels right.
Simon

 

[Bill Thomas]

When an ATD wears it's in all the pins & links etc and not usually the stops. This makes it sloppy and is usually the reason it refuses to fully return to full retard when you have one in your hand. It's as if the springs are too weak. To overcome this when I have reduced the advance by a bead of weld I have always done it on the retard stops so the springs are working all the time and the slack is taken up when fully retarded. Then retime the bike. Probably doesn't make much difference to the running operation, but just feels right.
Simon

I didn't think anybody used an ATD any more, They were always bad news, The shock wore out the pinion, Plus bits in the bottom of the T/case !, The "D" Distributor seemed to work better, Don't know why. Cheers Bill.

 

[bmetcalf]

I know that the old refurbisher who died who's name escapes me

Roy Price?