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E: Engine Thorspark on a Comet


James B

Website User
VOC Member
My 229 works OK, petrol taps do not leak (they are new). I gather most of them leak. I am not surprised as 70 years old. I will fit the Concentric at the weekend. Going back to main jet sizes, my 229 also has a 200 main jet so I am going to try that first. On the subject of the mag, I have fitted a Thorspark coil ignition from Sussex motorcycles. The unit fits inside the mag which does not need to be removed. You will have to find a place to fit the coil, I have fitted mine on the engine support next to the battery. You will also need a switch so it can be turned on and off. I made a bracket to fit in existing holes in the rear engine mount for the coil and the switch. This unit uses very little from the battery. I have a gel type battery in a dummy case (like most people I suspect).
I have a thorspark on order, due later this week. Glad to hear it’s a good thing :)

(Shared for amusement factor)
Also have a gel battery on order - should fit in the exide fake case. Found a convenient seller on eBay - who messaged me last night to say that they sold it to me without vat (they usually sell it to mobility carriages) and that I should send them my disability certificate to prove my right to the exemption ! Harrumph ! I’ve asked them to sort this out. Presumably they’ll send me an invoice for the difference

J
 

peter holmes

Well Known and Active Website User
VOC Member
It depends on how kind you feel, they should have checked your eligibility to receive goods without paying VAT due to a disability (which you do not have) they could just reissue an invoice with the gross figure that you have already paid, to include the VAT content and take the hit of the VAT themselves.
 

b'knighted

Well Known and Active Website User
VOC Member
You have to remove the points and the cam but it can be done with the mag in situ. If you set the engine to firing point before removing the mag points it may even be possible to fit the Thorspark rotor and stator without retiming. I wish I’d thought of that before doing the conversion!
 

Tony Wilkinson

Website User
VOC Member
Can you just confirm that you don't have to take the Mag' apart, And just sort the end cap ?. Cheers Bill.
Yes, just take out the points assembly and remove the cam ring (which can be quite tight). The new unit fits inside. I had to buy a deeper cover as the standard one would not fit back on as the new unit sticks out more.
 

timetraveller

Well Known and Active Website User
VOC Member
Bill, I think that is exactly what it is. Instead of points they are relying on what I think is a Hall Effect diode for the switching and the ATD for the advance and retard. The diode will have the same effect as the points by switching the power to the coil except that there should be no maintenance. It will either work or it wont.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Thanks, I didn't understand,
Bit like they used in the 70s on cars.250 seems a lot, Its only 75 for a distributor.
Cheers Bill
 

Tony Wilkinson

Website User
VOC Member
Bill, I think that is exactly what it is. Instead of points they are relying on what I think is a Hall Effect diode for the switching and the ATD for the advance and retard. The diode will have the same effect as the points by switching the power to the coil except that there should be no maintenance. It will either work or it wont.
Agreed, I like the whole fit and forget idea, nothing to adjust or wear out once fitted.
 

vibrac

Well Known and Active Website User
VOC Member
I suppose those with original dynamos trust Mr Miller dynamo more than Mr Lucas Mag what could be described as Hobson's choice :)
 

Bill Thomas

Well Known and Active Website User
VOC Member
I have a manual old type BTH on my old Comet, Been on there forever !, Racing / Road etc.
But I like Options. Cheers Bill.
 

James B

Website User
VOC Member
Looks like I’m going to need to use a strobe to time up the thorspark. I’ve always used a rod down the bore to measure piston position to time the mag but that’s not going to work here

Any thoughts on where I can get a timing mark onto a comet? Best I can think of is run it without primary cover, and mark up the front pulley. Anyone got a better idea?
 

Bill Thomas

Well Known and Active Website User
VOC Member
We did it the other day, With a standard ignition, By making a mark at the points and the body, But it being half speed, It's Plus or min' a bit. Cheers Bill.
 

timetraveller

Well Known and Active Website User
VOC Member
ClevTrev used to sell a device which fitted into the big end quill position, had a CD fitted to the shaft which was scribed with degree marks and which would allow the engine to be run with oil still going to the big end and allowed one to use a stroboscope. It was a clever bit of kit. I don't know if he still has any but if not maybe someone on this forum who lives near you might still have one.
 

Tony Wilkinson

Website User
VOC Member
Looks like I’m going to need to use a strobe to time up the thorspark. I’ve always used a rod down the bore to measure piston position to time the mag but that’s not going to work here

Any thoughts on where I can get a timing mark onto a comet? Best I can think of is run it without primary cover, and mark up the front pulley. Anyone got a better idea?
When I fitted mine, I removed the primary cover then used a rod to find TDC, marked the (inner) part of the rotor. Then attached a thin wire with a screw on the case and lined up with my first mark then marked the rod to find the BTDC and marked the rotor again. Line this mark up with the wire and you can fit the rotor. I checked my settings a few times before I was happy to fit the new rotor. I then fired up the bike and set with a strobe light making sure the marks lined up on full advance. It is a bit of a faf but works ok.
You can do the same thing using a timing disc but this method works ok.
 

peter holmes

Well Known and Active Website User
VOC Member
There are far better methods of finding TDC than a rod down the plug hole, using that method it is almost impossible to be degree perfect, Know Thy Beast gives a very good description of the best method to use.
 

timetraveller

Well Known and Active Website User
VOC Member
I agree. A stop down the plug hole and then rotate the engine both forwards and backwards till the piston hits the stop. Note the degree plate readings, split the difference, adjust the degree plate and then go back and check it at least once.
 

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