Author Topic: comet (Read 11170 times)

ERIC BAYLISS · « **on:** 06 Jul 2012 at 20:37 »

HI CAN ANY ONE PLEASE TELL ME WHAT CARB SHOULD BE ON A 250 COMET AND WHAT SIZE JETS SHOULD BE IN IT> THANK YOU>

ERIC BAYLISS · « **Reply #1 on:** 11 Jul 2012 at 20:38 »

ANOTHER QUESTION, CAN ANY ONE TELL ME WHAT THREAD IT IS ON THE CRANK,I NEED THE NUT THAT HOLDS THE CLUTCH FLY WHEEL ON. OR BETTER STILL HAS ANY ONE GOT A SPARE NUT.

Doug · « **Reply #2 on:** 13 Jul 2012 at 23:59 »

Eric,

Flywheel thread on the 250-350cc models like the Comet was 5/8-20.

-Doug

eddie · « **Reply #3 on:** 14 Jul 2012 at 13:59 »

In that case, Eric, you could try Postwar Spares for a rear wheel nut for a Mark series machine (they are 5/8" x 20tpi).

Regards,
Eddie.

ERIC BAYLISS · « **Reply #4 on:** 01 Aug 2012 at 12:32 »

Im still trying to find out what carb was on the 250/350.can any one please tell me what size it would be, it must be rather small acording to the flange on the manifold thank you

Doug · « **Reply #5 on:** 02 Aug 2012 at 01:43 »

Eric,

Douglas did not publish a handbook for those models that I ever saw, to specify the jet sizes. I would think the body itself it would have been whatever the Amal equivalent of the 274 was of the day.

-Doug

eddie · « **Reply #6 on:** 02 Aug 2012 at 08:15 »

Eric,
Attached is a scanned copy of the specification page from the 1934 publicity sheet. Regarding the carb, as Doug says - an Amal 74 or 274 with a .75" bore should be suitable - maybe the carb from a BSA C11 would be a good starting point.

Regards,
Eddie.

ERIC BAYLISS · « **Reply #7 on:** 02 Aug 2012 at 20:42 »

Hi Lads, thanks for the info, had a bit of luck and bought a pitmans book on the douglas for 1936,and in the maintenance it gives the carb numbers for the250,350 600 500aero and the endeavour.it lists a 74/007 21/32,with60 main jet4/4 slide and a62/079 needle.for the 250.so now I have got something to compare a later one to.thanks again eric

ERIC BAYLISS · « **Reply #8 on:** 10 Aug 2012 at 20:35 »

I am now in the process of making the cams but am still stuck for the small 20tooth gear that goes on the crank.can any one one please help. or make a good sugestion. thanks.

ERIC BAYLISS · « **Reply #9 on:** 12 Aug 2012 at 20:43 »

Just another question, can any one tell me when they stopped puting the keyway in the crank for the fly wheel clutch. Ive got one crank with a keyway and one without. thank you eric

ERIC BAYLISS · « **Reply #10 on:** 19 Aug 2012 at 13:45 »

I am still desperatly looking for the 20 tooth gear that goes on the crank,there was a mention some time ago of using old british lathe gears, unfortunately they are now as difficult to get as douglas spares.can any one help please even with a good idea. thanks eric

eddie · « **Reply #11 on:** 19 Aug 2012 at 14:07 »

Eric,
Surely, if you have found someone to re-manufacture the cam and its 40 tooth gear, then they ought to be able to make you the matching 20 tooth gear.

Eddie.

eddie · « **Reply #12 on:** 19 Aug 2012 at 14:24 »

Eric,
If you're still stuck, try Googling 'HPC Gears'.

Eddie.

ERIC BAYLISS · « **Reply #13 on:** 19 Aug 2012 at 20:47 »

Hi Eddie no I have not found someone to make the cam gear,I am making the cams myself by using modified mag gears.and turning the cams up myself.

ERIC BAYLISS · « **Reply #14 on:** 19 Aug 2012 at 21:01 »

Ive already tried hpc but they need either a patern or a good drawing with all of the measure ments on, unfortunatly I have not got one in either of my engines.so that is why I am stuck.I have not even got a worn out one that I could use as a patern

Doug · « **Reply #15 on:** 20 Aug 2012 at 01:10 »

Eric,

The pinion is, as you noted, 20T. The thickness is a uniform 0.375" (no bosses or hubs). Bore is 0.6255 or so, to suit crankshaft. Three 1/8" key ways (more like 0.127" wide) equidistant to allow split-tooth timing adjustments. One key way lined up with a tooth space, but I doubt that it critical.

Doug

21Aug12, fix typo. Doug

Jim · « **Reply #16 on:** 21 Aug 2012 at 08:21 »

Hello Eric,
I am not familiar with comets but if your magneto gear is 2.1 inch diameter (2 3/32 approx) then it is 20 diametral pitch or D.P. If this is the case then Myford change gears are the same and their 20 tooth gear is .375 wide with a .625 hole and a .125 keyway.If you Google Myford 20 tooth gear you should get something, or on British Ebay if you can find item number 120832582644 it is one. I imagine that a 20 tooth would be made out of steel, cast iron wouldn`t be any good. If your gear isn`t that size then all this is redundant and if you let me know what size your gear is I can at least work out what D.P it is. There used to be a firm in Oz that would sell you blank gears so I would imagine there should be somewhere in the UK that would also,
regards Jim

ERIC BAYLISS · « **Reply #17 on:** 21 Aug 2012 at 20:31 »

Thanks lads thats great information.

ERIC BAYLISS · « **Reply #18 on:** 23 Aug 2012 at 12:49 »

Hi Jim bought a 20 tooth myford gear unfortunately the outside diameter is wrong.it only measures 27.58. instead of 30.82. altough the hole is perfect.the mag gear is just as you said. hope you can help with this measurment. eric

eddie · « **Reply #19 on:** 23 Aug 2012 at 17:47 »

Eric,
Most prewar Douglas timing gears are 18DP - I know you say you have already contacted HPC, but they list a standard gear in their catalogue that is 18DP x 20T x 12mm wide with an O.D. of 31mm - the price is £12.52. Surely, this would be a good starting point - you would only have to open out the bore to suit your crankshaft and then cut the keyway.

Regards,
Eddie.

Jim · « **Reply #20 on:** 23 Aug 2012 at 20:32 »

Hello Eric,
what is the diameter of your magneto gear? regards Jim