Author Topic: Finding TDC?  (Read 918 times)

Offline Wylyetom

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Finding TDC?
« on: 01.04. 2011 07:47 »
Hi all, after the oil leak I have cleaned and checked the primary Side for any problems and am refitting the mag, I know that it has probably been mentioned on this forum before but as I am new to this can someone please tell me the best way to find TDC and time the mag on my road rocket, I think last time I did it I used cable ties, vernier calipers and lots of tea, I'm sure that you all know plenty of tricks to make it easy?

Offline Goldy

  • Warwickshire, England
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Re: Finding TDC?
« Reply #1 on: 01.04. 2011 10:23 »
I still use the "old 60,s" method. Remove the plugs and take a piece of metal rod about 6" long (150mm) and wrap some masking tape around it. Draw a pencil line around the masking tape. Stick another piece of masking tape down the side of the rocker box. Put the bike into top gear and turn the back wheel after the inlet valve has closed to the point were the piston is rising and then insert the metal rod onto the top of the piston. Keep rotating the rear wheel until the metal rod stops rising (TDC). Put a light pencil line level with the other line. Do this a few times to check the position and when it,s correct scribe the line fully. Measure the timing distance and put another pencil line on the rod i.e 3/8" above the other line and turn the rear wheel slightly backwards to descend the piston. Re insert the rod and rotate the rear wheel forwards until the pencil marks are in line. Wedge open the auto advance and insert a piece of cigarette paper ( have to be thin paper of tissue paper now) between the points. Pull on the paper with light pressure and rotate the mag until the paper just starts to pull out and then tighten the mag nut.  Have fun
56 A10 Golden Flash - Restore, ride, relive.                                          
56 C12 BSA project ongoing

Offline lawnmowerman

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  • 1959 Super Rocket. Kent, England
Re: Finding TDC?
« Reply #2 on: 01.04. 2011 11:12 »
I used the same method as Goldy. Although I bought an SRM piston stop and timing disc I was in a hurry to put the newly rewound mag back and see if it cured my problems (it did). I did not fancy taking off the left exhaust, footrest and primary cover so I made a timing tool from a surplus fencing bracket, thick galvanised wire and some zip ties and filed a groove in the wire at the right settings.
If the primary cover has to come off at some future point I will retime it with the piston stop and timing disc and then make an adjustable piston stop from an old spark plug without the washer with a bolt and locknut tapped down the centre and lock it off at the correct length so that I can use it to stop the piston at the correct BTDC setting for future use (thanks Muskrat for that tip).


1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)