Non-starting VB

[bob.lowery]

Hello everone, sorry for my lack of response but I have an ongoing broadband fault and whenever I sit at the computer it throws a hissy fit. I hasten to add that I am not looking for technical help with this problem, let's stick to bikes!! Many thanks to everyone for your suggestions, particularly to Paul Jameson for giving the number stamped on the camshaft (A6 664) as I now know that I have the correct one so I can eliminate this from possible problems. Regarding the various suggestions about ignition problems, I am using copper cored HT lead and a low impedance plug cap and a new spark plug. I am confident that there's a good spark in the cylinder by the way that it spits back so viciously!. When assembling the timing gear I have checked that when the dot on the crankshaft pinion is at the top the piston is at tdc also. After that its just a matter of sliding in the camshaft and followers (inlet follower first) and ensuring that the dots align. At that point the engine is at tdc on the firing stroke, both valves closed so after assembling the outer housing that's when I set the valve clearances. I note one suggestion about the electronic ignition giving a wasted spark on the exhaust stroke, but the trigger for the ignition fits on the end of the magneto shaft so it runs at half speed to give one spark every 2 revs, as a magneto does. Regarding the carb it's in good nick, new slide which is nice and snug, new float, and its jetted to the original Ariel spec - with unleaded fuel that may need some alteration (I have found with my other 2 bikes that they run rich on unleaded, anyone else agree?) but it should at least start and run to give a point to start from. When timing the ignition I put the bike in gear and rotate the rear wheel until the engine comes to tdc on the firing stroke, rotate the wheel back from this point to 1/4'' before tdc and set the ignition to spark at this point. I am clearly doing something stupid along the way, but I will go through the routine again and report back.

I hope that everyone is having a great Christmas, and best wishes for the New Year to you all

[paul.jameson]

Bob,
From your description, I think your valve timing may be wrong. When the piston is at TDC, the keyway in the timing pinion should be at TDC. The dot on the timing pinion is one tooth anticlockwise from the keyway - or it should be. I have heard of people having difficulty setting their valve timing because a batch of timing pinions and cam gears, recently made, have the dots in the wrong place. You are ok,apparently, if you change timing pinion and cam gear, but not if you use one of these with an original Ariel matching item. However, this is what I would class as a "sophisticated" fault and your problem might be something simpler, such as a previous owner fitting a slack wire advance mag instead of a tight wire advance one. Your advance-retard cable should run behind the magneto, NOT between the magneto and cylinder, for the correct tight wire advance magneto.

Paul

[ColinPeck]

Once again, to check valve timing without using the marks, both valves should be rocking at TDC non firing stroke. A few minutes job to check on a side valve, even if it's just to be able to cross the possibility off the list of possibles
Colin

[joegibbs]

Just a reminder on setting ignition timing. Bring up to top dead centre on compression stroke, turn back BEYOND the place you want the spark to happen. Then turn engine in it's normal direction of rotation up to the correct firing point. This takes account of slack/backlash between piston etc. and ignition firing point.