I believe Andrews sold the design to Megacycle.
Twin Valve Timing
- Thread starter youngjohn
- Start date
I believe Andrews sold the design to Megacycle.
Is there a similar chart for the Gary Robinson 105 cams for comparison?
Not so. Usually the inlet cam has more lift, as gas volume is accelerated by atmospheric pressure only, while exhaust gas is accelerated by explosion pressure after firing which needs smaller opening to pass the same volume, reducing stress and wear.
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At that point you need to also consider the relative diameter differences in the valves, lift is not the only factor in the scenario
Correct, by the same reason.
When I set my cam timing with Terry Prince 104 cams I did it without even fitting the heads. I put two dial indicators on the engine and they rested on very short push rods that I set into the followers. I think this method takes the measurement very directly and is accurate. Having all the other parts fitted can't possibly help to make it any more accurate. (even though most other people do it that way) I set the timing so that the inlet and outlet cams had equal lift with the engine about 4 degrees before TDC. I think that the figures from Terry suggested equal lift at TDC but I thought a little before was probably wouldn't hurt. The main difficulty was setting the front cylinder as once you set the rear cylinder (which is easy to do because there are 5 keyways) the only way to re set the front to match is by taking the gear off the front cam and re positioning it to get the right result. Once you find out how it is set though it is really easy to find out how many degrees you need to move it to make it right so you should only have to re move your cam gear once. If you have a fitting jig then that setting can quite easily be accomplished.
With the higher lift you have to check the clearances in a lot of places. I found that I had to grind some metal of parts of the valve lifters to prevent interference. I also had to run compression plates under my cylinders because the valves were going to hit the pistons otherwise. John McDougal suggested to me that this was the best way to solve that problem, and since my pistons were 8:1 anyway it seemed like a good idea. It worked well. My bike does 100 MPH in third gear, I haven't found out yet how fast it will go in fourth.
With the higher lift you have to check the clearances in a lot of places. I found that I had to grind some metal of parts of the valve lifters to prevent interference. I also had to run compression plates under my cylinders because the valves were going to hit the pistons otherwise. John McDougal suggested to me that this was the best way to solve that problem, and since my pistons were 8:1 anyway it seemed like a good idea. It worked well. My bike does 100 MPH in third gear, I haven't found out yet how fast it will go in fourth.
You have a bit to go yet Nigel !!, I was timed at 124 mph in third on my road Special !, It was a bit noisey afterwards !!. Cheers Bill.