Twin Valve Timing

[Cyborg]

So took a stab at setting the valve timing. Haven't checked lift at the valve yet, but so far.... set the rear cam for equal lift at 4 degrees BTDC. Gently locked the cam in place. Installed the 1/2 time pinion, but to line up the closest keyway I had to move the crank forward to about 2 degrees BTDC. Then rotated the crank 410 degrees because I figured it would be best for both cams to be timed the same. Put the cam in the freezer and the cam pinion in the oven to warm it up. Then installed the front cam, set equal lift and locked it in place as quickly as possible... ran to get the pinion out of the oven, lined it up to the teeth on the idler and gently tapped it onto the end of the cam ( just enough to get it to hold).... removed the nut and spacer holding the cam and ran over to the press to push the pinion all the way home. So now I have equal lift on the rear cam at 2 degrees BTDC and 2.5 BTDC degrees on the front cam. I assume this is close enough if some folks say that equal lift at TDC would be ok. I'm also assuming .5 degrees difference is just fine given the fact that there is a finite number of times one can remove and replace a cam pinion and the odds of getting it closer while maintaining my sanity is remote.
Just need to set up a forth dial gauge holder and I can plot both cylinders out in one go.

 

[greg brillus]

I will be very interested to see how your engine runs with the new MK 2 cam's of Terry's................I have a box full of them here, if that gives you any indication.

 

[Nigel Spaxman]

I think that if you are within 1/2 a degree that you can't get any closer than that. Mine didn't time exactly the same between the front and rear, but it was pretty close. After setting them my way, I installed the heads with inner valve springs only and checked them a few other ways. I checked the figures with the valve lifts at TDC that Terry had specified it was pretty close to .170". I also compared my engine with some figures for the Megacycle MKII cams that also have 105 degree lobe centers. I think for the Megacycle specs were opening and closing figures at .050 lift. I think Terry's cams had quite a bit less overlap than the Megacyle specs. I wrote it all down somewhere. Terry thinks his MKII 105 cams are the best ones for a road going Vincent, but I guess it depends how fast you want to go. You would think the extra lift and duration compared with the MKI cams can only help. My bike is never going to do 124 MPH in third gear that's for sure. Probably the standard MKII cams are better if you want to go faster.

My bike starts first kick idles perfectly and never pings at all. So far that gas mileage is about 50 MPG which is not that good really. Maybe this year with my new ignition system it will be a bit better. I am installing the Dyna 2000 with a vacuum advance switch. Apparently this can make quite a big difference. I think that with this vacuum switch I will be running a lot more advance when the engine is turning a moderate speeds on part throttle. When I am accelerating hard it will be running about the same as it was without the vacuum advance.

 

[Bill Thomas]

So took a stab at setting the valve timing. Haven't checked lift at the valve yet, but so far.... set the rear cam for equal lift at 4 degrees BTDC. Gently locked the cam in place. Installed the 1/2 time pinion, but to line up the closest keyway I had to move the crank forward to about 2 degrees BTDC. Then rotated the crank 410 degrees because I figured it would be best for both cams to be timed the same. Put the cam in the freezer and the cam pinion in the oven to warm it up. Then installed the front cam, set equal lift and locked it in place as quickly as possible... ran to get the pinion out of the oven, lined it up to the teeth on the idler and gently tapped it onto the end of the cam ( just enough to get it to hold).... removed the nut and spacer holding the cam and ran over to the press to push the pinion all the way home. So now I have equal lift on the rear cam at 2 degrees BTDC and 2.5 BTDC degrees on the front cam. I assume this is close enough if some folks say that equal lift at TDC would be ok. I'm also assuming .5 degrees difference is just fine given the fact that there is a finite number of times one can remove and replace a cam pinion and the odds of getting it closer while maintaining my sanity is remote.
Just need to set up a forth dial gauge holder and I can plot both cylinders out in one go.

Because of the strange firing of our Twins, When you are happy with your valve timing, I think it's worth checking the position of the points opening on the Mag', With the firing stroke of each cylinder, to make sure everything is on the right stroke. Cheers Bill.

Nigel, It was true, But just a bit of Fun !, I should not have done it !, God knows what the rev's were, Standard gearing, 110 mph in 3rd is 6000 !, But I was having a bad day, It only did 124 in 4th, I must have messed up something, So gave it a go in 3rd, If I had thought about it , There was no way I could have gone faster, But we didn't get many goes at the Flying 1/4 mile runs. Cheers Bill.

 

[Cyborg]

I think that if you are within 1/2 a degree that you can't get any closer than that. Mine didn't time exactly the same between the front and rear, but it was pretty close. After setting them my way, I installed the heads with inner valve springs only and checked them a few other ways. I checked the figures with the valve lifts at TDC that Terry had specified it was pretty close to .170". I also compared my engine with some figures for the Megacycle MKII cams that also have 105 degree lobe centers. I think for the Megacycle specs were opening and closing figures at .050 lift. I think Terry's cams had quite a bit less overlap than the Megacyle specs. I wrote it all down somewhere. Terry thinks his MKII 105 cams are the best ones for a road going Vincent, but I guess it depends how fast you want to go. You would think the extra lift and duration compared with the MKI cams can only help. My bike is never going to do 124 MPH in third gear that's for sure. Probably the standard MKII cams are better if you want to go faster.

My bike starts first kick idles perfectly and never pings at all. So far that gas mileage is about 50 MPG which is not that good really. Maybe this year with my new ignition system it will be a bit better. I am installing the Dyna 2000 with a vacuum advance switch. Apparently this can make quite a big difference. I think that with this vacuum switch I will be running a lot more advance when the engine is turning a moderate speeds on part throttle. When I am accelerating hard it will be running about the same as it was without the vacuum advance.

Just before I packed it in for the day, I installed a pushrod in #1 intake and cranked it over TDC. It read .171 lift, so assuming #2 is the same (and it should be), I guess I'm almost done with cam timing. Everything seems good so far, the only thing I'm questioning is the end play on the breather. The breather turns ok and backlash is fine, but there is almost 0 end play if that matters.

The ignition timing will happen shortly Bill. I have a mag that was completely gone through, rewound, new modern condenser etc etc. Had to mortgage my first born, but the nice fat spark will be appreciated. The thought of "getting it to fire on the correct stroke" has been intermittently rattling around in my head for a while. I'll have to sit and think about it for a bit. Any recommendations for degrees of advance with these cams, 8:1 pistons and decent fuel without ethanol?

 

[Cyborg]

I will be very interested to see how your engine runs with the new MK 2 cam's of Terry's................I have a box full of them here, if that gives you any indication.

ummm... you mean a box full of them that you haven't used yet?

 

[greg brillus]

Sorry, Been in engines and removed from further service............But see how you go, maybe you might be more lucky than me. If you set you ignition to 34 degrees full advance you should be fine, as modern fuels burn faster then less timing is needed. You might need also to adjust the stops on your ATD so you don't have as much total range, simply bend all four stops in a bit. The original range of a stock ATD is about 17 degrees, giving 34 crank degrees..........So 5 degrees in the retarded position plus 34 in the ATD = 39 degrees overall advance, but this is way too much nowadays. You still need the retarded ignition to be around 4 or 5 degrees BTDC or else the engine will run hot and maybe hard to start, but you want the overall advanced ignition no more than 34 degrees so this is why you need to reduce the travel range of the ATD from 17 back to 15 degrees of travel. Also when looking at the points end of the magneto the ramp on the camring that opens the points at the bottom when mounted on the engine is the number one(1) firing position counterclockwise rotation from this end of the mag, number one pickup at the rear of the mag closest to the front cylinder, remember number one cylinder is the REAR cylinder. Cheers and good luck.

 

[Bill Thomas]

I have not timed a Twin from scratch for a long time, And I don't do it like you have, But if you do the timing on the rear cylinder then go forward to the next cylinder, I don't think it works right. I seem to remember after doing the first one you have to turn the engine back a bit to start doing the 2 nd one, But it is easy to check, By looking if points are in the right place on the firing stroke, On both cylinders.
I may have lost it !!, The Wife thinks so !!. Good Luck. Bill.

 

[greg brillus]

The ignition timing split between one and two is longer than from two to one. If you consider the firing beat it is more 2-1 2-1 2-1 It is worth checking the timing of the front cylinder as well, and there should hopefully be no more than a couple of degrees difference in the split of the firing intervals. I did have one the other day that was out by 9 degrees. the end alloy housing of the mag was damaged and the cam ring distorted enough to cause the timing split to be so bad. Once I changed the end housing which too the load off the cam ring, the timing came back to within one to 1 1/2 degrees, good as gold.

 

[Bill Thomas]

Sorry, Been in engines and removed from further service............But see how you go, maybe you might be more lucky than me. If you set you ignition to 34 degrees full advance you should be fine, as modern fuels burn faster then less timing is needed. You might need also to adjust the stops on your ATD so you don't have as much total range, simply bend all four stops in a bit. The original range of a stock ATD is about 17 degrees, giving 34 crank degrees..........So 5 degrees in the retarded position plus 34 in the ATD = 39 degrees overall advance, but this is way too much nowadays. You still need the retarded ignition to be around 4 or 5 degrees BTDC or else the engine will run hot and maybe hard to start, but you want the overall advanced ignition no more than 34 degrees so this is why you need to reduce the travel range of the ATD from 17 back to 15 degrees of travel. Also when looking at the points end of the magneto the ramp on the camring that opens the points at the bottom when mounted on the engine is the number one(1) firing position counterclockwise rotation from this end of the mag, number one pickup at the rear of the mag closest to the front cylinder, remember number one cylinder is the REAR cylinder. Cheers and good luck.

You can't trust Vins Greg, I have a Mag where the cam ring is the other way round, It was built by one of our top men and he altered it to Manual for me.
These are Strange Bikes, Cheers Bill.