2S Cam into an 850

acotrel said:

Any four-stroke motorcycle should start first kick. Some guys go at it like a bull at a gate when they should do things slowly. If you push the piston well up the bore, you only have to flick it past compression and the motor will usually fire-up. If you take a long swinging kick, you will probably get bitten. My mate has a 450 Ducati - the other day it bit him in the ankle and really hurt him. A large capacity single cylinder four-stroke is a serious motorcycle - not to be underestimated.
In my situation, I have a piece of bone missing from inside my knee joint. I cannot afford to get it wrong. I did once with a Bonneville and ended up on the ground.

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Al from your description I don't believe you have ever tried to kickstart start a big single 4stroke
If you tried that with my old BSA b50 you'd be in serious trouble !

Thomasa said:

Back to the 2S cam... At the end of this riding season my ageing right knee began to complain about starting my Atlas. It has a Commando top end and bearings. That's 9:! compression IIRC. It also has the stock Atlas cam again if I remember correctly. Making it an E-start is not an option but perhaps a longer duration cam is along with a T-160 KS lever.

The primary drive has held up well over the years ( I had it apart to fix the side-stand lug last summer and a new alt. rotor) so I'm not afraid of a few more ponies that I might never use. I'm wondering if y'all think it would be worth the effort to change cams for easier starting. I have a spare 2S cam. Maybe just the T160 lever would do the trick. I also have factory Atlas mufflers with the ends cut out of the baffles. They look a bit shabby and I look at those Goldie repops and wonder how they perform... How 'bout Commando pea-shooters? What's involved in putting those on an Atlas frame to match a 2S cam?

I have the rest of the winter to work on it so time isn't an issue except for the Honey-do lists that seem to grow.

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I'd give the t160 kickstart a try first
There's a fair amount of work to make a 2s cam work properly
I don't know from personal experience if the 2s cam makes it any easier to kick
But the 3s dosent from memory

It starts fine. It's just that it puts a lot of pressure on my instep and knee. Not to mention the hardware in my hip from a crash a dozen years ago. I ride my 500 Matchless single more often because it's easier to start. Compression release and all...

Thomasa said:

It starts fine. It's just that it puts a lot of pressure on my instep and knee. Not to mention the hardware in my hip from a crash a dozen years ago. I ride my 500 Matchless single more often because it's easier to start. Compression release and all...

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Ages back there was a picture on here of someone fitting a similar xs1 650 Yamaha valve lifter to a commando
The other alternative is Stihl chainsaw decompression valve

The T160 folding kicker will give you more leverage and if you know how to kick your bike it will be a lot better, a 2S cam won't make it any easier.
Al you seen to not have the Norton kick start knack as what you said is wrong, as you use a roller starter using a grinder to spin start your bike, but then how long ago was that, in your own admission it's been well over 10 years ago.

Ashley

Thomasa said:

It starts fine. It's just that it puts a lot of pressure on my instep and knee. Not to mention the hardware in my hip from a crash a dozen years ago. I ride my 500 Matchless single more often because it's easier to start. Compression release and all...

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Obviously, the longer kickstart is the easiest thing to try, so I’d def do that before tearing the motor down personally.

I‘d also be very interested to hear if anyone has changed the cam, leaving all else equal, and what effect that had on ease of kicking.

When I built my 920 I knew the capacity and CR would present a challenge, I also used total seal rings to make it more of a challenge! But as I was using a Maney race cam (basically a 4S) I managed to convince myself that the long duration would compensate somewhat and make it easier to start.

I was very wrong, as dynodave tried to explain to me in a conversation on here once (Dave, you were RIGHT) !

Of course, I didn’t experiment back to back with other cams, but my experience leads me to believe that you should not expect too much of a difference in kick start lever effort from the 2S cam. And certainly not enough to justify the change and the work involved.

I also wonder about it giving extra power, as the 2S is designed to work with 10:1 CR, is 9:1 enough for it? Or would you just effectively be de-tuning it ?

Even with a 10:1 CR the 2S only improves power above 4,500 ish at the expense of power lower down, so it’s worth asking yourself if that’s what you really want.

Fast Eddie said:

Obviously, the longer kickstart is the easiest thing to try, so I’d def do that before tearing the motor down personally.

I‘d also be very interested to hear if anyone has changed the cam, leaving all else equal, and what effect that had on ease of kicking.

When I built my 920 I knew the capacity and CR would present a challenge, I also used total seal rings to make it more of a challenge! But as I was using a Maney race cam (basically a 4S) I managed to convince myself that the long duration would make it easier to start.

I was very wrong !

Of course, I didn’t experiment back to back with other cams, but my experience leads me to believe that you should not expect too much of a difference in kick start lever effort from the 2S cam.

I also wonder about it giving extra power, as the 2S is designed to work with 10:1 CR, is 9:1 enough for it? Or would you just effectively be de-tuning it ?

Even with a 10:1 CR the 2S only improves power about 4,500 ish at the expense of power lower down, so it’s worth asking yourself if that’s what you really want

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I've known plenty of people to fit a 2s cam and go back to a standard cam coz in the real world it makes a road bike slower
I've never heard anyone say it made it easier to kick over

This is how hard it is to kickstart a Combat 750...

No real difference to my other Commandos, 750 or 850.

B+Bogus said:

This is how hard it is to kickstart a Combat 750...

No real difference to my other Commandos, 750 or 850.

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Viewers should be aware that Mr Bogus is about 8 foot 6 inches tall !!

When you kick a Commando motor over to start it, both valves in one cylinder are closed. How can cam timings or profile change the pressure at TDC ? Different cams only enable a bigger gulp of mixture when the motor is running. I suppose if you stood there kicking the motor over rapidly at about 4000 RPM, the cam might make a difference.
Ashley, every Triumph 650 I ever owned was kick start and had race cams. I have even kick-started a 1000cc Vincent which was on 13 to 1 compression. It is the same procedure - push the piston up slowly up slowly until it is well up the bore, then give it a strong shove. If you kick a four-stroke motor over with the piston travelling from BDC, it will often bite you. The piston only needs to go past TDC to get a spark. The rate at which the piston travels up the bore does not usually change the strength of the spark, even with a magneto.
My electric start for my Seeley 850 needs to be used with 3rd gear engaged. It is powered by an angle grinder and It works, but my motor is only on about 9 to 1 compression. I am to old to bump start it, these days.
I have had old motorcycles since I was 15. When I was 29, I began road racing. Until then, every bike I had was kick start. If the bike will not start by kicking it, a bump start will not usually make it fire up. If you have compression, mixture and spark - it has to start, unless the ignition timing has slipped. Then you will hear it backfire through the exhaust.

acotrel said:

When you kick a Commando motor over to start it, both valves in one cylinder are closed. How can cam timings or profile change the pressure at TDC ? Cams only enable a bigger gulp of mixture when the motor is running. I suppose if you stood there kicking the motor over rapidly at about 4000 RPM, the cam might make a difference.
Ashley, every Triumph 650 I ever owned was kick start and had race cams. I have even kick-started a 1000cc Vincent which was on 13 to 1 compression. It is the same procedure - push the piston up slowly up slowly until it is well up the bore, then give it a strong shove. If you kick a four-stroke motor over with the piston travelling from BDC, it will often bite you. The piston only needs to go past TDC to get a spark. The rate at which the piston travels up the bore does not usually change the strength of the spark, even with a magneto.
My electric start for my Seeley 850 needs to be used with 3rd gear engaged. It is powered by an angle grinder and It works, but my motor is only on about 9 to 1 compression. I am to old to bump start it, these days.
I have had old motorcycles since I was 15. When I was 29, I began road racing. Until then, every bike I had was kick start. If the bike will not start by kicking it, a bump start will not usually make it fire up. If you have compression, mixture and spark - it has to start, unless the ignition timing has slipped. Then you will hear it backfire through the exhaust.

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Al I'd love to see you start a high compression single by bringing it almost to tdc then kicking it through compression!
This tells me without doubt you are talking rubbish!

Most motors usually only bite when you bounce the piston off compression and it reverses. If you push the piston slowly until it is well up the bore, then rapidly past TDC, you do not usually get bitten.

baz said:

Al I'd love to see you start a high compression single by bringing it almost to tdc then kicking it through compression!
This tells me without doubt you are talking rubbish!

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How many singles have you started ? A speedway Jawa can be started by pulling the back wheel around with your hand.

acotrel said:

How many singles have you started ? A speedway Jawa can be started by pulling the back wheel around with your hand.

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One turn of that rear wheel is about 5 revs of the motor. Some of you guys really need to go racing. This is all baby stuff. You learn it in the first 5 minutes.

I will see if I can find some video of my brother racing one of the Vincents. We have lived with this stuff for about 50 years. His best speedway sidecar had a 630cc Jawa single engine. The one meeting he took his son and wife to, in about 15 years - was the one in which he beat 3 1000cc Vincents in one race. He got the standing ovation from the crowd.

If you listen to the Vincent engine in this video, what compression ratio do you think the engine has ?
The guy in the red and white leathers. -

acotrel said:

When you kick a Commando motor over to start it, both valves in one cylinder are closed. How can cam timings or profile change the pressure at TDC ? Different cams only enable a bigger gulp of mixture when the motor is running. I suppose if you stood there kicking the motor over rapidly at about 4000 RPM, the cam might make a difference.
Ashley, every Triumph 650 I ever owned was kick start and had race cams. I have even kick-started a 1000cc Vincent which was on 13 to 1 compression. It is the same procedure - push the piston up slowly up slowly until it is well up the bore, then give it a strong shove. If you kick a four-stroke motor over with the piston travelling from BDC, it will often bite you. The piston only needs to go past TDC to get a spark. The rate at which the piston travels up the bore does not usually change the strength of the spark, even with a magneto.
My electric start for my Seeley 850 needs to be used with 3rd gear engaged. It is powered by an angle grinder and It works, but my motor is only on about 9 to 1 compression. I am to old to bump start it, these days.
I have had old motorcycles since I was 15. When I was 29, I began road racing. Until then, every bike I had was kick start. If the bike will not start by kicking it, a bump start will not usually make it fire up. If you have compression, mixture and spark - it has to start, unless the ignition timing has slipped. Then you will hear it backfire through the exhaust.

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The hot cams I have looked at close on inlet later than the stock cam.
This means that at kickover and at low to mid rpm the hot cams trap less mixture in the cylinder than the stock cam does, so the effective cr is lower with the stock cam. That is why the stock cam makes more power at low to mid rpm and the hot cam makes more at high rpm.
Once the ideal rpm is reached with the hot cam (comes "on cam"), the late closing effect of the cam actually helps to pack a little more mixture in than the stock cam does.

That late closing does ease kickover some, but the effect might be fairly small.
For example, it is enough on my 1360 that I can just kick it thru even with 11 to 1 cr. I doubt that I could manage this with stock cams.

A friend in Norway built a 1200 cc Egli with 9 to 1 cr and less aggressive cams than my 1360. On paper it should be much easier to kickover than my 1360. The cr is a lot lower and the engine is quite a bit smaller. The only thing not in his favour is the less aggressive cam, which is still not as early in closing as the stocker.
He is a sturdy fellow, a mountain biker, but has never been able to kick start the bike nor has anyone in the local vintage MC club. They have all tried and several ride kickstart Norton Commandos that they kick over easily.
He eventuallu fitted an estart type that normally works well on 1000 cc Vins, but the drive just kept shearing off.
End result the bike is bump start only and it requires a big hill at that!

So I think the cam type does make a difference to kickstart effort required, however since there is a huge range of cams out there, it's difficult to say just how much difference it makes.

Glen

acotrel said:

How many singles have you started ? A speedway Jawa can be started by pulling the back wheel around with your hand.

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I'd pay good money to see you start my old b50 or my mates thruxton by bringing it up to tdc and pushing it through !!
What do you think valve lifters are for?

worntorn said:

The 2s does not appear to be a profile for increasing the midrange.
From my reading, the performance cams all gain some top end at the expense of the middle, as compared to the stock SS type profile.
It's a trade off.
You could boost the CR to get some of that below 4500 rpm back. You can also do this with the stock cam and get an even stronger midrange. I'm running a stock cam at 9.8 to one static cr on the 920, no pinking.

Here are Jim Comstock's thoughts on the 2s in an 880.

"The 2S cam will be a little peaky. It will trade a bit of below 4500 rpm power for more power above 5000. Not a bad street cam if you ride in a sporting manner. The fact that the engine is larger does not mean the cam "comes on" earlier but the

fact that the engine is larger does make up for some of the lower RPM loss. It would likely be better on the street with some advance- maybe even up to about 10 degrees.

What I like to do when using the 2S or 4S on the street is grind a 4 inch radius on the lifters. That will give you the advantage of the extra lift without the losses you get with the long duration. That makes for a nice torquey street motor. Then install it with about 5 degrees advance. Jim"

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For folks that want to play with cam timing RGM sells what they call a special camshaft sprocket with 3 keyways. Part number RGM1080. Not particularly cheap, but more versatile than an offset woodruff key.

There was a guy in Melbourne who had a machine which broached keyways. I took my cam sprocket to a mate who put it on a fire brick and softened it by heating with the oxy-acetylene. Then I had two more keyways broached into it randomly. I did not bother to re-harden it. It is probably made from crap steel anyway.

Al Triumphs are a lot easier to kick over than any Norton and yes I have own a few kick start Triumphs even with race cams they are still easier to kick over than a Norton, as well most EI don't fully fire until the second stroke so having a full kick on the kicker is needed, my Joe Hunt takes a full kick on the lever when cold but once it's been fired up for the day will fire up on 1/2 a kick or lazy kick for the rest of the day, my motor has a lot of compression, my mates can't kick it to life and one of my mate's kicks his preunit Triumph with race cam and higher compression and he has troubles kicking my Norton, he just hasn't got the Norton kick start knack.
Be honest Al how long has it been since you have kicked a high compression Norton to life or any other kick start British bike, most of your stories are days gone by, in your own admission its been over 10 since you been on your Norton and the last 30/40 years only been out once or twice a year on the track, you talk about your 500 Triumph race bike, they are easy to kick over, big singles are harder to kick over but if you kick over a high compression Norton then a big bore single be similar style to kicking.
When I first brought my Norton new I was 17 years old and a skinny runt at that, I had skinny chicken legs but I learned the Norton kick start knack real quick and by the way I still have skinny chicken legs.

Ashley