Cams (2012)

marinatlas said:

Hi, is someone able to tell me the radius of the BSA cam followers??

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Standard BSA is 1 1/8 inch

Dolis said:

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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Thanks Jim!
I might try that.
Is there really a big differens on the road between the 2S and 4S?
I´m very satisfied with my 4S in my 828 cc engine.
When I first tuned it, from std 750, I felt I gained a lot of power all over.
I believe the exhaust is the same but the intake differs with less duration on the 4S.
Chris[/quote]

The 2S and 4S are pretty similar. I little wider powerband with the 4S. If you increase the compression ratio from 8.5 to 9.5 when you switch from a standard cam to a 4S cam you will usually stay about the same up to 4500 and then you will see a gain from there up. A 2S cam will not out-power a standard cam until around 5000 with the same compression ratio increase. Jim

hi Jim, with my Bike #2 engine, have decided on JS internals, 32mm flatslides on a revamped head using the specs and pics you posted/ sent me and a JS stage 1 cam, would you recoomend a re grind/reradius with the followers?
Will read the crank shaft threads to get the correct % balance with these internals.
Would a 3mm gasket suit this build?
Regards Mike

Brooking 850 said:

hi Jim, with my Bike #2 engine, have decided on JS internals, 32mm flatslides on a revamped head using the specs and pics you posted/ sent me and a JS stage 1 cam, would you recoomend a re grind/reradius with the followers?
Will read the crank shaft threads to get the correct % balance with these internals.
Would a 3mm gasket suit this build?
Regards Mike

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The JS1 grind should be good on the street with the standard 1 1/8 BSA lifter. Jim

Thanks for the advice
Regards Mike

I am using a combat cam in my motor with a 2 into one exhaust system. I've advanced it 15 degrees from standard, and it seems to be excellent. I am wondering if anyone else has done this ?

My Seeley 850 commando:

I have JS stage 1 with BSA lifters, Combat head, tuned 1 1/2" exhaust.
Cam is advanced 10 degrees. Strong down low, mid range monster, more than adequate up top.

acotrel said:

I am using a combat cam in my motor with a 2 into one exhaust system. I've advanced it 15 degrees from standard, and it seems to be excellent. I am wondering if anyone else has done this ?

My Seeley 850 commando:

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The cam grinders don't always get the key way perfectly located it is necessary to check the cam timing and adjust it as you & Pvisserill have done. I'm on them to get it right but it takes a few tries. Thats one mean & nasty looking Seeley.

If I understand the comment from Alan it is not an accidental timing shift due to keyway misalignment, he is making a deliberate change in the cam timing.

So, and again, if I understand him from comments on other forums he is making changes to suit things like the exhaust system.

I think Alan is asking for feedback from others who are doing the same, deliberate adjustment away from supplier figures.....

Of course just fitting the cam as is has the potential for misalignment you mention....I assume you recommend timing by degree wheel and using offset keys if needed to remove what is I hope minor misalignment?

The way I see it there are three ways to do it:

1 Just put it in with no checks, which must carry some misalignment risk
2 Put it in with adjustment to supplier specs, better than 1 surely everytime and seems sensible for any race motor as long as everything else is pretty much as the supplier anticipated for use with that cam
3 Put it in with adjustment suit your own complete inlet, exhaust, compression and ignition set up...and use, which might include personal riding style as well as discipline....but I would also suggest this all depends on you knowing something about the needs of your own set up...but get it right and it could be better than 2....

On 3 I assume the potential realignment of the pinion and chainwheels is also in scope to achieve what you want....

I think Alan is interested in 'yes or no and what works?' comments on 3, I have to say I am interested in that too, even if having selected my cam I am likely to do 2.

Steve

SteveA said:

If I understand the comment from Alan it is not an accidental timing shift due to keyway misalignment, he is making a deliberate change in the cam timing.

So, and again, if I understand him from comments on other forums he is making changes to suit things like the exhaust system.

I think Alan is asking for feedback from others who are doing the same, deliberate adjustment away from supplier figures.....

Of course just fitting the cam as is has the potential for misalignment you mention....I assume you recommend timing by degree wheel and using offset keys if needed to remove what is I hope minor misalignment?

The way I see it there are three ways to do it:

1 Just put it in with no checks, which must carry some misalignment risk
2 Put it in with adjustment to supplier specs, better than 1 surely everytime and seems sensible for any race motor as long as everything else is pretty much as the supplier anticipated for use with that cam
3 Put it in with adjustment suit your own complete inlet, exhaust, compression and ignition set up...and use, which might include personal riding style as well as discipline....but I would also suggest this all depends on you knowing something about the needs of your own set up...but get it right and it could be better than 2....

On 3 I assume the potential realignment of the pinion and chainwheels is also in scope to achieve what you want....

I think Alan is interested in 'yes or no and what works?' comments on 3, I have to say I am interested in that too, even if having selected my cam I am likely to do 2.

Steve

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Actually two is probably not much better than one. Unless your engine is identical to the engine the cam was developed for then you will not be taking advantage of the resonances of the intake and exhaust system and combustion chamber.

You can almost always find a few more ponies available with time spent on a dyno playing with cam timing.

The other option is to install the cam to the makers spec and then play with the intake and exhaust system until it works with the cam. Jim

I think first and foremost is the need to check for valve clash.
Willy nilly plug and play could cost you big time. Anyone talented enough to swap cams better be talented enough to dial it in. Then and only then should you attempt to adjust to suit you mood.

Peter said:

I think first and foremost is the need to check for valve clash.

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excellent advice

When I rebuilt my 850 motor I put in larger valves and a Megacycle 5600 cam.

The valves touched, as determined with the head on and rotating motor

had to take the new valves to a local machine shop and take 10 thou off all the around each valve

How much clearance does that leave you with?

When I set the cam timing up, I heated the sprocket to soften it then broached two more keyways into it. I used to race a bike with a Triumph motor in a featherbed frame. It was a 650 which was stroked down t o 63mm to give 500cc. I used a two int o one exhaust to get some torque so it was rideable. The cams were extremely long duration, but I found that the exhaust opening position was critical. If it opened before 85 degrees defore BDC, the exhaust got louder and the bike got slower. The way my Norton is currently set up the cam is intentionally advanced, and naturally the exhaust is closing early, but with the extractive exhaust, it all seems to work OK. It's probably a case of an error fixing an error. There is nothing flash about the motor. It has 34mm Mk2 Amals with tapered ports and runs on methanol with standard compression,standard valves. I've been running a CR box, but first gear is too high for our cluthch starts. So I recent ly sold a TZ350G and bought a TTI six speeder with the money. I haven't used it yet, but first gear is halfway between a standard commando ratio, and that of a manx. With the old four speed CR box, the motor used to come up very quickly through the rev range, and it was very difficult to keep it below 7,500 rpm. When I first raced the bike, I put the gearing up to knock its backside in, it just went faster. Most of our local circuit is very tight , with the CR 4 speed box, the bike was perfect everywhere except off the line. With the 6 speeder it should be a really convincing argument.
I'm using TZ350 fork yokes on the MK3 Seeley frame. With the 27 degree head angle the bike steers on the throttle, and when you are early in a corner , you can gas it really hard and as the weight comes off the front end, it will move in the direction in which it is laid over, so you never end up fighting it away from the edge of the bitumen. ( If it had another 10 BHP, you wouldn't do that.) When I first raced it, it was fitted with Ducati yokes with a lot of offset. Under brakes it stood up and turned, and nearly decked me. I turned it on again to drive it onto the grass, and it laid down again. - dangerous stuff. It is now the best handling bike that I've ever ridden.
The reason that I asked the original question, is that I'm amazed that such a crude motor can respond so well to a bit of fiddling. I've concentrated on torque rather than horsepower, and I find the comments about bigger valves and ports interesting. I wouldn't go down that path - what happens to the gas speeds?

The follwing is a reply I've made to a private message, might be of interest :
There are a couple of guys in our historic races who play with old matchless singles. I looked down the inlet port of one of them and it was huge. I said to them that if they bought a two valve Jawa speedway motor, they would start where the finished with that old garbage. They bought about three motors, and installed one in their featherbed framed racer. First time out it beat a good rider on a McIntosh (Walmsley) manx Norton. I mentioned to Neil Street one of our better speedway tuners, that they'd done virtually nothing to the motor. No rebalancing, cam mods or or porting. Neil said that on the speedway they are really buzzing along about 8000 rpm. The bloke who tunes the racer is George Campbell, brother of Keith, the famous Australian rider of the early sixties who was killed in Europe. George believes in tuning to the max. He's operated on the Mahle piston to make it lighter, and is trying a lot of other things. I think he will tune it to a standstill. I don't believe he is aware that those motors had a slighly bigger carburettor in the fifties, and were regulated to a smaller size to reduce the power output. I really believe in tapered ports. I believe that when the ports are opened out right down to the valve, the gas speed suffers, and cylinder filling is not optimal. Long before I would ever go down that path with my Norton, I'd buy the superlight pistons and the longer carillo rods, make a stronger crankshaft, and look for more reliable revs.

acotrel said:

The follwing is a reply I've made to a private message, might be of interest :
There are a couple of guys in our historic races who play with old matchless singles. I looked down the inlet port of one of them and it was huge. I said to them that if they bought a two valve Jawa speedway motor, they would start where the finished with that old garbage. They bought about three motors, and installed one in their featherbed framed racer. First time out it beat a good rider on a McIntosh (Walmsley) manx Norton. I mentioned to Neil Street one of our better speedway tuners, that they'd done virtually nothing to the motor. No rebalancing, cam mods or or porting. Neil said that on the speedway they are really buzzing along about 8000 rpm. The bloke who tunes the racer is George Campbell, brother of Keith, the famous Australian rider of the early sixties who was killed in Europe. George believes in tuning to the max. He's operated on the Mahle piston to make it lighter, and is trying a lot of other things. I think he will tune it to a standstill. I don't believe he is aware that those motors had a slighly bigger carburettor in the fifties, and were regulated to a smaller size to reduce the power output. I really believe in tapered ports. I believe that when the ports are opened out right down to the valve, the gas speed suffers, and cylinder filling is not optimal. Long before I would ever go down that path with my Norton, I'd buy the superlight pistons and the longer carillo rods, make a stronger crankshaft, and look for more reliable revs.

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There is no question that ports that are too large for the flow potential of the valve is bad for velocity and power. The 32mm ports on a Commando head are too large to reach any beneficial velocity when the valve size is only 1.5 inches.

A 1.5 inch valve will make more power on a correctly shaped 28mm port than on a 32mm port of any shape.

Watch Kenny's bike outpower the well developed 750 Yamaha at Road America in the video posted recently. It uses a 3mm oversized intake valve and a 30mm raised port. It makes impressive power and still has a wide powerband. Jim

Acotrel, have been following all the threads on here and have had some great advice and been given heaps of tech tips from a some of the very knowledgible gurus on here, all state pretty much the same , crank at no more than 60% BF, some mild cam (not extreme), the internals you speak of, raise the CR no more that 10:1, std valves with the tapered ports, (no mirror finish for the polish) std valves, with minimal shaping around the guides, a great head job basically then good carbs and tune the exhaust accordingly. Jury still seems to be out on 2 into 1 versus 2 into 1 into 2 or just traight 2 into 2 ,all seem to agree on reverse cone megaphones (slightly baffled but prety much straight through) This is seems to all add up to what i am striving for with Bike #2 for some sporty twisty road use at speed use and fun on the track days with out spending a large fortune and making the engine unrealiable.
No doubt there will be some comments on this
Regards Mike

Keep talking you guys, I'm loveing this.
Acotrel, I think you might be a Mildura boy.
Neil was certainly a very knowledgeable and friendly man, had the pleasure many times at the Long track
and Speedway, while Phil was home from England. Saw that old Honda head working in the flesh.
Go young Crumpy.
AC.

AC,
My brother doug is into historic speedway sidecars, we've known Neil Street since about 1960. He's built two motors for my brother - a 600cc Jawa two valve, and the 880 JAP motor for this, just before he died last October :
http://www.youtube.com/watch?v=Rk_Nkv0imrw

Douglas Cotterell @ Mildura :
http://www.youtube.com/watch?v=F9rWQppj2oI