Combat with Norris RX camshaft

Dances with Shrapnel » Wed Jul 11, 2012 12:33 pm
Hello illf8ed,

I took it that you went flat for increased duration but if flat is what the cam was specified on then your measurements are close enough. The cam may be set to slightly favor top end performance with a later intake valve opening (thus closing).

What I was trying to say was, if you were using flat lifters and the specs were for radius lifters, then you would have to use lobe centers to set timing or split the difference between opening and closing event and adjsut accordingly. A single point degree measurement would not suffice (ex IN open of IN close at a specified lift) as you would be comparing apples to oranges.

I do see earlier in this thread where the pictures of the spec sheet show two sets of cold lash settings, 0.006/0.008 and 0..13/0.013. The questions is which ones are correct. I am assuming you are using a cast iron barrel with alloy push rods. If you are using alloy barrels and/or steel pushrods you need to make adjustments to the valve lash specifcations to accomodate the different thermal rates of expansion.

Assuming your intake tract and exhaust primary pipes are stock, for tuning intake and exhaust lengths, to take full advantage of the new valve timing you may want to consider lengthening the intake tract for starters and see how the motor responds. This takes dyno time and/or lots of seat time. Same with the exhaust pipe length although I don't know where you would start (lengthen or shorten). There are imperical formulas out there to calculate primary pipe length and then see if the motor is happier with the change. Lots of texts books and on line references for this subject matter.

I would start with jetting and if you can get it on a dyno with an exhaust gas analyzer to see where you are at.

Click to expand...

Aw jeeze Dances, now this is the level of real scientific detail we all crave to make use of. I don't know enough but suggest simple stuff. Now I seek some slapping around on how much your detail items list with thermally compensated optimization matters. That is would the mis-match of flat or radiused cam and/or lifters and lash make enough difference to prevent mostly decent power reving. I mean would it prevent performance enough not to sense the potential of the combo - just knowing its not yet dialed in for best response power band, ie: would over sights of your pointers cause such sad performance it accounts for this instant failure to come on cam?

The reason i ask is trying to learn some way to determine what to expect in significance of one type deflect-fault adding to another. Peel's case it was dramatic difference on the most simple of crazy things - I not believed anyone telling me the tale either. If each type issue can do about same amount of power rubbing then nothing for it but do em all one a time to know for sure. Labor of love or addiction, which blend so easy.

hobot said:

Aw jeeze Dances, now this is the level of real scientific detail we all crave to make use of.

Click to expand...

Not so, not for all, only for the elite - your term, not mine.

hobot said:

I don't know enough but suggest simple stuff.

Click to expand...

Stating the obvious? I am trying to be ambiguous here.

hobot said:

Now I seek some slapping around on how much your detail items list with thermally compensated optimization matters.

Click to expand...

More than happy to oblige, as usual.

The stock Norton twin runs cast iron barrels (relatively low coefficient of thermal expansion) and alloy pushrods (relatively high coefficient of thermal expansion). With vintage race Nortons you usually find the opposite, alloy barrels and steel pushrods. With my ultra short stroke I run zero (or near zero) lash when cold; this motor runs alloy barrels, steel pushrods and an Megacycle N480 cam. What is really important is the lash when hot. I don't care to present the college physics or material science calcs to show the difference and magnitude but look up the coefficients, assume say 225 degree Farenheit delta temp and compare the two scenarios. In the stock engine, the pushrods will grow more than the barrel, in the race engine scenario I cited above, the barrel will grow more than the pushrods.

hobot said:

That is would the mis-match of flat or radiused cam and/or lifters and lash make enough difference to prevent mostly decent power reving. I mean would it prevent performance enough not to sense the potential of the combo - just knowing its not yet dialed in for best response power band, ie: would over sights of your pointers cause such sad performance it accounts for this instant failure to come on cam?

Click to expand...

The short answer - yes, the long answer is "depends". Illf8ed stated that he does not want a science project and I doubt he wants to screw with porting and compression ratios. What's left? Jetting, ignition timing, intake port length, exhaust system primary length and exhaust sytem extractor design. These are all accessible and reasonably easy to screw around with if one so desires. In the context of this thread, forget about the science fair of everything else. One can go about things willy nilly or take a more organized and systematic approach. As an example, it takes little to no effort to take another valve/cam reading and know exactly where you are (flat versus radiused lifters); otherwise you are lost.

hobot said:

The reason i ask is trying to learn some way to determine what to expect in significance of one type deflect-fault adding to another. Peel's case it was dramatic difference on the most simple of crazy things - I not believed anyone telling me the tale either. If each type issue can do about same amount of power rubbing then nothing for it but do em all one a time to know for sure. Labor of love or addiction, which blend so easy.

Click to expand...

It's like the Dagwood sandwich principle, you can keep on stacking on uncertainty and unknowns but at some point you need to step back and realize you have a cluster f*ck. A particular jetting or primary pipe length may work well in a particular instance but unless you know exactly what valve timing, compression ratio, jetting, atmospheric conditions etc, you don't know jack. And if it blows up or you don't take the time to find out and document then you are lost.

It's like the Dagwood sandwich principle, you can keep on stacking on uncertainty and unknowns but at some point you need to step back and realize you have a cluster f*ck. A particular jetting or primary pipe length may work well in a particular instance but unless you know exactly what valve timing, compression ratio, jetting, atmospheric conditions etc, you don't know jack. And if it blows up or you don't take the time to find out and document then you are lost.

Click to expand...

Oh ugh, just as I thought, everyone is stumped on what may or may not work in various combinations till its tried a few ways several times.

I won a bet with pro V8 engine builder that had never done a vapor motor ie: propane. Nor me. He bet my combo wouldn't make much over 300 hp with the 360 hp rated evaporator using a jet boat camshaft. He was right until I paid $250 for one more dyno pull with the cam advanced a 3rd time, but this time only .5 degree and made 366 hp and only 7% off gasoline power break in yet propane has 15% less energy. At 4600 rpm the carb ran lean and pooped out compared to gas 449 hp @ 5600 rpm. I hunted up propane racers to be told just file the three finger thick fuel needles thinner to feed more top end power. So there ya go I ain't completely engine stupid, likely just a lack of propane stifling this Combat's RX cam duh.

The cam timing will tend to dictate at what rpm's the peak outputs availiable . Provideing something else isnt inhibbiting it / throwing it out .

The general idea is to get it pulling like a tractor ( runnning on nitro ) or a chargeing bull , perhaps .
Scrawney little carbs or restrictive or coagulative silencors can create all sorts of pressure wave irregularities .Flat spots & deranged jetting & cross effects.

So if the sucker will breath & stay together , we're half way there .Trying a few alternative bolt ons for comparison , if available one can learn a few things
about the devices preferances and abilities . Such as takeing the mufflers off to see if theyre stuffing up the equation . :lol:

Obviously a hot cam isnt going to gain optimum advantages whithout a few other things in kilter to the new parrameters .
Crabs , Valve gear , No porting obstructions . at Least .

Though for road use - touring - cruiseing , unless its on the autobahn , it could be counter productive .
Generally when something gets to crankey , its a pig on the gravle . Unless your going 110 % :shock:
This isnt quite the same as takeing the time to enjoy the sceneary .

Heres a balanced approach for a CB 750 .

http://forums.sohc4.net/index.php?topic=27902.25

( I hope ) for winning Daytona . If the Triumphs stuff things up .

Maybe selecting a "RX" grind is overreaching a bit. The "R" grind might be a better choice for the street. If I were building the bike to race or for track use I'd certainly select a "RX" over the "R". Having used a "R" , I can attest to its performance. It will wake up your otherwise stock Norton without making a bunch of other changes.

I can attest that a drag race only cycle can be a pleasure to run in slow traffic like pits lanes or college towns and chug-a-lug like normal bikes in deep sand ruts off road lugging in 4th at 10 mph, so only took a bit off idle throttle blip to get instant scary tire spin power response.

On Ms Peel, after putting on dual Amals and spiffed up CHO head, it took her surprise power down, but she was still decent as regular Combats - but when the muffler mounts broke carrying the long dong Dunstall, a day or so before 1000 mile rally trip, so no time to fix it, I was forced to ride open 2>1 1.5" header, it was so bad could hardly get motion going from a start w/o extra throttle rpm, was touchy to not stall just rolling around the rally gravel lanes and then had to be careful not too give much throttle at once in traffic or bogged right out dead and even at hi rpm and hi throttle in low gears she was a pig that puffed unpleasant coughs like a low compression Harley. Point being the RX cam ain't the issue but some combination is working against its breathing. Before I left Ohio rally I put in a washer on a bolt to turn at angles for variable back reflection - which gave a bit better low down response - but not worth the effort for the little help it gave. The famous Peaky 2S cam feels to me as good as 850 std cam down low but then keeps kicking up response w/o end - till valve float.

hobot said:

Point being the RX cam ain't the issue but some combination is working against its breathing.

Click to expand...

+1

With a little fettling, illf8ed should be able to get the RX cam working for him.

Dances with Shrapnel said:

Hello illf8ed,

I took it that you went flat for increased duration but if flat is what the cam was specified on then your measurements are close enough. The cam may be set to slightly favor top end performance with a later intake valve opening (thus closing).

What I was trying to say was, if you were using flat lifters and the specs were for radius lifters, then you would have to use lobe centers to set timing or split the difference between opening and closing event and adjsut accordingly. A single point degree measurement would not suffice (ex IN open of IN close at a specified lift) as you would be comparing apples to oranges.

I do see earlier in this thread where the pictures of the spec sheet show two sets of cold lash settings, 0.006/0.008 and 0..13/0.013. The questions is which ones are correct. I am assuming you are using a cast iron barrel with alloy push rods. If you are using alloy barrels and/or steel pushrods you need to make adjustments to the valve lash specifcations to accomodate the different thermal rates of expansion.

Assuming your intake tract and exhaust primary pipes are stock, for tuning intake and exhaust lengths, to take full advantage of the new valve timing you may want to consider lengthening the intake tract for starters and see how the motor responds. This takes dyno time and/or lots of seat time. Same with the exhaust pipe length although I don't know where you would start (lengthen or shorten). There are imperical formulas out there to calculate primary pipe length and then see if the motor is happier with the change. Lots of texts books and on line references for this subject matter.

I would start with jetting and if you can get it on a dyno with an exhaust gas analyzer to see where you are at.

Click to expand...

Appreciate the feedback. I'm not an engineer nor have a desire for the advanced technical aspects. Not familiar with your reference to lengthening intake tract...how do you do that? Playing with the carb jetting is well within my capability. Barring success with that I'm inclined to follow JimC's comment that the RX may be too much cam for my requirement. Thinking I should have gone with a combat cam rather than an unknown. Rode it to work today. The impression I have is the engine makes more noice and revs freer than before, but makes no more or maybe less power - seat of the pants dyno.

David

I like it when its not my dilemma as I do know the lack luster joy of a good runner with dulled down power response. I too hate to actually have to focus and act on details whose significance mostly depends on some other unkown items details, ugh. Well 3 choices I see, one pull apart and re attach-alter stuff to racer level involvement or take apart and put in milder cam made to work well in your configuration or just part it out for profit and spite or as a so so runner at a loss.

illf8ed said:

Appreciate the feedback. I'm not an engineer nor have a desire for the advanced technical aspects. Not familiar with your reference to lengthening intake tract...how do you do that? Playing with the carb jetting is well within my capability. Barring success with that I'm inclined to follow JimC's comment that the RX may be too much cam for my requirement. Thinking I should have gone with a combat cam rather than an unknown. Rode it to work today. The impression I have is the engine makes more noice and revs freer than before, but makes no more or maybe less power - seat of the pants dyno.

David

Click to expand...

What I mean by lengthening the intake tract is increasing the distance between the intake valve and the bell mouth of the carb. For engine tuning it is a function of distance (length) and intake tract volume.

The engine performs as a tuned oscilator both on the intake and exhaust; when everything is in synch well ssorted engines can achieve well over 100% fill of the engine on each intake stroke. That is where a given engine gets it's peak torque and power characteristics from.

Scroll down to the second to last item on the following URL to see manifold (intake tract) bits and pieces offered by Steve Maney.

http://stevemaney.com/products.html

As an example, with a combination of those bits and pieces you can increase the distance between the intake valve and bell mouth of the carbs. For testing purposes you could have somebody weld up a steel test pair of manifold with the appropriate diameter (not sure if you are 32mm or 30mm). A rubber hose and hose clamps are used to connect and seal the various pieces.

It really comes down to how much you want to screw around with it. You can spend a fair amount of time testing, experimenting and learning before you approach the amount of time and effort needed to change out a camshaft. I can also appreciate where someone would want to come back to a known such as a Combat cam.

I hope this helps.

Dances with Shrapnel said:

illf8ed said:

Appreciate the feedback. I'm not an engineer nor have a desire for the advanced technical aspects. Not familiar with your reference to lengthening intake tract...how do you do that? Playing with the carb jetting is well within my capability. Barring success with that I'm inclined to follow JimC's comment that the RX may be too much cam for my requirement. Thinking I should have gone with a combat cam rather than an unknown. Rode it to work today. The impression I have is the engine makes more noice and revs freer than before, but makes no more or maybe less power - seat of the pants dyno.

David

Click to expand...

What I mean by lengthening the intake tract is increasing the distance between the intake valve and the bell mouth of the carb. For engine tuning it is a function of distance (length) and intake tract volume.

The engine performs as a tuned oscilator both on the intake and exhaust; when everything is in synch well ssorted engines can achieve well over 100% fill of the engine on each intake stroke. That is where a given engine gets it's peak torque and power characteristics from.

Scroll down to the second to last item on the following URL to see manifold (intake tract) bits and pieces offered by Steve Maney.

http://stevemaney.com/products.html

As an example, with a combination of those bits and pieces you can increase the distance between the intake valve and bell mouth of the carbs. For testing purposes you could have somebody weld up a steel test pair of manifold with the appropriate diameter (not sure if you are 32mm or 30mm). A rubber hose and hose clamps are used to connect and seal the various pieces.

It really comes down to how much you want to screw around with it. You can spend a fair amount of time testing, experimenting and learning before you approach the amount of time and effort needed to change out a camshaft. I can also appreciate where someone would want to come back to a known such as a Combat cam.

I hope this helps.

Click to expand...

Ouch. This is more technical than I want to get involved. Also eliminates the stock ham can air filter with cooresponding ignition switch bracket that I'm particularly fond of. Thanks anyway. Will continue with carb jetting and playing with ignition timing. If no joy, goodbye RX.

Don't forget, there's also the exhaust system primary pipe length and megaphones. Maybe a little easier to fool around with.

Messing with the intake tract is not an absolute necessity.

Dances with Shrapnel said:

Don't forget, there's also the exhaust system primary pipe length and megaphones. Maybe a little easier to fool around with.

Messing with the intake tract is not an absolute necessity.

Click to expand...

Years ago, I had the good fortune to spend some time in C.R. Axtell's shop. This camshaft thread reminds me of some of the things I picked up while there. Camshaft and engine development takes a good understanding of applied mathematics. Kevin Cameron's Cycle World monthly column does an excellent job of explaining some of the mystery of engines and the associated math.

Unless you know what you are doing, I think it's very easy to spend a lot of time and money and end up with very little increased performance to show for it when trying to seriously modify an engine. I certainly don't have the expertise, but I've been fortunate enough to know people who do and wise enough to learn from them. Having been viewing this forum for almost five years, I see some real expertise. I'd name them, but I'd probably leave someone out who is deserving. They know who they are, anyway. Needless to say, there's a lot of chafe among the wheat here, too.

IF youre running the Camshaft at 0.012 and the required clearance is 0.020 thats a 0.08 interfearance . :shock:

WHEN the follower is at the HEEL ( as well as 8 thou extra lift .) Problem being the heel radius / ramp .

IF we assumed there was 8 thou ' ramp ' from opposite the lobe to the opening period ( 8 thou differance in Radius ) to smooth the operation ,
Effectively it wouldnt close much or for long . THE POINT BEING the period of opning and closeing is being interfered with / prolonged .
Duration wise . Opening ( just a nadge lift wise but perhaps considerably degree wise ) Earlier and Closeing Later .

This probably wasnt what Mr Norris had in mind when he configured the parameters . This would provide the hissing spitting back and opping . :shock:

Therefore the first thing to do is try the Specified Clearance . IF it this to that , try the larger for more deciseive opening / closeing opperation .

All this is comeing from the mug who ran his 2S cam at 0.016 ( around twice whats specified ).

The Only ' Noise ' was the music off the valves flung open & seating . NONE of the usual :shock: ? top end rattle it later had with a Std cam & clearances .
or was it the small tank blocking it less . Niet . One stood along side the thing occasionally . or even wandered about admireing it .
Except for the noise with the std. cam . Bother , Whatve I done . :shock:

Sounded more like the piston rods in a Steam Locomotive , with the .016 Clearance . NOT a rattle . THEREFORE . If all else fails . . . read the instructions . 8)

illf8ed said:

Will try the video when I get some time.
Head got some minor milling at Raber's last winter. I'm getting nervous about piston to valve clearance, so don't want to risk reducing that more. Did put in some .060" shorter pushrods and that made it possible to get some adjustment with new mushroom adjusters. Running .012" clearance although Norris suggested .020.

Click to expand...

Just re read your earlier post. The lash specifications for the RX cam are 0.006" and 0.008". The 0.020" is only for cam checking and timing purposes, not for running. Maybe some of poor performance is due to excessive lash. If valve to piston clearance is a question then it should be checked. It can be done in a crude way with a dial indicator without pulling the head.

Whoops . a Major ' Foot in the Mouth .' .



Now WHERE was this / :lol:

Hokay ' Somebody " shouldnt be in a rush and read all the posts . I will when Ive finished this .

Yea . The TWENTY tho. clearance IS used when SETTING ( measureing / recording ) theValve Timing . opening / closeing . Shoudve twigged .

According to this chap 9spec sheet ) its 6 & 8 ' sevice ' clearance . BUt ' Specifications may change without notice " ???? IF ones with youres , ITS for IT . And may be correct .

========================

Thing I really meant to whine about 8) is valve to piston clearances . Where you go with that trepidly ( Fingertips - NO force . )is wind the adjusters in , 40 thou and carefully turn engine
usually at the crank before primary . Plugs OUT . If it turns freely , rather than needing LEVERAGE . ( DONT ) you know it clears by 40 thou ( a mm , 0 this is normal for road .

Tuning the adjusters in a turn and a half ( Hobot will say correct turns ) For .060 - Sixty thou . and turn through gingerly . a Tonk / Tink / tap DONT LEVER IT , would tell you its touched .IF it did.

which likely it wont . Then youll know.

Onne can deduce from this what clearance youve got , valve to piston .

Whowever , if theyer shimmed to full lift plus .040 , DONT wind in past 40 , as thats all youll get . tecnicallly the pushrods would lock it at 60 without that clearance fully open . pretty basic .

The ' Overlap ' bit is where the suckers both the same between the lobes .


My 2S combat cam was the 3S lift on the intake ( 170 or 280 or whatever is actually correct , set three dgrees early for a 3S . being a 2s of course not realised untill it was removed .

looking at the Lift / degree charts shouldnt be a chore . On a post here somewhere .

After a few drinks it should all click into place . Forget all the numbers for starters . Its fred Flintstone stuff . I push this here thus , and this goes there . The figures are how far .

:idea:

The area to be cautious testing Valve / iston clearance is around T D C . piston going up , valve going down . Or opening faster than the piston recedes .

I wasn't too concerned about valve to piston clearance with the RX. A combat cam has more lift at the intake than the RX and this is a combat engine. I made sure anyway using "clay" gauge. Set up issues are in the past. Working on carb and ignition adjustments to see if the RX can be tuned to my expectation. I'm not going to consider additional engine modifications. The goal was only to change out the standard camshaft a previous owner installed....bad idea. Looking back it would have been a safer move to install a combat cam as it is a known variable.

Hi David, did you made any progress in your tuning ?
As i have a spare RX cam on the bench, I had decided to build up another engine , he will have a combat head as you , i had just found a set of 750 cases , just missing now a cylinder , so soon I will put eveything on the bench and go , I will try to time that cam by the lobe center way, as it seems more accurate and more simple (that's what I had done previously with the Johnson's cam and later on with the JS cam, as I was a newbie in cam timing except the std commando set up , I had found that way much more simple , though I had tried to time them trough the valves , and check several times to find everytime some discrepancies.........but a newbie!), may be your ignition is not enough advanced , or your gas not flowing enough??

Dave,
To post videos, upload them to Youtube, and post the link. I'd really like to see your bike.
Best Regards,
Al

Yes video please as more interesting than online porn. Am I missing something, looking at the begining, seem RX is performing fairly well not at all falling on its breathless face. Next to CR, cams are most sensitive to exhaust configurations, so that might be 1st place to get even more grining going. Change one thing, then diddle all the other stuff around that, then change another thing and diddle what ever else to dial in too much or not enough to know if the main change being tested helped or hurt. If the RX becomes redundant I may what to try it if my D+ is a bit too much.