New cam or not this is the question.

Hey guys... As you may or may not know, the Camshaft in my recently destroyed engine has some damage to one of the exhaust lobes, and is showing signs of discolouration (may be rust caused by condensation from sitting) on the drive end of the shaft where the oil seal sits. It is repairable in both cases but about the same price as a new Cam. The problem is this, the guy who is doing the bottom end for me says that he has fitted a couple of new 2s Cams recently and they don't seem to perform as they should. Has anyone heard of this or witnessed it first hand, or got a good one for sale ?... AC.

Had a 2S in my original Combat and it performed quite well though the timing was bit out from spec. Lift was 2S spec. but timing more like std when measured with degree wheel. Depends what yr guy means my not performing so well. There's not a lot under 3000 rpm but at 4500 they really come in and you can feel the surge. Best not used with high geared bike as they need to be revved. Have a PW3 in mine now after many years with a std cam. It's good but makes the exhaust really loud under load. It does have more bottom end than 2S though. Still needs to be revved. Unfortunately the people who supply 2S copies get them from the same source I believe (Dave Newman Cams UK). Ask them if they can guarantee 2S specs to within a few thou lift and at least 2-3 degrees on timing. I doubt it somehow and the same goes for std cams which are really the best all round for a 'nice' motor.

2S cams require high compression to function properly. Some drob these into stock motors and expect wonders and are disappointed with the results.

If you have Combat (shaved head, 32mm carbs) verify the you have the required 10.5 to 1 minimum compression. Otherwise get your self a 560nr and ride off into the sunset with the best of both worlds. I have installed a comparable JSMotorsport stage 1 cam kit and am ready to fire it up. Waiting for 50 degree day.

On the other hand, a stock cam is thoroughly proven but may require lowering the compression to 9.5 to 1 or lower.

Can the person doing the repair promise the cam with be within spec? If so it might be just as well to go that route.

Russ

Thanks guys,.... Hey Kieth1069, The PW3, Do you think it is a better all round cam than the 2s, it sounds as though it is, more bottom end and still a good hit mid to high ?My 72 is definitely a Combat... And a question for experience... I assume the Pistons are all the same for the 750, and that the Combat has a different H/C head. Yeah ?.. Or do I need Combat pistons..AC.

Hi , the pistons are the same , just the head had been shaved 1mm down to achieve the 10/1 ish ratio,my personnal advise would be to go for a 560-NR grind , or any 5S/ 360 Johnson, more friendly than the 2S, the Webcam are good but don't know the equivalent...........

Hi Aussiecombat,

Most of the new cams from the UK are made from chilled cast iron. I'm not such a fan of this material because it's very brittle. If you torque the sprocket nut to factory specs the end of the cam can snap right off!
I have an original 2S cam with non scrolled journals in OK condition. PM me if you're interested.

Thanks guys,.. Leave it with me. I think I'm leaning towards the regrind as it can be done right here...AC. P.S. I have a guy here with a 4s cam, He says they are better all round than the 2s ? But do they fit ? Are the lobes higher ?

Thanks guys,.... Hey Kieth1069, The PW3, Do you think it is a better all round cam than the 2S, it sounds as though it is, more bottom end and still a good hit mid to high ?

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Yes I think it is better all round than 2S (or 4S) as it doesn't have the peakiness of those grinds. As mentioned here these hu9gh lift cams do still need highish compression and ports properly opened up to make best use (not just enlarged to max). Mine has an 030" compression plate under the barrel so I'm at about 9.3:1 with Combat head and 32mm carbs. I've had to drop my needles to the lowest position (106 jets and 220 mains) as it was eight stroking at 1/4 to 1/2 throttle on acceleration. It really needs setting up on a Dyno but is getting amazing mileage with mixed high speed and medium speed work........62-66 mpg.

Sounds good, How is the modification done to the Cam well, for the higher lift. ? Assuming the is a mod. What front sprocket are you running Kieth ? I thought I might go up from 21 to 22 if I get the better cam. It should pull it along nicely at just under 4000 revs... AC.

Depends on your cases and how much lift they can handle but usually the tight spots are the drive and timing areas, top and bottom of what remains of the original tunnel. I used a Dremel with a rasp and finished off with a 50mm dia flap wheel in a normal hand drill aiming for 1mm clearance. I was also able to retain the spring insulators and maintain 1.2mm spring coil gaps at max lift. Previously the Combat head had come without insulators on the inlets but the 2S has a little more lift on inlet side. The exhaust was also OK even though the 2S has a lot less lift than PW3 on this side. This gets it all working fine but the expert engine builders will probably advise aiming for specific valve seat pressures closed and open. I used springs from a former UK specialist (now deceased) and these have an opposite coil wind to the std RGM springs I had been using. I installed them only because I found a note from the same outfit specifying their use with the 2S cam. They are actually weaker than the RGM parts but seem to rev to 6500 ok without obvious float.

Beside the cam 'tunnel', the cylinder barrel 'sleeves' may need relieving too.
One neat thing about more aggressive cams and higher CR combos is lower octane requirements and better ignition curve to get more power out faster burning fuel. Later intake closing lowers effective CR at lower lugging rpms but as piston speed rises tends to out run the combustion pressure spikes as the ram air effect comes into play with rpm. Camshafts are worth while to have cryogentic tempered and maybe dry friction coated.

What front sprocket are you running Kieth ? I thought I might go up from 21 to 22 if I get the better cam. It should pull it along nicely at just under 4000 revs... AC

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21T but a 35/72 belt so overall is equivalent of 22T, bit high really but like you say, fair cruising at 4000 rpm and just over 72mph. What you lose is the ability to pull from 2000 rpm in top. Mine has never done that well with all the headwork it came with. Maybe an 850 wouldn't be affected so much.
As Hobot says watch the lifter/tappet bore clearance. Mine was Ok with some NOS 750 bored 850 castings I got from Norvil back in late 02.