camshaft timing

hi there, I need your advise about cam timing, i am currently finishing my two engines for my seeley,
-the "best one "is fitted with JS goodies : piston/rods and stage one cam , while Jim Schmidt recommend to time inlet at 0,155" at TDC with a tolerance going to 0,160" and such going for a LCA of 104°, I need to advance the cam 15° to succed 0,166" and 99°/100° LCA, need to say I do not use a vernier but only doing it by remeshing the gears, I had started with std marks , then going by 5° increments, thus ending with that 15° degres advance , thinking it was the best compromise....?
- the second one , called the "donkey"is supplied with Johnson 380 the asked LCA is 102°(inlet) , on std mark I got 99/100°, and when retarding the cam 5° , I reach 105°..............
spent all the afternoon in the shed , dismantling heads , playing with the dials , what do you think, should I go like this which mean the n°1 is a little advanced and the donkey a bit retarded ( I remenber Ludwig prefering retarding a bit taking in acount the backlash of the timing chain/gears), I know I should do the famous tiny step on the key to go 2°+ or -, but I do not feel well doing that, same for the vernier , had listen some vernier badly made or the pin failing..........

I'm trying to learn cam stuff for my special so hope to learn lingo and concepts with you. A bit confused by the lobe angle references as I thought that was ground into cam as fixed relation in single cam Nortons. Retarding cam , which delays intake closing for more ram filling, narrows and rises its peak power rpm, while advancing, which closest intake sooner, helps lower rpm torque but softens top end with less ram in air. Bet the valves hitting pistons limits retarding very much. Narrower Lobe separation angles tend to clash valves together. I've paid for dyno tests on V8's and know even half a degree cam fudging can be worth the tedium. Implies filing the key step risk to get best joy.

Hi Hobot, yes with our Norton, we can only play with the lobe center line , as the lobe separation angle is fixed by the cam grinder, so if we advance the inlet the exhaust will follow.......not like the triumph ! ( just guess , because I had never owned any trump!), may be i could try with another cam sprocket if any discrepancy within keway ? but I am at the end of my pile of parts in the shed ,and just remaining one sprocket , so that will be a one shot........my "donkey" engine had got all the parts staying all over, just that Johnson cam was new, Atlas barrels , combat head , GPM pistons, 850 cases, std crank but dynamicaly balanced to 84% (I know you are playing with BF), the other one was balanced to 70% but with JS goodies, and steal crank.....

Hm, motto comes to mind then, measure twice, fit once. Ms Peel has vernier cam sprocket and I played a couple times advance retard but for life of my inexperience couldn't get far off straight up 2S cam or valves touched pistons. Peel vernier pin stayed locked in until sent over 6000 rpm by cam drive, yep that was 1/2 crank rpm. Turnips two cams allow separate degree tweaks plus mixing matching cam so has it over Norton in that department.

Fuel octane, CR and ignition timing may influence your best cam degree's too. Fudge one and must fudge others to squeeze most joy least damage out of it.

Peels is isolastic forever so BF is non issue except for how it might effect power pulses on rear patch behavior on very edges experiments. Loose upright hill climbs too. Feed back by real racers mostly agree heavier crank delivered better track times, so I might try over 100% BF, but by Metally slugs not spent uranium which ain't as cheap or dense : )

I have a JS stage 1 cam. I had to advance it 10 degrees to get it right. Adding 3 to 4 thou on the tappet adjusters really added some pop. It was at 5 thou exhaust and intake. Jim sent out an update for these parameter to 8 on intake and 10 on exhaust for hot street usage.

I checked my cam by obtaining TDC and then validating the valve position of the non combustion cylinder visually through the exhaust port after removing the pipe. Not very scientific but effective.

I had gone 5 degrees retarded first the 5 advanced then 10 to being it home, and it does bring it home. You are going to love that cam. Brought to red line in second gear yesterday and wasn't mentally prepared for the incredible pull. A supported seat would have been nice. A roll on throttle first gear wheelie is not far off. I have a 20 tooth sprocket and a 19 would do it I am sure.

Hello Marinatlas

Because of variations in cam masters - Your particular cam has a few thousands more lift than the ones I'm selling now.

You can do the math and make calculations, but be sure to actually check what's happening by the "look see" method as below.

Looking in through the exhaust port with a tiny flashlight – the intake and exhaust valves should have the same lift or its prefered that the intake have a few thousands of an inch more lift than the exhaust. This gives you close to an "even split" or rather - it is prefered that the intake is slightly advanced. All of this was worked out years ago by C.R. Axtell on his dyno when building race winning motors.

The relatinship between the intake and exhaust is what is important - more so than the amount of lift on the intake valve. I'll edit my instructions so there is no confusion and I have been comunicating with the cam machinist to make sure these cams get the correct timing.

I've settled down to these tappet specs - Use .006” in & .008” ex valve clearance (.005” minimum and .008 in, .010 ex max). If tappets are noisy you can tighten them up but then you risk increased heat & pitting.

I personally run them tighter to keep things quiet (down to .003") but Jim Comstock recommended more clearance to give the valves more cooling off time on the seats. Jim C installed the complete kit plus beehive springs in a motor that Kenny Cummings is fitting into a racer that you are going to hear more about when the time is right.

The lightweight springs and lifters give you accurate cam timing with less weight slinging around bending & flexing things similar to the advantages of an overhead cam engine with less tendency for valve float at extreme RPMs.

hi Jim , many thanks for your support, yesterday I had tried to retard the inlet cam timing back to +10° , instead of +15°, and it is better , getting 104,5° LCA, and as per your advise the inlet slightly more lift than the exhaust......first time I had tried to time , I should be not enough to my job !
Now i should go back to check the 380 Johnson cams of the donkey engine, again...........

Egar , the ' Overlap ' is usually something like ( maybe) equal about T.D.C. , swinging it through with no plugs .

Setting VALVE to suit Cam , in respect of CLEARANCE . There should be perhaps .040 ( 1 mm ) Off Coilbound .

The valve seats shimmed to correct clearance.

THEN theres the ' Piston Clearance ' , Swinging through with PLASTIGAUGE or the like across valve pockets .
Ordinarilly this is .040 too . or .060 .BUT a hot cam gets them in closer and you get them in closer ,

Presumably always more at piston , as a missed shift , the slack ( WHAT SLACK ) in bearings , shells , wrist pins,
and stretch in rods , whip in crank , and other wierd things , take it up .

So Dont miss shifts ( more a Triump failing (oops) ).
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Essential to get it all workable . Clearances opened to check timing ( .020 at adjuster ) gives more accurate indication .
YOURE obliged to use a degree wheel and pointer . Double checking top and bottom dead centre .

Write it all down . Ea " slack Gone " point . a ciggarette paper strip at adjuster to valve gives accurate indication ,

If it moves its free , if its stuck , its on the lobe .
You need to get the old Zen bit Engaged , and green tea , no ' stimulants ' . Double check, if variation , refine the technique .

If the Head Gaskets .040 , a turn through with gasket ommitted will bear results. Turn Thriough GENTLY of course.
a ' tick , clack or ping ' indicates CONTACT , hence No Strong Arm Techniques .