Valve clearances, why so different.

Jim, Please explain the "getting hot " reason, ie what happens with small valve clearance and correct clearance :?: surely if the correct clearance is 8 thou and we adjust to 4 thou the valve will be opened only a fraction of a degree early, as stock drive set ups can be 1-3 degrees variation what would a millie second make by a tappet three-four thou tight, you will have the excuse my persistance on this topic.
Regards John[/quote]

John, The quieting ramps on the cam have a very slow rate of lift and start several degrees before the main ramp starts. Depending on the cam it may be 10 or 20 degrees long [or longer]. It is only designed to take up the slop or clearance in the valve train before the main ramp comes into play. It is not meant to open the valve.

If you take up to much clearance with the adjuster then the quieting ramp will lift the valve slightly off it's seat long before the main ramp comes into play. It will not have much effect on how the engine runs because the valve is only lifted a tiny bit but it can easily take away the minumum period of time each cycle that the valve needs to be on its seat to transfer it's heat to the head.
Next time you are adjusting your valves notice how the clearance goes away as you rotate the engine and the lobe gets near the lifter. The clearance will go away quite a while before the valve starts visibly moving.

Vise-versa- if you have too much clearnce the ramp can not take up all the slack so the main ramp hits the lifter hard making it noisy and causing shock damage to the valve train. Jim

When it gets totally out of phase , the float can have the follower free falling as the lobe swings throuh . knocking it off ,
on a variety of engines .

To my understanding , theres a type of concertina / harmonics going on .If the masses and accelerations are In Phase ,
the operateing loads or forces are lessened . Free Horsepower . Well , at least , set up right , opperateing losses are
minimised .

The old positive oil feed to lobes / followers may well be a H.P. increase ( bullshit = a reduction in H.P. loss ! ) improvement
through reduced drag (fricrtion) thus lower Temp . , smoother operation .The term ' Cushion ' was oft used in decades past .
The quantity of oil between lobe / follower would need to be correct , to provide this , or itd hydroplane . :lol:

SEPERATEING the functions , From the follower above , is where we can get this ' in phase ' concetina motion .
The Clearances are imperitive to this , in fact are the tuneing to get it in phase.So in fact , the Tightest possible,
is probably not at all what is required.

Haveing acchied this , AT the follower base / Cam interface , the pressue should become progressive and cyclinc ,
further reduceing losses through eliminateing unnessesary excessive pressure , and negative ( shock load )
pressure cycles .In fact getting the whole thing operateing progressively in the manner of forces / actuation .

The weight of the lifter then , is part of this ' throw through ' , or the heart of it . The piggy in the middle ,

From radial to reciprical forces . with the rockers being Oscilateing of course , to reverse direction .
A strobe light should freeze the motion for observation , though dont go cutting holes in the engine to get a closer look . :shock:

Well I think I've got the guist of it, thanks all.
Jim... Does the addition of the Concave Radius to the Lifters, as I have, make a difference to the necessary clearance.?
And, why is the 4s Cam, valve clearance suggested as .016 on both sides, where as many other cams are less on the inlet,
than on the exhaust.?
AC.

AussieCombat said:

Well I think I've got the guist of it, thanks all.
Jim... Does the addition of the Concave Radius to the Lifters, as I have, make a difference to the necessary clearance.?
And, why is the 4s Cam, valve clearance suggested as .016 on both sides, where as many other cams are less on the inlet,
than on the exhaust.?
AC.

Click to expand...

Just taking a quick look at aftermarket Norton cams, they seem pretty evenly split between those that use the same clearance for both valves and those that are different (typically .002" more clearance for exhaust). Axtell cams used the same clearance for both, Norris go both ways, as does Megacycle. Factory cams go either way. Production cams have different specs for intake and exhaust clearance, but 2S and 4S use same clearance for both. I've always assumed the exhausts were set a little looser because the exhaust valve gets hotter, and so expands more. No idea if that's the only reason for the difference.

Ken

I am slowly confirming that the "Technical People" of this world, make things up, just to confuse people like me.
But hey, I CAN REVERSE A DOUBLE ARTICULATED VEHICLE THAT WIEGHS IN AT 65 TONNES, AND, CHANGE 18 GEARS
WHILE I TALK TO THE WIFE ON THE PHONE AND EAT MY SANDWICHES, ALL AT THE SAME TIME.
Sorry, didn't mean to shout.
Lol. hehehehe.

AussieCombat said:

I am slowly confirming that the "Technical People" of this world, make things up, just to confuse people like me.
But hey, I CAN REVERSE A DOUBLE ARTICULATED VEHICLE THAT WIEGHS IN AT 65 TONNES, AND, CHANGE 18 GEARS
WHILE I TALK TO THE WIFE ON THE PHONE AND EAT MY SANDWICHES, ALL AT THE SAME TIME.
Sorry, didn't mean to shout.
Lol. hehehehe.

Click to expand...

Are you sure its the wife you are talkin to :?: :lol:
I have googled about every thing about cams and these black art ramps. same conclusions ' Clearance for expanding parts [heat] ramps for soft opening start.
I can only conclude the differant tappet clearance is to do with timing .
I hope you are a little wiser, me personaly ; well still some fine details to question..by the way i aint Technical...just curious

Ok what about the valve seat width on heat transfer now ya got the cam settled down on seats long enough? Are any these significant factors in our breed?

AC, The convex [radius ground lifter] will not change the needed clearance.

I will keep my Norton very far away from your vehicle while your eating your sandwich and talking on the phone. Jim

hobot said:

Ok what about the valve seat width on heat transfer now ya got the cam settled down on seats long enough? Are any these significant factors in our breed?

Click to expand...

Sure the valve seat width is very important. If it is too narrow it won't have much contact area but luckily it will widen very soon all by itself.
If it is more than about .080 wide it will pack up with carbon and prevent contact and will get too hot. This is probably the most common reason Norton valves pit or burn. Jim

Its a non issue on my factory Combat but its important issue on excess fuel burner Ms Peel. IIRC her exhaust seat in .060". I'm not sure about the seat sealing ramp profile on her Norris D cam, but this post educated me more to be pensive going by ear adjustinh lash tighter than spec. I've bought Maney steel pushrods 6 yrs ago but told him to wait till engine assembled to order the correct length. Now i DON'T know what to order d/t the confusion of expansion differences. I've a few sets of pr's on handle to diddle with gasket/CR changes, once I ever get a runner to risk by my hands in it. The valves are Dreer supplied K/W kit just before he went American Norton saga.

A funny asside and power miracle of past Peel revolved around valve seats, Peels Combat head had its valve seats popped right out durring the squeeze of -300' F cyrogenic tempering, so was sent to MAP who sent to a shop that decided not to do heads no more but told no one so CHO head was lost for over a year, so I put on a standard head and sloppy intruding manifold gasket with 34 Miki carb, just for run it, then I hit the 1000 mile mark and tried to break the engine but instead broke my beliefs in what it means to accelerate a floating front into and out of turns. I thought I'd get even higher top end and acceleration by putting on two new 932's but it lowered the top end power curve, so thought is was the small head ports, so put on the recovered CHO head, to really be disappointed. Then stuck throttle over rev event wiped out the hi rpm power so never got to put back to best accidental set up.

Oh yeah even the best combo was just poo poo till I got fed up with my failures and shot out the megaphone baffle plate ---
OHHHH LAA LAA, I became an elite sports bike squid hunter teaser tempter tester up to indicated speeds no one outside our fun and games can believe. In '04/'05 for 3 seasons I had daily fantastic experiences on Ms Peel. To run with or spank the new angry hot dogs really takes some periods of WOT/Red Line heat loads to valves and gear box bushes. EGT 1375 F, CHT 425F, oil 195 F. just about right.

BTW it takes more than just enough power to play life death racer games in tight public blinds, as modern sports bikes can easy out handle the faster sweeper turns than un-tamed Commando's.

If you expand on Ludwigs lead and I invite you to take a look at my cam profile page:
http://atlanticgreen.com/camsurvey.htm
Sorry some profiles are older and lack the needed details at the base circle and ramps.
As you bring up each profile such as the 4S, imagine a little 30deg triangle that sits on the base circle/0 lift....you will slide it up to touch the profile where it will then be tangent to the ramp. That is the point .016 at which it contacts and starts to lift. If the clearance is to big the approach angle will approach 45 deg tangent and the lift will be more like crashing into a brick wall. If the clearance is to small the valve gets picked up to early and the valve is just barely cracked open for a long while (on the exhaust, the high velocity flame eats at the valve) (on the intake, the exhaust is ineffective to supply scavenging) .

I agree with comnoz and it is the different ramps that determine the lash, among other things to lesser degrees.
I can envision the same cam having different lash if aluminum barrels have steel push rods or iron barrels with aluminum push rods :roll:
Try the 30 deg ramp on various profiles and they will intersect tangent at different lifts off the base circle....therefore different lash. Now wouldn't it be nice if base circles were a bit more precision so it made adjusting the valves a worth while exercise.....some are real garbage

I am selecting 30 deg only for example, since I did not do an actual tangent angle calculation and don't know what the particular cam designer intended as the initial acceleration rate.

I believe there is not much lash difference needed between flat or radiused lifters since the differential is largest through the mid lift of the profile and minimized at base circle and peak lift regions.

:mrgreen:

If you take up to much clearance with the adjuster then the quieting ramp will lift the valve slightly off it's seat long before the main ramp comes into play. It will not have much effect on how the engine runs because the valve is only lifted a tiny bit but it can easily take away the minimum period of time each cycle that the valve needs to be on its seat to transfer it's heat to the head.

Click to expand...

That makes sense to me, up to a point, but rather than provide the cam with a long quietening ramp and then negate it with wide clearances why didn't they use a shorter ramp and regular clearances for the same effect?

Cheers! ~ Gary