Cam timing 101 (2011)

I have got the sheet on camshaft timing off the NOC site. And I just want to check my standard 850 cam, nothing wild. I have searched for explanations but I would like to ask the following.

CLEARANCE AT LIFT

The table list both 0.020 & 0.040 is this reffering to the distance left before coil bind?

Is there a cam lift at TDC setting for the standard cam? or can this be calculated? it is not listed in this artical.

They also refer to the 8 degree lead of intake over exhaust, can someone explain this to me please. I understand this is the critical setting to aim for.

I have the engine set up in a stand with a degree wheel dialed in ready to go.

Cheers Richard

When the valve opens/closes is partly dependent on valve clearance, so prior to measuring or adjusting the timing you should set the valve clearances to a particular value.

It's common to quote valve timing angles with the clearances set wide (e.g. 0.040") because the cam profiles have "quietening ramps" which ease the valve "relatively" gently off it's seat and back on again. The ramps only affect the first few thou of valve lift and they make it difficult to tell when the valve is starting to open and when it is finally fully closed. By setting wide clearances the ramps don't come into play and you establish or set the valve timing more accurately.

Having read the stuff on the NOC site though I'm not sure that's a good explanation!

stockie- you will need to find TDC-top dead center- with head off,fabricate a piston stop( or use a dial indicator) rough in tdc on your degree wheel when piston is all the way up- mark the wheel where the pointer says ZERO degrees- now go 20 degrees forward on the wheel and read your dial indicator, now go back 20 degrees past tdc in the other direction on the degree wheel at the pointer, read the dial indicator- if the dial indicator read the same number in both directions, proceed to dial in the cam, if not adjust the pointer accordingly to split the difference for your starting point

here's a more thorough review on the simple scope of this real mechanics task.
I was able to attach degree wheel by a magnet but not real stable if bumped but not much reason to bump it or the wire indicator I also have used a magnet to hold as lazy mechanic I am. Tricky part is how far to open engine to get a good read on a rocker adjuster or reach down to lifter contact. Rockers ratio alters the cam profit numbers porportionally but not the points of max lift so can still ID cam and set it right.
http://www.cranecams.com/uploads/instructions/803.pdf

Most of the timing ' opening and closeing ' figures are quoted SET at .020 clearance ( tappets ) so as to get a deciseive
figure , on Nortons .( typically cam lift / duration graphs use this setting. to allow for ' compressability ' in valve gear )


The .040 may well be Both the ' off coil boud ' * at Full Lift and also the required Piston / Valve Clearance .

The dreaded " 8 Deg. Early , is perhaps the easyest to set.Apart from the valve springs Not wanting to let the cam sit
on the flanks .

The ' Overlap ' , both intake and exhaust lifters not fully down ( you wont get both fully shut at the ' between the lobes'
on the intake / Exhaust stroke .) Rock the Cam , get them ( the Lift ) EQUAL . Now thats 'Degree'd .Moved back 8 deg.
' EARLY ' , and the crankshaft set at T.D.C. . Not a Iota out . hence the 'Go Ea. Side ' Check method kindly mentioned .

One fits the sprockets and Chain . Multi keyways give a better chance of finding a position where it all fits 'spot on ' .
If its almost , neraly , but not quite , one moves the cam forward / early another degree or two ONLY .Unless you
dont ride in town , where a degree or so later will be o.k.

* if the r.p.m.s are going to be made use off , shimming the valve seats is required . IN ANY CASE it should be seen to
that the movement of the valves at the SPRINGS is not all taken up , with a 40 thou surplous travle available at Full Lift .

" Conventional valve gear requires stiff springs to assue accurate closing of the valves at high r.p.m..
A considerable amount of power is required to compress these springs when the valves are opened .
Some of that power is returned to the engine when the springs expand against the cams closeing ramps ."

Just think off the poor timing chain . ! :shock: Meticulous preperation pays dividends in seeking performance .

Richard,

There's a similar table of cam data on the Old Britts website where they make it clear that the opening and closing points are determined when the lift is 0.040", what's not clear is where the lift is being measured: at the camshaft or at the valve?

On the Johnson Cams website they define "Lift" as, "The amount of lift at tappet in pushrod engines, lift at valve in OHC engines, measured in inches." So, it looks like you should be setting things up with the cylinder head off reading lift directly off the cam followers or a suitably supported push rod.

Cheers! ~ Gary

I think all the factory cams , spec'd ' lift @ T.D.C.' , measured at base not valve .Thus lift @ Lifter / Follower.
Means haveing the head off , or some multiplication .

Any combination other than stock, will have specific conditions that must be met.

I'm assuming (I haven't been taking specific notes over the last 20 years):

Some cams have radical "ramp" profiles (totally different from quieting ramps)

Some cams have altered profiles, but still use flat followers, others require radius-ground profiles

Some cam builders give thier set-up procedures related to non-typical measurement procedures (measuring at the valve vs measuring at the follower)

Some cams specify .020, others .040, etc.

Some pistons have deeper valve pockets than others

Some valve seats are a bit more sunken into the head over the years of abuse, resulting in different opening and closing positions relative to the cam/followers

You really need to know ALL the details, (and measure very precisely) or you might be off. In SOME cases this can mean serious problems, other times, it can simply result in poor performance. Typically you can spot serious problems the first time you attempt to rotate the engine through 720 degrees of crank rotation (not always)...

If you just want to check (or set) your cam timing, a simple and accurate method is by measuring the lobe center of the intake lobe. That's what most of the serious engine bulder's I've known use. If you are more interested in finding out what cam profile you have, then you need to take more detailed measurements of the amount of lift at different points.

You can take your measurements with the head on by locating the dial indicator on the valve spring retainer, or with the head off by using a long extension on the dial indicator to reach the top of the tappet. If you measure at the tappet, you get the actual lift curve of the cam. If you measure at the valve, you are getting the actual lift curve at the valve. You can convert one to the other by including the effect of the valve clearance and the lift ratio of the rocker arms ( 1.13 to 1).

This is the instruction sheet Axe used to give out to explain how to time his cams using lobe centers. You can find other cam timing instructions on-line, but this one always seemed pretty clear to me.





If you just want to check the lift of a stock cam, the factory specs the lift as .375" at the valve. That's with stock .006" clearance (intake valves). You'll probably measure a bit less than that.

Ken

Concerning the camshaft info on the NOC site, I've always found their explanation of the 8 degree lead really confusing. They state

"The crucial figure with these cams seems to be the 8o lead of inlet lobe over exhaust lobe. To achieve this lead, the the timing can be advanced or retarded in 5o stages as follows."

The lead of the intake lobe over the exhaust lobe is fixed by the cam grinder, isn't 8 degrees, and can't be "achieved" by altering the cam timing as installed. I'm sure they know what they mean, bit I never did. I also think they've made some mistakes in their table, don't correctly interpret the meaning of measuring timing at .020" vs. at .040", and their equations for lobe centers aren't correct. But that's a whole other topic.

Ken

Thanks Ken - nice piece of history there.

Thank you Ken and others.

You can imagine the scene, I have my dgree wheel, I have got various DTI gauges and what not. I have made uo a nice piston stop to get the TDC lined up accurate ETC And I just wante to verify the standard 850 timing was as it should be? The engine ran with prodigious torque down low, I am not a racer so I don't spend much time above about 4500RPM. The 21 tooth froont spocket sees me doing the Australian legal 110 kph at around 4000RPM.

But, I like to check stuff. With so many explanations, I am tempted to pack up my tricks and just det the cam as per the book.

the NOC information is a little hard to fathom, the instructions are saying set the timing at 13 thou, sot set the clearances to 16thou, and use a 3 thou feeler gauge to establish opening and closing points. That all cool with me, no problems. But then the graph started mentioning 0.020 & 0.040 clearances, that is what confused me.

The inlet lift at TDC was what I used on my T150 some time back, and that made me feel comfortable it was on the mark, they list TDC lift for the Combat and other cams but not the standard 850, why?

And Ken I am glad you explained the 8 degree lead, I could imagine it was possible to play around with that setting on a Triumph, but I could not se how that would alter on a combined exhaust and inlet cam.

So is there a published loce centre on inlet for the standard cam, or has anyone worked out the lift at inlet at a certain tappet clearnace? I have the head fitted now.

It would be nice to try out my tools? I will check the opening and closing degrees at the 16 thou rocker clearnace with a 3 thou feeler and report back tonight.

Thanks Richard

stockie2 said:

So is there a published loce centre on inlet for the standard cam, or has anyone worked out the lift at inlet at a certain tappet clearnace? I have the head fitted now.

Click to expand...

There's a lobe center angle for a standard cam on the Johnson Cams site: -

http://www.johnsoncams.com/jc_n_cams.html

It's 102 deg; or if you take take the 38 btdc/63 abdc opening and closing angles and calculate using the Axtell method it works out at 102.5 deg.

So, why don't you do the following: -

1) Turn engine until inlet valve opens and achieves 0.040" lift, then note the angle on the degree wheel (it might not be 38 btdc because you're measuring at the valve not the valve lifter).
2) Continue to turn engine until the inlet valve starts to close and when the valve is at the same lift as in 1), above, as indicated by the dti, note the angle on the degree wheel (again it might not be the specified 63 abdc).
3) Use the degree wheel angles from 1) & 2) and the Axtell calculation to work out the lobe center angle, it should be 102.5 deg.

It doesn't matter what your valve clearances are (as long as they are sensible) as they will affect the opening and closing angles equally and still result in the same lobe center angle. The fact that you are measuring lift at the valve rather than the tappet (or cam follower) shouldn't matter either since the valve gear geometry should be exactly the same at 0.040" valve lift regardless of whether the valve is on its way up or down.

Cheers! ~ Gary

Digging this thread up as I'm getting ready to set up a Web312A cam.

Web indicates the following specs for this cam:

Valve Lash (Inch):.006"
Valve Lift (Inch):0.390
Advertised Duration:310°
Duration @ 0.050": 270°
Lobe Center:104°
Intake Opens 31°Before TDC
Exhaust Opens 59°Before BDC
Intake Closes 59° After BDC
Exhaust Closes 31° After TDC

Valve Timing Is Checked With Zero Valve Lash @ 0.050 Inches Of Valve Lift.

Though they provide duration at 0.050, they don't specify what the actual lift should be here. Also, in their general set up instructions (not specific to any cam), they instruct to measure lift at the valve retainer on pushrod engines (not at follower).

So, after I've confirmed/adjusted lobe centers as close to 104 degrees as possible, I'm assuming the main value I should be concerned with is duration @ 0.050?

Anyone with experience degreeing webcams please chime in, did you take all the measurements from the retainer?

Cheers!

When you're done racking your brains out with the number crunching - check your work by turning the crank to TDC and check the lift on the intake and on the exhaust. With a symmetrical cam you want the intake to have .010" or so more lift than the exhaust. You can visually check by peeking into the exhaust port with a tiny flashlight. Once you verify the in/ex lift difference for a particular cam - that's all you have to do next time. All symmetrical cams (intake and exhaust lobes are identical) seem to come out with about .010" to .020" more lift on the intake. If the lift is the same - its timed "straight up" or "even split".

Acadian - the specs Web provided are "straight up" or "even split". But it should run better with a little bit of intake lead (approx .010" more intake lift than on the exhaust at TDC).

You guys are admirably meticulous. I suggest the cam timing which is best for your motor is the setting which best suits the inlet and exhaust system you are using. And you will only find that out by trial and error and by test riding the bike. What I usually do is set the tappets to normal running clearance and turn the motor forward until I reach the point at which I want the inlet to open, then install the cam sprocket. My cam sprocket has three keyways which were broached at random positions, so I can get the inlet opening point to within about 3 degrees of the recommended. With the 850 cam, the recommended settings are in the manual. I then check the inlet and closing points are where they should be and I write down what I achieve. I also look at the timings tables in Tuning For Speed, especially looking at the timings for the 7R AJS. That gives me some confidence that the timings I am using make sense. I rotate the motor and check I have clearance in the combustion chamber by levering the valves down a few times as the pistons pass TDC. Then I start test riding the bike and varying the cam timing to find the optimum setting. With my 2 into 1 exhaust, my 850 cam is now set 12 degrees ahead of standard. If I was using the Combat cam I have in my drawer, I would probably start testing at 6 degrees ahead of standard timings. With the 850 cam advanced that much, I believe the exhaust valve closes too early. With the exhaust valve opening so early, noise is a problem.
When you buy the hot cam for your bike, you don't usually know what type of exhaust system the guy who created it was using. With the Triumph Tiger 100 race kit which came out in 1953, both the recommended exhaust pipe lengths and valve timings for use with the E3134 cams are specified . With Commandos there are many options for the exhaust system. If the exhaust system tends to be restrictive, I would try advancing the cam timings.

According to many , Equal lift at 4 degrees btdc exhaust stroke works for about any ic engine, lawnmower or racebike.
I first used this method with the experimental TPrince MK 5 cams on the 1360 Egli.
It runs very well, it is a great producer of G forces.
Have used it since on a couple of other totally different engine, both were crisp as could be.
A friend of mine has switched over to this method vs his old method of timing by opening and closing points.
Same result, easier to do and stronger running engines.
It's probably very close to, if not the same as the method Jim Schmidt describes.
I like using the equal lift point because it is very easy to find.

Glen

IMHO if you have to advance a cam 12 degrees you have the wrong cam.

acotrel said:

With my 2 into 1 exhaust, my 850 cam is now set 12 degrees ahead of standard.

Click to expand...

Similar to what Glen said.

Axtell's cam specs usually pointed to about 2 (to 4?) degrees advancement from a straight up split. This gives you a bit more mid range punch than an even split.