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Camshaft 101....2 & 3

4.1K views 19 replies 8 participants last post by  got wake?  
#1 ·
So, I've had a few questions and thought I could shed some light for newbies and create something to talk about for the experienced.

Cam 101

Specs are measured at .040' / 1mm valve lift. (this will take out any lash and dictates actual installed and running duration) = true indication. All off road engines use this standard. Both OEM and aftermarket. There is no other way to compare. Cheating can be done by using 0 lash / valve clearence compared to using actual lash. Zero lash will show a higher duration. Monster specs are at recommended lash.

(note that japanese cars also use 1mm valve lift. And american cars use 0.050" valve lift, but they can use lifter lift too because they have different available rocker arms / ratio's. And lifter lift can allow a better description of what your buying)

IVO = intake vlve opens at _* before top top dead center
IVC = intake valve closes at _* after bottom dead center
EVO = exhaust valve opens at _* before bottom dead center
EVO = exhaust valve close at _* after top dead center.

To get the duration.

2006-2008 stock
intake = 5 + 180 + 45 = 230* duration
exhaust = 50 + 180 + 0 = 230* duration
Overlap = the degrees between intake opening and exhaust closing.
Stock = 5* + 0* = 5* overlap.

2009+ stock
intake = 5 + 180 + 45 = 230* duration
exhaust = 55 + 180 + 5 = 240* duration
Overlap = the degrees between intake opening and exhaust closing.
Stock = 5* + 5* = 10* overlap.

Monster Cams
intake = 20 + 180 + 62 = 262* duration
exhaust = 64 + 180 + 15 = 259* duration
overlap = 20* + 15* = 35* overlap.
 
#2 ·
Cam 102

Steep lobe ramps can keep valves open wider / longer than a shallow ramp. Getting more air in. Measuring at the standard valve lift gives a really good indication of true duration. When the valves are open 1mm - initial ramp is over. So duration is duration. BUT throughout the lift cycle, different ramps can have valves always open farther. Usually giving better top end performance over bottom end trade off.

You can even have the same duration many many different ways.
Eg:
IVO - 15 IVC - 50
IVO - 20 IVC - 45
IVO - 7 IVC - 58

All have 245* of duration. You could add probably 50 other combinations. Duration is only part of the story.

So their is total duration. There is duration vs open/closing points. There is ramp / lift during the cycle. There is the total lift. Then there is "time at full lift". Cams are very complex in the design. There's alot to change, they have different effects and then to make sure its right for a particular engine. But wait - there's one more.
 
#3 ·
Cam 103

But one of the most important factor is "when the intake valve closes" vs piston postion. This plays a huge role on rpm / scavenging effect / low rpm pumping losses. And why people degree a cam or look at the intake centerline. This will dictate where exactly the intake valve closes in exact relation to the piston position. You can install 'any' cam at 102, 104, 105, 106, 108, 112, 114, 120 etc etc. (adjustable gears). The spec is not given to be measured. Its given as to where that cam should be installed, in that particular motor. The spec, intake centerline, lobe closing ramp, and valve clearence are designed and given for each cam, in each engine.

Here's why.

Intake centerline is full open intake in comparison to piston postion. (in crankshaft degrees). Lobe seperation is in cam degrees, and indicates full lift of intake to full lift of exhaust. Lobe separation is what kind of specs out if its a bottom end cam, mid or top cam. Cuz it basically references the duration amount of a particular cam.

Why there is different intake centerlines.

Ok, so its in crankshaft degrees. BUT. Where exactly is the piston? Say its halfway down the bore. Now, stroke the motor. Your cam is still installed at the same crankshaft degrees. BUT - the piston is now 1/4 inch away from that halfway bore position. You need to change the intake centerline degree in order to get that valve closing again when the piston is halfway down the bore. Longer and shorter connecting rods will also change the piston position vs crankshaft degree too. (but with the exact same stroke!!!).

So every engine has a different piston position vs crank degrees. The rod length, stroke and crank web radius size all spec this. But the only way we can know where it is on a particular engine is to compare piston postion to crank degrees and reference from that.

What else effects the intake centerline?

- head gasket thickness.
- base gasket thickness.
- valve lash (clearence)
- cam gear slop
- cylinder or head maching
- timing chain stretch
- camshaft and rocker arm machining tolerences
- head and cylinder casting variances / tolerences off the assembly line.

As you can see, the above 8 variables will change a measured intake centerline. Adjust any of the above to "install" that cam at the recommended centerline. Most dont care or its beyond their control. Hell, a timing chain can easily stretch and show a difference of 5* from new.

The easy answer = Drop it in and run it. Enjoy. If your dedicated to get the most power out of a build - this is another key setup for the engine builder. (just like deck height and squish).

Its easy to get 90% of an engines power...... It's that last 10% that separates the men from the boys.
 
#4 · (Edited by Moderator)
The easy answer = Drop it in and run it. Enjoy. If your dedicated to get the most power out of a build - this is another key setup for the engine builder. (just like deck height and squish).
interesting read 800VTwin. but i cant help but think you have no regard for engine builders? to think that there is so much slop in an engine/timing is just scary.

i also must say, having set a few cams myself, lash is always at zero, or from the lifter. how do you set lash so accurately? why is seat to seat cheating? the only really accurate mesurement needed for cam timing is the intake line. or the exhaust line? the rest is just for comparison and really tested on the dyno. but intake is the accepted standard. you can make up any timing point if you wish, it just makes things harder. why dont you tell me in spanish? LOL. that is what standards are for. so we all understand and can easily do it.

i also cant help but believe cam makers and OE specs are not seat to seat, to make the numbers look as good as possible? so if your cams are with lash and at 1mm your's will seem small?

just asking.
 
#5 ·
interesting read 800VTwin. but i cant help but think you have no regard for engine builders? to think that there is so much slop in an engine/timing is just scary.
Have you ever even measured any engine?

Timing chains stretch. It's a given. This will change timing and can by 5* easily.

Have you built an engine?

- Many people have a surface machined when their engine is apart. Head or cylinder. Either because the surface was off or they had a sleeve installed.

- there are many gaskets available. OEM and aftermarket are different thicknesses.
Most shops even supply 2 different choices for base gasket thicknesses. 0.010, 0.16 and 0.032)

Different kits have different head gasket thicknesses. (0.022 - 0.056)

Pistons can have different pin to deck height.

And oem castings are far from tigh tolerenced. (head height, cylinder height) But mainly - Go measure the stock camshaft to gear play on a stone stock bike.

A stock engine, a built engine from an average builder or backyard guy or even a build consisting of many different brand products can be way way out. 10* is easily found. And 10* is alot of change !!!!

Its not slop. Well, the cam gear is slop. It's tolerence's and part changing. The reason people "degree their cam". I have total reguard for engine builders. I just don't keep secrets. I give the information to users so they can make a better build too.
 
#18 ·
bwahahahahahaha, show me an engine builder outside of serious automotive racing that works with tenths?! most engine builders don't even have the equipment to hold a one thou tolerance, let alone tenths.... and machinists rarely work with half a thou, tool and dye makers are the ones working with half a thou and tenths, or even millionths. here's a better question, where are there engine builders with a QC dept and measuring equipment to check tenths?
 
#7 · (Edited by Moderator)
I think you should stop hanging around those engine builder and build some yourself.

Seat to seat with no lash means nothing. It's bogus or cheating to get a longer duration on paper just like you said. But when installed in an engine- your back to real world use. Using a specified lift sets the standard, where they all can be compared.

BUT- Open a manual (got a canam one?) the specs are given @ 1mm lift. Look in your performance catolog. See if its seat to seat or at 0.050" lift?

Yes, my specs given are in a running engine. You do not run cams with no lash. I wanted certain specs during use. Do they seem small???

How is it not possible to set lash so accurately? It's within 0.001-0.002" - you cant do that? So.... all casted parts are dead accurate but lash is something that can't be set?

So, lemme guess. Your timed cams are perfect with no lash. But since you dont run your engine that way, after your job is completed and you set your valves up - your intake centerline is off. And if you cant set lash accurately, they could be more off? You have magic factory castings and your timing chain does not stretch.

I'm not sure of your reference to "engine builders". Who's these builders? But I think your referencing automotive performance shops or machine shops or nascar or ??? There are a few atv shops here on this site that build atv's for people. Most atv people do jobs themselves. Most are bought and installed themselves. Most engines never see clay.

So, you installed a few cams. I take that as you have a slotted timing gear and you set it up to match the spec'd intake centerline. (just off by valve lash duration change)
This is an atv site. There is no slotted cam gear available for this engine. And its extremely hard to make a reliable one based on the design.

So like i said - drop in and enjoy.
 
#8 ·
How is it not possible to set lash so accurately? It's within 0.001-0.002" - you cant do that?
no i do not think so. that is why there is a range. it is always seat to seat, unless being installed. and at that point it is only about centerline @ crank degree.

i think i will bail now as you are a scary dude.

no fancy ECM will ever correct for a poorly assembled engine.
 
#10 ·
Speechless.....

I am not sure of what your actually thinking / talking about. (in most of your answers)

What below applies here.

A - you think everybody who has engine work on their atv done goes to a proffesional engine builder.
B - you've never even looked at your engine at all.
C - you dont even own or ever seen a service manual for your atv.
D - you think off the assembly line atv motors are exactly perfect and "set up".
E - you dont own feeler blades or know what they are.
F - you cannot read or don't read specs or manuals and dont understand cams at all.
G - all of the above
 
#14 · (Edited by Moderator)
#17 ·
I'm glad you guys have the time to research all this stuff and post up the info. I just have time to put parts on/in and then go pull the trigger and try to keep the front tires pointed in a safe direction...
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Good info guys, keep it coming.
 
#19 ·
No worry wake. The same guys can't adjust valve clearence within 0.001". Not even a 0.002 range. Lol.

As you said, most stuff like engines, industrial machines, shafts & bearings all work within thousands. Even at that, all millrights or machinists are not equal.

Piston tolerance is not even a tenth of a thou. Some OEM's may claim that. But its more like half a thou. The rotax service manuals give the tolerence on all new parts. Lowest from half a thou but most up to 10 thou.

I am sure your gun barrels and hardware are tighter toleranced than most engine parts.
 
#20 ·
only the chamber specs and bore ID for the barrel were tight tolerances. most everything else was +-.001" at the tightest, but usually was +-.003". and the barrel was done on the same machine in two operations, no human intervention, so repeating less than .001" tolerances weren't difficult. cut down my jugs on that machine. got them both within half a thou of where i was shooting for. but how many engine builders have $400k turning centers? the shops that actually make the engine parts from scratch most likely do, but most engine builders don't have that kind of capacity. iirc mrrpm got a 5 axis machine, which i am envious of. but i got out of all that earlier this year anyways. i was on a fast pace to have a heart attack or end up in the nut house before i turned 30!