Suck Squeeze Bang Blow

kopcicle

antidisestablishmentarian
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Suck Squeeze Bang Blow
or for the politically correct and exacting but humorless engineers '
Intake Compression Power Exhaust

There are two major pressure changes in a four stroke internal combustion engine , when you light the fire which is easy for you youngsters with your electronic ignition and when you let go of it . You go to people like Falicon with your cranks and A.P.E. or Branch with your heads . Pistons are weight matched within 1/8 gm or less .Even intake and exhaust ports are cc'd .Combustion chambers are volume matched within 1/4 cc or less . Some spend thousands on dyno time getting the perfect jetting or fuel map .
Then you adjust valves with a feeler gage ?
The valve clearances suggested by the manufacturer are just that a suggestion to keep you from holding a valve open or beating your valve train to death . Until Yamaha recently decided to experiment with 90 degree cranks all the inline fours used a flat (180 degree) crank with #1 and #4 at TDC and #2 and #3 at BDC . each pair firing alternately . Until the CBRXX no one thought to balance out this rocking couple but that's a story for another day . The point is why would you want to introduce any further variations in balance by scattering major pressure pulses over as much as 10 degrees of crank rotation ?
Use a positive piston stop to establish TDC and adjust the degree wheel to match a pointer . Insert the correct feeler gage between one exhaust valve and the rocker and adjust till there is a slight drag . So far this is basic a valve adjust . Now place a dial indicator on the spring retainer of this exhaust valve and preload it at least 0.060" . Pick some arbitrary lift distance like 0.030" and mark it on the dial . Rotate the crank until that valve has opened 0.030" and mark the degree wheel . If you started with #1 now go over to #4 and adjust the exhaust valve so there is that slight drag on the feeler gage and move the dial indicator to that retainer and preload it . When it has moved 0.030" look at the degree wheel . It should be 360 degrees out from #1 AND ON THE SAME MARK . Unless lady luck intervenes it won't be . Variations in cam indexing and tolerance as well as deformation of the top of the valve make it unusual in the extreme for all this to work with simply a feeler gage .
In the end all exhaust valves should be opening at the same place in degrees plus or minus 180 degrees at 0.030" lift and be within specified lash limits . If you have gone this far then repeat for the intakes even though the effect on the engine is not nearly as dramatic and closing more critical than opening .
Now of course when confronted selective shim valve adjustment you are limited to just how close you can get to ideal . Or are you ? If you have enough experience to have adjusted valves on an 8 valve kawasaki , Suzuki or other then you remember they came in half millimeter sizes ie 2.30 , 2.35 etc . I have sizes in 2.325 , 2.375 . If you think this is overkill imagine what you find in a factory race team's box of shims . I don't have to imagine it , I've seen it .
I do have a curious and humorous way of doing this that I have used to demonstrate the principal in a classroom and as a garage joke with friends . I'll set up the degree wheel ahead of time and expose the valve adjustment . I found a hose that just screws into the spark plug holes rather than continually removing the valve from my compression tester .
To the end of the hose I attach a rubber , yes a prophylactic , un-lubed , with a rubber band . The compression stroke inflates the "balloon" and the exhaust opening rapidly deflates it .If you really want to drive yourself crazy try the above procedure with the dial indicator and then repeat it with the balloon . I recommend a very little light oil on the seat . Now observe what a change of just 0.001" (insert a feeler guage between the rocker tip and valve or the cam lobe and "lifter" ) does in relation to opening in degrees . Then for those that obsess try just a 0.00025" or 1/4 thou change and record the difference in degrees at actual opening *. This "shade tree" device , with a little practice will also give a indication of low pressure cylinder sealing that a leak down tester will not unless equipped with gages costing several hundreds of dollars .

I'll attempt reason without anecdote or explanation .
If your cam specs are @ 0.040 lift and intake opens 19 degrees BTDC and closes 46 degrees ABDC and exhaust opens 34 degrees BBDC and closes 16 degrees ATDC ....
ALL exhaust valves are opening at 34 degrees before bottom dead center for their respective cylinder AND staying within acceptable valve clearances ( .007" to .010" ).
The lash or static clearance has far less impact on engine performance if kept within the manufacturer's specified limits than does adjusting the exhaust valves to open at a specific point in crank rotation .
I lifted representative specifications from an older megacycle 493-x1 cam

So it's up to you . Call it lazy to use just a feeler gage and get out simple tools and take a little extra time and get it right or use just a feeler gage and get close .

~kop

* 0.00025" or 1/4 thou @ actual lift was a difference of 4 degrees in exhaust opening measured on a SOHC Honda 750 ~kop
 
Suck Squeeze Bang Blow-we can make your motor go
feel free to quote me ;D
 
Still trying to live up to it Pj ? (how is the physiotherapy going ? Still 3 times a week?)

~kop
 
Nope, had surgery last August, physio stopped in Sept~Oct (I forget when, not that it matters)
I got to have a more major surgery in April because the first one didn't work.
Will be completely out of action for 3~6 months
 
Agree 100% that cams are rarely ground the same from one cylinder to the other and sometimes the differences are significant. In addition all cams have long acceleration and deceleration ramps that make actual closing/opening times appear to be almost arbitrary at times.

Sometimes the whole cam shape is phase shifted and other times it's more a matter of grinding tolerances. Production cams seem to be much better than aftermarket for some reason.

And yes, so events are much more important than others in terms of cylinder pressures.

And some cams have ridiculous acceleration and jerk rates that they could never last. They just pound valve gear to death. And of course people have been playing with crank angles for years on Brit twins trying to work out the optimal phase differences.
 
I tried adjusting the valves on my DS7, but I couldn't find them :eek:
But then she's kinda kinky too. She'll suck and squeeze at the same time, and bang and blow at the same time. Or is it blow/suck and squeeze/bang? I forget ;D

(hint: it's a 2-stroke)
 
Sorry for resurrecting this one. I was talking to kop in the shout box and I have some related questions...

So what is the correct way to set the valve clearances? Use a timing wheel to ensure proper opening and closing times rather than just going with .003" and .004"?
 
Valve clearance and valve timing are different things.
You time the cam with ZERO clearance and measure at 0.040" or 0.050" lift with degree whel and dial indicator. When cam timing is et, you adjust valves to running clearance (0.002" in, 0.003" ex for most Honda's)
 
So when kop says, "Call it lazy to use just a feeler gage and get out simple tools and take a little extra time and get it right", what are the correct tools?

And how does one adjust the cam timing? The cam gear only attaches to the cam one way and there are only so many teeth on the gear...
 
Unless gear is pressed on to cam, you slot he sprocket to get timing right.
I have pics of setting up am timing in my 360 build
 
Awesome. Thanks for the help, pj.

Is there anything that can/should be done about uneven lobes on the cam? Theoretically speaking, let's say left cylinder is closing 14° ATC, but the right is closing 15° ATC.

Also, does cam timing change throughout the life of the cam chain? When I adjust the tensioner, is it changing my cam timing by a bit as well? I know decreasing the distance between the cam and the crank causes a change in timing, but I'm not sure if that's a function of the chain or the actual distance between the two...
 
Cam timing gets retarded as chain wears but it's not an issue (unless your racing)
If you check a new motor, usually you'll find cam timing is a few degrees advanced and bike gets progressively better after a few thousand miles. As everything beds in and wear out, retarded cam timing allows slightly more rpm so rarely do people really notice any difference (with motors under 30,000 miles)
 
I adjust valves with a dial indicator and a degree wheel to open at exactly 90 , 180 , 360 degrees apart depending on engine AND within manufactures recommended limits . To large and the pieces beat themselves to death , too small and a valve is held open . As I described I've seen as much as 4 degrees difference in opening with just .00025" difference in clearance ( not a typo 1/4 thousandth) at opening . You'll be relieved to know that once on the ramp the differences are much less .

Indexing a cam by splitting lobe centers or otherwise is one thing . Having your valves (exhaust especially ) open at the same point in crankshaft degrees is yet another .

~kop

Yes Pete I obsess
 
kopcicle said:
. As I described I've seen as much as 4 degrees difference in opening with just .00025" difference in clearance ( not a typo 1/4 thousandth) at opening .

Yeah, but that doesn't have to mean much when it
occurs where the slope of the valve lift graph is small,
e.g. at the very beginning of lift or at lobe center.
Very little variation of lift leads to big changes of
the corresponding crank angle, this is why we try
to check timing at a steep point of the valve lift graph,
as e.g. 1mm or so.

Best regards
Sven
 
Sven is right, the quietening/lift/closure ramps are long and it's easy to get huge timing shifts with small changes in gap. Gaps should be set to stock because that's in theory where there's enough gap so the valves don't get stuck open when hot and not so much that the cams are battered to dewath by too much clearance.

Aftermarket cams are also never ground as accurately as the time card might suggest and always require some judicious juggling and difference splitting to get a set of valve timing events where you need them to be.
 
Have to admit I don't really dig the whole procedure...

Let a multi cylinder crank be given with whatever offset
angle of crankpins for reference. Let the cams not match
with these angles properly.
At least "exhaust opens" shall be adjusted to be at the same
crank angle for all cylinders. As the cams can't be turned on
their shaft, we try to get "eo" degreed in by slightly varying
the valve lash within its permitted interval.
We found that a change in lash of only .00025" can correlate
with a crank angle of 4°, so it shouldn't be a problem to com-
pensate even bigger variations of timing (as .00025 is by far
smaller than the permitted range of valve lash).

But what's imho been unconsidered is the fact that the
couple (4°; .00025") refers to the opening ramp of the
cam, whereas timing of "eo" will be defined/checked at a
valve lift of .030". As mentioned above, the valve lift
curve is much(!!) steeper in this area (that's the reason
why we use it for degreeing), so any change in valve lash
will correspond with far(!!) smaller changes in crank angle
here. Other way round: to compensate a false timing of 4° at
.030" valvelift it takes by far more than the mentioned
.0025" change in valve lash.

So what I'm trying to say is that with this method any
failure in timing worth mentioning can perhaps be
cured at operating lash, but not at a reasonable lift
used for degreeing in.

Like to hear your opinion!

Best regards
Sven
 
teazer said:
Aftermarket cams are also never ground as accurately as the time card might suggest and always require some judicious juggling and difference splitting to get a set of valve timing events where you need them to be.

That's soo true, today I adjusted some White brothers camshaft for my XT500 engine
and it was quite far from what the timing sheet said. Yes, I took special care and double
checked each measure...


DSC08052%20-%20Kopie.JPG


(milled down a rockerbox for better access to cam sprocket and spring retainers)


Best regards
Sven
 
Is there a formula for determining when valve float will take place? That moment when the equal and opposite reaction of the valve spring fails? Is shimming a valve advisable to reduce valve float?
 

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