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Author Topic: Suck Squeeze Bang Blow  (Read 10484 times)

Offline crazypj

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Re: Suck Squeeze Bang Blow
« Reply #10 on: Aug 12, 2011, 19:43:01 »
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
'you can take my word for it or argue until you find out I'm right'
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CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
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Offline Sonreir

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Re: Suck Squeeze Bang Blow
« Reply #11 on: Aug 12, 2011, 20:00:38 »
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...
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Offline crazypj

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Re: Suck Squeeze Bang Blow
« Reply #12 on: Aug 12, 2011, 20:58:46 »
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)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline kopcicle

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Re: Suck Squeeze Bang Blow
« Reply #13 on: Aug 14, 2011, 21:23:02 »
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 .

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Offline scm

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Re: Suck Squeeze Bang Blow
« Reply #14 on: Aug 14, 2011, 22:16:15 »
. 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
someone built it anyway ...

Offline teazer

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Re: Suck Squeeze Bang Blow
« Reply #15 on: Aug 15, 2011, 00:29:19 »
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.

Offline scm

  • Posts: 244
Re: Suck Squeeze Bang Blow
« Reply #16 on: Aug 15, 2011, 09:40:22 »
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
« Last Edit: Aug 15, 2011, 09:44:24 by scm »
someone built it anyway ...

Offline scm

  • Posts: 244
Re: Suck Squeeze Bang Blow
« Reply #17 on: Aug 15, 2011, 14:30:48 »
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...




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


Best regards
Sven
someone built it anyway ...

Offline mizuchaud

  • Posts: 25
Re: Suck Squeeze Bang Blow
« Reply #18 on: Aug 15, 2011, 15:00:18 »
sven, wish I had a nice window for daylight in my garage like you have there...
looks so clean.

Online Texasstar

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Re: Suck Squeeze Bang Blow
« Reply #19 on: Apr 12, 2013, 20:11:45 »
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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