cstraub wrote:... Sweep method was used when it was built.
When you say that, do you mean that it was supposedly set up for minimum sweep and that the approach caused guide wear, or did you mean they focused on getting the pattern centered, regardless of side effects? Your method is elegant and much quicker than working to minimize sweep via a retainer-mounted dial indicator, but by my reckoning should result in exactly the same geometry, since "90° at half lift"* results in the minimum possible sweep.
*FWIW, our 8200 RPM, 0.720" lift Yella Terra-rocker steel valve SBF road racer has run two full seasons with no noticeable guide wear using the dial indicator approach, but I will check it for 90°, JIC.
Scott's method should work fine
never done it that way- have to give it a try
his way is mathematics
I've used mechanics
should get you to the same place
thanks Scott et all
btw
some really crazy videos on the right side of the page
I watched the crane one and we actually did some early stockers that way to get more valve lift
IDK how it would work with today's high lift cams, it even wore the guides back in the day
your camgrinder must know what method you plan on using or use the one your camgrinder suggests
if they know WTF they are talking about- some don't, they just copy and grind cams
I liked the video too. I have never done it that way beither. the midlift 90 deg is the point of tangency to the valve line of action. this is the same thing that is accomplished with the narrowest wear pattern. By definition, the narrowest wear pattern is as near to tangency that can get.
Scott's method works very nicely, it is definitely less subjective. but in the engine compartment can be a little bit of a hinderance. I think I will head towards that method, or atleast a hybrid of the two. thanks for the doing that video.
The big question I get confronted with is how much off-center is really permissable. I can do engineering and eccentric load calcs, but often times people just want to know how close can you really get to the edge. Optimally, I say to break the valve tip diameter (not the valve stem diameter) into thirds, and try to stay within that middle third. But at the absolute max, into fourths, and stay within the middle two, but absolutely no more.
Its kind of spring coil bind. I have target values and I have absolute minimums.
I'll have to watch it again
but to me the drill would be
find the lash at the valve
convert to clearance at the cam - inverse of rocker ratio
determine the base circle
determine the gross lift including lash clearance
subtract the clearance from the cam lift to give net lift- - that's what you want to find the mid lift of
follow his procedure with turning the adjuster
I've rotated the cam to half net lift with a dial indicator and fixed the valve at half lift with a clamp on an old stem seal
fixed the rocker at tangent by adjusting the height of the fulcrum (with a little spring on stud rockers) shims with shaft rockers, lash caps, whatever like cutting the stands, then measured for pushrods.
sometimes the fulcurm has to be moved in or out or shorter or longer arms used
If we are getting into exactness and accuracy within the methods, in the video, you cannot truly say that that lift at the valve equals lift at the stud. There is an additional component, due to angle between the stud and valve that is not accounted for. However, You can say lift at the valve can be used at the stud to get 'close enough '. What is happening at this point is that when the point of tangency is obtained, or close, then there is is a reasonably wide window of adjustment. The assertion that lift at the valve equals lift at the stud is within that 'close enough' realm. I'll run some numbers, once i can get out and make some measurements.
For example, if you obtain tangency at zero lift, then lower the rocker pivot height 1/2 of the lift, you end up darn close to tangency at mid lift (the desired outcome), but not exact. Unless the rocker stud and valve are parallel, its not exact. There is a trig component at work. If you say the valve stem is adjacent leg (of the triangle)' then the rocker stud will be the hypotenuse. So the cosine of the angle will provide the multiplier for the true measurement of converting valve lift to stud adjustment. The angle does not even have to be perfect, it just has to be in there to get that much closer to perfection.
With the wear pattern method, the trig Is already in there (ragu). The problem with wear pattern checking is that it is somewhat clumsy and not exact either. Its the same thing, it puts you 'close enough'.
Perfect is perfect. However, nearly perfect (+/- from perfect) is quite forgiving, in terms of adjustment.
Regardless, the video is awesome and demonstrates a great quick way to obtain proper length. Easily, as close as measuring wear pattern, if not closer. I have thought about some videos too, they can be extremely helpful.
This question may seem vague, so here goes, if you could not get your roller sweep pattern centred on the valve tip, what would be better?
A roller sweep off centre to the intake or exhaust side? What are the downfalls for having it intake side or exhaust side?
I don't think it matters which way. BTW, just to reiterate: with the pushrod length correctly selected, the only ways to adjust 'off center' contact are a different fulcrum to roller length in the rocker, or if like most engines where the valve is not parallel to the stud, a mix of shimmed/cut rocker shaft stands, longer/shorter valves or the addition of lash caps.
Crap---My goal is too try all these methods. Im into my 3rd day and 4th jar of moonshine. I start out pretty good but about half way thru the jar, I furget what I had done and I have to start over--but I have been able to keep the rocker on the valve,,I think. I have got blue dykem all over he-- and back and Bernice aint gonna wash my clothes no more with that blue stuff on them.
reed
xanadu wrote:This question may seem vague, so here goes, if you could not get your roller sweep pattern centred on the valve tip, what would be better?
A roller sweep off centre to the intake or exhaust side? What are the downfalls for having it intake side or exhaust side?
I dont think that matters either.What does matter is the farther away from center (with in reason) the contact patch is on the valve tip, then the contact patch's surface area decreases. This concentrates pressure into a smaller area. Depending valve spring pressure, this could spell out problems with brinelling.
What I would do in a situation where the contact patch is way off (but what is way off?) I would move the studs inboard/ outboard the amount needed to center. If shaft rockers, I would move the stands inboaed/ outboard the amount needed to center. I guess this is one of the ''fun'' areas of engine building....and then there's the Spin-Tron.
wyrmrider wrote:Nice post Buddy
some use a horizontal dial indicator instead of dykem to get minimum sweep
I prefer to do it like so,,,,, I use the piston as a valve stop at whatever lift I have & open the valve by hand with the rocker, no pushrod involved until you have your height
But Scott's way is just as good & you don't need the tool
I keep intending to spring for a 0.100"+ range test indicator (lever arm instead of a plunger, for those not familiar with it), to eliminate issues with the indicator fouling a tall valve cover rail or whatever. Also, then I could dazzle onlookers by quoting sweep to four decimal places...
