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Setting rocker lash.....

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When setting the lash on my roller rocker arms (or even stock rocker arms) the book says to start by watching rocker arms on 10 and 12 rock all the way down to open said valves then to adjust the lash on rocker arms 1 and 3. And so on. When watching these arms go through the motions and trying to catch them at just the right depth (the bottom), invariably it seems to me that one of the two will depress a bit differently than the other, that is, they don't seem to be all the way down (and perhaps the valves all the way open?) at the same time. Is this my imagination and should I try and set each valve lash as a single set or go in pairs and assume that this is close enough. I use the starter to get close then adjust the final drop of the rocker arm with a BFW. What do ya'll do?

Bill
 
HI TR6BILL,What the book is indicating but evidently not telling you the whole story is this is the NO 13* method of adjusting valves on a 6 Clyn Engine. From your example; valves 10 and 12 are open so the valves to adjust are: 13*-10=3 and 13*-12=1 . This numerical relation ship is maintained until all the valves are set to the proper lash specification. ---Fwiw--Keoke
 
Hello Bill,
that is the way that Triumph specify and I have always done it that way. I agree that there seems to be a slight difference in timing between the pairs specified but the pair that is being adjusted is on the cam base circle which has a fairly large angular tolerance before the gap starts to move.

Alec
 
Yes. The #13 rule should work fine. I've never noticed the slight difference you've noted.
One thing: I usually put the car in 3rd or 4th gear on level ground and push it to get the valve "just so".
 
AFAIK, that "slight difference" means nothing in terms of applying the "Rule of 13" (or "Rule of 9" on the four-cylinder). All that matters is that you're adjusting a valve that isn't already partially opening or closing, and it's easiest to identify which valves to adjust when by that "Rule of..." method.
 
I read this artical about adjusting valve lash and push rod length when roller rockers are being used and wondered if the same follows for non roller rockers. I think it assumes the cam is concentric except for the lobe part of the cam. And, if the wiped part of the end of the valve stem is wiped simularly with roller and non roller rockers, it shure seems rollers would give up a great deal of power vs non roller to be used at the rear wheels.

.............. we should address how the rocker tip travels across the tip of the valve. You might think the tip remains in the same place throughout the entire lift curve. But as it creates lift, the rocker arm travels in an arc that sends the rocker tip across the valve-stem tip. Amazingly, the rocker-arm tip moves quite a bit, especially if the pushrod length is not correct. Proper pushrod length tends to minimize the amount of rocker-tip travel across the valve tip.


To establish exactly how much shorter to make our new pushrod, we used this Comp Cams adjustable pushrod. For every turn of the threads on the pushrod, it adds 0.050 inch to the overall length. Think of it as a pushrod micrometer.
It's worth discussing the fact that the rocker tip is actually quite busy across the valve-stem tip. Even with proper pushrod length, the rocker tip starts from the inboard side of the rocker. As lift begins, the rocker tip moves toward the center of the valve tip, approaching the middle of the valve at approximately half of maximum valve lift. As lift continues, the rocker tip moves past the valve tip's center toward the outboard edge of the valve stem at max lift. Then as the valve begins to close, the rocker tip retraces its movement back to where it began. In essence, the rocker tip sweeps across the valve-stem tip and then returns. This is what the rocker tip does with proper pushrod length. With either too-short or too-long pushrods, the roller tip starts in the wrong position and travels much farther. This can lead to all kinds of dangerous situations, all of which can also create valvetrain problems.

It's worth mentioning that this improper pushrod length can also cause increased valveguide wear, even in engines with relatively low mileage. This is especially true with higher rocker-arm ratios due to the additional side load imparted on the valve-stem tip. Any time the rocker arm pushes laterally across the top of the valve-stem tip, a certain amount of lateral leverage is generated against the guide. The only way to minimize this is to reduce the amount of leverage on the valve from the rocker arm. The easiest way to do that is to establish the proper pushrod length!
 
vettedog, first, the tip of the rocker location on the valve has NOTHING to do with the push rod length, it has to do with the (in our case) HEIGHT and LOCATION of the rocker shaft and the design of the rocker (if original rocker, the profile surface on the tip of the rocker). we have a shaft mounted rocker and we can shim up the pedestals or machine them shorter. we could make different pedestals to put the shaft exactly where we want it.
the push rod length will affect the angle that the push rod is at and moves through and the loction of where the ball and socket mate at the ROCKER. if you want to optimize you cam, this is where to do it. the rocker to valve and rocker to pushrod each have their own arcs to optimize.
rob
 
Rob:
I was interested in the "wipe" action of the rocker on the end of the valve stem where it would seem logical that the apex of the cam lobe would place the point of contact at the edge of the valve stem. Is that the way The TR6 nonroller rocker contacts the valve stem? In the past I was only concerned about the gap between the rocker tip and the valve stem but now I am wondering what kind of timing, max valve opening, etc. is being done with the static setting of the valve lash.
 
vettedog72, first, i cannot tell you specifics about the six since i am a four guy but the geometry etc is not specific when you look at push rod motors with , in our case, rocker shaft mounted rockers. second, valve lash clearance is set ONLY for the thermal expansion of the valve and valve train components so that, at hottest, operating temperature the valve will still close 100%. otherwise you can burn your valves,loose compression, and if the clearance is too much, you give away lift and duration at the VALVE as well as you can beat up your valve train with shock(if too loose), not good (we get this every time during warm up). the transmission of movement from the cam to the valve is NOT in direct proportion to the cam movement plus the quoted ratio of the rockers. there are two sides to look at. first the valve side. setting the height of the rockershaft by shimming or machining the pedestals and/or grinding the valve stem tops to get the roller tip to sweep from the outside of the valve stem to the inside where at 50% the roller tip contact is centered on the valve stem. this is the standard practice. but also the angle ,from the line from the center of the rockershaft to the valve stem contact when the valve is at 50% lift to the line on the centerline of the valve, should be 90 degrees. this gives the most valve displacement. second the cam side. the push rod goes through an angular movement with the rotation of the rocker as well. we need to leave the height that we set for the valve side alone because we want to keep the contact on the valve as close to center as possible to keep thrust from the stem to the guide as little as possible. the length of the pushrod does two things: it affects the angle the push rod is at AND the contact point of our adjuster which gives the true angle line from the rockershaft to contact point. this combination of lines,pushrod centerline to rocker line should also be 90 degrees at 50% lift for max optimization.
this is the standard optimization. this should come close with the rockers you buy without too much work but every engine is just a little bit different than the next. there is a new set-up you can read about in "circle track" magazine, jan 2006, that is very interesting and that we can probably duplicate because of the design of our motors.
pick it up and read before you bolt together. it is a good excercise to measure up accurately all the locations,lengths,angles, of you valve train and draw at about 4 times actual size and model the movement (ie each position of all the pieces at increments from full closed to full open). the only linear movement is the lifter and the valve. all the others are arcs. have fun
rob
 
Thanks tr:
Your helpful response is golden. I am trying to understand the concept and am making the model as you suggested. I have learned more in reference to the rocker, push rod, and valve with your response than the long winded articles I have been reading.


I will be back with question when this info is absorbed.

Are you an engineer or "just" an extraordinary motor head?
 
vettedog, i am a mechanical designer in pulp and paper engineering. my schooling is from the british columbia institute of technology, mechanical engineering technologist and a cad/cam technologist. i design pulp mills for a living and do A LOT OF GEOMETRY!!! cars,motorcycles,airplanes are my passion, though, and have spent about 25 yrs studinging race cars and design in my pass time. and FYI i just found that there is a free modeling program from lotus engineering that you can use. it is for one cylinder only and i have not tried it yet but it looks interesting. hope this helps. ps i have read a lot of stuff in magazines that is pure BS. it helps to have some background to weed out the truth.
rob
 
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