Someone walk me thru my rocker installation....

[Guest]

Ok, I have decided that because I had my head shaved by 0.120" I would need slightly shorter push rods. The advice went from stock length to shorter-by-length-of-shave length. I settled on 0.100" shorter chromoly push rods. My roller rockers (which I have had on the head for two years with stock-everything) are 1.55:1 ratio and the geometry of changing the push rods has eluded me. That is why I went with some sage advice and dove in blindly. When all else fails, guess... Anyway, the question of the day is: how should I set the adjustable ball screws in the rocker arms (I installed the longer screws just in case.) And how to set up the rocker assembly from total scratch? When is a valve completely open and how much should one tighten down on the adjustment screw before no more tightening is needed? Making sense yet? I have been assured that no valve will hit a piston with the setup I have, so how open is open? Since I plan on cranking this monster on Thanksgiving, I really don't need a huge screwup at this point. Is there a copy of "Rocker Arms for Dummies" in PDF version on the web?

(After all this turning of my crank with my new GP2 cam, before the all-important initial startup, I will have to lay in some more white grease on my cam lobes from the bottom with an injection tube. I have turned it so much that pretty much all the break-in gunk is off the lobes.)


Bill

 

[piman]

Re: Someone walk me thru my rocker installation...

Hello Bill,

I would firstly say that I have no experience of roller rockers. Basic principles, however, remain the same.
In an ideal set up the valve should be at 50% lift with the rocker horizontal, i.e. when closed the rocker is at 90 degree + x degrees and fully open at 90 degrees minus X degrees. This gives the optimum valve travel. In practice this will vary. If Triumph achieved the ideal with a standard cam and you fit a higher lift cam with the same base diameter then the + x will be less than the - X I talked about above.

Basically you need to just set your valve clearances as per manufacturers specification (Either or the cam\rocker manufacturer I mean, not Triumph. I assume when you say ball screws you mean the screws that rest on the push rods). Once you have done that then that should be correct. To prove that there is clearance between the valves and the pistons go round each valve in turn with a (say) 60 thou feeler between the rocker and valve tip and rotate the engine until the valve goes past full lift. If you have any sudden tightening of the engine, the valve is touching and you have less than about 50 thou clearance which is too close.

Sorry this is so long but It's difficult to explain and try to be clear.

Alec

 

[Alan_Myers]

Re: Someone walk me thru my rocker installation...

Hi Bill,

I haven't installed roller rockers on my car, yet, but have been giving it consideration and have done a bit of research.

Frankly, I planned to avoid any additional lift with a higher ratio rockers, the cam going into my car will give all the lift and duration necessary. Most cams are designed with standard ratio in mind, unless there is something else specified on the cam spec sheet. On the other hand, 1.55:1 is probably only a minor increase. Stock is probably 1.5:1.

One thing you have to watch for, especially when increasing rocker ratio, is spring bind. That's when compression of the valve spring causes the coils to actually come in contact with each other. This can pull the locks out of the spring keeper, break springs or even bend the valves. Combining a high lift cam with increased ratio rockers can particularly lead to problems.

There is usually a specification of a minimum amount of clearance needed within the coils of the springs. It's about 3mm on my TR4, I recall correctly, but might be different for your car.

Ideally, it would probably be best to compress the springs before installing them, measuring the height at maximum compression. Then compare that to the length of the spring at full cam lift, i.e. at the top of each lobe, when installed. You might be able to test and observe the maximum spring comgression in your setup, just turning the engine over by hand. I'm not familiar with your particular setup, so just be sure to check it.

You could pour some STP over the cam for the initial startup, too.

Was the cam hardened before installing? I assume you are using new cam followers?

Custom length for the pushrods is best determined by measuring for each one with a special, adjustable dummy pushrod. This will take into account not only the change in head dimensions, but also a re-ground camshaft, and/or any change in head gasket thickness.

 

[Rick O.]

I suggest you study the install docs available for download at the Isky website. The GP2 cam has 0.258 lobe lift, which puts you at 0.400 at the valve with your 1.55 rockers, well within the margin for a non-interference fit for both the valves and their springs (no coil bind). You need to ask Richard Good what his recommended valve lash settings are. After that, just screw the adjusters down to that (cold) setting (may be different for the intake and exhaust). Did you go with 0.100-short pushrods because of your roller geometry?

 

[LastDeadLast]

I asked Richard this same question, his reply:

[ QUOTE ]
With my GP2 or GP3 cam I
would recommend 0.016" intake and 0.018" exhaust. With another cam just
figure 0.001" more than the manufacturer's recommended lash.


[/ QUOTE ]

 

[trfourtune]

hey,
the usual set up to look at is: the motion of the roller across the valve stem first. accepted practice is @ 50% lift the roller in dead centered on the valve stem, so the roller sweeps across the stem from one side to the other in its motion. this is adjusted by the height of the rocker shaft by shimming or milling the rocker shaft pedestals. then you look at the length of the push rods. the length will affect the angle of the push rod through its motion. this can be a bit complicated but if you want to get the most lift at the valve this is what will affect it. this relationship between the imaginary angle of the rocker(centerline of shaft to ball/shaft pivot point) on the push rod side, to the angle of the push rod, is what determines the optimization of movement. the circle track guys with push rod v8s are a whealth of information on this. they have some new theories beyond the common practice that optimizes better because of the Rate of valve opening that can be better. i read an article in "cirle track" about Crane's new roller rockers that put the roller at the center of the valve stem at full open instead of 50% because it improves the rate of valve opening at different time in the movement. in our triumphs, we can come close to what Crane does just by the height setting of our pedestals and the length of our push rods. now your completely confused but this is what the magic of engine building is all about.