Newbie setting valve train geometry

[cgates30]

I'm trying to set up my valvetrain geometry on a 2056 build. I'm using the Porsche swivel foot rocker adjusters with 1.7L rockers. I've filed the rockers down 0.060" and the fit is still tight using the 27.1cm push rods that I was trying to reuse. To get a little more room, I used 0.050 shims to raise the rocker shaft. As an example, now with the shims I am getting 0.410" intake valve lift when fully open and 0.362" on the exhaust. The intake for this cam should be 0.393" and the exhaust should be 0.368". The adjusters look nice and parallel with the valve stems at the 0.205" and 0.184" positions.

These numbers are within 5% of the spec lift, so I'm wondering what are the benefits of trying to get closer to the spec? Since the exhaust is a little under spec, would it be useful to try and find a pushrod length that would give a better lift? Also, if changing the pushrod length helps to get more lift, wouldn't it be good to try to get all of them a little (within 5%) more lift than the spec? (Is it even possible to do that?)

[Piledriver]

About the best you can do is attempt to get the adjuster dead parallel to the valve stem at mid-lift.

You may need thicker shims under the rocker stands: I have used .080" thick "grade 8" washers from the hardware store several times. (may need a bit of a trim on the OD not to rub on the rockers)

You may lose a little lift (or maybe not) but it will result in minimum side loads on the guides, which is actually the primary goal here, as you are not shooting for a 10/10ths max performance deal.

The 911 swivel feet help reduce guide wear a lot by themselves, even if the geometry is less than perfect.

Having said that, a set of cut to length pushrods should be budgeted in/purchased, helps prevent bad calls trying to reuse parts that shouldn't be.

You will likely find you need different I/E pushrod lengths for best effect.

[wreck]

Something to take into account is rocker ratio , reading through various forums I've read people testing 1700 rockers found that the ratio on the inlets average around 1.32 and the exhausts 1.25 . everyone just says they are 1.3 , I wonder if the cam manufacturer just go with the 1.3 on both lobes .
It's something I'm going to check when I do the rocker geometry on an engine I'm putting together, hopefully soon .
Can you give some feed back on the ratios you've got .
cheers Derek

[cgates30]

My shims are washers I got from the hardware store. I had to file them smooth to get the same thickness. Without the shims, there isn't much if any adjustment to be made with zero lash. The shims do allow for some adjustment and at half lift the adjuster looks like it is in line with the valve stem. I'm not sure of the exact rocker ratio.

The way I'm understanding it, with a shorter pushrod the adjuster has to be extended more and the rocker ratio multiplies that by a factor of 1.3 (nominally). So, shorter pushrods should create more lift by a multiple of 1.3 times how the pushrod was shortened. In that regard, your comment that the exhaust pushrods could be shorter than the intake follows what I saw when using the same length pushrods made the exhaust lift a little under the target.

As you mention, the side loading is a concern so you don't want to shorten the pushrods below the point where the valve stem to adjuster aren't in line. At least that's how I'm understanding it.

[cgates30]

My cam should give me 0.393" lift for the intake and 0.368" on the exhaust.

For cylinders 1, 2, and 4 I got 0.400+/-" intake and 0.363+/-" on the exhaust.

On #3, I'm getting 0.369" on the intake and 0.353" on the exhaust. I've tried changing the pushrod length and changing the shim thickness, but can't get anything better.

I did not measure the cam beforehand, but I'm wondering if this means my cam wasn't ground properly? Is there anything else I can do to improve my lift values on #3, or do I have to split the case and get another cam?

[Piledriver]

You can check the cam lift simply by measuring lift at the pushrods, directly.

Swap the rockers around, first.

[cgates30]

Derek and Piledriver,
I just checked the ratio of the exhaust and it is 1.25. Measuring lift from the pushrod, I got 0.284". Multiplying by 1.3 gets me 0.369" which is what I should be getting. On the intake, I measured 0.301" on the pushrod and 0.369" on the valve spring retainer, giving me a 1.23 ratio. If the rockers were 1.3 like the manufacturer thought, then I'd be right at the specs.

The valve lift on the other three cylinders is pretty much where it needs to be, so there must be a good deal of variability and I just got lucky that I got three intakes/exhaust rockers were 1.3 instead of lower.

Now, the challenge is where do I get 1.3 rocker arms.

[Piledriver]

ADHD engine builders (and anyone building something to race) have been known to go through bins of used rockers to find a fully matching set with max ratio...
I haven't run into that issue yet, maybe EMW or one of the other type4um members has deep bins of spares you could buy a few pairs from?

The exhausts are usually closer to 1.25 but it sounds like you hit the lottery...

If all else fails put the low lift ones on #3.

[wreck]

I've 2 sets and haven't measured them yet. You may be able to adjust the pushrod length to change the geometry to increase the lift on that cylinder . A good friend builds Formula Vee (Type 1) engines here in Oz and can spend a whole day just on pushrod length and shimming rockers to get the maximum allowed lift on all the valves . If you want to try more rockers EMW have stocks of old ones .

[cgates30]

It seems like someone could weld the 2L rocker arms closed and make jig to locate a new hole and get the desired ratio. It's probably harder than that.

I've played with adjusting pushrod length and shims and couldn't buy more lift. I think adjusting pushrod length and shimming is to get the mid-lift alignment between the adjuster screw and valve stem. The lift is a function of the rocker arm ratio, from what I can tell.

[Piledriver]

Getting the hardening right again in the cup might be iffy.
One semi-sane way to get that right would be weld on some additional material and drill/thread for a "cup" style adjuster screw on the pushrod side.
(basically just using as a hardened cup, not adjustable in final form)
That would also allow significantly changing the geometry of the rocker arm, aside from just the ratio...

If that would be durable enough is questionable, but they do weld submarines together.

I'm tempted to try that on some 2L rockers, if only to see how much ratio can be had before running out of pushrod tube.