Wipe pattern opinions

[Tennesseejed]

Hi all,

 

I'm currently rebuilding my first 280z head (N42) and interested on opinions as far as setting the wipe pattern.

 

Pic 1:

 

 

Pic 2:

 

 

Pic 3:

 

 

I gather from my many hours of reading here at HybridZ that it is accepted, if not prefered, to have wipe pattern closer to the pivot side.

 

The cam is a Schneider Stage III and the rocker arms are reconditioned.

 

As part of rebulding my head, I shaved .050" and had .055" shims made. Not really sure why I added an extra .005" to the shim thickness other than I am reusing my timing chain and I'm sure it has stretched some.

 

I used SI valves which are advertised as 116.3mm (intake) and 117.3 (exhaust). Stock N42 valves are 115.2 (intake) and 116.0 (exhaust)(source: How to Modify)

 

I figured that if I was going to shave and shim .050", and the SI valves are approximately .040" longer than stock valves, then if I needed to adjust my wipe pattern at all, a lash pad in the neighborhood of .010" - .030" would suffice.

 

Wrong.

 

In the picture above, I am using the stock lash pad with additional shims of .095", .120" and .135" respectively.

 

I measured my stock lash pads at .160", but this is probably incorrect because I measured from the top to the bottom, not from the top to the bottom center with a mic. I.e, where the valve tip rests is recessed.

 

I suspect I overlooked the fact that my Schnieder cam has a smaller lobe base in order to make the lobe lift greater. In fact, while I had my stock cam (now trashed), I measured the difference in lobe center - but have apparently lost my notes.

 

I am asking for opinions and advice on the these four topics:

 

1. Of the wipe patterns in the pictures, are any acceptable?

 

2. Is the Nissan lash pad measured from top to bottom or top to bottom center?

 

3. Assuming, for the sake of argument, that my stock lash pads are .160", adding a .135" shim (Pic 3) means I need a .295" lash pad. I'm using new Schneider retainers, but the rocker arm end will certainly be elevated above the top of the retainer cup.

 

4. Should I go at this a different way? I.e, should I ditch the .055" cam tower shim, use a .015" set of tower shims I have and buy a Kameari adjustable cam sprocket? Perhaps there are other ideas/solutions?

 

This engine is NA and a daily Summer driver. I am concurrently installing Megasquirt, but I'm 40 years old and my days of playing stoplight rice rocket jock are behind me. Sure, the engine will see 6500 revs when I can, but I'm leaning more towards a solid and dependable engine then trying to lower 1/4 mile times. NNTTIAWWT.

[Pyro]

I prefer to place the wipe pattern closer to the valve. This makes the valve train quieter.

 

stock lash pads are around 0.120" thick due to the recess. After market lash pad are flat on the bottom.

 

When I setup the wipe pattern, I buy extra thick pads and lathe them down to the size I need. I also machine a recess in the lash pad (like the stock pad). Not necessary to machine the recess, just makes me feel good.

[Tennesseejed]

I prefer to place the wipe pattern closer to the valve. This makes the valve train quieter.

 

stock lash pads are around 0.120" thick due to the recess. After market lash pad are flat on the bottom.

 

When I setup the wipe pattern, I buy extra thick pads and lathe them down to the size I need. I also machine a recess in the lash pad (like the stock pad). Not necessary to machine the recess, just makes me feel good.

 

Thanks for the feeback Pyro.

 

Assuming the contour of the rocker arm is consistent, and I believe it is, it would seem that setting the wipe pattern to one side or the other on the rocker arm would only effect lateral forces on the valve stem. I realize this is pretty fully dicussed in other threads.

 

My only concern with this head would be, given the shaving and shimming an whatnot, in order to move the wipe pattern to the valve side, I will probably need some very tall lash pads.

 

Pic 3 above is the stock lash pad - .120" (thank you) - plus .135". So I'm at .255" already. I think I'd have to go well over .300" to move the wipe pattern to the valve side.

 

I am having a friend machine custom lash pads. So avaibility is not the issue; the issue is having the rocker arm tip rest well above the top of the retainer cup.

[cygnusx1]

I like the position of the lash pads where they are on your photos. Looks good to me. The closer to the pivot, the higher the lift you get from the cam. I set all of mine as close as possible to the pivot, running a stock cam. I actually manually filed a couple of the lash pads carefully to get them dialed in.

[Tennesseejed]

After spending a couple more hours carefully shimming and checking wipe patterns, I think I have decided to split the difference between a centered wipe and a wipe on the pivot edge.

 

The pros seem to be increased increased lift and decreased lash pad height. Cons appear to be increased valve train noise.

 

Thanks for the input, I appreciate it.

 

I did run into a curious problem that has me temporarily sidtetracked - Perhaps someone could share some advice: two of my rocker studs get very tight after being screwed more than halfway in. All the threads are clean and I have tried lube. After about 30 or 40 ft/lbs I got a little nervous about doing damage.

 

I'm pretty sure the studs can take it, but is this common after having a head tanked or should I be worried?

[stprasinz]

sounds like debri, perhaps, is the pivot mared? Chase threads on both the head, and the pivot. Check for depth clearance. Or you have a gremlin hiding in there.... lurking in the threads waiting to damage something in a moments notice

[Tennesseejed]

Well after a pretty serious battle with the flu, I finally managed to get back into the garage and work on the head.

 

Not much new here, but did want to post an update that it might help my fellow novice head builders.

 

Here is a pic of rockers with the final wipe patterns:

 

 

When I was getting started I wasn't sure how to mock up the lash pads to test the wipe pattern. After a few moments of serious MacGyvering I came up with a solution.

 

These boxes are shim stacks to set valve lash on dirt bikes (my YZ450F in particular) and the shims come in thickness from 1.2mm to 3.5mm.

 

 

These shims fit nicely between the lash pad guides and make it a breeze to adjust the wipe pattern by using shim of different thickness.

 

 

With regard to the two troublsome rocker pivots, after chasing the threads a few times, they now adjust suitably.