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Head reassembly - rocker geometry issues


Kuro

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Hi all, I'm hoping someone out there (with more experience than I have) can help me out.

 

The wipe pattern on my rocker arms is at the very edge of the valve side -  meaning there's no wipe edge visible on the valve side of the pad.

 

The head was warped a total of .007" so somewhere around the area of 14-16 thousandths of an inch (or .014 - .016 inches) was removed (7-8 thousandths from the top and 7-8 thousandths from the bottom of the head.  Cam tower shims are .015"

 

I have a competition (3 angle) valve job done, have stock l28et rocker arms and lash pads.

 

My cam specs are .480 Lift  x 272 Duration on 110 Lobe center.

 

Lash is set at .25mm (exhaust), .20mm (intake) as it should be but I can't seem to get the wipe pattern closer to the pivot side.   What made an acceptable difference was replacing the stock lash pad with a 2mm nut for testing purposes. A difference of over 1mm less the stock lash pads which are approx 3mm.

 

Is there something I'm doing wrong?  This test shows that I would need a lash pad that's thinner than stock but I don't see lash pads offered in 2mm sizing. What other [better] options should be considered?   Any and all help would be appreciated.

 

 

 

 

 

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I think that the proper way is to measure head thickness and shim up to the stock head thickness of 4.218".  If the block deck was resurfaced that needs to be taken in to account, I believe.  If it's a motor new to you the head might have already been resurfaced and at the limit before you started.  Maybe you need more shim.

 

Also, weren't you installing a turbo motor?  P90A hydraulic pivots might take extra care or behave differently compared to the more common solid pivots.    

 

No expert, just working my memory.

 

 

Edit - I got the 4.218" number directly from the Honsowetz "How to Modify..." book page 55, but it looks like it's the wrong number.

Edited by NewZed
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It is a p90, not a p90a. I measured the head height and it's currently at 4.2315 or 107.5mm but the problem is that I can't find the definitive stock untouched p90 height spec. I've read 4.25 was the stock height, if that's the case it should be well within acceptable boundaries.

 

Yes the shaved head must be taken into account, but the shims should have made it close to where it should be.

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Are you using the correct valves?

 

P90 and P79 valves are 2mm shorter than N42/N47 valves...

That was it Xnke Thank you for your help! 2mm taller valves caused my issue. Now I need to source the p90 valves. Anyone need to buy stainless n42/n47 valves?

post-16316-0-09902100-1393296490_thumb.jpg

Edited by Kuro
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Xnke  - nice catch. I was thinking lash pads and tower shims if the head was cut down. 

 

Kuro keep us updated with the change out. 

 

Yep I was thinking the same but I didn't see how I would need to shim the towers any more than I had already, and I was already at the thinnest lash pads but my wipe pattern was falling off the rocker pad on the valve side.  So I knew I was doing something wrong.  I wish I measured those valves before I put them in lol.   I'm sure the correct valves are going to put things in alignment, I will most likely need new lash pads (probably a tad bit thicker after this) but I'll cross that bridge when I get to it.    Thanks again guys!

Edited by Kuro
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