Rocker Geometry Woes

[Zed Head]

"green-eyed Lillith" brings up some interesting search results...

 

So, it's looking like the loose pivot lock nut is the cause?  Still curious.  Not really clear how you received the head or what you did to it before driving.  You have the most interesting thread going.  My biggest problem right now is working up a way to modify my heater coolant control valve so I can fine tune the heat output (I have one of those Honda valves but small movement lets lots of coolant through), and waiting for a small oil leak to drop the oil level low enough so that I can add some seal conditioner (my leak-free engine started leaking).

 

I might watch most of the game then leave for the last 5 minutes, like I did for the NFC Championship game, when they were sucking.

[rossiz]

well... 1 hr. and the head was on my bench. the #2 exhaust valve was bent - replaced it, new valve guide seal, and just for kicks i decided to check the rocker wipe pattern.

 

unfortunately, while this 2nd head from datsun parts llc was better in terms of machine work and threaded holes, it was also set up with the same rocker geometry. the lash pads are too short and the cam lobes go right off the back of the rocker arm wiper pads. when i got the head, i looked at the wipe patterns that were already established and it looked correct, but i was mistaken.

 

i pulled all the rockers, covered the wiper pads with sharpie and made a couple of shims to find the magic dimension required. i ended up with a shim that was 1.45mm and it worked dead-on for all 12 rockers, putting the wipe pattern right in the middle. so now i know how much additional lash pad height i need, but my existing pads have a recess in the bottom which the top of the valve stem goes into, and i don't know how to measure them... do i just measure them from the bottom ring to the surface that the rocker nose sits on?

 

bent valve

 

rocker pattern with shim

     

 

lash pad shim

   

 

[siteunseen]

I measured mine with the first of the flat part of my dial calipers clamped down the "channel".  .160" for stock ones.

 

A little further back than your picture #8.

 

1.45mm is .06" on top of .160" stock so will you get .175s?  They don't make .172s.  There's plenty of .175"s   http://schneidercams.com/7191738StandardWearCap-1.aspx

[240260280z]

Id bet a rocker hanging up when the cam swept off it contributed to the boom.

 

I'd send it back to llc with a bill for labour and down time if the lash pads were too short.

[Zed Head]

Maybe Seahwaks offensive coordinator Darrell Bevell is advising DPLLC on how to choose lash pads.

[rossiz]

i'm absolutely done with dpllc - not worth the argument at this point, so i'm just going to get the lash pads i need and do it myself.

it'll be another $100 that i didn't save going with a "less expensive" head, which i'm considering to be great life training...

 

i will create a small clamp-on fixture to allow me to measure the actual height of my current lash pads from the inside of the dish on the bottom up to the slot where the rocker arm sits, then i'll add the required shim height and hopefully i'll be in the ballpark of a standard set of solid lash pads.

[240260280z]

Well you took a bullet for all of us.  Thanks for that.

 

If you ever need parts let me know, we have a few 280z's out to pasture at our barn here in eastern Canada.

[Zed Head]

Stepping back and looking at your whole saga, it seems apparent that the DPLLC guy doesn't know what he's doing.  Or the mechanic he's using doesn't.  Or both.  Or he has a collection of heads in a warehouse somewhere and he just went and pulled another with the same problem as the first one.  Maybe all rebuilt to the wrong specs.  Regardless, it would probably help somebody out in the future to let DPLLC know that the second head's lash pads were off also.  He either doesn't know or doesn't care.  Maybe he's getting screwed by another guy who's rebuilding his heads.  Still, he might be able to fix the problem for some future buyer.

[HuD 91gt]

Unfortunate to hear.   But if it makes you feel any better, your tough lesson learned is a lesson learned for anyone reading this.  Hopefully saving a few of us from some harder time. Cheers, and thanks.

[gundee]

I have seen this twice before. In both cases the valve siezed in the valve guide.

Both of these heads were built by Rebello. I don't know what is going on with

his machinist but i will not be sending my head there.

[rossiz]

yes - i'm going to give him a call to let him know. he has his heads done by a shop local to him in california and i'm pretty sure they're following a recipe vs. setting them up carefully. they clean, paint, deck 3 surfaces, do a valve job, then assemble from a stockpile of parts.

 

they do the prep work well, but i'm guessing they just use oem lash pads and call it a day.

[Zed Head]

Only adding this link to fill out the story.  I feel like we should start a crowd-funding campaign to support rossiz's illumination of DPLLC's competency.

 

Anyway, looks like there is another option for cylinder heads.  Wonder where they come from.  Actually a little cheaper then DP.

 

http://www.oreillyauto.com/site/c/search/Cylinder+Head/02257/C0332.oap?make=Nissan&vi=1209237&model=280Z&year=1976

 

Who wants to be the lab rat?

 

 

Post #163 of this thread from another forum is interesting also, re rocker arms and cams - http://forums.hybridz.org/topic/112117-new-cam-and-rockers-odd-looking-at-500-miles/page-9#entry1133995