Rocker Geometry Woes

[rossiz]

been losing a lot of oil and not a drop is on the ground. we're talking a quart every 2 tanks of gas, maybe more. oddly there is no tell-tale blue smoke and it doesn't smell like it either. a good amount of oily, cruddy buildup on the plugs. i have good, pretty even compression, so i'm guessing valve stem seals. i didn't know just how much oil it was losing until i saw the oil pressure was lower than usual, and it took 2 quarts - yikes! i keep topping off, but on friday it started making a HORRIBLE squealing/screeching sound from the valve cover - in time with the engine - sounded like dry metal contact. i mean, it was really loud, scared the crap out of me. i added oil (it took a quart) and the noise went away.

 

so i pulled the valve cover, figuring something was amiss under there. i have a re-built n42 head from datsun parts llc, with about 2K miles on it. the head looked clean and nicely machined when i got it, but there were some issues i had to deal with:

• most of the valve cover bolt holes were stripped, as were half of the manifold bolt holes. i drilled and installed heli-coils
• the #6 exhaust stud hole  had snapped off and someone re-drilled a new hole next to it. so i removed the old broken bit of stud, filled the "new" hole with threaded rod and re-drilled/heli-coiled the original one.

i figured these were just things you have to deal with on 35+ yr old re-conditioned parts, and while it bugged me, i just fixed things and moved on.

 

then an oiler bar from larry hassler wouldn't fit - bumped the top of the rocker arms. hmmmm.... something fishy about the geometry.

 

i started pulling out rocker arms and to my horror, they were set up so high that the wipe pattern was off the back of every single lash pad - and the edge of the lash pads are now beveled/ground down from the cam. fortunately the cam lobes look fine, with no discernable lip at the edge of the wear marks, but it seems that the bucket shims on top of the valve stems are all way too short. and now i'm wondering if the jacknob that assembled my head even bothered to put valve seals in. i'm hoping that the rockers are not ruined - the back edges look pretty bad, but if the setup put the pattern in the center, that shouldn't matter, right?

 

here's the question: how do i figure out what size bucket shims to order? i measured the height of the existing ones, from the bottom surface (the surface that would come in contact with the bench when you set them down) to the top bearing surface (which comes in contact w/the rocker) and they are all between 4.32 mm and 4.47 mm. it seems expensive to order multiple sets of shims, but is that the only way? do they sell a setup kit with an assortment to find the right size? 

 

       

[Zed Head]

Bummer that you have to deal with more problems but lucky that you found it early.  

 

I think that you might have some nomenclature/naming a little off.  What you're calling the "lash pad" is normally called the rubbing pad.  The "bucket shims" are the lash pads.  There's a sentence in my Honsowetz How to Modify book that says "The only sure way to determine correct lash-pad thickness is to check the cam-lobe wipe pattern".  Page 70.  Trial and error.  I've seen it described that if the valve stems are all trimmed to the same length out of the head that you only have to do one.  But I've also seen that some builders leave random valve lengths in the head so each requires a different lash pad.

 

On the rocker arms, since they're been wearing on half the pad you'll need to carefully check that there's not a discontinuity in the middle of the pad.  Worn and unworn.

 

On the oil usage - if DPLLC installed a high lift cam it may be pushing the retainers ( I think that's the part) down in to the valve seals, damaging them.  Page 63 of said book says that 0.460" (11.7 mm) valve lift is the maximum.  Rocker arm ratio is ~1.5 I believe (although others have measured differently), if you have cam specs.   ~7.80 mm (0.307") max  Or you could look at a seal.  There's a Ford valve seal out there that people use with high lift cams.  DP might have used stock seals with a high lift cam.  Doesn't really look like he knows a lot.

 

Thanks for sharing though.  You should get back to him with what you found and see if he tells you "tough luck" or offers help.  At least he should pay for the lash pads and new seals.  That would be good to know.

[Zed Head]

Hey, since the cam and rocker arms took so much abuse but still survived, could you share the names of the companies that made them?  ITM and Paraut are typical rocker arm companies.  I have a thread on Hybridz collecting info about rocker arms, just because they, or the cams. seem to fail so often.  You have dodged the bullet, so far.

[240260280z]

Dang that is horrible. What a bum to sell you a head with so many problems. I thought that store was doing a good service for the Z community .... what a bum.

[LeonV]

Holy hell. I would absolutely not take a chance on reusing those rockers, that may eventually lead your cam to fail.

[rossiz]

oh... yes - totally got my terminology mixed up - i'm used to the rocker setup on ducati desmo engines, which use bucket shims to set the lash (there is no threaded adjustor) - the bucket shims are on the valve end of the rockers, up against the cam lobes and look a little bit like our lash pads.

so what i meant to say was that the rocker arm wiper areas are way off center and i need a correct set of lash pads. the cam is supposed to be a stock grind, so i don't think it's over-lifting for the seals - but i'm gonna pull all the springs and replace the seals, and i may find something else wonky when i do. i'm actually hoping to find a problem with the seals, as i would MUCH rather fix it that way than deal with rings...

i will check the rockers and cam for markings and let you know what i find out as far as manufacturer.

i will also call dp and see what he has to say. it sure would be great if they would man up and cover the seals & pads, but i'm not holding my breath...

the one "good" thing is that while the geometry is clearly off, the wipe areas are extremely consistent - which leads me to hope that i may find one lash pad size to do them all. in the mean time, i'm gonna research suppliers of lash pads...

[71Nissan240Z]

If you need rockers I have a decent matching set of them I pulled off an mn47. Won't use them since the head on the car I have right now is mated with a performance cam and the mn47 is not. Lash pads are standard thickness at .160 if u need those too.

[71Nissan240Z]

Ya I would polish those rockers or get new used ones like rossiz said

[hr369]

Is it possible that he put in different size valves? I've read where 81-83 valves are .080 shorter.

 

Nah.. on second thought he probably used what was already in the head, even if it

did need to be replaced.

 

Somebody has a new apprentice?

[Zed Head]

I just noticed that the rocker arms appear to be from different sources.  One would assume that the rough casting shape would be the same for a common manufacturer but you can see that the portion of the casting on the inside of the wear/rubbing/contact pad is different on several of the arms.  Less material.  The shape of the "foot" that sits on the lash pad is different also for the ones that have the different contact pad seat.  Kind of fits the impression I've had of DPLLC that he collects parts, used and new, from various places, then assembles engines and heads from his collection.  Not trying to pile on, just noting.  Maybe a little ammo for you to use when talking to Al (the owner, apparently).

 

Interesting also that the cam actually wore some of the casting after it fell off of the pad.  The wear pad is supposed to be harder than the casting, apparently, so probably no extra cam damage.

 

Good luck.

[Captain Obvious]

I just noticed that the rocker arms appear to be from different sources.

 

I wouldn't worry too much about the different raw castings. I would expect that those rockers are not cast one at a time, but in fact come out of a multi-cavity mold many at a time. The parts that come out of the same cavity of the same mold should be like peas in a pod, but probably differ (innocently) from parts that come out of other cavities even within the same mold.

 

I haven't looked under my valve cover to see what mine look like, but that's what I would expect. There's no way they were casting these things one at a time when they were used twelve per engine.

 

Doesn't mean that the rebuilder didn't just grab random rockers off a pile, but just saying that Datsun probably did the same thing back at the factory and (if done right) there shouldn't be anything wrong with that, if done right.

 

If done right. 

[Zed Head]

Look at the pictures and you'll see that design isn't the same.  Not small differences.  Even someone carving their own arms from a chunk of wood to be used for forming the sand mold would get them closer than that.